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Littérature scientifique sur le sujet « Cell-Embryo »

Auteur : Grafiati
Publié le 9 novembre 2024

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Articles de revues sur le sujet "Cell-Embryo"

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HOGUE, CHERYL. « EMBRYO STEM CELL SAND RESEARCH ». Chemical & ; Engineering News 79, no 29 (16 juillet 2001) : 21. http://dx.doi.org/10.1021/cen-v079n029.p021.

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Barone, Vanessa, et Carl-Philipp Heisenberg. « Cell adhesion in embryo morphogenesis ». Current Opinion in Cell Biology 24, no 1 (février 2012) : 148–53. http://dx.doi.org/10.1016/j.ceb.2011.11.006.

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Yang, Yi, Jia-Peng He et Ji-Long Liu. « Cell–Cell Communication at the Embryo Implantation Site of Mouse Uterus Revealed by Single-Cell Analysis ». International Journal of Molecular Sciences 22, no 10 (13 mai 2021) : 5177. http://dx.doi.org/10.3390/ijms22105177.

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As a crucial step for human reproduction, embryo implantation is a low-efficiency process. Despite rapid advances in recent years, the molecular mechanism underlying embryo implantation remains poorly understood. Here, we used the mouse as an animal model and generated a single-cell transcriptomic atlas of embryo implantation sites. By analyzing inter-implantation sites of the uterus as control, we were able to identify global gene expression changes associated with embryo implantation in each cell type. Additionally, we predicted signaling interactions between uterine luminal epithelial cells and mural trophectoderm of blastocysts, which represent the key mechanism of embryo implantation. We also predicted signaling interactions between uterine epithelial-stromal crosstalk at implantation sites, which are crucial for post-implantation development. Our data provide a valuable resource for deciphering the molecular mechanism underlying embryo implantation.
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Liu, Yuan, Xinbo Li, Jing Zhao, Xingchun Tang, Shujuan Tian, Junyi Chen, Ce Shi et al. « Direct evidence that suspensor cells have embryogenic potential that is suppressed by the embryo proper during normal embryogenesis ». Proceedings of the National Academy of Sciences 112, no 40 (22 septembre 2015) : 12432–37. http://dx.doi.org/10.1073/pnas.1508651112.

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The suspensor is a temporary supporting structure of proembryos. It has been proposed that suspensor cells also possess embryogenic potential, which is suppressed by the embryo as an effect of the embryo–suspensor interaction. However, data to support this hypothesis are not yet available. In this report, using an in vivo living cell laser ablation technique, we show that Arabidopsis suspensor cells can develop into embryos after removing the embryo proper. The embryo proper plays a critical role in maintaining suspensor cell identity. However, this depends on the developmental stage; after the globular embryo stage, the suspensors no longer possess the potential to develop into embryos. We also reveal that hypophysis formation may be essential for embryo differentiation. Furthermore, we show that, after removing the embryo, auxin gradually accumulates in the top suspensor cell where cell division occurs to produce an embryo. Auxin redistribution likely reprograms the fate of the suspensor cell and triggers embryogenesis in suspensor cells. Thus, we provide direct evidence that the embryo suppresses the embryogenic potential of suspensor cells.
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Yeung, Edward C., et Sandra K. Law. « Embryology of Calypso bulbosa. II. Embryo development ». Canadian Journal of Botany 70, no 3 (1 mars 1992) : 461–68. http://dx.doi.org/10.1139/b92-061.

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Calypso bulbosa is a terrestrial orchid that grows in north temperate regions. After fertilization, the zygote enlarges and grows towards the chalazal end of the embryo sac. An unequal cell division gives rise to a smaller terminal cell and a larger basal cell. A constriction forms in the basal cell. Further growth results in a U-shaped embryo. Two patterns of initial terminal cell division have been observed. In a majority of developing embryos, the terminal cell first divides periclinally and then anticlinally. In approximately 5% of the embryos, the initial division of the terminal cell is anticlinal. Despite differences in early cell division patterns, subsequent embryo development is the same. The suspensor consists of a large, highly vacuolated basal cell and a 4-celled filamentous region. Highly conspicuous starch granules are present within the basal cell of the suspensor. At maturity, the embryo proper is small, consisting of approximately 24 cells and lacking marked differentiation of the apical end. Starch and lipid are the main storage products within the embryo proper. Key words: Calypso orchids, embryo development, suspensor.
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Bedzhov, Ivan, Sarah J. L. Graham, Chuen Yan Leung et Magdalena Zernicka-Goetz. « Developmental plasticity, cell fate specification and morphogenesis in the early mouse embryo ». Philosophical Transactions of the Royal Society B : Biological Sciences 369, no 1657 (5 décembre 2014) : 20130538. http://dx.doi.org/10.1098/rstb.2013.0538.

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A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.
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KWON, Ivo. « EU Policy and Legislation on Stem Cell Research ». Korean Journal of Medical Ethics 7, no 2 (décembre 2004) : 247–57. http://dx.doi.org/10.35301/ksme.2004.7.2.247.

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EU policy on the research of the human embryo and stem cell is based on the 1997 Convention - Convention for the Protection of Human Rights and Dignity of the Human Being with regard to the Application of Biology and Medicine : Convention on Human Rights and Biomedicine. The purpose of this convention is to protect the dignity and identity of all human beings without discrimination, respect for their integrity and other rights and fundamental freedoms with regard to the application of biology and medicine. Applying this convention's view to the human embryo and stem cell research, 1) the human embryo research can only be permitted only if it protect the embryo for the purpose of the health and medicine. 2) Making human embryo is prohibited by any method-IVF or SCNT technique. 3) Other stem cell resources(adult stem cell, cord blood stem cell, etc) can be used under the condition of full informed consent without any financial interest of the donor. 4) In all cases, the privacy and human right as well as health of all related persons should be guaranteed. As a result, the research on the human embryo and stem cell has not been done actively except in few country. But now most member states permit stem cell research using spare embryo, but prohibit therapeutic cloning by SCNT. However EU itself has failed to agree with to fund the scientific research on stem cell using spare embryo. It is hardly to say the decision on stem cell research in the future by EU, but EU will continue to stress on the basic human right, social justice and human freedom in the field of biotechnology and its applications.
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Zhang, M., L. Sui, Y. Li, Z. Chen, Y. Zhang, T. Liu, J. Xu, X. Zhang et Y. Zhang. « 96 EFFECT OF TWO DIFFERENT EMBRYO TRANSPORTERS ON DEVELOPMENT OF PORCINE PARTHENOGENETIC EMBRYOS ». Reproduction, Fertility and Development 26, no 1 (2014) : 162. http://dx.doi.org/10.1071/rdv26n1ab96.

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In the present study, we investigated two embryo transport methods, including a commercial cell transporter and a self-made, simple embryo transporter, for the pre-implantation development of porcine parthenogenetic embryos. The cleaved embryos were randomly distributed between the two types of embryo transport methods and were conserved in vitro for 2, 3, and 4 h. Embryo development efficiency testing and blastocyst differential staining were utilized to assess embryo developmental quality. There were no significant differences in embryo early development efficiency between the commercial cell transporter group, self-made embryo transporter group, and control group. The blastocyst hatch rate (7.75 ± 2.96%) in the self-made simple embryo transport method maintained for 3 h was significantly higher compared to the other groups (P < 0.05). The results (Table 1) showed that blastocyst differential staining showed that the ratio of inner cell mass (ICM) to total cells in both the 2-h-transport group and 3-h-transport group from the self-made simple embryo transport method and the 4-h-transport group from the commercial cell transporter were significantly higher than other groups (P < 0.05).The self-made simple embryo transporter and commercial cell transporter are both effective for transport and conservation of embryos for 3 h. Table 1.Effect of different modes of transport and transit time on embryo development1
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Raz, V., J. H. Bergervoet et M. Koornneef. « Sequential steps for developmental arrest in Arabidopsis seeds ». Development 128, no 2 (15 janvier 2001) : 243–52. http://dx.doi.org/10.1242/dev.128.2.243.

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The continuous growth of the plant embryo is interrupted during the seed maturation processes which results in a dormant seed. The embryo continues development after germination when it grows into a seedling. The embryo growth phase starts after morphogenesis and ends when the embryo fills the seed sac. Very little is known about the processes regulating this phase. We describe mutants that affect embryo growth in two sequential developmental stages. Firstly, embryo growth arrest is regulated by the FUS3/LEC type genes, as mutations in these genes cause a continuation of growth in immature embryos. Secondly, a later stage of embryo dormancy is regulated by ABI3 and abscisic acid; abi3 and aba1 mutants exhibit premature germination only after embryos mature. Mutations affecting both developmental stages result in an additive phenotype and double mutants are highly viviparous. Embryo growth arrest is regulated by cell division activities in both the embryo and the endosperm, which are gradually switched off at the mature embryo stage. In the fus3/lec mutants, however, cell division in both the embryo and endosperm is not arrested, but rather is prolonged throughout seed maturation. Furthermore ectopic cell division occurs in seedlings. Our results indicate that seed dormancy is secured via at least two sequential developmental processes: embryo growth arrest, which is regulated by cell division and embryo dormancy.
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Srivatsan, Sanjay R., Mary C. Regier, Eliza Barkan, Jennifer M. Franks, Jonathan S. Packer, Parker Grosjean, Madeleine Duran et al. « Embryo-scale, single-cell spatial transcriptomics ». Science 373, no 6550 (1 juillet 2021) : 111–17. http://dx.doi.org/10.1126/science.abb9536.

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Spatial patterns of gene expression manifest at scales ranging from local (e.g., cell-cell interactions) to global (e.g., body axis patterning). However, current spatial transcriptomics methods either average local contexts or are restricted to limited fields of view. Here, we introduce sci-Space, which retains single-cell resolution while resolving spatial heterogeneity at larger scales. Applying sci-Space to developing mouse embryos, we captured approximate spatial coordinates and whole transcriptomes of about 120,000 nuclei. We identify thousands of genes exhibiting anatomically patterned expression, leverage spatial information to annotate cellular subtypes, show that cell types vary substantially in their extent of spatial patterning, and reveal correlations between pseudotime and the migratory patterns of differentiating neurons. Looking forward, we anticipate that sci-Space will facilitate the construction of spatially resolved single-cell atlases of mammalian development.
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Thèses sur le sujet "Cell-Embryo"

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Spanos, Sophia. « Cell death during preimplantation embryo development ». Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398228.

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Chisholm, J. C. « Cell diversification in the mouse early embryo ». Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384438.

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Ridyard, Marc Steven. « Cell adhesion-related signaling molecules in embryo development ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ46910.pdf.

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Anderson, Jon E. « Cell cycle regulation in the early porcine embryo / ». free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9974607.

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Selleck, Mark Anthony James. « Hensen's node and cell commitment in the chick embryo ». Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293410.

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Storey, Kate Gillian. « Cell lineage and pattern formation in the earthworm embryo ». Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.346430.

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Hughes, Julian Richard. « mRNA localisation and cell polarity in the Drosophila embryo ». Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445657/.

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Asymmetric localisation of mRNA transcripts to specific sites within the cytoplasm is a widely employed mechanism for targeting of proteins and generating cell polarity. The mechanism and function of mRNA localisation has been extensively studied in Drosophila melanogaster, where, for example, the Egalitarian/Bicaudal- D/dynein complex mediates transport of mRNA transcripts, towards microtubule minus-ends, during oogenesis and in syncytial blastoderm embryos. However, it is not known whether the Egalitarian/Bicaudal-D/dynein mRNA transport machinery is required to localise mRNAs in somatic cell types in the Drosophila embryo. In this thesis, I show that the Egalitarian/Bicaudal-D/dynein complex is active in embryonic epithelial cells and neuroblasts and mediates asymmetric localisation of inscuteable, wingless and crumbs, but not miranda, mRNA transcripts, indicating that this is a general mechanism for mRNA localisation in Drosophila. I provide preliminary evidence that y-Tubulin mediates asymmetric miranda localisation. I have also explored the role of mRNA localisation in protein targeting in epithelial cells and neuroblasts, and find that asymmetric localisation of inscuteable and wingless, but not crumbs, mRNA transcripts is required to enhance the targeting of their protein products. I find that asymmetric localisation of wingless mRNA and protein is not required to support Wingless function in the embryo, although, Inscuteable activity is significantly reduced when inscuteable mRNA localisation is disrupted, and neuroblasts display defects in apico-basal polarity and metaphase spindle length. In conclusion, mRNA localisation acts to enhance protein targeting and activity in somatic cell types in the Drosophila embryo.
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Prigent, Serena. « Biochemical regulation of cell mechanics in C. elegans Embryo ». Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS395.

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L’architecture et la dynamique du cortex d’Actine joue un rôle central dans la contractilité cellulaire et la morphogénèse des tissus. La modulation locale de la dynamique du réseau d’Actomyosine dépend majoritairement de la cascade d’activation de RhoA. Dans ma thèse, j’ai combiné des approches de microscopie quantitative en TIRFM, de l’imagerie en molécule unique, des simulations numériques et de la modélisation mathématique simple pour explorer l’architecture dynamique du réseau sous-jacent aux contractions pulsées dans un modèle simple : le jeune embryon de C. elegans. En se concentrant sur la Formine, élongateurs de l’Actine, nous avons observé que l’élongation de la F-Actine était catalysée par une population spécifique de Formines corticales – appelées Formines élongatrices – qui montrent une mobilité de type balistique. Nous avons ensuite montré que les Formines saturent les extrémités barbées disponibles et convertissent un gradient biochimique local de l’activité de RhoA en un réseau d’architecture polaire. Dans une seconde étude, en se concentrant sur la cinétique de la cascade d’activation de RhoA, nous avons développé un modèle numérique simple. Celui-ci tire profit des mesures des paramètres dynamiques de la Myosine, un effecteur terminal de la cascade d’activation de RhoA, pour prédire l’évolution temporelle de cette cascade. Je propose ici que ce modèle simple et générique – qui peut par essence s’adapter à n’importe quelle cascade – offre un cadre mathématique simple pour comprendre la dynamique temporelle des cascades d’activation, et le délai et changement dans la forme de la réponse qui peuvent être observés entre l’entrée et la sortie
Actin network architecture and dynamics play a central role in cell contractility and tissue morphogenesis. Local modulations of Actomyosin network dynamics depend largely on the activation of the RhoA activation cascade. In my thesis, I combined quantitative microscopy using TIRFM, single-molecule imaging, numerical simulations and simple mathematical modeling, to explore the dynamic network architecture underlying pulsed contractions in a simple model, the C. elegans early embryo. Focusing on the Actin elongator Formin, we observed that F-Actin elongation was catalyzed by a specific subpopulation of cortical Formins – termed elongating Formins – that displayed a characteristic ballistic mobility. My results also showed that Formin-mediated F-Actin elongation rate was dependent on the phase of the cell cycle and embryonic stage. We subsequently showed that elongating Formins saturate available barbed ends of Actin filaments, converting a local biochemical gradient of RhoA activity into a polar network architecture. In second study, focusing on the kinetics of the RhoA activation cascade, we developed and functionally challenged a simple numerical model. This model takes advantage of the measurements of the dynamical parameters of the Myosin, downstream effector of the RhoA activation cascade, to predict the temporal evolution of this cascade. I propose that this simple and generic model – which can in essence fit any activation cascade – offers a simple mathematical framework to understand the temporal dynamics of signaling cascades, and the delay and change in the shape of the response which can be observed between the input and the output of a cascade
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Bloom, Theodora Leah. « Protein phosphorylation and cell diversification in the mouse early embryo ». Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/250962.

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This dissertation reports the results of studies into the control of compaction of the mouse preimplantation embryo. Compaction is a post-translationally controlled rearrangement of cell contacts and the cytoskeleton that occurs at the 8-cell stage of development. This re-arrangement seems to be necessary for the differentiation of the two cell types present in the blastocyst. Protein phosphorylation is a post-translational modification believed to be important in the modulation of cell shape and cytoskeletal assembly. It is therefore feasible to propose a role for protein phosphorylation in compaction. Two types of approach have been used to investigate the possible role of protein phosphorylation in compaction. Firstly, embryos have been treated with two drugs, 6-dimethylaminopurine (DMAP) and a phorbol ester (phorbol myristate acetate, PMA), each of which seems to affect both protein phosphorylation and compaction. DMAP is an adenine analogue and putative inhibitor of protein phosphorylation that was found to perturb the cell cycle of mouse embryos. In addition, DMAP caused rapid cellular flattening of 4-cell and 8-cell embryos. However, this flattening was not accompanied by cell polarisation and did not seem to be mediated by the cell adhesion molecule uvomorulin. It is therefore unlikely to be related directly to the flattening that occurs at compaction. Phorbol esters, such as PMA, are potent stimulators of the membrane-associated, Ca2+- and phospholipid-dependent protein kinase, protein kinase C (PKC). Incubation in medium containing PMA had some effects on the cytoskeleton of oocytes and early embryos but caused severe, widespread disassembly of the cytoskeleton and reversal of flattening in 8-cell embryos. These effects of PMA, seen specifically at the 8-cell stage, may be related to the spatially restricted disassembly of the cytoskeleton that occurs naturally during compaction at the 8-cell stage. This interpretation provides indirect evidence for a possible role for PKC activity, and hence protein phosphorylation, in the process of compaction. The relationship between protein phosphorylation and the events occurring at the 8-cell stage has been examined more directly by labelling 4-cell and 8-cell embryos with [32P]orthophosphate and examining the phosphoproteins obtained by one and two-dimensional gel electrophoresis. By synchronising groups of embryos precisely to successive cleavage divisions prior to labelling, changes in phosphoprotein profile associated with passage through the 4-cell and 8-cell stages have been described. While many of the 32P-labelled phosphoproteins detectable after electrophoresis in one or two dimensions are similar at each stage examined, there are some changes associated specifically with passage through the 8-cell stage which may be related to the cell flattening and polarisation occurring at this time. In addition, the profile of 8-cell embryos differed according to the duration of pulse-labelling with [32Pjorthophosphate or the inclusion of "chase" periods. Finally, several treatments that affect features of compaction, including exposure to DMAP and PMA, have been used to assess the link between the observed changes in phosphoprotein profile and the events of compaction. Embryos were also incubated in protein synthesis inhibitors, which cause premature cell flattening in 4-cell embryos and in Ca2+-free medium, which prevents intercellular flattening and delays polarisation of 8-cell blastomeres. In each case, the relative labelling intensity of some of the phosphoproteins characteristic of untreated 8-cell embryos was altered. The behaviour of these phosphoproteins suggests that they may be important in the mechanism by which cells flatten and polarise or in the maintenance of flattened, polarised, cells; they now provide a focus for future study.
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李燕柳 et Yin-lau Lee. « Embryotrophic effects of Vero cell on preimplantation mouse embryo development ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31223023.

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Livres sur le sujet "Cell-Embryo"

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Canada, Library of Parliament Science and Technology Division. Human embryo stem cell research. Ottawa : Library of Parliament, 2000.

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Leese, Henry J., et Daniel R. Brison, dir. Cell Signaling During Mammalian Early Embryo Development. New York, NY : Springer New York, 2015. http://dx.doi.org/10.1007/978-1-4939-2480-6.

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Brevini, Tiziana A. L., et Georgia Pennarossa. Gametogenesis, Early Embryo Development and Stem Cell Derivation. New York, NY : Springer New York, 2013. http://dx.doi.org/10.1007/978-1-4614-5532-5.

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Humphrey, Richard A. Embryo factory : The stem cell wars : a novel. Eugene, OR : ACW Press, 2003.

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Espejo, Roman. Human embryo experimentation. Sous la direction de Espejo Roman 1977-. San Diego, CA : Greenhaven Press, 2002.

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Ginette, Serrero, et Hayashi Jun, dir. Cellular endocrinology : Hormonal control of embryonic and cellular differentiation : proceedings of the First International Symposium on Cellular Endocrinology, held in Lake Placid, New York, August 12-16, 1985. New York : A.R. Liss, 1986.

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National Research Council (U.S.). Human Embryonic Stem Cell Research Advisory Committee., dir. The National Academies' guidelines for human embryonic stem cell research : 2008 amendments. Washington, D.C : National Academies Press, 2008.

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V, Greer Erik, dir. Embryonic stem cell research. New York : Nova Science Publishers, 2006.

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Denker, Hans-Werner. Trophoblast Invasion and Endometrial Receptivity : Novel Aspects of the Cell Biology of Embryo Implantation. Boston, MA : Springer US, 1990.

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National Research Council (U.S.). Human Embryonic Stem Cell Research Advisory Committee., dir. The National Academies' guidelines for human embryonic stem cell research : 2008 amendments. Washington, D.C : National Academies Press, 2008.

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Chapitres de livres sur le sujet "Cell-Embryo"

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Zakeri, Zahra, et Richard A. Lockshin. « Cell Death : Shaping an Embryo ». Dans When Cells Die II, 25–58. Hoboken, NJ, USA : John Wiley & Sons, Inc., 2005. http://dx.doi.org/10.1002/0471476501.ch2.

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Singh, Natalia N., et David W. Barnes. « Neurogenesis in Zebrafish Embryo Cell Cultures ». Dans Animal Cell Technology : Basic & ; Applied Aspects, 43–49. Dordrecht : Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-017-0728-2_8.

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Ziomek, Carol A. « Cell Polarity in the Preimplantation Mouse Embryo ». Dans The Mammalian Preimplantation Embryo, 23–41. Boston, MA : Springer US, 1987. http://dx.doi.org/10.1007/978-1-4684-5332-4_2.

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Lawrence, Peter A. « Cell Lineage and Cell States in the Drosophila Embryo ». Dans Ciba Foundation Symposium 144 - Cellular Basis of Morphogenesis, 131–55. Chichester, UK : John Wiley & Sons, Ltd., 2007. http://dx.doi.org/10.1002/9780470513798.ch8.

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Hodor, Paul G., et Charles A. Ettensohn. « Mesenchymal Cell Fusion in the Sea Urchin Embryo ». Dans Cell Fusion, 315–34. Totowa, NJ : Humana Press, 2008. http://dx.doi.org/10.1007/978-1-59745-250-2_18.

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Graham, Anthony. « Whole Embryo Assays for Programmed Cell Death ». Dans METHODS IN MOLECULAR BIOLOGY™, 729–34. Totowa, NJ : Humana Press, 2008. http://dx.doi.org/10.1007/978-1-60327-483-8_52.

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Fleming, Tom P. « Cell Differentiation in the Mouse Preimplantation Embryo ». Dans Mechanism of Fertilization : Plants to Humans, 679–97. Berlin, Heidelberg : Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-83965-8_48.

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Sharma, Akriti, Mette H. Stensen, Erwan Delbarre, Momin Siddiqui, Trine B. Haugen, Michael A. Riegler et Hugo L. Hammer. « Detecting Human Embryo Cleavage Stages Using YOLO V5 Object Detection Algorithm ». Dans Communications in Computer and Information Science, 81–93. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-17030-0_7.

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AbstractAssisted reproductive technology (ART) refers to treatments of infertility which include the handling of eggs, sperm and embryos. The success of ART procedures depends on several factors, including the quality of the embryo transferred to the woman. The assessment of embryos is mostly based on the morphokinetic parameters of their development, which include the number of cells at a given time point indicating the cell stage and the duration of each cell stage. In many clinics, time-lapse imaging systems are used for continuous visual inspection of the embryo development. However, the analysis of time-lapse data still requires the evaluation, by embryologists, of the morphokinetic parameters and cleavage patterns, making the assessment subjective. Recently the application of object detection in the field of medical imaging enabled the accurate detection of lesion or object of interest. Motivated by this research direction, we proposed a methodology to detect and track cells present inside embryos in time-lapse image series. The methodology employed an object detection technique called YOLO v5 and annotated the start of observed cell stages based on the cell count. Our approach could identify cell division to detect cell cleavage or start of next cell stage accurately up to the 5-cell stage. The methodology also highlighted instances of embryos development with abnormal cell cleavage patterns. On an average the methodology used 8 s to annotate a video frame (20 frames per second), which will not pose any delay for the embryologists while assessing embryo quality. The results were validated by embryologists, and they considered the methodology as a useful tool for their clinical practice.
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Iio, Masayoshi, Yoko Fuke et David W. Barnes. « Cell Biology of Serum-Free Mouse Embryo (SFME) Cells ». Dans Cell Biology and Biotechnology, 26–34. New York, NY : Springer New York, 1993. http://dx.doi.org/10.1007/978-1-4684-9418-1_3.

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Sanders, Esmond J. « Roles for Tgfß1 in Chick Embryo Cell Transformation ». Dans Formation and Differentiation of Early Embryonic Mesoderm, 251–61. Boston, MA : Springer US, 1992. http://dx.doi.org/10.1007/978-1-4615-3458-7_21.

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Actes de conférences sur le sujet "Cell-Embryo"

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Michelin, Gael, Leo Guignard, Ulla-Maj Fiuza, Patrick Lemaire, Christophe Godine et Gregoire Malandain. « Cell pairings for ascidian embryo registration ». Dans 2015 IEEE 12th International Symposium on Biomedical Imaging (ISBI 2015). IEEE, 2015. http://dx.doi.org/10.1109/isbi.2015.7163872.

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Michelin, Gael, Leo Guignard, Ulla-Maj Fiuza et Gregoire Malandain. « Embryo cell membranes reconstruction by tensor voting ». Dans 2014 IEEE 11th International Symposium on Biomedical Imaging (ISBI 2014). IEEE, 2014. http://dx.doi.org/10.1109/isbi.2014.6868105.

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Teichert, Gregory H., Quentin T. Aten, Melanie Easter, Sandra Burnett, Larry L. Howell et Brian D. Jensen. « A Metamorphic Erectable Cell Restraint (MECR) ». Dans ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-70475.

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This paper introduces a metamorphic erectable cell restraint (MECR) to provide cell restraint in genetic research. A micro-electromechanical systems (MEMS) metamorphic mechanism with two phases of motion was designed to grasp individual embryos about their midplane. The first phase of motion lifts a compliant gripper approximately 40 μm (about half the diameter of an embryo). The gripper then closes in the second phase to grasp the embryo. The metamorphic mechanism includes compliant mechanism components which are analyzed here. A microscale prototype was fabricated from polysilicon and used to demonstrate the mechanism’s two phase motion.
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Wang, Zi, Dali Wang, Husheng Li et Zhirong Bao. « Cell Neighbor Determination in the Metazoan Embryo System ». Dans BCB '17 : 8th ACM International Conference on Bioinformatics, Computational Biology, and Health Informatics. New York, NY, USA : ACM, 2017. http://dx.doi.org/10.1145/3107411.3107465.

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Mohammad, A. « T-CELL DEVELOPMENT FROM EMBRYO TO THE PETRI DISH ». Dans Конференция «Перспективы применения генной терапии и биомедицинского клеточного продукта» с блоком летней школы для молодых ученых. Федеральное государственное бюджетное учреждение «Национальный медицинский исследовательский центр эндокринологии» Министерства здравоохранения Российской Федерации, 2022. http://dx.doi.org/10.14341/gnct-2022-47.

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Abbasi, Ali A., M. T. Ahmadian, Ali Alizadeh et S. Tarighi. « Application of Hyperelastic Models in Mechanical Properties Prediction of Mouse Oocyte and Embryo Cells at Large Deformations ». Dans ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-65034.

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Biological cell studies have many applications in biology, cell manipulation and diagnosis of diseases such as cancer and malaria. In this study, inverse finite element method (IFEM) combined with Levenberg-Marquardt optimization algorithm has been used to extract and characterize material properties of mouse oocyte and embryo cells at large deformations. Then, the simulation results have been validated using data from experimental works. In this study, it is assumed cell material is hyperelastic, isotropic, homogenous and axisymmetric. For inverse analysis, FEM model of cell injection experiment which implemented in Abaqus software has been coupled with Levenberg-Marquardt optimization algorithm written in Matlab; based on this coupling the optimum hyperelastic coefficients which give the best match between experimental and simulated forces are extracted. Results show that among different hyperelastic material models, Ogden material is well suitable for characterization of mouse oocyte cell and Mooney-Rivlin or polynomial are suitable for characterization of mouse embryo cell. Moreover the evaluated Poisson ratio of the cell is obtained to be equal to 0.5, which indicates the structural material of mouse oocyte and embryo, are compressible.
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Sharma, Akriti, Mette H. Stensen, Erwan Delbarre, Trine B. Haugen et Hugo L. Hammer. « Explainable Artificial Intelligence for Human Embryo Cell Cleavage Stages Analysis ». Dans ICMR '22 : International Conference on Multimedia Retrieval. New York, NY, USA : ACM, 2022. http://dx.doi.org/10.1145/3512731.3534206.

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Supatto, Willy, Amy McMahon, Scott E. Fraser et Angelike Stathopoulos. « Quantitative imaging of the collective cell movements shaping an embryo ». Dans 2008 42nd Asilomar Conference on Signals, Systems and Computers. IEEE, 2008. http://dx.doi.org/10.1109/acssc.2008.5074361.

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Liu, Cheng-Hsien, Kuo-Wei Chang, Pei-Yu Chang, Yi-Jung Sung, Hong-Yuan Huang, Da-Jeng Yao, Shih-Kang Fan, Wensyang Hsu et Chin-Jung Li. « Embryo lab chip taking advantage of microfluidics and cell co-culturing ». Dans TRANSDUCERS 2015 - 2015 18th International Solid-State Sensors, Actuators and Microsystems Conference. IEEE, 2015. http://dx.doi.org/10.1109/transducers.2015.7181004.

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Chan, Kwok Kin, et XiaoQi Wang. « Abstract 3876 : Cell cycle checkpointin vivoin developing mouse embryo liver cells ». Dans Proceedings : AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010 ; Washington, DC. American Association for Cancer Research, 2010. http://dx.doi.org/10.1158/1538-7445.am10-3876.

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Rapports d'organisations sur le sujet "Cell-Embryo"

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Bhaskaran, Jahnavi, et Natasha Mutebi. Human stem cell-based embryo models. Parliamentary Office of Science and Technology, UK Parliament, février 2024. http://dx.doi.org/10.58248/pn716.

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This POSTnote summarises the emerging technology of human stem cell-based embryo models, discussions around their regulation and their wider ethical societal implications. It introduces the scientific background and the potential applications of the models. It also outlines the challenges and opportunities in introducing their regulation and discusses stakeholder initiatives to address regulatory gaps.
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Petitte, James, Hefzibah Eyal-Giladi et Malka Ginsburg. The Study of Primordial Germ Cell Development as a Tool for Gene Transfer in Chickens. United States Department of Agriculture, octobre 1991. http://dx.doi.org/10.32747/1991.7561071.bard.

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The ability to introduce novel genetic material into the genome of commercial poultry has been impeded by a lack of kowledge regarding the origin in the early embryo of the target cell of interest, namely, the germ cell. Hence, this project investigated the emergence of primordial germ cells (PGCs) during the early development of the avian embryo to aid in efforts to produce transgenic poultry on a routine basis. The strategy was to introduce foreign DNA into the area of the unincubated embryo that is destined to give rise to the germ line. The objectives of this project were: 1) to identify and localize a subpopulation of cells in the early embryo which will give rise to PGCs, 2) to determine the best location and stage of development to transfer donor cells for efficient germline chimerism, and 3) to transfect donor cells to produce transgenic/germline chimeric embryos. We show that by using the monoclonal antibody SSEA-1 and by various cell culture techniques that germ cells appear to segregate from the somatic lineages at St. X., a process that is gradual and continues through St. XIV. Using microsurgical transplantation between quail and chick embryos, we demonstrated that the inner 1/3 of the area pellucida between states X-XII gives rise to about 2/3 of the germ cell population at the time of their residence in the germinal crescent. Because of the non-localized emergence of PGCs, attempts to introduce foreign DNA into clonal precursors of germ cells through liposome-mediated transfection yielded unacceptable levels of efficiency. However, through our investigation of germ cell origins, an in vitro model of germ cell differentiation was developed that could offer a means of determining the factors required for the long term culture of avian PGCs thereby providing a convenient means of manipulating the avian genome.
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Halevy, Orna, Zipora Yablonka-Reuveni et Israel Rozenboim. Enhancement of meat production by monochromatic light stimuli during embryogenesis : effect on muscle development and post-hatch growth. United States Department of Agriculture, juin 2004. http://dx.doi.org/10.32747/2004.7586471.bard.

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The original objectives were: A. To determine the critical embryonic age for monochromatic green light stimulation. B. To follow the ontogeny of embryos exposed to monochromatic green light vs. darkness. C. To investigate the effects of monochromatic green light illumination on myoblast and fiber development in the embryo. D. To investigate the stimulatory effect of light combinations during embryo and post-hatch periods on growth and meat production. E. To evaluate the direct effect of monochromatic green light on cultured embryonic and adult myoblasts. The overall purpose of this study was to investigate the effect of monochromatic light stimuli during incubation period of broilers on muscle development and satellite cell myogenesis. Based on previous studies (Halevy et al., 1998; Rozenboim et al., 1999) that demonstrated the positive effects of green-light illumination on body and muscle growth, we hypothesized that monochromatic light illumination accelerates embryo and muscle development and subsequently enhances muscle growth and meat production. Thus, further decreases management costs. Under the cooperation of the laboratories at the Hebrew University of Jerusalem and University of Washington we have conducted the following: 1. We have established the critical stage for exposure to green monochromatic light which has the maximal effect on body and muscle growth (Objective A). We report that embryonic day 5 is optimal for starting illumination. The optimal regime of lighting that will eliminate possible heat effects was evaluated by monitoring egg core temperature at various illumination periods. We found that intermitted lighting (15 min. on; 15 min. off) is optimal to avoid heat effects. 2. We have evaluated in detail gross changes in embryo development profile associated to green light stimuli vs. darkness. In addition, we have investigated the stimulatory effect of light combinations during embryo and post-hatch periods on body and muscle growth (Objective B,D). 3. We have studied the expression profile of muscle regulatory proteins during chicken muscle cell differentiation in cultures using newly developed antibodies. This study paved the way for analyzing the expression of these proteins in our photo stimulation experiments (Objective C). 4. We have studied the pattern ofPax7 expression during myogenesis in the posthatch chicken. Experimental chick pectoralis muscles as well adult myoblast cultures were used in this study and the results led us to propose a novel model for satellite cell differentiation and renewal. 5. The effects of monochromatic green light illumination during embryogenesis have been studied. These studies focused on fetal myoblast and satellite cell proliferation and differentiation at pre- and posthatch periods and on the effects on the expression of muscle regulatory proteins which are involved in these processes. In addition, we have analyzed the effect of photo stimulation in the embryo on myofiber development at early posthatch (Objective C). 6. In follow the reviewers' comments we have not conducted Objective E. The information gathered from these studies is of utmost importance both, for understanding the molecular basis of muscle development in the posthatch chicks and for applied approach for future broiler management. Therefore, the information could be beneficial to agriculture in the short term on the one hand and to future studies on chick muscle development in the embryo and posthatch on the other hand.
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Ohad, Nir, et Robert Fischer. Control of Fertilization-Independent Development by the FIE1 Gene. United States Department of Agriculture, août 2000. http://dx.doi.org/10.32747/2000.7575290.bard.

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A fundamental problem in biology is to understand how fertilization initiates reproductive development. During plant reproduction, one sperm cell fuses with the egg to form an embryo, whereas a second sperm cell fuses with the adjacent central cell nucleus to form the endosperm tissue that supports embryo and/or seedling development. To understand the mechanisms that initiate reproduction, we have isolated mutants of Arabidopsis that allow for replication of the central cell and subsequent endosperm development without fertilization. In this project we have cloned the MEA gene and showed that it encode a SET- domain polycomb protein. Such proteins are known to form chromatin-protein complexes that repress homeotic gene transcription and influence cell proliferation from Drosophylla to mammals. We propose a model whereby MEA and an additional polycomb protein we have cloned, FIE , function to suppress a critical aspect of early plant reproduction and endosperm development, until fertilization occurs. Using a molecular approach we were able to determine that FIE and MEA interact physically, suggesting that these proteins have been conserved also during the evolution of flowering plants. The analysis of MEA expression pattern revealed that it is an imprinted gene that displays parent-of- origin-dependent monoallelic expression specifically in the endosperm tissue. Silencing of the paternal MEA allele in the endosperm and the phenotype of mutant mea seeds support the parental conflict theory for the evolution of imprinting in plants and mammals. These results contribute new information on the initiation of endosperm development and provide a unique entry point to study asexual reproduction and apomixis which is expected to improve crop production.
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Hansen, Peter J., et Zvi Roth. Use of Oocyte and Embryo Survival Factors to Enhance Fertility of Heat-stressed Dairy Cattle. United States Department of Agriculture, août 2011. http://dx.doi.org/10.32747/2011.7697105.bard.

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The overall goal was to identify survival factors that can improve pregnancy success following insemination or embryo transfer in lactating dairy cows exposed to heat stress. First, we demonstrated that oocytes are actually damaged by elevated temperature in the summer. Then we tested two thermoprotective molecules for their effect on oocyte damage caused by heat shock. One molecule, ceramide was not thermoprptective. Another, insulin-like growth factor-1 (IGF) reduced the effects of heat shock on oocyte apoptosis and oocyte cleavage when added during maturation. We also used lactating cows exposed to heat stress to determine whether bovine somatotropin (bST), which increases IGF1 levels in vivo, would improve fertility in summer. Cows treated with bST received a single injection at 3 days before insemination. Controls received no additional treatment. Treatment with bST did not significantly increase the proportion of inseminated cows diagnosed pregnant although it was numerically greater for the bST group (24.2% vs 17.8%, 124–132 cows per group). There was a tendency (p =0.10) for a smaller percent of control cows to have high plasma progesterone concentrations (≥ 1 ng/ml) at Day 7 after insemination than for bST-treated cows (72.6 vs 81.1%). When only cows that were successfully synchronized were considered, the magnitude of the absolute difference in the percentage of inseminated cows that were diagnosed pregnant between bST and control cows was reduced (24.8 vs 22.4% pregnant for bST and control). Results failed to indicate a beneficial effect of bST treatment on fertility of lactating dairy cows. In another experiment, we found a tendency for addition of IGF1 to embryo culture medium to improve embryonic survival after embryo transfer when the experiment was done during heat stress but not when the experiment was done in the absence of heat stress. Another molecule tested, granulocyte-macrophage colony-stimulating factor (GM-CSF; also called colony-stimulating factor-2), improved embryonic survival in the absence of heat stress. We also examined whether heat shock affects the sperm cell. There was no effect of heat shock on sperm apoptosis (programmed cell death) or on sperm fertilizing ability. Therefore, effects of heat shock on sperm function after ejaculation if minimal. However, there were seasonal changes in sperm characteristics that indicates that some of the decrease in dairy cow fertility during the summer in Israel is due to using semen of inferior quality. Semen was collected from five representative bulls throughout the summer (August and September) and winter (December and January). There were seasonal differences in ion concentration in seminal plasma and in the mRNA for various ion channels known to be involved in acrosome reactions. Furthermore, the proportion of sperm cells with damaged acrosomes was higher in post-thaw semen collected in the summer than in its counterpart collected in winter (54.2 ± 3.5% vs. 51.4 ± 1.9%, respectively; P < 0.08Further examination is required to determine whether such alterations are involved in the low summer fertility of dairy cows.
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Ohad, Nir, et Robert Fischer. Regulation of Fertilization-Independent Endosperm Development by Polycomb Proteins. United States Department of Agriculture, janvier 2004. http://dx.doi.org/10.32747/2004.7695869.bard.

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Arabidopsis mutants that we have isolated, encode for fertilization-independent endosperm (fie), fertilization-independent seed2 (fis2) and medea (mea) genes, act in the female gametophyte and allow endosperm to develop without fertilization when mutated. We cloned the FIE and MEA genes and showed that they encode WD and SET domain polycomb (Pc G) proteins, respectively. Homologous proteins of FIE and MEA in other organisms are known to regulate gene transcription by modulating chromatin structure. Based on our results, we proposed a model whereby both FIE and MEA interact to suppress transcription of regulatory genes. These genes are transcribed only at proper developmental stages, as in the central cell of the female gametophyte after fertilization, thus activating endosperm development. To test our model, the following questions were addressed: What is the Composition and Function of the Polycomb Complex? Molecular, biochemical, genetic and genomic approaches were offered to identify members of the complex, analyze their interactions, and understand their function. What is the Temporal and Spatial Pattern of Polycomb Proteins Accumulation? The use of transgenic plants expressing tagged FIE and MEA polypeptides as well as specific antibodies were proposed to localize the endogenous polycomb complex. How is Polycomb Protein Activity Controlled? To understand the molecular mechanism controlling the accumulation of FIE protein, transgenic plants as well as molecular approaches were proposed to determine whether FIE is regulated at the translational or posttranslational levels. The objectives of our research program have been accomplished and the results obtained exceeded our expectation. Our results reveal that fie and mea mutations cause parent-of-origin effects on seed development by distinct mechanisms (Publication 1). Moreover our data show that FIE has additional functions besides controlling the development of the female gametophyte. Using transgenic lines in which FIE was not expressed or the protein level was reduced during different developmental stages enabled us for the first time to explore FIE function during sporophyte development (Publication 2 and 3). Our results are consistent with the hypothesis that FIE, a single copy gene in the Arabidopsis genome, represses multiple developmental pathways (i.e., endosperm, embryogenesis, shot formation and flowering). Furthermore, we identified FIE target genes, including key transcription factors known to promote flowering (AG and LFY) as well as shoot and leaf formation (KNAT1) (Publication 2 and 3), thus demonstrating that in plants, as in mammals and insects, PcG proteins control expression of homeobox genes. Using the Yeast two hybrid system and pull-down assays we demonstrated that FIE protein interact with MEA via the N-terminal region (Publication 1). Moreover, CURLY LEAF protein, an additional member of the SET domain family interacts with FIE as well. The overlapping expression patterns of FIE, with ether MEA or CLF and their common mutant phenotypes, demonstrate the versatility of FIE function. FIE association with different SET domain polycomb proteins, results in differential regulation of gene expression throughout the plant life cycle (Publication 3). In vitro interaction assays we have recently performed demonstrated that FIE interacts with the cell cycle regulatory component Retinobalsoma protein (pRb) (Publication 4). These results illuminate the potential mechanism by which FIE may restrain embryo sac central cell division, at least partly, through interaction with, and suppression of pRb-regulated genes. The results of this program generated new information about the initiation of reproductive development and expanded our understanding of how PcG proteins regulate developmental programs along the plant life cycle. The tools and information obtained in this program will lead to novel strategies which will allow to mange crop plants and to increase crop production.
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Yahav, Shlomo, John Brake et Orna Halevy. Pre-natal Epigenetic Adaptation to Improve Thermotolerance Acquisition and Performance of Fast-growing Meat-type Chickens. United States Department of Agriculture, septembre 2009. http://dx.doi.org/10.32747/2009.7592120.bard.

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: The necessity to improve broiler thermotolerance and performance led to the following hypothesis: (a) thethermoregulatory-response threshold for heat production can be altered by thermal manipulation (TM) during incubation so as to improve the acquisition of thermotolerance in the post-hatch broiler;and (b) TM during embryogenesis will improve myoblast proliferation during the embryonic and post-hatch periods with subsequent enhanced muscle growth and meat production. The original objectives of this study were as follow: 1. to assess the timing, temperature, duration, and turning frequency required for optimal TM during embryogenesis; 2. to evaluate the effect of TM during embryogenesis on thermoregulation (heat production and heat dissipation) during four phases: (1) embryogenesis, (2) at hatch, (3) during growth, and (4) during heat challenge near marketing age; 3. to investigate the stimulatory effect of thermotolerance on hormones that regulate thermogenesis and stress (T₄, T₃, corticosterone, glucagon); 4. to determine the effect of TM on performance (BW gain, feed intake, feed efficiency, carcass yield, breast muscle yield) of broiler chickens; and 5. to study the effect of TM during embryogenesis on skeletal muscle growth, including myoblast proliferation and fiber development, in the embryo and post-hatch chicks.This study has achieved all the original objectives. Only the plasma glucagon concentration (objective 3) was not measured as a result of technical obstacles. Background to the topic: Rapid growth rate has presented broiler chickens with seriousdifficulties when called upon to efficiently thermoregulate in hot environmental conditions. Being homeotherms, birds are able to maintain their body temperature (Tb) within a narrow range. An increase in Tb above the regulated range, as a result of exposure to environmental conditions and/or excessive metabolic heat production that often characterize broiler chickens, may lead to a potentially lethal cascade of irreversible thermoregulatory events. Exposure to temperature fluctuations during the perinatal period has been shown to lead to epigenetic temperature adaptation. The mechanism for this adaptation was based on the assumption that environmental factors, especially ambient temperature, have a strong influence on the determination of the “set-point” for physiological control systems during “critical developmental phases.” In order to sustain or even improve broiler performance, TM during the period of embryogenesis when satellite cell population normally expand should increase absolute pectoralis muscle weight in broilers post-hatch. Major conclusions: Intermittent TM (39.5°C for 12 h/day) during embryogenesis when the thyroid and adrenal axis was developing and maturing (E7 to E16 inclusive) had a long lasting thermoregulatory effect that improved thermotolerance of broiler chickens exposed to acute thermal stress at market age by lowering their functional Tb set point, thus lowering metabolic rate at hatch, improving sensible heat loss, and significantly decreasing the level of stress. Increased machine ventilation rate was required during TM so as to supply the oxygen required for the periods of increased embryonic development. Enhancing embryonic development was found to be accomplished by a combination of pre-incubation heating of embryos for 12 h at 30°C, followed by increasing incubation temperature to 38°C during the first 3 days of incubation. It was further facilitated by increasing turning frequency of the eggs to 48 or 96 times daily. TM during critical phases of muscle development in the late-term chick embryo (E16 to E18) for 3 or 6 hours (39.5°C) had an immediate stimulatory effect on myoblast proliferation that lasted for up to two weeks post-hatch; this was followed by increased hypertrophy at later ages. The various incubation temperatures and TM durations focused on the fine-tuning of muscle development and growth processes during late-term embryogenesis as well as in post-hatch chickens.
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Wolfenson, David, William W. Thatcher et James E. Kinder. Regulation of LH Secretion in the Periovulatory Period as a Strategy to Enhance Ovarian Function and Fertility in Dairy and Beef Cows. United States Department of Agriculture, décembre 2003. http://dx.doi.org/10.32747/2003.7586458.bard.

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The general research objective was to increase herd pregnancy rates by enhancing corpus luteum (CL) function and optimizing follicle development, in order to increase conception rate and embryo survival. The specific objectives were: to determine the effect of the duration of the preovulatory LH surge on CL function; to determine the function of LH during the postovulatory period on CL development; to optimize CL differentiation and follicle development by means of a biodegradable GnRH implant; to test whether optimization of CL development and follicle dynamics in timed- insemination protocols would improve fertility in high-yielding dairy cows. Low fertility in cattle results in losses of hundreds of millions of dollars in the USA and Israel. Two major causes of low fertility are formation of a functionally impaired CL, and subsequent enhanced ovarian follicle development. A functionally impaired CL may result from suboptimal LH secretion. The two major causes of low fertility in dairy cattle in US and Israel are negative energy status and summer heat stress; in both situations, low fertility is associated with reductions in LH secretion and impaired development of the ovulatory follicle and of the CL. In Florida, the use of 450-mg deslorelin (GnRH analogue) implants to induce ovulation, under the Ovsynch protocol resulted in a higher pregnancy rates than use of 750-mg implants, and pregnancy losses tended to decrease compared to controls, due probably to decrease in follicular development and estradiol secretion at the time of conceptus signaling to maintain the CL. An alternative strategy to enhance progesterone concentrations involved induction of an accessory CL by injection of hCG on day 5 after the cows were inseminated. Treatment with hCG resulted in 86% of the cows having two CLs, compared with 23% of the control cows. Conception rates were higher among the hCG-treated cows than among the controls. Another approach was to replace the second injection of GnRH analogue, in a timed-insemination protocol, with estradiol cypionate (ECP) injected 24 h after the injection of PGF₂ₐ Pregnancy rates were comparable with those obtained under the regular Ovsynch (timed- AI) program. Use of ECP induced estrus, and cows inseminated at detected estrus are indeed more fertile than those not in estrus at the time of insemination. Collectively, the BARD-supported programs at the University of Florida have improved timed insemination programs. In Ohio, the importance of the frequency of LH episodes during the early stages of the estrous cycle of cattle, when the corpus luteum is developing, was studied in an in vivo experiment in which cows were subjected to various episodic exposures to exogenous bovine LH. Results indicate that the frequent LH episodes immediately following the time of ovulation are important in development of the corpus luteum, from the points of view of both size and functionality. In another study, rates of cell proliferation and numbers of endothelial cells were examined in vitro in CLs collected from cows that received post-ovulation pulsatile LH treatment at various frequencies. The results indicate that the corpora lutea growth that results from luteal cell proliferation is enhanced by the episodes of LH release that occur immediately after the time of ovulation in cattle. The results also show that luteal endothelial cell numbers did not differ among cows treated with different LH doses. In Israel. a longer duration of the preovulatory LH surge stimulated the steroidogenic capacity of granulosa-derived luteal cells, and might, thereby, contribute to a higher progesterone output from the bovine corpus luteum. In an in vivo study, a subgroup of high-yielding dairy cows with extended estrus to ovulation interval was identified. Associated with this extended interval were: low plasma progesterone and estradiol concentrations and a low preovulatory LH surge prior to ovulation, as well as low post- ovulation progesterone concentration. In experiments based on the above results, we found that injection of GnRH at the onset of estrus increased the LHpeak, prevented late ovulation, decreased the variability between cows and elicited high and uniform progesterone levels after ovulation. GnRH at estrus onset increased conception rates, especially in the summer, and among primiparous cows and those with low body condition. Another study compared ovarian functions in multiparous lactating cows with those in nulliparous non-lactating heifers. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins that may account for the differences in fertility between heifers and cows.
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