Thèses sur le sujet « Postembryonic »

Thesis (M.S.)--University of North Carolina at Chapel Hill, 2009.
Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Biology." Discipline: Biology; Department/School: Biology.

A functional central nervous system (CNS) is composed of numerous types of neurons. Neurons are derived from a limited number of multipotent neural stem cells. Previous studies have suggested three major strategies nature uses to diversify neurons: lineage identity specification that gives an individual neural stem cell distinct identity based on its position in the developing CNS; temporal identity specification that gives neurons derived from a neural stem cell distinct identities based on their birth-order within the lineage; and binary cell fate specification that gives different identities to the two sister postmitotic neurons derived from the terminal division of a common precursor. Through the combination of the three strategies, almost unlimited neuron types can be generated. To understand neuronal diversification, we have to understand the underlying molecular mechanisms of each of the three strategies. The fruit fly Drosophila melanogaster, has been an excellent model for studying neuronal diversity, mainly due to its easily traceable nervous system and an impressive collection of genetic tools. Studies in fly have provided us fundamental insights into lineage identity, temporal identity, and binary cell fate specifications. Nevertheless, previous studies mostly centered on the embryonic ventral nerve cord (VNC) because of its simpler organization. Our understanding of the generation of neuronal diversity in the fly brain is still rudimentary. In this thesis work, I focused on the mushroom body (MB) and three antennal lobe neuronal lineages, studying their neuronal diversification during postembryonic brain development. In Chapter I, I reviewed the previous studies that have built our current understanding of the neuronal diversification. In Chapter II, I showed that MB temporal identity changes are instructed by environmental cues. In Chapter III, to search for the potential factors that mediate the environmental control of the MB temporal identity changes, I silenced each of the 18 nuclear receptors (NRs) in the fly genome using RNA interference. Although I did not identify any NR important for the regulation of MB temporal identities, I found that unfulfilled is required for regulating axon guidance and for the MB neurons to acquire all major subtype-specific identities. In Chapter IV, I demonstrated that the Notch pathway and its antagonist Numb mediate binary cell fate determination in the three classical antennal lobe neuronal lineages— anterodorsal projection neuron (adPN), lateral antennal lobe (lAL), and ventral projection neuron (vPN)—in a context-dependent manner. Finally, in Chapter V, I did detailed lineage analysis for the lAL lineage, and identified four classes of local interneurons (LNs) with multiple subtypes innervating only the AL, and 44 types projection neurons (PNs) contributing to olfactory, gustatory, and auditory neural circuits. The PNs and LNs were generated simultaneously but with different tempos of temporal identity specification. I also showed that in the lAL lineage the Notch pathway not only specifies binary cell fates, but is also involved in the temporal identity specification.

To understand the molecular basis of developmental control of cell division during C. elegans organogenesis, two different approaches were taken. First, a screen was performed to identify mutants with altered numbers of intestinal nuclei using a reporter transgene specific to the intestinal nuclei. The intestine displays three different cell division patterns; mitosis, karyokinesis and endoreplication, therefore, in this screen we could potentially isolate mutants in genes affecting any of these different cell cycles. An F2 semi-clonal screen was performed and mutants with fewer or supernumerary numbers of intestinal nuclei were isolated. One mutant, rr31, with twice the wild type complement of intestinal nuclei was mapped and the defect was subsequently shown to be due to a gain-of-function mutation in the cell cycle phosphatase cdc-25.1. Further characterization of the cdc-25.1(gf) mutant, showed that the extra intestinal cells arise from an additional division of the intestinal cell precursors during embryogenesis, and that this phenotype is unique to the intestinal lineage. (Abstract shortened by UMI.)

Initiation of postembryonic development is an important event for normal C. elegans development. Extrinsic factors affect development as well as intrinsic developmental cues. In order to investigate the molecular basis of initiation of postembryonic development, a genetic screen was performed to identify temperature-sensitive mutants that cannot initiate the cell divisions associated with postembryonic development at the restrictive temperature. Hydroxyurea (HU), a DNA replication inhibitor, was used as a tool to select against worms that initiate postembryonic cell divisions and/or the developmental program. 1,600,000 haploid genomes were screened, and 20 mutants have been isolated. 6 of them have been mapped to a relatively small genetic interval, and one inx-6 has been cloned and encodes an innexin family protein. Mutation of inx-6 caused abnormalities in pharyngeal pumping, resulting in worms that could not feed. The functions of a cyclin B homologue (ZC168.4) in postembryonic development have also been studied since cyclin B mutants also have postembryonic developmental arrest phenotype. Results indicate that zygotic expression of cyclin B is absolutely required for normal postembryonic development. Moreover, we found a novel function of this cyclin B homologue, which demonstrates an uncommon paternal effect required for spermatogenesis and/or fertilization.

Postembryonic neuroblasts (pNBs) in the Drosophila larval CNS are considered to be neural stem cells production most of the neurons of the adult Drosophila central nervous system (CNS). The pNBs are derived from the embryonic neuroblasts (NBs). After a period of quiescence at the end of embryogenesis they reactivate during larval life and proliferate extensively for a limited period. The pNBs are able to self-review in each division and also to produce a precursor cell that will generate two postmitotic cells that fully differentiate at metamorphosis. Therefore, the pNBs provide a good model to investigate the mechanisms involved in the regulation of neural stem cells. The aim of this research was to investigate whether Notch signalling and the transcription factor Grainyhead have roles in regulating pNBs processes. Before investigating the regulation of the pNBs behaviour it was first necessary to characterise in more detail the characteristics of these cells and their progeny. Several genes that are expressed in the embryonic CNS were selected to further study. Among these I identified some factors that are expressed only in specific pNB lineages, such as Gsb-p and others that are expressed at a specific stage in all lineages such as Prospero. Based on their expression pattern it appears that Gsb-p is likely to perform a similar function in the larval CNS as in the embryo. In contrast the distribution of Prospero suggest different roles in the pNB lineages. The result was first that the Notch pathway is active in the pNBs, indicated by the expression of Notch target gene mg. However, the results obtained, using clonal analysis to manipulate Notch function in the pNB lineages, indicate that Notch does not have a role in maintaining the undifferentiated state of the pNBs or their proliferative state. In contrast to its function in vertebrate systems where it is able to regulate the uncommitted state of the neural progenitor cells. The analysis of grh mutant indicated that Grh has a role in regulating the proliferation and/or cell death of the pNBs.

A widely used distinction among articles that usually composed an arthropod appendage is the one between true articles and annuli. This distinction is often claimed to be based on the anatomy of the muscular system, true articles have intrinsic musculature while annuli do not. Annuli are also usually considered a subdivision of a true article. Recently, it has also been noted that annuli tend to be produced later during development. Observations on development of Drosophila appendages also seem to support a basic difference between the process that produce true article and the one that produce annuli. In the present project I studied selected aspects of article anatomy and development, in order to understand: a) which are (if present) the developmental similarities among annuli of different appendages and different arthropods, and b) which are (if present) the developmental differences between annuli and true articles. I decided to focalise the research on two topics: a) the relationships between muscles, muscle insertions and joints, and b) the mechanism of annulation in flagellar structures (terminal part of an appendage composed of only annuli) and its relationship with growth at the cellular level. According to the definitions of true articles and annuli given above, the anatomy of the muscular system is the most important aspect. For the most studied true articles, those of insect leg, there is evidence of a close developmental relationship between the development of the arthrodial membrane cells (epidermal cells that produce the joint) and muscle insertions. However some variation is expected as annuli are supposed to be joint without any muscle insertion. Parts of appendages composed of only annuli often show indeterminate postembryonic increasing in the number of annuli. The mechanism by which new annuli are produced has been studied only in few species or groups, and only for the antennae. Where both the mechanism of article production and the overall growth have been studied, a close relationship between the two was noted, but little is known about the development of the epidermis (cellular division, differentiation and apoptosis) during segmentation. Different models have been employed to study the relationships between muscles, muscle insertions and joints and these are: the naupliar appendages (first antennae and exopod of both second antennae and mandibles) of the cirriped crustacean Balanus improvisus Darwin, 1854, the exopod of the naupliar second antennae of the branchiopod crustacean Artemia sp., the antennae of the centipede Lithobius forficatus (Linnaeus, 1758) and the rami of the pleopods of the malacostracan crustacean Gammarus roeselii Gervais, 1835. In these models the segmentation, the muscular system and the postembryonic changes have been studied. Literature on naupliar appendages anatomy and postembryonic development has also been reviewed in detail. There are some muscles running parallel to the proximo-distal axis throughout the first antennae and the exopod of both second antennae and mandibles in the nauplii of B. improvisus. These muscles have insertions on every joint. The exopod of both second antennae and mandibles increase in article number during naupliar development and new joints have new intermediate insertion of already present muscles. Very similar conditions are usually found in the naupliar appendages of other crustaceans. Unexpected results have been obtained on the exopod of naupliar second antennae of Artemia. The exopod has 8-10 natatory setae (number with individual variation) on the posterior-ventral side, which have some cuticular folds at their base, resembling a joint; on the opposite side there are 8-14 (number with individual variation) cuticular folds. Number and position of setae and cuticular folds do not match and thus complete joints are lacking. Three muscles are present within the exopod; they run parallel to the proximo-distal axis and have insertions at the base of a seta (for the two muscles that are on that side) or on a cuticular fold (for the single muscle that run on that side). Since setae and cuticular folds do not match, there is mismatch also in the muscular insertions of the two sides. In the antennae of L. forficatus there are four muscles that run parallel to the proximo-distal axis throughout their length. These muscles have an insertion on each joint. The rami of the pleopods of G. roeselii have two muscles that run parallel to the proximo-distal axis throughout their length, with insertion on each joint. Thus, even if the articles of the antennae of Lithobius are usually considered true articles and those of the naupliar exopod of second antennae and mandibles of Balanus (and other crustaceans) as well as those of the rami of the pleopods of Gammarus are usually considered annuli, there is no difference on the presence/absence of muscular insertions. Anatomical differences are present in the structure of the muscular insertion (tendon matrix) and of the joint (extent of arthrodial membrane). All the appendages originally studied here or those discussed in the review that increase in article number during postembryonic development produce new joints with new intermediate insertions of already present muscles. The mechanism of annulation in flagellar structures has been studied in detail in the flagellum of the second antennae of isopod crustaceans. Asellus aquaticus (Linnaeus, 1758) has been the main species studied, with observations on both normal postembryonic development and regeneration; other species studied have been Idotea chelipes (Pallas, 1766), Lirceus fontinalis Rafinesque-Schmaltz, 1820 e Sphaeroma serratum (Fabricius, 1787). Most of the flagellum of A. aquaticus is composed of "quartets": four articles units where each article has a specific setal distribution pattern. New articles and quartets are produced during the whole life, in the proximal part of the flagellum: the first article divides and produces articles that, relatively independently from each others, divides three more times producing a quartet. During regeneration the mechanism is identical, although there are some difference in the relative development of different quartets, irrespectively of the amputation point. In L. fontinalis (Asellidae) most of the flagellum is composed of couples of articles, each one of which bearing setae correspondent to those of two articles of an A. aquaticus quartet. The mechanism of production is also very similar, but articles produced by the first one divide just once. In L. fontinalis some variability is, anyhow, present and it is sometimes possible to observe three articles units (an article produced by the first one divided twice) and even four article units identical to those of A. aquaticus. In S. serratum (Sphaeromatidae) most of the flagellum has articles with subequal setal pattern; the mechanism of new article production involves the division of the first article and one further division of the articles produced by it. In I. chelipes (Idoteidae) most of the flagellum has articles with subequal setal pattern; the mechanism of new article production involves, unlike S. serratum, the division of the first article only. The mechanism of annulation in flagellar structures and its relationship with growth at the cellular level has been studied in two models (already used for other observations previously described): the flagellum of the second antennae of A. aquaticus and the rami of the pleopods of G. roeselii. The pleopodal rami of G. roeselii increase their article number for the whole life. New articles are produced in the proximal part, by division of the first article only. In this structure, as well as in the second antennal flagellum of A. aquaticus, mitotic figures are found only in the proximal part and going distally, to "older" parts, nuclei becomes more spaced and longer. Thus, in both the models studied there is a proximal proliferative zone; cells produced there are then moved distally by the production of new cells and they go through a shape change. How this process is related to the diversity of the segmentation mechanism is not currently understood. The production of joints and muscle insertions are developmentally correlated processes. Evidence for it was already available for the articles (except tarsomeres) of insect leg, but I have shown in this thesis this is also true for other arthropod appendages, since new joints produced during postembryonic development have also new muscle insertions, if a muscle is present. Joints without any muscle insertion can occur in arthropod appendages, but these have either no muscle passing through or just tendon(s); the occurrence of joints without any muscle insertion but with muscle(s) passing through is currently very doubtful. Thus, the traditional distinction between true article and annuli based on the presence/absence of intrinsic musculature is wrong; articles usually considered annuli may have muscle insertion. Functionally, however, this distinction is still valid, since articles with intermediate insertions of muscles parallel to the proximo-distal axis can not move the appendage independently from other articles as the other true articles (equipped with intrinsic and antagonist muscles confined within them) can do. The naupliar antennal exopod of Artemia also provide evidence that joints and muscle insertions are developmentally correlated processes. In this model there are not complete joints, but just "partial" cuticular folds, but also these (which are probably derived from a complete joint) have muscle insertions. A general difference in the timing of expression of true articles and annuli was previously noted and has been here discussed in some deep. A difference in timing exists, but it is not between true articles and annuli (if defined by the presence/absence of muscle insertions) but between articles with independent movements and articles with movements not independent to each others. Also this ontogenetic difference is connected with the different functional morphology of these articles. Flagellar structure also exhibits similarities in their postembryonic development, and these similarities are connected to the presence of a specific proximal "growth zone" (a zone where both new articles are produced and mitoses are localized). The phylogenetic distribution of this growth zone is discussed and it is here proposed to be an ancestral condition for the postembryonic development of (first) antennae and rami of postantennulary appendages of, at least, mandibulate (myriapods, insects and crustaceans) arthropods.

In the present thesis, we have studied the metamorphosis of the cockroach Blattella germanica, focusing on two main periods of development, the embryonic and the postembryonic. In the embryonic development, we have studied the role of the juvenile hormone (JH), analysing the genes Methoprene-Tolerant (Met), Taiman (Tai), Krüppel homolog 1 (Kr-h1), and JH acid methyltransferase (JHAMT). We have also studied the transcription factor E93, which has a key role in adult morphogenesis, but that has never been studied in the embryo. Results have shown that both, JH and E93 play important roles during embryo development, especially in early stages. Regarding the postembryonic period, we studied the CREB binding protein (CBP) Nejire and the Transforming Growth Factor β (TGF-β) signalling pathway. Results have shown that both play relevant roles in the transition from the last nymphal stage to the adult.
En la presente tesis hemos estudiado la metamorfosis de la cucaracha Blattella germanica, centrándonos en dos períodos principales de desarrollo, el embrionario y el postembrionario. En el desarrollo embrionario, hemos estudiado el papel de la hormona juvenil (JH), analizando los genes Methoprene-Tolerant (Met), Taiman (Tai), el Krüppel homolog 1 (Kr-h1) y JH acid methyltransferase (JHAMT). También hemos estudiado el factor de transcripción E93, que tiene un papel clave en la morfogénesis adulta, pero que nunca se ha estudiado en el embrión. Los resultados han demostrado que tanto la JH como el factor E93 desempeñan papeles importantes durante el desarrollo del embrión, especialmente en etapas tempranas. En cuanto al período postembrionario, estudiamos la proteína de unión a CREB (CBP) Nejire y la vía de señalización Transforming Growth Factor β (TGF-β). Los resultados han demostrado que ambos desempeñan papeles relevantes en la transición entre la última fase ninfal y el adulto.

This thesis investigates the roles of embryonic and postembryonic neurogenesis in the transformation of the larval antennal center (LAC) into the adult antennal lobe (AL) in the brain of the sphinx moth Manduca sexta. By means of birthdating methods, postembryonic neurogenesis in the CNS was first observed in the brain of the mid-first larval instar, and then proceeded in an anterior-to-posterior pattern. Five stereotypic neuroblast nests (three lateral, two medial) were identified that appeared to be associated with the LAC. Cell death was observed shortly after onset of postembryonic neurogenesis from the mid-first larval instar until wandering stage W2. Fates of the five LAC-associated lineages were traced histologically with respect to the anterior, medial, and lateral cell groups (AC, MC, LC) of the AL. At pupal stage P3, the three lateral nests coalesce and give rise to the postembryonic component of the LC, which is clearly distinguishable by pupal stage P4. Nests D and E remain separate and give rise to the postembryonic components of the AC and MC, respectively. A pronounced sexual dimorphism in the number of neurons in the MC was observed as early as pupal stage P5. The increased number of neurons in lineage E of males is evident as early as larval stage V-O, suggesting that regulation of postembryonic lineage size may contribute to the dimorphism of adults. The cellular distributions of two neuropeptide phenotypes (allatotropin-like-immunoreactivity, ATIR; and FMRFa-like-immunoreactivity, FIR) were examined immunocytochemically in larval, pupal and adult olfactory regions. Both phenotypes were found in a small number of cells lateral to the LAC, but significantly greater immunostaining was observed in the LC of the AL. For both ATIR and FIR, double-label immunocytochemistry (using BrdU) demonstrated that a subpopulation of the cells observed in the adult are born postembryonically. The larval and adult positions of ATIR and FIR neurons, of an identified serotonin-immunoreactive neuron, and of the five neuroblast nests, were compared. In every case, the lateral position of cells with respect to the LAC neuropil, regardless of embryonic or postembryonic origin, predicts a positional fate in the LC of the AL.

INDROVÁ E. 2008: Development and growth of the benthic water bug (Aphelocheirus aestivalis (Fabricius, 1794) (Insecta: Heteroptera: Aphelocheiridae). MSc. Thesis, University of South Bohemia, Pedagogical Faculty, České Budějovice. 62 pp. Postembryonic morphogenesis of the benthic water bug (A. aestivalis) was studied. Morphometric characters were measured in specimens of population from the Dračice River (South Bohemia: Třeboňsko). Differential characters of individual developmental stages are described and illustrated. Growth of this species is characterised by diagrams and equations of selected body parametres.

The series of two fossil species belonging to the order Palaeodictyoptera from the Late Carboniferous of Kuznetsk Basin in Russia were re-examined. The two species as Tchirkovaea guttata and Paimbia fenestrata were investigated with emphasis on the wing growth and development in comparison with the structure of developing wings in recent mayflies. This fossil material of T. guttata and P. fenestrata was long considered by previous authors as undisputed evidence for a unique type of wing development in the Palaeozoic insects. The idea was that the larvae of these insects possessed the wings, which became articulated and fully movable already earlier during the postembryonic development and that these gradually growing wings changed their position from longitudinal to perpendicular to the body axis. Moreover, the development was supposed to include two or more subimaginal instars, implying that the fully winged instars moulted several times during postembryonic development. After detailed study of the available fossils and subsequent comparison of the fossil evidence with the development of wings in the recent mayfly Cloeon dipterum it was discovered, that the alleged series of immature, subimaginal and imaginal wings of T. guttata and P. fenestrata do not provide clear evidence that would support...

The diploma thesis observed the indicators of growth in individual developmental stages of our native crayfish (Astacus astacus, Austropotamobius torrentium, Astacus leptodactylus) and non-native crayfish (Pacifastacus leniusculus, Orconectes limosus) under experimental conditions. The next aim of work was to describe the time of hatching of these species, the moulting interval, the frequency of moulting and increase after individual moulting during the first vegetation season in two different temperatures (15{$\rm^o$}C a 21{$\rm^o$}C).