Academic literature on the topic 'Amphibian embryo research'

The appearance of the embryonic shield, a slight thickening at the leading edge of the blastoderm during the formation of the germ ring, is one of the first signs of dorsoventral polarity in the zebrafish embryo. It has been proposed that the shield plays a role in fish embryo patterning similar to that attributed to the amphibian dorsal lip. In a recent study, we fate mapped many of the cells in the region of the forming embryonic shield, and found that neural and mesodermal progenitors are intermingled (Shih, J. and Fraser, S.E. (1995) Development 121, 2755–2765), in contrast to the coherent region of mesodermal progenitors found at the amphibian dorsal lip. Here, we examine the fate and the inductive potential of the embryonic shield to determine if the intermingling reflects a different mode of embryonic patterning than that found in amphibians. Using the microsurgical techniques commonly used in amphibian and avian experimental embryology, we either grafted or deleted the region of the embryonic shield. Homotopic grafting experiments confirmed the fates of cells within the embryonic shield region, showing descendants in the hatching gland, head mesoderm, notochord, somitic mesoderm, endoderm and ventral aspect of the neuraxis. Heterotopic grafting experiments demonstrated that the embryonic shield can organize a second embryonic axis; however, contrary to our expectations based on amphibian research, the graft contributes extensively to the ectopic neuraxis. Microsurgical deletion of the embryonic shield region at the onset of germ ring formation has little effect on neural development: embryos with a well-formed and well-patterned neuraxis develop in the complete absence of notochord cells. While these results show that the embryonic shield is sufficient for ectopic axis formation, they also raise questions concerning the necessity of the shield region for neural induction and embryonic patterning after the formation of the germ ring.

Vertebrate model systems are central to characterize the outcomes of ethanol exposure and the etiology of fetal alcohol spectrum disorder (FASD), taking advantage of their genetic and morphological closeness and similarity to humans. We discuss the contribution of amphibian embryos to FASD research, focusing on Xenopus embryos. The Xenopus experimental system is characterized by external development and accessibility throughout embryogenesis, large clutch sizes, gene and protein activity manipulation, transgenesis and genome editing, convenient chemical treatment, explants and conjugates, and many other experimental approaches. Taking advantage of these methods, many insights regarding FASD have been obtained. These studies characterized the malformations induced by ethanol including quantitative analysis of craniofacial malformations, induction of fetal growth restriction, delay in gut maturation, and defects in the differentiation of the neural crest. Mechanistic, biochemical, and molecular studies in Xenopus embryos identified early gastrula as the high alcohol sensitivity window, targeting the embryonic organizer and inducing a delay in gastrulation movements. Frog embryos have also served to demonstrate the involvement of reduced retinoic acid production and an increase in reactive oxygen species in FASD. Amphibian embryos have helped pave the way for our mechanistic, molecular, and biochemical understanding of the etiology and pathophysiology of FASD.

Abstract Because of higher extinction rates due to human and natural factors, more basic and applied research in reproductive biology is required to preserve wild species and design proper strategies leading to sustainable populations. The objective of the review is to highlight recent, inspiring breakthroughs in wildlife reproduction science that will set directions for future research and lead to more successes in conservation biology. Despite new tools and approaches allowing a better and faster understanding of key mechanisms, we still know little about reproduction in endangered species. Recently, the most striking advances have been obtained in nonmammalian species (fish, birds, amphibians, or corals) with the development of alternative solutions to preserve fertility or new information about parental nutritional influence on embryo development. A novel way has also been explored to consider the impact of environmental changes on reproduction—the allostatic load—in a vast array of species (from primates to fish). On the horizon, genomic tools are expected to considerably change the way we study wildlife reproduction and develop a concept of “precision conservation breeding.” When basic studies in organismal physiology are conducted in parallel, new approaches using stem cells to create artificial gametes and gonads, innovations in germplasm storage, and more research on reproductive microbiomes will help to make a difference. Lastly, multiple challenges (for instance, poor integration of new tools in conservation programs, limited access to study animals, or few publication options) will have to be addressed if we want reproductive biology to positively impact conservation of biodiversity.

Humans and animals adapt to space flight conditions. However, the adaptive changes of fully formed organisms differ radically from the responses of vertebrate embryos, foetuses, and larvae to space flight. Development is associated with active cell proliferation and the formation of organs and systems. The instability of these processes is well known. Over 20 years has passed since the last systematic experiments on vertebrate reproduction and development in space flight. At the same time, programs are being prepared for the exploration of Mars and the Moon, which justifies further investigations into space flight’s impact on vertebrate development. This review focuses on various aspects of reproduction and early development of vertebrates in space flights. The results of various experiments on fishes, amphibians, reptiles, birds and mammals are described. The experiments in which our team took part and ontogeny of the vertebrate nervous and special sensory systems are considered in more detail. Possible causes of morphological changes are also discussed. Research on evolutionarily and taxonomically different models can advance the understanding of reproduction in microgravity. Reptiles, in particular, geckos, due to their special features, can be a promising object of space developmental biology.

After its publication in 1999 as a DNA-binding and SMAD-binding transcription factor (TF) that co-determines cell fate in amphibian embryos, ZEB2 was from 2003 studied by embryologists mainly by documenting the consequences of conditional, cell-type specific Zeb2 knockout (cKO) in mice. In between, it was further identified as causal gene causing Mowat-Wilson Syndrome (MOWS) and novel regulator of epithelial–mesenchymal transition (EMT). ZEB2’s functions and action mechanisms in mouse embryos were first addressed in its main sites of expression, with focus on those that helped to explain neurodevelopmental and neural crest defects seen in MOWS patients. By doing so, ZEB2 was identified in the forebrain as the first TF that determined timing of neuro-/gliogenesis, and thereby also the extent of different layers of the cortex, in a cell non-autonomous fashion, i.e., by its cell-intrinsic control within neurons of neuron-to-progenitor paracrine signaling. Transcriptomics-based phenotyping of Zeb2 mutant mouse cells have identified large sets of intact-ZEB2 dependent genes, and the cKO approaches also moved to post-natal brain development and diverse other systems in adult mice, including hematopoiesis and various cell types of the immune system. These new studies start to highlight the important adult roles of ZEB2 in cell–cell communication, including after challenge, e.g., in the infarcted heart and fibrotic liver. Such studies may further evolve towards those documenting the roles of ZEB2 in cell-based repair of injured tissue and organs, downstream of actions of diverse growth factors, which recapitulate developmental signaling principles in the injured sites. Evident questions are about ZEB2’s direct target genes, its various partners, and ZEB2 as a candidate modifier gene, e.g., in other (neuro)developmental disorders, but also the accurate transcriptional and epigenetic regulation of its mRNA expression sites and levels. Other questions start to address ZEB2’s function as a niche-controlling regulatory TF of also other cell types, in part by its modulation of growth factor responses (e.g., TGFβ/BMP, Wnt, Notch). Furthermore, growing numbers of mapped missense as well as protein non-coding mutations in MOWS patients are becoming available and inspire the design of new animal model and pluripotent stem cell-based systems. This review attempts to summarize in detail, albeit without discussing ZEB2’s role in cancer, hematopoiesis, and its emerging roles in the immune system, how intense ZEB2 research has arrived at this exciting intersection.

Hypothermic storage of sperm in a liquid state without freezing, without the use of either liquid nitrogen or dry ice as well as special cryological equipment is an interesting and attractive research line in reproductive biology in terms of practical application. Historically, hypothermia is the very first approach to the preservation of genetic material, but, despite this, the methods of hypothermic storage of gametes and embryos have not received proper development and application in animal husbandry, giving way to cryopreservation. One of the main reasons for this is the high species-specific resistance to cold storage. The technologies for hypothermic storage of sperm existing today and recommended for use in fish farming and in sturgeon breeding in particular are still not effective enough and require further improvement. This short review outlines the history of the development of technologies for the hypothermic storage of sturgeon sperm, considers a number of methodological approaches, concepts and ideas behind these developments. The male reproductive system in sturgeons, the structure and physiology of spermatozoa have a number of features that distance them from teleost fishes, but partly relate to amphibians and higher vertebrates. This made it possible to apply to sturgeons some successful approaches and achievements in the development of methods for hypothermic storage of mammalian (mouse and human) sperm. Thus, the most effective and possibly promising approach is partial or complete replacement of seminal plasma with salt-free isotonic solutions based on sugars (oligosaccharides) and albumin. The purpose of this review is to draw the attention of fish farmers and researchers to developments and advances in hypothermic sperm storage.

Severe declines of the mountain yellow-legged frog (MYLF, Rana muscosa) led to establishment of a captive population at the San Diego Zoo Institute for Conservation Research. With less than 200 adults estimated to remain in the wild, the Institute’s MYLF colony currently holds approximately 30% of the entire gene pool. Simulating natural seasonality by artificial brumation and manipulation of atmospheric temperature and light cycles is an integral part of this species’ management in captivity. However, over 5 years, the number of females that have oviposited has decreased from 80% in 2011 to 28% in 2014. It is unclear if changes in reproduction are related to husbandry or a lack of information regarding the natural reproductive cycles of these animals. Therefore, we examined the effects of hormone treatments on reproduction in the MYLF captive population. Prior to breeding, 21 females and 18 males were evenly assigned to either a control group (IP injection of PBS) or hormone-treated group [IP injection of gonadotropic releasing hormone (GnRH, D-Ala6, des-GLy10 ethylamide LHRH derivative) at 0.4 µg g–1 of body weight and metoclopramide (dopamine inhibitor) at 10 µg g–1 of body weight]. Males and females were housed in groups of 3 males and 3 females and allowed to choose their mate. Once a male had amplexed a female they were housed in pairs until oviposition occurred or until males ceased amplexus. Responses recorded during this study included amplexus, spermiation, oviposition, and embryonic cleavage. There was no significant difference in the number of eggs deposited by females treated with hormones and untreated controls (P = 0.1949) nor were there any differences between groups in the number of embryos that cleaved (P = 0.673) or survived to tadpole stage (P = 0.629). No significant differences were detected between the numbers of males that amplexed in the control or treated groups (P = 0.1120). Urine collected from 10/18 amplexed males (7 hormone-treated and 3 controls) indicated that 57% percent of hormone-treated males and 67% of control males were spermiating at the time of collection. Therefore, hormone treatments did not increase the number of eggs oviposited or the number of males spermiating or amplexing. Closer analysis of individual female reproductive histories indicated that 48% of captive female MYLF oviposited just once in 5 years, 40% in 2 consecutive years, 8% oviposited eggs in 2 consecutive years, skipped a year, and then oviposited again in 2 consecutive years, and 4% oviposited in 3 consecutive years. The number of females ovipositing in 2015 was significantly higher than 2012 (P = 0.0002), 2013 (P = 0.0001), and 2014 (P = 0.0026), but not 2011 (P = 0.0885), suggesting breeding may not occur annually in females. Understanding the breeding cycles of MYLF females will enable managers to determine if and when hormone administration is efficacious in captive amphibian breeding populations.