The neural crest (NC) is a multipotent cell population in vertebrate embryos with extraordinary migratory capacity. The NC is crucial for vertebrate development and forms a myriad of cell derivatives throughout the body, including pigment cells, neuronal cells of the peripheral nervous system, cardiomyocytes and skeletogenic cells in craniofacial tissue. NC induction occurs at the end of gastrulation when the multipotent population of NC progenitors emerges in the ectodermal germ layer in the neural plate border region. In the process of NC fate specification, fate-specific markers are expressed in multipotent progenitors, which subsequently adopt a specific fate. Thus, NC cells delaminate from the neural plate border and migrate extensively throughout the embryo until they differentiate into various cell derivatives. Multiple signalling pathways regulate the processes of NC induction and specification. This review explores the ongoing role of the Wnt/β-catenin signalling pathway during NC development, focusing on research undertaken in the Teleost model organism, zebrafish (Danio rerio). We discuss the function of the Wnt/β-catenin signalling pathway in inducing the NC within the neural plate border and the specification of melanocytes from the NC. The current understanding of NC development suggests a continual role of Wnt/β-catenin signalling in activating and maintaining the gene regulatory network during NC induction and pigment cell specification. We relate this to emerging models and hypotheses on NC fate restriction. Finally, we highlight the ongoing challenges facing NC research, current gaps in knowledge, and this field’s potential future directions.
Tetrapods and fish have adapted distinct carbamoyl-phosphate synthase (CPS) enzymes to initiate the ornithine urea cycle during the detoxification of nitrogenous wastes. We report evidence that in the ureotelic subgenus of extremophile fish Oreochromis Alcolapia , CPS III has undergone convergent evolution and adapted its substrate affinity to ammonia, which is typical of terrestrial vertebrate CPS I. Unusually, unlike in other vertebrates, the expression of CPS III in Alcolapia is localized to the skeletal muscle and is activated in the myogenic lineage during early embryonic development with expression remaining in mature fish. We propose that adaptation in Alcolapia included both convergent evolution of CPS function to that of terrestrial vertebrates, as well as changes in development mechanisms redirecting CPS III gene expression to the skeletal muscle.
The kinetic properties of phosphorylase (EC 2.4.1.1) and 6-phosphofructokinase (EC 2.7.1.11) extracted from a crassulacean acid metabolism (CAM) plant, Kalanchoe daigremontiana Hamet et Perrier, and a C4 plant, Atriplex spongiosa F. Muell., were compared. The phosphorylase from the CAM plant was strongly inhibited by P1 (1 mM), phosphoenolpyruvate (PEP) (2 mM) and glucose (4 mM). The C4 phosphorylase was less strongly inhibited by P1, and not at all by PEP or glucose. The C4 6-phosphofructokinase was, at Km levels of substrate, about 100 times more sensitive to inhibition by PEP than the CAM enzyme. These results are discussed as the basis for a biochemical regulation of carbohydrate metabolism in CAM plants at night.
Although it is widely accepted that the cellular and molecular mechanisms of vertebrate cardiac development are evolutionarily conserved, this is on the basis of data from only a few model organisms suited to laboratory studies. Here, we investigate gene expression during cardiac development in the extremophile, non-model fish species, Oreochromis (Alcolapia) alcalica. We first characterise the early development of O. alcalica and observe extensive vascularisation across the yolk prior to hatching. We further investigate heart development by identifying and cloning O. alcalica orthologues of conserved cardiac transcription factors gata4, tbx5, and mef2c for analysis by in situ hybridisation. Expression of these three key cardiac developmental regulators also reveals other aspects of O. alcalica development, as these genes are expressed in developing blood, limb, eyes, and muscle, as well as the heart. Our data support the notion that O. alcalica is a direct-developing vertebrate that shares the highly conserved molecular regulation of the vertebrate body plan. However, the expression of gata4 in O. alcalica reveals interesting differences in the development of the circulatory system distinct from that of the well-studied zebrafish. Understanding the development of O. alcalica embryos is an important step towards providing a model for future research into the adaptation to extreme conditions; this is particularly relevant given that anthropogenic-driven climate change will likely result in more freshwater organisms being exposed to less favourable conditions.
The neural crest is a population of cells that emigrates from the dorsal neural tube during early embryogenesis and migrates extensively to give rise to a myriad of cell types. Patterns of migration are controlled largely by extracellular cues in the environment. Neural crest cells are initially multipotent, but the mechanism whereby cells choose and become committed to individual fates remains a longstanding source of contention. Cell fate specification – the selection of an individual cell fate from all the possibilities available to a multipotent progenitor – is generally considered to be a progressive process. However, a recent flurry of single‐cell transcriptional profiling studies indicates a more dynamic process in which cells with retained multipotency display expression of competing genetic modules specifying different fates. Extracellular cues in the migratory and postmigratory environment act together with intrinsic transcription factors to ensure that specific fates are chosen. Key Concepts The neural crest is an important tissue, as reflected in its nickname, ‘the fourth germ layer’. Neural crest cells give rise to many different cell types. Neural crest cells are induced at the boundary of the developing neural plate and prospective epidermis. Neural crest induction depends on BMP signalling in the prospective epidermis and Wnt signalling from the underlying mesoderm. These signals induce neural crest in two phases, specification of the neural plate border, and specification/maintenance of definitive neural crest. Neural crest migration patterns are complex, and usually specific to the derivative fate adopted. Neural crest migration is controlled by the environmental distribution of repellent and attractive/permissive signals, with specific receptor expression in the neural crest cells determining their response. All neural crest cells are initially multipotent, with specification of individual derivative fates resulting from competition between genetic modules controlling pairs of fates. Nevertheless, it is proposed that these specified cells retain a cryptic full multipotency, most visible in adult neural crest‐derived stem cells. Neural crest fate specification is then a dynamic process in which extracellular factors influence the transcriptional state of the cell, eventually driving it towards a specific fate choice. Fate specification results from transcriptional activation of key genes encoding (a combination of) specific transcription factors. These transcription factors, together with ongoing extracellular signals, activate and maintain the fate‐specific gene regulatory networks that characterise each cell type.
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