Evidence from Drosophila and also vertebrates predicts that two different sets of instructions may determine the development of the rostral and caudal parts of the body. This implies different cellular and inductive processes during gastrulation, whose genetic requirements remain to be understood. To date, four genes encoding transcription factors expressed in the presumptive vertebrate head during gastrulation have been studied at the functional level: Lim‐1, Otx‐2, HNF‐3β and goosecoid. We discuss here the potential functions of these genes in the formation (...) of rostral head as compared to posterior head and trunk, and in the light of recent fate map and expression analyses in mouse, chick, Xenopus and zebrafish. These data indicate that Lim‐1, Otx‐2 and HNF‐3β may be involved in the same genetic pathway controlling the formation of the prechordal mesendoderm, which is subsequently required for rostral head development. goosecoid may act in a parallel pathway, possibly in conjunction with other, yet unidentified, factors. (shrink)

Adult neurogenesis is an exciting and rapidly advancing field of research. It addresses basic biological questions, such as the how and why of de novo neuronal production during adulthood, as well as medically relevant issues, including the potential link between adult neural stem cells and psychiatric disorders, or how stem cell manipulation might be used as a strategy for neuronal replacement. Current research mainly focuses on rodents, but we review here recent examination of non‐mammalian vertebrates, which demonstrates that bona fide (...) adult neural stem cells exist in these species. Importantly, especially in teleost fish, these cells can be abundant and located in various brain areas. Hence, non‐mammalian vertebrate species provide invaluable comparative material for extracting core mechanisms of adult neural stem cell maintenance and fate. BioEssays 29:745–757, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Adult stem cell populations must coordinate their own maintenance with the generation of differentiated cell types to sustain organ physiology, in a spatially controlled manner and over long periods. Quantitative analyses of clonal dynamics have revealed that, in epithelia, homeostasis is achieved at the population rather than at the single stem cell level, suggesting that feedback mechanisms coordinate stem cell maintenance and progeny generation. In the central nervous system, however, little is known of the possible community processes underlying neural stem (...) cell maintenance. Recent work, in part based on intravital imaging made possible in the adult zebrafish, conclusively highlights that homeostasis in neural stem cell pools may rely on population asymmetry and long‐term spatiotemporal coordination of neural stem cell states and fates. These results suggest that neural stem cell assemblies in the vertebrate brain behave as self‐organized systems, such that the stem cells themselves generate their own intrinsic niche. (shrink)