17-P021 Nanog-dependent segregation of germ line and soma in axolotl animal caps by patterning signals: Induction of primordial germ cells (PGCs) by FGF

Abstract

lineages. Because Nanog is required for the development of primordial germ cells (PGCs) in mice and axolotls, we propose that the deletion of Nanog in species often employed as experimental models, such as frogs and teleosts (Zebrafish; Danio rerio), has been compensated by the evolution of predetermined germ cells in these organisms. Our data highlights Nanog as a major component of the gene regulatory network that governs early development in the major trunk of chordate evolution. Maintenance of multipotency is a central question in stem cell biology. In the mouse embryo, mesodermal cells of the dorsal somite, the dermomyotome, give rise to different lineages such as vascular smooth and skeletal muscle. These multipotent stem cells express the Pax3 and Pax7 transcription factors, essential for the myogenic lineage. Here we identify a novel negative feedback loop between Pax3/7 and Foxc2. Using both genetic approaches and manipulation of external signals in somite explants, we demonstrate that the Pax3/7:Foxc2 ratio modulates myogenic versus vascular cell fates of dermomyotomal cells. This exemplifies the importance of such a mechanism of reciprocal repression in the maintenance and lineage commitment of multipotent stem cells. Fgf10 has been implicated in maintenance of stem cells in various embryonic and non-neural organs such as teeth and stomach. We have previously used Fgf10-LacZ reporter mice to show that the localization and fate of Fgf10-expressing cells in the adult mouse brain points to an involvement of Fgf10 in the control of neurogenesis in quiescent neurogenic niches (Hajihosseini etal., 2008. MCN 37: 857-868). In the adult hypothalamus, expression of Fgf10 is restricted to tanycytes which reside in the median eminence, at the floor of the third ventricle. Here, we have used a set of immunolabelling and neurosphere culture studies to study whether these Fgf10-expressing cells in the adult hypothalamus are neural stem cells or lineage-restricted neural progenitors.We find that in addition to Fgf10, tanycytes express BLBP, Nestin and Musashi. Fgf10 is downregulated as descendants of tanycytes migrate into the surrounding hypothalamic nuclei and express DARPP32 or the mature neuronal marker, NeuN. In invitro assays, we found that cells derived from the median eminence can generate neurospheres as efficiently as those derived from the lateral subventricular zones. Moreover, in differentiation assays, these neurospheres give rise to all three neural lineages: neurons (TuJ1+), astrocytes (GFAP+) and oligodendrocytes (olig2+). These data suggest that the adult hypothalamus contains a quiescent population of neural stem cells and, as in non-neural tissues, Fgf10 may play a critical role in the maintenance and/or differentiation of subpopulations of neural cells. Further studies are underway to verify and dissect the role of Fgf10 in this system. Pluripotency defines the ability of cells to produce all somatic cells and germ line cells. In mammals, primordial germ cells (PGCs) are induced from pluripotent c...