17-P005 Molecular characterization of neural stem cells in medaka

While adult neurogenesis in mammals is mainly restricted to two telencephalic zones, in teleost fishes, neurogenesis has been observed in many brain areas. Hence, the medaka (Oryzias latipes) represents an excellent model to study neural stem cells (NSCs). In order to detect NSCs, we have relied on the fact that adult stem cells divide more slowly than quickly amplifying progenitor cells. By using two different thymidine analogs and performing long pulses separated by a long period of time, we have managed to identify cells that are double-labelled in the medaka brain. These slow-proliferating cells are likely to be NSCs. We have looked more precisely at neurogenesis in a cortical structure of the dorsal midbrain, the optic tectum. Cell proliferation occurs at its margin throughout life. With the thymidine analog labeling, we have identified some slow-dividing cells, in the tectum, forming a narrow line at the very periphery of the proliferative zone. This topographic organization allowed us to perform an insitu hybridization screen on medaka embryos and find a dozen of genes whose expression corresponds to this thin line of putative NSCs. By analyzing the functions of these genes, we hope to identify essential genes for adult NSC and embryonic NSC biology. We should be able to bring cues on the conserved features between fish and mammal stem cells and examine whether neurogenesis in adult teleosts is merely the continuation of an embryonic phase or a distinct process involving adult specific mechanisms for stemness maintenance.