Fibroblast growth factor 10 is a negative regulator of postnatal neurogenesis in the mouse hypothalamus

New neurons are generated in the postnatal rodent hypothalamus, with a subset of tanycytes in the third ventricular (3V) wall serving as neural stem/progenitor cells. However, the precise stem cell niche organization, the intermediate steps and the endogenous regulators of postnatal hypothalamic neurogenesis remain elusive. Quantitative lineage-tracing in vivo revealed that conditional deletion of fibroblast growth factor 10 (Fgf10) from Fgf10-expressing beta-tanycytes at postnatal days (P)4-5 results in the generation of significantly more parenchymal cells by P28, composed mostly of ventromedial and dorsomedial neurons and some glial cells, which persist into adulthood. A closer scrutiny in vivo and ex vivo revealed that the 3V wall is not static and is amenable to cell movements. Furthermore, normally beta-tanycytes give rise to parenchymal cells via an intermediate population of alpha-tanycytes with transient amplifying cell characteristics. Loss of Fgf10 temporarily attenuates the amplification of beta-tanycytes but also appears to delay the exit of their alpha-tanycyte descendants from the germinal 3V wall. Our findings suggest that transience of cells through the alpha-tanycyte domain is a key feature, and Fgf10 is a negative regulator of postnatal hypothalamic neurogenesis.