Hedgehog Signaling Regulates Neurogenesis in the Larval and Adult Zebrafish Hypothalamus.

Neurogenesis is now known to play a role in adult hypothalamic function, yet the cell-cell mechanisms regulating this neurogenesis remain poorly understood. Here, we show that Hedgehog (Hh)/Gli signaling positively regulates hypothalamic neurogenesis in both larval and adult zebrafish and is necessary and sufficient for normal hypothalamic proliferation rates. Hh-responsive radial glia represent a relatively highly proliferative precursor population that gives rise to dopaminergic, serotonergic, and GABAergic neurons.

Heat-shock-mediated conditional regulation of hedgehog/gli signaling in zebrafish.

Background: Hedgehog (Hh) signaling is required for embryogenesis and continues to play key roles postembryonically in many tissues, influencing growth, stem cell proliferation, and tumorigenesis. Systems for conditional regulation of Hh signaling facilitate the study of these postembryonic Hh functions.

Results: We used the hsp70l promoter to generated three heat-shock-inducible transgenic lines that activate Hh signaling and one line that represses Hh signaling.

Graded hedgehog and fibroblast growth factor signaling independently regulate pituitary cell fates and help establish the pars distalis and pars intermedia of the zebrafish adenohypophysis.

The vertebrate adenohypophysis forms as a placode at the anterior margin of the neural plate, requiring both hedgehog (Hh) and fibroblast growth factor (Fgf) mediated cell-cell signaling for induction and survival of endocrine cell types. Using small molecule inhibitors to modulate signaling levels during zebrafish development we show that graded Hh and Fgf signaling independently help establish the two subdomains of the adenohypophysis, the anteriorly located pars distalis (PD) and the posterior pars intermedia (PI). High levels of Hh signaling are required for formation of the PD and differentiation of anterior endocrine cell types, whereas lower levels of Hh signaling are required for formation of the PI and differentiation of posterior endocrine cell types.