Analysis of pathways and proteins that pattern olig2+ cells within the zebrafish central nervous system.

Abstract

The cerebellum, which forms from anterior hindbrain, coordinates motor movements and balance. Sensory input from the periphery is relayed and modulated by cerebellar interneurons, which are organized into layers. The mechanisms that specify the different neurons of the cerebellum and direct its layered organization remain poorly understood. Drawing from investigations of spinal cord, we hypothesized that the embryonic cerebellum is patterned on the dorsoventral axis by opposing morphogens. We tested this using zebrafish. Here we show that expression of olig2, which encodes a bHLH transcription factor, marks a subset of PNs. In combination with other markers, olig2 reveals a dorsoventral organization of cerebellar neurons in embryos. Disruption of Hedgehog signaling, which patterns the ventral neural tube, produced a two-fold increase in the number of olig2+ PNs. By contrast, olig2+ PNs did not develop in embryos deficient for Wnt signaling, which patterns dorsal neural tube, nor did they develop in embryos deficient for both Hedgehog and Wnt signaling. Our data indicate that Hedgehog and Wnt work in opposition across the dorsoventral axis of the cerebellum to regulate formation of olig2+ PNs. Specifically, we propose that Hedgehog limits the range of Wnt signaling, which is necessary for olig2+ PN development.