Myostatin is a negative regulator of adult neurogenesis in zebrafish

Intrinsic and extrinsic inhibition of axonal and neuronal regeneration obstruct spinal cord (SC) repair in mammals. In contrast, adult zebrafish achieve functional recovery after SC damage. While studies of innate SC regeneration have focused on axon regrowth as a primary repair mechanism, how local neurogenesis impacts functional recovery is unknown. We uncovered dynamic expression of myostatin b (mstnb) in a niche of dorsal ependymal progenitors after complete SC transection in zebrafish. Genetic loss-of-function in mstnb impaired functional recovery, although glial and axonal bridging across the lesion were unaffected. Using a series of transgenic reporter lines, we quantified the numbers of stem, progenitor, and neuronal cells in the absence of mstnb. We found neural stem cell proliferation was reduced, while newborn neurons were increased in mstnb null tissues, suggesting mstnb is a negative regulator of neurogenesis. Molecularly, neuron differentiation genes were upregulated, while the neural stem cell maintenance gene fgf1b was downregulated in mstnb mutants. Finally, we show that human FGF1 treatment rescued neuronal gene expression in mstnb mutants. These studies uncover unanticipated neurogenic functions for mstnb in adult zebrafish, and establish the importance of local neurogenesis for functional SC repair.