Elongation of the developing spinal cord is driven by Oct4-type transcription factor-mediated regulation of retinoic acid signaling in zebrafish embryos.

Abstract

Elongation of the spinal cord is dependent on neural development from neuromesodermal progenitors in the tail bud. We previously showed the involvement of the Oct4-type gene, pou5f3, in this process in zebrafish mainly by dominant-interference gene induction, but, to compensate for the limitation of this transgene approach, mutant analysis was indispensable. pou5f3 involvement in the signaling pathways was another unsolved question. We examined the phenotypes of pou5f3 mutants and the effects of Pou5f3 activation by the tamoxifen-ERT2 system in the posterior neural tube, together confirming the involvement of pou5f3. The reporter assays using P19 cells implicated tail bud-related transcription factors in pou5f3 expression. Regulation of tail bud development by retinoic acid (RA) signaling was confirmed by treatment of embryos with RA and the synthesis inhibitor, and in vitro reporter assays further showed that RA signaling regulated pou5f3 expression. Importantly, the expression of the RA degradation enzyme gene, cyp26a1, was down-regulated in embryos with disrupted pou5f3 activity. The involvement of pou5f3 in spinal cord extension was supported by using mutants and the gain-of-function approach. Our findings further suggest that pou5f3 regulates the RA level, contributing to neurogenesis in the posterior neural tube.