Abstract

In the spinal cord, excitatory V2a and inhibitory V2b interneurons are produced together by the final division of common P2 progenitors. During V2a and V2b diversification, Tal1 is necessary and sufficient to promote V2b differentiation and Vsx2 suppresses the expression of motor neuron genes to consolidate V2a interneuron identity. The expression program of Tal1 is triggered by a Foxn4-driven regulatory network in the common P2 progenitors. Why the expression of Tal1 is inhibited in V2a interneurons at the onset of V2a and V2b sub-lineage diversification remains unclear. Since transcription repressor Vsx1 is expressed in the P2 progenitors and newborn V2a cells in zebrafish, we investigated the role of Vsx1 in V2a fate specification during V2a and V2b interneuron diversification in this species by loss and gain-of-function experiments. Invsx1knockdown embryos or knockout Go chimeric embryos,tal1was ectopically expressed in the presumptive V2a cells, while the generation of V2a interneurons was significantly suppressed. By contrast, invsx1overexpression embryos, normal expression oftal1in the presumptive V2b cells was suppressed, while the generation of V2a interneuron was expanded. Chromatin immunoprecipitation and electrophoretic mobility shift assays in combination with core consensus sequence mutation analysis further revealed that Vsx1 can directly bind total1promoter and represstal1transcription. These results indicate that Vsx1 can directly represstal1transcription and plays an essential role in defining V2a interneuron sub-lineage during V2a and V2b sub-lineage diversification in zebrafish.Keywords:V2 interneuron diversification;V2a interneuron specification;Vsx1;Tal1;transcriptional repression;spinal cord;zebrafish