Goldfish vsx1 inhibits chordamesoderm gene ntl expression at the dorsal midline

Abstract

vsx1 (visual system homeobox-1), a homeobox gene originally identified from an adult goldfish retinal cDNA library, has been shown to regulate retina progenitor proliferation, differentiation and functional maintenance of bipolar cells in vertebrates. However, in all the examined vertebrate species, vsx1 transcripts can be also detected at the early developmental stage, suggesting that it may play an important role in regulating early embryogenesis as well. Here, we investigated the function of vsx1 in early embryogenesis of goldfish (Carassius auratus) with both overexpression and gene knockdown approaches. It was found that vsx1 overexpression specifically blocked dorsal midline structure formation and vsx1 knockdown led to disorganized dorsal midline structure. Whole-mount in situ hybridization revealed that the midline expression of ntl, a key regulatory gene for chordamesoderm, was repressed by vsx1 overexpression but enhanced in the vsx1 knockdown. Furthermore, VSX1 protein could bind ntl promoter directly and was sufficient to inhibit ntl promoter-driven reporter gene green fluorescence protein transcription. Together, these results suggested that vsx1 may act to repress ectopic expression of ntl in neural progenitor cells to ensure neural tube development in a spatially coordinated pattern during early embryogenesis.