Restricted expression of a new paired-class homeobox gene in normal and regenerating adult goldfish retina.

We describe the cloning and expression pattern of a new paired-class homeobox gene, Vsx-1, in the continuously growing retina of the goldfish. Vsx-1 belongs to a subset of paired-class homeobox genes that lack a second DNA binding domain, the paired-domain, and is closely related to the C. elegans ceh-10 gene. In the adult goldfish, Vsx-1 expression is restricted to the neural retina. In the central, mature retina, Vsx-1 mRNA is synthesized in a subset of differentiated cells in the inner nuclear layer in a pattern suggestive of bipolar cells. In immature retina, adjacent to the retinal margin, Vsx-1 is expressed in a relatively broader subset of newly postmitotic cells but is downregulated in some of these cells to form the mature expression pattern. Following retinal injury, during the early phase of regeneration, Vsx-1 mRNA synthesis appears to be upregulated in cells in the inner nuclear layer and is expressed de novo in cells outside this layer. By virtue of its identity as a transcriptional regulatory gene and its patterns of expression, we speculate that Vsx-1 may stabilize the differentiated state of a subset of cells in the inner nuclear layer and may be involved in cellular differentiation during retinal development and regeneration.