VSX-1 AND VSX-2 - DIFFERENTIAL EXPRESSION OF 2 PAIRED-LIKE HOMEOBOX GENES DURING ZEBRAFISH AND GOLDFISH RETINOGENESIS

Vsx-1 and Vsx-2 are two homeobox genes that were cloned originally fro m an adult goldfish retinal library. They are members of the paired-li ke:CVC gene family, which is characterized by the presence of a paired homeodomain and an additional conserved region, termed the CVC domain . To analyze the possible roles for Vsx-1 and Vsx-2 in eye development , we used in situ hybridization to examine their expression patterns i n zebrafish and goldfish embryos. Vsx-2 is initially expressed by prol iferating neuroepithelial cells of the presumptive neural retina, then it is down-regulated as differentiation begins, and it is finally ree xpressed at later stages of differentiation in a subset of cells, pres umed to be bipolar cells, in the inner nuclear layer. In contrast, Vsx -1 is expressed only weakly in undifferentiated, presumptive neural re tina and is then up-regulated selectively in presumptive bipolar cells at early stages of differentiation (when Vsx-2 is turned off), before decreasing to an intermediate level, which is maintained in the diffe rentiated (adult) retina. The restricted expression patterns of Vsx-2 correspond to the observed phenotypes in mice with the ocular retardat ion mutation (or(J)), further supporting the notion that Vsx-2 and Chx 10 are homologues. The sequential complimentary and then corresponding expression patterns of Vsx-1 and Vsx-2 suggest that these similar tra nscription factors may be recruited for partially overlapping, but dis tinct, functions during the development of the retina. (C) 1997 Wiley- Liss, Inc.