Regulation of eye formation by the Rx and pax6 homeobox genes.

The Rx and pax6 homeobox genes are among the earliest genes expressed in the eye primordia and play crucial roles in the specification of ocular fate. These genes exhibit strong conservation of sequence and expression patterns among vertebrates. As transcription factors, Rx and Pax6 exert their effects through the activation and repression of downstream targets. Overexpression of each protein induces ectopic retinal tissue formation, as well as induction of the other. pax6 gene mutations have been correlated with an array of human diseases, and a similar array of mutations potentially exists for the human Rx gene. Based on functional studies, the vertebrate Rx and pax6 genes are likely to regulate cell proliferation and are required for the initial commitment to retinal and lens cell fate, respectively, while pax6 appears to play additional roles in the formation of the retina and cornea.