Homeobox genes in the genetic control of eye development

Vertebrate eye formation is a complex process which involves early specific ation of the prospective eye territory, induction events, patterning along the polarity axes and regional specification, to bring about the proper mor phogenetic movements, cell proliferation, cell differentiation and neural c onnections allowing visual function. The molecular machinery underlying suc h complex developmental events is presently under an intense research scrut iny and many associated genetic factors have been isolated and characterize d. These studies produced striking knowledge in the field, especially with respect to uncovering the role of key genes and their possible evolutionary conservation. Presently, a major task is to define the complex interaction s connecting the multiplicity of molecular players that regulate eye develo pment. We recently identified two homeobox genes, Xrx1 and Xvax2, and studi ed their function by using the Xenopus embryo as a developmental model syst em. Xrx1 and Xvax2 control key aspects of eye development. In particular, X rx1 appears to play a role in the early specification of anterior neural re gions fated to give rise to retina and forebrain structures, and in promoti ng cell proliferation within these territories. On the other hand, Xvax2 is involved in regulating the eye proximo-distal and/or dorsoventral polarity , and the morphogenetic movements taking place during formation of the opti c stalk and cup. Here we review the experimental results addressing the rol es of Xrx1 and Xvax2 and their vertebrate orthologues, and discuss their re lationship with other molecules also playing a related function in eye deve lopment.