Developmental malformations of the eye: the role of PAX6, SOX2 and OTX2.

Eye development initiates as an evagination of the early neural plate, before the closure of the neural tube. Structural malformations of the eye such as anophthalmia and microphthalmia arise very early in development. It is not surprising therefore that three of the genes currently identified to play a significant role in these developmental eye anomalies are also major players in brain development and regionalization. However, as has been emerging for a high proportion of transcriptional regulators studied, these genes have evolved to play multiple roles throughout development, and perhaps even in adult tissue maintenance. This complex spatiotemporal expression pattern requires elaborate regulatory systems which we are beginning to unravel. A major component of these complex regulatory networks is a series of cis-acting elements, highly conserved through evolution, which spread large distances from the coding region of each gene. We describe how cross regulation for PAX6, SOX2 and perhaps OTX2 has now been uncovered, pointing to the mechanisms that can fine-tune the expression of such essential developmental components. These interactions also help us understand why there is significant phenotypic overlap between mutations at these three loci.