Molecular Mechanisms of Development and Differentiation of the Eye of Drosophila and Vertebrates

Abstract

The development of the eye is compared in Drosophila and vertebrates. Although the structure of the compound eye of invertebrates and of the cameral eye of vertebrates differs morphologically, there are striking similarities at the molecular level. Three groups of genes control the morphogenesis of the eye: the genes responsible for eye rudiment formation, neurogenic genes, and proneural genes. In the eye rudiments of Drosophila and vertebrates, the homologous regulatory homeobox-containing genes ey/Pax6, so/Six3, rx/Rx, and optix/Optx2 are expressed. Transcription factors encoded by these conservative genes are involved in specific interactions with DNA. Another set of homologous genes, eya/Eya and dac/DACH/Dac, is also expressed during this developmental period. These genes encode nuclear transcription factors that are devoid of DNA-binding domains but are involved in the protein–protein interactions that control gene expression. Transcriptional complexes, which are products of homeobox-containing genes and nuclear factors, control morphogenesis of the eye in Drosophila and vertebrates. A similar set of homologous regulatory and nuclear genes controls morphogenesis during formation of the ectopic eyes in Drosophila and vertebrates. Molecular biology approaches have allowed eye development to be examined at the level of developmental mechanisms. It has become evident that progress in understanding the mechanisms of eye development is due to studies carried out on Drosophila. Supporters of the idea of the polyphyletic origin of the compound and cameral eyes have noted significant differences in their structure and have failed to find distinct common features in their development. The hypothesis of the monophyletic origin of eyes has been substantiated by the results of molecular investigations.