A conserved blueprint for the eye?

Although the eyes of all organisms have a common function, visual perception, their structures and developmental mechanisms are quite diverse. Recent research on eye development in Drosophila has identified a set of putative transcription factors required for the earliest step of eye development, specification of the field of cells that will give rise to the eye. These factors appear to act in a hierarchy, although cross-regulation may amplify the eye fate decision or promote progression to the next step. Surprisingly, homologous proteins are also involved in vertebrate eye development, suggesting that this regulatory network was present in a primitive common ancestor and that it has been adapted to control visual organ formation in multiple species. The identification of genes acting upstream and downstream of these transcription factors will contribute to our understanding of the establishment of a developmental field, as well as of the divergence of regulatory pathways controlling the formation of eye structures.