At first glance, the eyes of chicks and Drosophila have little in common. However, on p. , Blanco and co-workers report that at least one of the genetic regulatory circuits involved in eye development has been largely conserved during evolution. In chick, lens-specific regulation of the δ1-crystallin gene is achieved by the cooperative binding of the transcription factors PAX6 and SOX2 to the 30 bp DC5 fragment within the gene's enhancer. Using reporter genes,Blanco et al. show that the DC5 fragment is active in the Drosophila compound eye, specifically in the cone cells that secrete Crystallin. Other studies, including a loss-of-function analysis, indicate that the DC5 element in Drosophila is regulated by the cooperative binding of D-PAX2 and SOXN. Since PAX6 and PAX2 derive from the same ancestor, this indicates that while Pax6 took over Crystallin regulation in vertebrates during evolution, Pax2 retained this function in flies.
