Expression of evolutionarily conserved eye specification genes during Drosophila embryogenesis

Eye specification in Drosophila is thought be controlled by a set of seven nuclear factors that includes the Pax6 homolog, Eyeless. This group of gene s is conserved throughout evolution and has been repeatedly recruited for e ye specification. Several of these genes are expressed within the developin g eyes of vertebrates and mutations in several mouse and human orthologs ar e the underlying causes of retinal disease syndromes. Ectopic expression in Drosophila of any one of these genes is capable of inducing retinal develo pment, while loss-of-function mutations delete the developing eye. These nu clear factors comprise a complex regulatory network and it is thought that their combined activities are required for the formation of the eye. We exa mined the expression patterns of four eye specification genes, eyeless (ey) , sine oculis (so), eyes absent (eya), and dachshund (dac) throughout all t ime points of embryogenesis and show that only eyeless is expressed within the embryonic eye anlagen. This is consistent with a recently proposed mode l in which the eye primordium acquires its competence to become retinal tis sue over several time points of development. We also compare the expression of Ey with that of a putative antennal specifying gene Distal-less (Dll). The expression patterns described here are quite intriguing and raise the p ossibility that these genes have even earlier and wide ranging roles in est ablishing the head and visual field.