Eye specification in Drosophila is thought be controlled by a set of seven 
nuclear factors that includes the Pax6 homolog, Eyeless. This group of genes is 
conserved throughout evolution and has been repeatedly recruited for eye 
specification. Several of these genes are expressed within the developing eyes 
of vertebrates and mutations in several mouse and human orthologs are the 
underlying causes of retinal disease syndromes. Ectopic expression in Drosophila 
of any one of these genes is capable of inducing retinal development, while 
loss-of-function mutations delete the developing eye. These nuclear factors 
comprise a complex regulatory network and it is thought that their combined 
activities are required for the formation of the eye. We examined the expression 
patterns of four eye specification genes, eyeless (ey), sine oculis (so), eyes 
absent (eya), and dachshund (dac) throughout all time points of embryogenesis 
and show that only eyeless is expressed within the embryonic eye anlagen. This 
is consistent with a recently proposed model in which the eye primordium 
acquires its competence to become retinal tissue 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 possibility that these genes have even 
earlier and wide ranging roles in establishing the head and visual field.