We have cloned a chick homologue of Drosophila dachshund (dac), termed Dach1. 
Dach1 is the orthologue of mouse and human Dac/Dach (hereafter referred to as 
Dach1). We show that chick Dach1 is expressed in a variety of sites during 
embryonic development, including the eye and ear. Previous work has demonstrated 
the existence of a functional network and genetic regulatory hierarchy in 
Drosophila in which eyeless (ey, the Pax6 orthologue), eyes absent (eya), and 
dac operate together to regulate Drosophila eye development, and that ey 
regulates the expression of eya and dac. We find that in the developing eye of 
both chick and mouse, expression domains of Dach1 overlap with those of Pax6, a 
gene required for normal eye development. Similarly, in the developing ear of 
both mouse and chick, Dach1 expression overlaps with the expression of another 
Pax gene, Pax2. In the mouse, Dach1 expression in the developing ear also 
overlaps with the expression of Eya1 (an eya homologue). Both Pax2 and Eya1 are 
required for normal ear development. Our expression studies suggest that the 
Drosophila Pax-eya-dac regulatory network may be evolutionarily conserved such 
that Pax genes, Eya1, and Dach1 may function together in vertebrates to regulate 
neural development. To address the further possibility that a regulatory 
hierarchy exists between Pax, Eya, and Dach genes, we have examined the 
expression of mouse Dach1 in Pax6, Pax2 and Eya1 mutant backgrounds. Our results 
indicate that Pax6, Pax2, and Eya1 do not regulate Dach1 expression through a 
simple linear hierarchy.