EYES ABSENT - A GENE FAMILY FOUND IN SEVERAL METAZOAN PHYLA

Genes related to the Drosophila eyes absent gene were identified in ve rtebrates (mouse and human), mollusks (squid), and nematodes (C. elega ns). Proteins encoded by these genes consist of conserved C-terminal a nd variable N-terminal domains. In the conserved 271-amino acid C-term inal region, Drosophila and vertebrate proteins are 65-67% identical. A vertebrate homolog of eyes absent, designated Eya2, was mapped to Ch romosome (Chr) 2 in the mouse and to Chr 20q13.1 in human. Eya2 shows a dynamic pattern of expression during development. In the mouse, expr ession of Eya2 was first detected in 8.5-day embryos in the region of head ectoderm fated to become the forebrain. At later stages of develo pment, Eya2 is expressed in the olfactory placode and in a variety of neural crest derivatives. In the eye, expression of Eya2 was first det ected after formation of the lens vesicle. At day 17.5, the highest le vel of Eya2 mRNA was observed in primary lens fibers. Low levels of Ey a2 expression was detected in retina, sclera, and cornea. By postnatal day 10, Eya2 was expressed in secondary lens fibers, cornea, and reti na. Although Eya2 is expressed relatively late in eye development, it belongs to the growing list of factors that may be essential for eye d evelopment across metazoan phyla. Like members of the Pax-6 gene famil y, eyes absent gene family members were probably first involved in fun ctions not related to vision, with recruitment for visual system forma tion and function occurring later.