Chicken Eyes absent 2 gene: isolation and expression pattern during development.

In all vertebrates studied (human, mouse, chicken), there are at least three genes related to Drosophila eyes absent (eya) gene. The chicken Eyes absent 2 (Eya2) cDNA was isolated from 14 day embryonic chicken lenses, and a complete open reading frame encoding a 59 kDa protein was elucidated. The chicken Eya2 protein is moderately conserved and 78-82% identical to the mouse and human Eya2. The Eya2 gene demonstrated a dynamic expression pattern in different tissues of diverse embryological origin. Expression of Eya2 was first detected at Hamburger and Hamilton stage 9 in the foregut. At later stages of development, Eya2 mRNA was detected in neural crest derivatives (dorsal root ganglia, branchial arches and cranial nerve ganglia). In the cranial placodes, expression of Eya2 was first detected in the nasal pit at stage 13. In the eye, expression of Eya2 was first convincingly detected in neural retina at stage 24 (day 4). The highest level of Eya2 mRNA in the lens was detected around day 9. Eya2 is also expressed in the cornea and iris. Therefore, chicken Eya2, as well as mouse Eya2, is expressed relatively early in the nasal (but not in the lens) placode and may mediate induction of the nasal placode. Expression of Eya2 in the wing and limb buds is consistent with its proposed role in the patterning of limb connective tissues.