The zebrafish eya1 gene and its expression pattern during embryogenesis

The eyes absent-like genes encode a group of putative transcriptional coactivators with a sole representative in Drosophila and several members in mammals. Haploinsufficiency of the human EYA1 gene results in branchio-oto-renal syndrome characterized by developmental anomalies of the branchial arches, the three compartments of the ear and the kidney. As a first step towards a functional analysis of this gene in lower vertebrates, we isolated its zebrafish homologue, eya1, and studied its expression pattern during embryogenesis. The eya1 cDNA predicts a protein with 84.7% identity with the human homologue. Transcripts are first detected at the tailbud stage in presumptive cranial placodal precursor cells. Thereafter, eya1 expression continues in anterior pituitary, olfactory, otic, and lateral line placodes. Aside from these placodal sites of expression, eya1 transcripts were observed in the somites, developing pectoral fins, and branchial arches. No expression was found in pronephros or Wolffian duct of the zebrafish renal system. Within the developing ear, eya1 expression becomes confined to the ventral part of the otic vesicle from where the acoustic ganglion precursor cells arise and the sensory patches differentiate. In the lateral line, eya1 is expressed in the placodes, ganglia, migrating primordia, and receptive organs at all developmental stages, including both the differentiating hair and supporting cells. Taken together, these results indicate a remarkable similarity in both the structure and expression pattern of eya1 between higher and lower vertebrates, suggesting that the function of this gene has been conserved throughout vertebrate evolution.