Multiple roles of the eyes absent gene in Drosophila

The eyes absent (eya) gene plays an essential role in the events that lead to formation of the Drosophila eye; without expression of eya in retinal progenitor cells, they undergo programmed cell death just prior to the morphogenetic furrow, leading to an eyeless or reduced eye phenotype. The eya gene has recently been found to be highly conserved to humans, defining a new gene family. Insights into the gene's function in the fly, therefore, are likely to be relevant to the role of its homologs in vertebrates. Detailed studies at the subcellular level indicate that the Eya protein is localized to the nucleoplasm, suggesting a role in control of nuclear events. The eya gene shows expression and roles in tissues other than the eye, including subsets of cells of the adult visual system, brain, and ovary, as well as an elaborate expression pattern in the embryo. Various mutations in the eya gene cause loss of ocelli, female sterility, or lethality. Analysis of the embryonic lethal phenotype indicates that mutant alleles show defects in head morphogenesis. These data indicate that eya has critical roles in morphogenesis of a number of tissues in the animal, in addition to its role in early eye formation. Despite multiple roles at multiple stages of development of the fly, both the type I and type II forms of the protein, when expressed ectopically during larval development, can direct eye formation.