eyeless (ey)

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A Drosophila gene located at 4–2.0 that controls eye development. Mutations result in the complete loss or the reduction in size of the compound eye. Also severe defects occur in the brain structures essential for vision, olfaction, and the coordination of locomotion. The most studied mutation, ey 2, is caused by the insertion of a transposable element (q.v.) in the first intron of the gene. The ey 2 phenotype is the result of cell death in the eye imaginal discs (q.v.) during the third larval instar. The ey gene is expressed in the eye primordium in the embryo during the development of the eye imaginal disc and in the pupa when rhodopsin (q.v.) is being synthesized. Also, eyeless is expressed in the cells of Bolwig organs (q.v.) which serve as larval eyes. The ey transcription unit is about 16 kb long. Two transcripts are produced by alternative splicing (q.v.). The Ey proteins are 838 and 857 amino acids long, and they function as transcription factors (q.v.). The proteins contain an N-terminal paired (q.v.) domain and a homeobox (q.v.). The wild-type allele of eyeless is a master control gene for eye morphogenesis in this species. This has been shown by experimentally activating the gene in imaginal discs that normally give rise to organs other than eyes. After eclosion, flies appear with organized clusters of ommatidia on their antennae, legs, halteres, and wings. . Since eye development in Drosophila is controlled by more than 2,500 genes, most of these must be under the direct or indirect control of ey +. The Small eye (Sey) (q.v.) genes of mice and rats and the Aniridia (q.v.) gene of humans are homologs of the eyeless gene. Ey homologs have also been found in the zebrafish, quail, chicken, sea urchin, and squid. The squid homologous gene when activated in developing Drosophila also initiates the formation of ectopic eyes. These findings suggest that all metazoans share the same master control genes for eye morphogenesis. See Chronology, 1995, Halder et al.; developmental control genes, downstream genes, Drosophila targeted gene expression technique.

Subjects: Genetics and Genomics.

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