The Eye-loss mutant, eym is a new allele of eyg, lacking an enhancer required for eye development in Drosophila

Pax genes are crucial for eye development in various organisms including Drosophila melanogaster. Eye gone (eyg) is one of the Pax genes and is involved in head and eye development in Drosophila. Eye missing (eym) is known as a recessive mutation that shows an eye-loss phenotype. Although the responsible gene was mapped as 3-67.9 on the recombination map, the gene and the molecular mechanism inducing its phenotype have not been clarified. Here we show that eym1 has a nucleotide replacement in the eyg intron and that much of the CD enhancer required for the eyg expression in the second instar larvae is deleted. The eyg mRNA expression is drastically reduced in the second instar eym1 mutants and eyg overexpression compensates for the eym eye-loss phenotype. In eym eye discs, cell proliferation and neural cell differentiation is inhibited. The wg protein is misexpressed in the dorsoventral compartment boundary in eym1 eye discs. Taking these data together, we demonstrate that eym is a new allele of eyg, thus eygeym, and the reduction of eyg transcription in the second instar larvae causes an eye-loss phenotype via the deletion of its enhancer.