RETROTRANSPOSON-INDUCED ECTOPIC EXPRESSION OF CUT CAUSES THE OM(1A) MUTANT IN DROSOPHILA-ANANASSAE

Optic morphology (Om) mutations in Drosophila ananassae map to at leas t 22 loci scattered throughout the genome. They are semidominant, neom orphic, nonpleiotropic, and are associated with the insertion of a ret rotransposon, tom. The Om(1A) gene, which is cytogenetically linked to the cut locus, was cloned using a DNA fragment of the cut locus of Dr osophila melanogaster as a probe. Three of the eight alleles of Om(1A) examined have insertion of the tom element within a putative cut regi on. The gamma-ray-induced revertants of Om(1A) are accompanied with cu t lethal mutations and rearrangements within the cut coding region. In the eye imaginal discs of the Om(1A) mutants, differentiation of phot oreceptor clusters is suppressed, abnormal cell death occurs in the ce nter and the cut protein is expressed ectopically. D. melanogaster fli es transformed with a chimeric cut gene under the control of a heat-in ducible promoter show excessive cell death in the region anterior to t he morphogenetic furrow, suppressed differentiation to photoreceptor c lusters and defect in the imaginal eye morphology when subjected to te mperature elevation. These findings suggest that the tom element inser ted within the Om(1A) region induces ectopic cut expression in the eye imaginal discs, thus resulting in the Om(1A) mutant phenotype.