IDENTIFICATION OF GENES REQUIRED FOR DROSOPHILA EYE DEVELOPMENT USINGA PHENOTYPIC ENHANCER-TYPE

A novel method of P-element, mutagenesis is described for the isolatio n of mutants affecting the development of the Drosophila compound eye. It exploits the interaction between the Bride of Sevenless (Boss) lig and and the Sevenless (Sev) receptor tyrosine kinase that triggers the formation of the UV-sensitive photoreceptor neuron, R7. Transposition of a boss cDNA transgene, in an otherwise boss mutant background, was used as a ''phenotypic trap'' in live flies to identify enhancers exp ressed during a narrow time window in eye development. Using a rapid b ehavioral screen, more than 400,000 flies were tested for restoration of R7. Some 1,800 R7-containing flies were identified. Among these, 21 independent insertions with expression of the boss reporter gene in t he RS cell were identified by a external eye morphology and staining w ith an antibody against Boss, Among 900 lines with expression of the b oss reporter gene in multiple cells assessed for homozygous mutant phe notypes, insertions in the marbles, glass, gap1, and fasciclin II gene s were isolated. This phenotypic enhancer-trap facilitates (i) the iso lation of enhancer-traps with a specific expression pattern, and (ii) the recovery of mutants disrupting development of specific tissues. Be cause the temporal and tissue specificity of the phenotypic trap is de pendent on the choice of the marker used, this approach can be extende d to other tissues and developmental stages.