Molecular characterization of three genes expressed in the compound eye of Drosophila melanogaster

Two genomic eye-specific (ES) clones, A21 and A22, isolated by subtractive hybridization techniques in Drosophila, were found to co-localize with the electroretinogram-defective mutant locus, JK1285, defined by two mutually non-complementing EMS-induced alleles, JK1285 and JK1503. The JK1285 and JK1503 mutants are known to be defective in the responses of post-synaptic laminar interneurons to photoreceptor cell synaptic input. All three genes encoded by the A21 and A22 genomic clones were characterized at the molecular level and shown by a variety of approaches to not correspond with the JK1285 locus. One of these genes, designated A21-2, is expressed very abundantly, and shows a unique pattern of expression, in that one transcript is expressed only in the adult eye and another is expressed in a wide variety of adult fly tissues. A second gene, A22, expresses one large transcript eye-preferentially and two smaller transcripts in many tissues throughout the fly head and body, at all stages of development. The A21-2 and A22 genes appear to encode novel proteins with no discernible homology with other known proteins. Functional studies of the A21-2 gene were initiated by the in vivo induction of antisense mRNA expression, using a photoreceptor cell- and developmental stage-specific promotor. Preliminary mutant phenotypes were observed on intracellular recordings of photoreceptor cells expressing A21-2 antisense mRNA. A stock carrying a P-element insertion in the 3 ′ untranslated region of the A22 gene was identified and used to generate fly stocks carrying disruptions of the A22 gene, mediated by the imprecise excision of the P-element. Neurotransmitter was shown to be synthesized to wild-type levels in the JK1285 and JK1503 mutants and the synaptic transmission defects in these mutants were shown to be likely of pre-synaptic origin. The JK1285 locus was further characterized as displaying behavioral defects with regard to multiple sensory systems, as well as alterations in various aspects of the physiology of the giant fiber pathway. A partial, positional cloning of the JK1285 locus was achieved using P1 clones obtained through the Drosophila genome project