Regulatory autonomy and molecular characterization of the Drosophila out at first gene.

Our previous work has shown that the expression of the Drosophila decapentaplegic (dpp) gene in imaginal disks is controlled by a 30 kb array of enhancers located 3' of the dpp coding region. Here, we describe the cloning and characterization of out at first (oaf), a gene located near this enhancer region. Transcription of oaf results in three classes of alternatively polyadenylated RNAs whose expression is developmentally regulated. All oaf transcripts contain two adjacent open reading frames separated by a single UGA stop codon. Suppression of the UGA codon during translation, as seen previously in Drosophila, could lead to the production of different proteins from the same RNA. During oogenesis, oaf RNA is expressed in nurse cells of all ages and maternally contributed to the egg. During embryonic development, zygotic transcription of the gene occurs in small clusters of cells in most or all segments at the time of germband extension and subsequently in a segmentally repeated pattern in the developing central nervous system. The gene is also expressed in the embryonic, larval and adult gonads of both sexes. We also characterize an enhancer trap line with its transposon inserted within the oaf gene and use it to generate six recessive oaf mutations. All six cause death near the beginning of the first larval instar, with two characterized lines showing nervous system defects. Last, we discuss our data in light of the observation that the enhancers controlling dpp expression in the imaginal disks have no effect on the relatively nearby oaf gene.