Our previous work has shown that the expression of the Drosophila deca
pentaplegic (dpp) gene in imaginal disks is controlled by a 30 kb arra
y 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 clas
ses of alternatively polyadenylated RNAs whose expression is developme
ntally regulated. All oaf transcripts contain two adjacent open readin
g 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 oog
enesis, oaf RNA is expressed in nurse cells of all ages and maternally
contributed to the egg. During embryonic development, zygotic transcr
iption of the gene occurs in small clusters of cells in most or all se
gments at the time of germband extension and subsequently in a segment
ally repeated pattern in the developing central nervous system. The ge
ne 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 enhance
rs controlling dpp expression in the imaginal disks have no effect on
the relatively nearby oaf gene.