Family of developmentally regulated, maternally expressed Drosophila RNA species detected by a v-myc probe.

Drosophila melanogaster genomic sequences that hybridize with v-myc have been reported (B.-Z. Shilo and R. A. Weinberg, Proc. Natl. Acad. Sci. U.S.A. 78:6789-6792, 1981). We have detected Drosophila RNA sequences that also hybridize with v-myc. In an attempt to characterize these RNA sequences, we used v-myc hybridization probes to isolate Drosophila genomic segments. None of the Drosophila genomic or cDNA clones that we have isolated hybridize with the 3' exon of v-myc. Preliminary nucleotide sequence analyses have revealed sufficient homology to account for the observed hybridization between v-myc and the Drosophila clones but have failed to detect significant amino acid sequence homology. Thus is seems unlikely that the mRNA sequences or the genomic sequences that we have isolated by hybridization with v-myc represent homologs of the vertebrate myc gene. Despite the lack of structural homology between the cloned Drosophila sequences and v-myc, we have investigated the pattern of expression of those RNA species that hybridize with v-myc. Polyadenylic acid-containing transcripts of 2.7, 2.2, and 1.7 kilobases (kb) in embryos, pupae, adults, and Kc cells and an additional 1.4-kb transcript in adults were complementary to the Drosophila genomic clones and to v-myc. The 1.7- and 2.2-kb transcripts were localized on polyribosomes in Kc cells. The 1.7- and 2.2-kb transcripts were present after 45 min, 2 h, and 4 h of embryonic development, but by 16 h of development their levels had decreased by more than sixfold. During metamorphosis, two peaks of expression of the 1.7- and 2.2-kb transcripts were observed, at 6 and 72 h postpupariation. The 1.4-kb RNA species was first detected at 72 h postpupariation. In adults, the 1.7- and 2.2-kb transcripts were detected only in ovaries in females, whereas the 1.4-kb transcript was present in female nonovarian RNA and in males. These results suggest that the transcripts in early embryos are of maternal origin.