Yolk protein induction in males of several Drosophila species

Abstract

The three yolk-protein genes of D. melanogaster (YP1, YP2 and YP3) are normally expressed in the female from the time of eclosion, but not in males. Expression can be induced in males of any age by treatment with a steroid hormone, 20-hydroxyecdysone. Yolk polypeptides can be identified in haemolymph from females of several Drosophila spp by their cross-reactivity to anti-yolk polypeptides antibodies prepared against D. melanogaster yolk proteins. Western blotting was used to show the accumulation of yolk polypeptides in males of several D. melanogaster sibling spp ( D. simulans, D. mauritiana, D. orena, D. erecta, D. yakuba and D. teissieri) and one other spp ( D. virilis), 16 hr after 20-hydroxyecdysone treatment. YP-homologous transcripts were identified in females of the Drosophila melanogaster sibling spp by RNA hybridization to cloned D. melanogaster YP genes (pYP1, pYP2 and pYP3). YP-homologous transcripts accumulated in males of D. melanogaster sibling spp 16 hr after treatment with 20-hydroxyecdysone; but comparisons between hybridizations to a mixed YP1/2/3 gene probe and YP1-specific probes suggested that the yolk polypeptide genes may not always be transcribed in a coordinated fashion in these males. This difference was no longer apparent after translation into yolk polypeptides had occurred. Steroid treatment of males appeared not to stimulate expression of all genes, since the levels of some haemolymph polypeptides did not appear to be affected by 20-hydroxyecdysone, while other such polypeptides were detected at reduced levels after the hormone treatment which led to expression of the yolk polypeptide-genes in this sex.