Steroid regulation of glue protein genes in Drosophila melanogaster

Transcript accumulation of the 3C glue protein gene Sgs-4 was induced in cultured salivary glands of Drosophila third instar larvae by supplementing the culture medium with 20-OH-ecdysone. The salivary glands were isolated from hormone-deficient larvae of the temperature-sensitive mutant l(1)su(f)ts67g, which were shifted from permissive (25 degrees C) to restrictive temperature (30 degrees C) at 60 h after oviposition. At the permissive temperature the glue protein are expressed during the latter half of the third instar. At the restrictive temperature there is no detectable or an extremely reduced accumulation of the 3C glue protein gene transcripts in these larvae. Induction of transcript accumulation was demonstrated by increased amounts of glue gene RNAs in the 20-OH-ecdysone supplemented salivary glands. Maximum accumulation was reached within 1 h after supplementation. The induction of accumulation was inhibited by a concentration of cycloheximide that repressed total protein synthesis, suggesting that 20-OH-ecdysone acts indirectly on the 3C glue gene by inducing synthesis of a protein(s) required transcript accumulation. We also show that there is a more rapid disappearance of 3C transcripts from salivary glands cultured in the presence of 20-OH-ecdysone than from glands cultured in its absence. This hormone-induced disappearance is, in contrast to the 68C transcripts, not inhibited by cycloheximide.