Different effects of 93D on 87C heat shock puff activity in Drosophila melanogaster and D. simulans

Abstract

It is known that treatment of the 93D heat shock locus in Drosophila melanogaster with two inducers, eg. benzamide (BM) or colchicine plus heat shock, causes the 93D puff in polytene nuclei to regress and, at the same time, the 87A and 87C heat shock puffs to be expressed unequally. In view of the close phylogenetic relationship and similar banding pattern of polytene chromosomes of the sibling species D. melanogaster and D. simulans, we examined the expression of the 93D puff and its effects on the transcriptional activity of the 87A and 87C heat shock puffs in salivary glands of D. simulans and D. melanogaster x D. simulans hybrid larvae by autoradiography. As in D. melanogaster, the 93D puff was selectively induced by BM or colchicine and regressed when heat shock treatment was given in addition in D. simulans and in the interspecific hybrid. However, unlike in D. melanogaster, the relative activity of the 87A and 87C heat shock puffs on D. simulans chromosomes remained equal in glands exposed to heat shock in combination with BM or colchicine. In the nuclei of interspecific hybrids, the 87A and 87C loci on the two homologues responded in the same way as those of the respective parents. There was no evidence of a transvection effect. It is known that the 87C locus of D. simulans differs from that of D. melanogaster in not carrying the heat-inducible αβ sequences and therefore, it is proposed that the 93D effect on 87C puff activity in D. melanogaster is mediated via the αβ sequences. However, the role of possible structural differences in the 93D locus of the two species cannot be ruled out.