Pp. Davino et al., THE ROLE OF THE BR-C LOCUS ON THE EXPRESSION OF GENES LOCATED AT THE ECDYSONE-REGULATED 3C PUFF OF DROSOPHILA-MELANOGASTER, Mechanisms of development, 49(3), 1995, pp. 161-171
During the third larval instar, the steroid moulting hormone ecdysone
activates three temporally distinct puff sets on the D. melanogaster s
alivary gland polytene chromosome: the so-called intermoult, early and
late puffs. Hormonal regulation of intermoult puffs is quite complex
and, so far, largely not understood. In order to further investigate t
his aspect, we have analysed the effects of mutations in a key regulat
or of the ecdysone response at the onset of metamorphosis, the Broad-C
omplex (BR-C) locus, on the expression of genes mapping at the 3C inte
rmoult puff. On the basis of an accurate examination of 3C intermoult
gene activity in single, carefully staged, third instar larvae of wild
-type and BR-C mutant strains, we were able to subdivide these genes i
nto two groups. Each group is characterised by a different temporal ex
pression profile, so that at the beginning of the wandering stage the
transcription of the first group declines as group II. transcription i
s induced. Interestingly, the BR-C locus appears to play a regulatory
role in establishing this transcriptional switch. By using mutants of
each of the three lethal complementation groups, we precisely defined
the role of BR-C functions in this developmental transition and we sho
w that this locus also plays an essential role in the early pre-metamo
rphic hormonal response.