20-Hydroxyecdysone, but not juvenile hormone, regulation of yolk protein gene expression can be mapped to cis-acting DNA sequences

Abstract

The three yolk protein genes (yps) of Drosophila melanogaster are expressed in the ovary and fat body of the adult female. Their levels of expression in the fat body depend upon both juvenile hormone (JH) and 20-hydroxyecdysone (20E). Using transformed lines of flies with various flanking sequences from the yp genes and lacZ, Adh, or native yp genes as reporters, the regulation of the three yp genes by 20E and the JH analogue ZR515 (methoprene) was investigated. For 20E, induction of reporter gene expression in males was assayed and, for JH, upregulation of the genes in nutritionally deprived females, which express yolk proteins (YPs) at very low levels, was followed. We were able to map 20E inducible sites upstream of yp3 and sites located 3' and within the coding sequence or introns of yp3 which can interact to respond to 20E. There are also sites in the intergenic spacer between yp1 and yp2. Evidence for repressors was also found upstream of the yp genes, suggesting downstream 20E inducible elements may be important in vivo. There appears to be a difference in the response to 20E in the fat body of the thorax and abdomen between different constructs in males. It is not clear whether those sequences which respond to 20E are genuine ecdysone response elements (i.e., binding sites for the ecdysone receptor) or if the effect is indirect. Methoprene upregulation of YPs, however, was only ever observed using native yp genes as reporters, suggesting that this hormone may act on intron sequences or yp coding sequences, or perhaps by influencing stability of the yp mRNA.