Species differences in the temporal pattern of Drosophila urate oxidase gene expression are attributed to trans-acting regulatory changes.

The Drosophila melanogaster urate oxidase (UO)-encoding gene is expressed in the third-instar larva and adult. In contrast, the Drosophila pseudoobscura UO gene is only expressed in the adult, whereas the Drosophila virilis UO gene is expressed only in the third-instar larva. UO activity in these three Drosophila species is detected exclusively within the Malpighian tubules. By using P-element mediated germ-line transformation, UO genes from D. pseudoobscura and D. virilis were integrated into the D. melanogaster genome. The D. virilis and D. pseudoobscura UO transgenes were expressed in the third-instar larva and adult Malpighian tubules, which is the D. melanogaster temporal pattern of UO gene expression. These observations indicate that differences in the temporal patterns of regulation of UO genes among these three Drosophila species are not likely to be due to evolutionary changes in the sequence or complement of UO cis-acting regulatory elements. The species differences in UO regulation are probably the result of changes in one or more trans-acting factors required for UO gene expression in the third-instar larval and adult stages.