Evolution of Cis-Regulatory Sequences in Drosophila

Altered expression of genes during development is one mechanism that might underlie morphological diversity in animals. Comparison has shown that differences in gene expression often correlate with differences in morphology between species. However, many of these examples involve slowly evolving traits between widely diverged taxa, making investigation of how such changes came about all but impossible. Changes in expression of a specific gene can be due to changes in the activity of trans-acting regulatory factors or to evolution of the cis-acting sequences of the gene itself. A number of studies indicate that cis-regulatory regions can undergo significant sequence turnover even when their function is maintained. In other cases, however, regulatory regions of considerable sequence similarity mediate a different gene expression pattern. These observations make it difficult to predict a change in transcriptional output from an examination of the sequence alone. Here we review recent observations on the evolution of cis-regulatory sequences between Drosophila species and some other species of dipteran flies. We look at specific cases that have been investigated in detail, where the function of the regulatory element is either maintained or has evolved to mediate a different transcriptional pattern of gene activity. The examples chosen illustrate the necessity to identify the interactions between the proteins that bind the element, and to verify binding sites through in vivo assays. Although the number of such studies is still small, they suggest that changes in gene regulation might be an important factor in the evolution of animal morphology. (C) 2008, Elsevier Inc.