Multiple cis-acting sequences contribute to evolved regulatory variation for Drosophila Adh genes

Abstract

Drosophila affinidisjuncta and Drosophila hawaiiensis are closely related species that display distinct tissue-specific expression patterns for their homologous alcohol dehydrogenase genes (Adh genes). In Drosophila melanogaster transformants, both genes are expressed at high levels in the larval and adult fat bodies, but the D. affinidisjuncta gene is expressed 10-50-fold more strongly in the larval and adult midguts and Malpighian tubules. The present study reports the mapping of cis-acting sequences contributing to the regulatory differences between these two genes in transformants. Chimeric genes were constructed and introduced into the germ line of D. melanogaster. Stage- and tissue-specific expression patterns were determined by measuring steady-state RNA levels in larvae and adults. Three portions of the promoter region make distinct contributions to the tissue-specific regulatory differences between the native genes. Sequences immediately upstream of the distal promoter have a strong effect in the adult Malpighian tubules, while sequences between the two promoters are relatively important in the larval Malpighian tubules. A third gene segment, immediately upstream of the proximal promoter, influences levels of the proximal Adh transcript in all tissues and developmental stages examined, and largely accounts for the regulatory difference in the larval and adult midguts. However, these as well as other sequences make smaller contributions to various aspects of the tissue-specific regulatory differences. In addition, some chimeric genes display aberrant RNA levels for the whole organism, suggesting close physical association between sequences involved in tissue-specific regulatory differences and those important for Adh expression in the larval and adult fat bodies.