Transvection regulates the sex-biased expression of a fly X-linked gene.

Abstract

Sexual dimorphism in animals results from sex-biased gene expression patterns. These patterns are controlled by genetic sex determination hierarchies that establish the sex of an individual. Here we show that the male-biased wing expression pattern of the <i>Drosophila biarmipes</i> gene <i>yellow</i>, located on the X chromosome, is independent of the fly sex determination hierarchy. Instead, we find that a regulatory interaction between <i>yellow</i> alleles on homologous chromosomes (a process known as transvection) silences the activity of a <i>yellow</i> enhancer functioning in the wing. Therefore, this enhancer can be active in males (XY) but not in females (XX). This transvection-dependent enhancer silencing requires the <i>yellow</i> intron and the chromatin architecture protein Mod(mdg4). Our results suggest that transvection can contribute more generally to the sex-biased expression of X-linked genes.