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

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Science  22 Jan 2021:
Vol. 371, Issue 6527, pp. 396-400
DOI: 10.1126/science.abc2745

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Enhancer-gene interactions drive split

In many species across the animal kingdom, male and female phenotypes differ. One such example is the wing spot seen in male Drosophila biarmipes flies but not the female flies. Galouzis and Prud'homme investigate the X-linked yellow gene and its enhancer. Investigating the genetics of the trait, they found evidence that the male-specific phenotype is caused by a trans interaction between the enhancer and gene that silences the gene when it is present in only one copy in the male (which only has a single X chromosome) versus the two copies found in the female. This gene thus appears to be regulated by differing genomic interactions in male and female flies and is an example of the phenomenon known as transvection.

Science, this issue p. 396

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 Drosophila biarmipes gene yellow, located on the X chromosome, is independent of the fly sex determination hierarchy. Instead, we find that a regulatory interaction between yellow alleles on homologous chromosomes (a process known as transvection) silences the activity of a yellow 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 yellow 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.

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