Journal Article

Little Evidence for Demasculinization of the <i>Drosophila X</i> Chromosome among Genes Expressed in the Male Germline

Colin D. Meiklejohn and Daven C. Presgraves

in Genome Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 4, issue 10, pages 1007-1016
Published in print January 2012 |
Published online September 2012 | e-ISSN: 1759-6653 | DOI: http://dx.doi.org/10.1093/gbe/evs077

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Male-biased genes—those expressed at higher levels in males than in females—are underrepresented on the X chromosome of Drosophila melanogaster. Several evolutionary models have been posited to explain this so-called demasculinization of the X. Here, we show that the apparent paucity of male-biased genes on the X chromosome is attributable to global X-autosome differences in expression in Drosophila testes, owing to a lack of sex chromosome dosage compensation in the male germline, but not to any difference in the density of testis-specific or testis-biased genes on the X chromosome. First, using genome-wide gene expression data from 20 tissues, we find no evidence that genes with testis-specific expression are underrepresented on the X chromosome. Second, using contrasts in gene expression profiles among pairs of tissues, we recover a statistical underrepresentation of testis-biased genes on the X but find that the pattern largely disappears once we account for the lack of dosage compensation in the Drosophila male germline. Third, we find that computationally “demasculinizing” the autosomes is not sufficient to produce an expression profile similar to that of the X chromosome in the testes. Our findings thus show that the lack of sex chromosome dosage compensation in Drosophila testes can explain the apparent signal of demasculinization on the X, whereas evolutionary demasculinization of the X cannot explain its overall reduced expression in the testes.

Keywords: Drosophila; X chromosome; sex-biased gene expression

Journal Article.  6620 words.  Illustrated.

Subjects: Bioinformatics and Computational Biology ; Evolutionary Biology ; Genetics and Genomics

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