Role of testis-specific gene expression in sex-chromosome evolution of Anopheles gambiae

Abstract

Gene expression in Anopheles gambiae shows a deficiency of testis-expressed genes on the X chromosome associated with an excessive movement of retrogene duplication. We suggest that the degeneration of sex chromosomes in this monandrous species is likely the result of pressures from X inactivation, dosage compensation, and sexual antagonism.

Figure 1—

(A) Dipteran retrogene events. We find an excess of X-to-A retrogene events occurring within the Anopheles lineage, but not on the branch prior to the Anopheles and Aedes split. X, X chromosome. A, autosomes. Excess = [(O – E)/E] × 100. (B) Tissue-specificity of retrogenes and progenitors. Retrogenes show a higher incidence of tissue-specific gene expression. Unpaired Wilcoxon test: P < 0.05. (C) X-chromosome enrichment of genes expressed in reproductive tissue. Consistent with previous studies, there is a deficiency of testis-specific genes on the Anopheles X chromosome, but an over-representation of male accessory gland genes (expected X: 9.6%; χ² test: *P < 0.05).