Imperial College London, Department of Life Sciences, Imperial College Road, London, SW7 2AZ, UK.
BMC Evol Biol. 2012 May 18;12:69. doi: 10.1186/1471-2148-12-69.
In a number of organisms sex-biased genes are non-randomly distributed between autosomes and the shared sex chromosome X (or Z). Studies on Anopheles gambiae have produced conflicting results regarding the underrepresentation of male-biased genes on the X chromosome and it is unclear to what extent sexual antagonism, dosage compensation or X-inactivation in the male germline, the evolutionary forces that have been suggested to affect the chromosomal distribution of sex-biased genes, are operational in Anopheles.
We performed a meta-analysis of sex-biased gene expression in Anopheles gambiae which provides evidence for a general underrepresentation of male-biased genes on the X-chromosome that increased in significance with the observed degree of sex-bias. A phylogenomic comparison between Drosophila melanogaster, Aedes aegypti and Culex quinquefasciatus also indicates that the Anopheles X chromosome strongly disfavours the evolutionary conservation of male-biased expression and that novel male-biased genes are more likely to arise on autosomes. Finally, we demonstrate experimentally that transgenes situated on the Anopheles gambiae X chromosome are transcriptionally silenced in the male germline.
The data presented here support the hypothesis that the observed demasculinization of the Anopheles X chromosome is driven by X-chromosome inactivation in the male germline and by sexual antagonism. The demasculinization appears to be the consequence of a loss of male-biased expression, rather than a failure in the establishment or the extinction of male-biased genes.
在许多生物体中，性偏向基因在常染色体和共享性染色体 X（或 Z）之间是非随机分布的。关于冈比亚按蚊的研究对于雄性偏向基因在 X 染色体上的代表性不足产生了相互矛盾的结果，不清楚性拮抗、剂量补偿或雄性生殖细胞中的 X 失活等进化力量在多大程度上影响了性偏向基因的染色体分布，这些进化力量已被提议影响性偏向基因的染色体分布。
我们对冈比亚按蚊的性偏向基因表达进行了荟萃分析，该分析提供了证据表明，X 染色体上的雄性偏向基因普遍代表性不足，随着观察到的性别偏向程度的增加，这种代表性不足的程度增加了。黑腹果蝇、埃及伊蚊和库蚊之间的系统基因组比较也表明，冈比亚按蚊的 X 染色体强烈不利于雄性偏向表达的进化保守，并且新的雄性偏向基因更有可能在常染色体上产生。最后，我们通过实验证明，位于冈比亚按蚊 X 染色体上的转基因在雄性生殖细胞中是转录沉默的。
这里呈现的数据支持这样的假设，即观察到的冈比亚按蚊 X 染色体去男性化是由雄性生殖细胞中的 X 染色体失活和性拮抗驱动的。去男性化似乎是雄性偏向表达丧失的结果，而不是雄性偏向基因的建立或灭绝失败的结果。
