Sex-biased gene expression in a ZW sex determination system.
Studies of the transcriptome have shown that a substantial fraction of interspecific differences in gene expression is the result of sex-biased gene expression. These results suggest that sex-dependent selection may be an important force in generating differences between species but to date all studies have focused on Drosophila. We examined a sample of the transcriptome in the gonads of two species of Xenopus to provide an additional test of how sex-biased gene expression may contribute to differences in gene expression between species. In contrast to Drosophila, Xenopus provides an example of a ZW system with morphologically indistinguishable sex chromosomes. About 81% of the transcriptome was differentially expressed between X. laevis and X. muelleri and there were more genes that were male-biased compared to the number of genes that were female-biased or non-sex-biased. While there were more genes up-regulated in males of Xenopus, the largest magnitude difference in expression between species occurred in female-biased genes, and male-biased genes were proportionally more abundant for the smallest changes in expression between species. Our results suggest that more genes have a role in the function of the testis compared to the ovary and female-biased genes play a principle role in expression divergence between species. These results differ from those in the Drosophila XY system in that more female-biased genes had >4-fold difference of expression between species than male-biased genes, suggesting that ZW sex chromosomes may facilitate enhanced gene expression divergence between species.
Malone
John H
JH
Department of Biology, The University of Texas--Arlington, Box 19498, Arlington, TX 76019, USA.
Hawkins
Doyle L
DL
Michalak
Pawel
P
D000818:Animals; D005260:Female; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012727:Sex Characteristics; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D013045:Species Specificity; D014982:Xenopus laevis / Q000235:genetics*
D012333:RNA, Messenger