Sex-specific gene expression in eastern oyster, Crassostrea virginica, gonad and mantle tissues

The eastern oyster (Crassostrea virginica) is a protandrous hermaphrodite of commercial importance. As with many marine invertebrates, little is known about sex determination and differentiation systems in this species. Such knowledge has important implications not only for understanding the evolution of sex but also for applied questions in aquaculture. In order to examine mechanistic differences in reproductive development between the sexes, we compared the transcriptomes of gonad and mantle tissues from six male and six female oysters. A total of 7675 transcripts were differentially expressed between male and female gonads (3936 and 3739 were upregulated in males and females, respectively). Transcripts identified include those associated with sex in other invertebrate and vertebrate species such as Dmrt1, Sox-30, Bindin, Dpy-30, and Histone H4 in males and Foxl2, Vitellogenin, and Bystin in females. GO terms associated with transcripts upregulated in male gonads include protein modification, reproductive process, and cell projection organization, whereas RNA metabolic process and amino acid metabolic process were associated with transcripts upregulated in females. Far fewer transcripts were differentially expressed between male and female mantle tissues, with 87 transcripts upregulated in females and 16 upregulated in males. However, 41% of transcripts identified as differentially expressed between mantle tissues were also differentially expressed between male and female gonads including Histone H4 and Bystin. This study represents the first characterization of eastern oyster male and female gonad transcriptomes. We further identify differing expression profiles between male and female mantle tissues, which provides evidence for sex-specific functions of the mantle and suggests that this tissue could harbor biomarkers for identifying oyster sex non-destructively.