Sex-specific gene expression in eastern oyster (Crassostrea virginica) gonad and mantle

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 tissue from 6 male and 6 female oysters. A total of 7,675 transcripts were differentially expressed between male and female gonads (3,936 and 3,739 up-regulated 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 up-regulated in male gonad include protein modification, reproductive process, and cell projection organization, while RNA metabolic process and amino acid metabolic process were associated with transcripts up-regulated in females. Far fewer transcripts were differentially expressed between male and female mantle tissue, with 87 transcripts up-regulated in females and 16 up-regulated 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 tissue, providing evidence for sex-specific functions of the mantle and suggesting this tissue could harbor biomarkers for identifying oyster sex non-destructively.

东方牡蛎（Crassostrea virginica）作为一种具有商业价值的雌雄同体的两栖贝类，其性决定与分化系统在众多海洋无脊椎动物中鲜有研究。此类知识的掌握不仅对性别的进化机制有着深远的意义，而且在水产养殖的实践应用中也具有重要意义。为了探究雌雄生殖发育的机制差异，本研究对比分析了6只雌性和6只雄性牡蛎的生殖腺和壳体的转录组。结果显示，在雌雄生殖腺之间共有7,675个转录本表现出差异表达（其中雄性中有3,936个和雌性中有3,739个转录本上调）。这些转录本包括与其它无脊椎动物和脊椎动物性别相关的基因，如Dmrt1、SOX-30、bindin、dpy-30和雄性中的histone H4，以及雌性中的foxl2、vitellogenin和Bystin。与雄性生殖腺相关的GO术语包括蛋白质修饰、生殖过程和细胞突起组织，而与雌性生殖腺相关的GO术语则包括RNA代谢过程和氨基酸代谢过程。在雌雄壳体组织之间，差异表达的转录本数量相对较少，其中雌性中有87个转录本上调，雄性中有16个转录本上调。然而，在壳体组织中被识别为差异表达的41%的转录本同样在雌雄生殖腺之间存在差异表达，包括Histone H4和Bystin。本研究首次对东方牡蛎雌雄生殖腺的转录组进行了表征，并进一步揭示了雌雄壳体组织的不同表达模式，为壳体组织的性别特异性功能提供了证据，并暗示该组织可能含有用于非破坏性鉴定牡蛎性别的生物标志物。