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

Authors: Proestou, Dina; Delomas, Thomas; Sullivan, Mary; Markey Lundgren, Kathryn

Submitted to: Invertebrate Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2024
Publication Date: 2/7/2024
Citation: Proestou, D.A., Delomas, T.A., Sullivan, M.E., Markey Lundgren, K.R. 2024. Sex-specific gene expression in eastern oyster gonad and mantle tissues. Invertebrate Biology. 143(1):e12418. https://doi.org/10.1111/ivb.12418.
DOI: https://doi.org/10.1111/ivb.12418

Interpretive Summary: The eastern oyster aquaculture industry will benefit greatly from technologies that cost-effectively advance selective breeding. Several hatchery activities can be optimized to reduce effort and augment selection precision. One such activity involves targeted broodstock conditioning; i.e, preparing only the highest valued male and female parents for spawning. Because oysters cannot be sexed externally, we do not know which individuals to mate until sacrifice on spawning day, resulting in some uncertainty and a potential reduction in selection. Therefore, it is important to develop protocols that will allow us to sex organisms earlier in the reproductive conditioning process. This research represents the first step in addressing the problem by identifying genetic markers that differentiate female and male oysters. We compared gene expression patterns in mature male and female gonad and mantle tissues and characterized sex-biased differences. Many of the female- and male-specific genes are homologous to those involved in sex differentiation in model organisms; however, novel transcripts were also identified. Furthermore, we demonstrated that sex-specific differences can be detected in the non-reproductive mantle tissue, which is much easier to sample non-destructively. Our results hold promise for the development of a non-destructed sex identification assay that can applied early during the broodstock conditioning process.

Technical Abstract: 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 for understanding the evolution of sex and more 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.