Sex-specific transcriptomic signatures in Pacific oyster hemolymph

Authors: SONG, JINGWEI - Oregon State University; MAURELLI, ODILE - Oregon State University; YEATS, MARK - Oregon State University; Thompson, Neil; BANKS, MICHAEL - Oregon State University; Calla, Bernarda

Submitted to: Genes and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2025
Publication Date: 8/30/2026
Citation: Song, J., Maurelli, O., Yeats, M., Thompson, N., Banks, M., Calla, B. 2026. Sex-specific transcriptomic signatures in Pacific oyster hemolymph. Genes and Development. 16(9).1033. https://doi.org/10.3390/genes16091033.
DOI: https://doi.org/10.3390/genes16091033

Interpretive Summary: Pacific oysters are the main cultivated shellfish in the Pacific Northwest and around the world. The development of oyster hatcheries and nurseries have greatly reduced the dependency on unpredictable natural settlements for consistent oyster production. To maximize the efficiency of this artificial rearing and to aid breeding programs, it is essential to understand the reproductive patterns of Pacific oysters. These animals may switch sex from male to female or vice versa on every reproductive cycle. In this study we investigated if hemolymph, the analog of blood in invertebrates, could carry early signals of sex determination in the oyster that can help predict the sex before the oyster gonad is fully mature. For that purpose, we sampled hemolymph from animals at several time points during early gonad development and analyzed their gene expression levels. The sexes of the animals were obtained at the end of the maturation period to draw a correlation between early hemolymph gene expression and sex. We identified several candidate markers to predict Pacific oyster sex using hemolymph

Technical Abstract: Sex determination and differentiation exhibit remarkable molecular diversity across taxa, driven by genetic, epigenetic, and environmental factors. Invertebrates with sequential hermaphroditism, such as the Pacific oyster (Magallana gigas), represent poorly understood systems despite their keystone ecological role and substantial aquaculture segment. To identify sex-related molecular markers during gametogenesis, we repeatedly sampled hemolymph from artificially conditioned oysters over two months, followed by terminal sexing. RNA-sequencing analysis of five males and five females revealed subtle but discernible sex-specific transcriptional signatures in hemolymph. We show that gametogenesis proceeds asynchronously among female and male oysters. Complex physiological trade-offs were discovered between sexes during gonad maturation, such that females prioritized while males suppressed cell division in early maturation. Females exhibited higher expression of solute carrier family (SLC) genes, suggesting enhanced nutrient exchange during oogenesis. Temporal dynamics highlighted differential expression of genes regulating cross-membrane ion gradients (e.g., transient receptor potential channels) and signal transduction (e.g., signal transducer and activator of transcription), previously linked to environmental sex determination (ESD) in other species such as turtles and alligators. Together, these findings underscore that gametogenesis in Pacific oyster is complex and dynamic, and molecular pathways of ESD may be partially conserved between invertebrate and vertebrate species.