Integrated transcriptomics and metabolomics reveal tolerance mechanisms to hypoxia stress in Yesso scallop, Mizuhopecten yessoensis
Global warming and human activities have led to an increased frequency of hypoxia in coastal regions. Hypoxia not only affects the growth and development of scallops but can also cause death, posing a significant challenge to the health and sustainability of aquaculture. Its effects on scallop growth and immune system have been widely reported, but studies on the effects of hypoxic stress on the metabolism of Yesso scallop Mizuhopecten yessoensis are not fully understood. Additionally, the molecular mechanisms of hypoxic stress on damage to the Yesso scallop are still limited. In this study, we deploy high-throughput RNA sequencing (RNA-Seq) and non-targeted liquid chromatography-mass spectrometry (LC-MS) based metabolomics analysis to investigate the alterations in key genes and metabolites in scallops after 24 hours of hypoxia stress (DO: 1 ± 0.1 mg/L). A total of 704 differentially expressed genes (DEGs) and 302 differentially expressed metabolites (DEMs) were identified in the gill tissues of Yesso scallops under hypoxic conditions, respectively. DEGs and DEMs were involved in energy metabolism, antioxidant responses, immune responses, and inflammatory responses, as well as processes of cell apoptosis and cell proliferation. KEGG enrichment analysis shows that the mTOR signaling pathway is a significantly enriched pathway shared by DEGs and DEMs. These findings suggest that Yesso scallops cope with acute hypoxic stress by changing energy metabolism, inhibiting cell apoptosis and proliferation, and increasing immune defense strategies. Overall, the results of this study provide a new understanding of how Yesso scallops respond to hypoxia and provide target genes for the selection and breeding of low-oxygen-tolerant scallops. Overall design: To study the molecular mechanisms of scallops responding to hypoxia, we conducted transcriptome sequencing analysis on scallops after hypoxia treatment. A total of 60 scallops individuals were randomly divided into two groups and used in the hypoxia experiment. The control group had a dissolved oxygen (DO) level set at 9.0 ± 0.9 mg/L, whereas the DO level for the group under hypoxia stress was maintained at 1.0 ± 0.1 mg/L. After 24 hours of treatment,  three scallops were randomly selected from each group, dissected to obtain gill tissue, quickly frozen in liquid nitrogen, and then stored in a -80°C freezer.