Full-Length Transcriptome of Red Swamp Crayfish Hepatopancreas Reveals Candidate Genes in Hif-1 and Antioxidant Pathways in Response to Hypoxia-Reoxygenation

Red swamp crayfish is particularly prone to exposure to hypoxia-reoxygenation stress on account of the respiration and rhythmic, light-dependent photosynthetic activity of the algae and aquatic grass. Up to now, the regulation mechanisms of the adverse effects of hypoxia-reoxygenation for this species were still unknown, especially the roles of the antioxidant enzymes in reducing oxidative damage during reoxygenation. To screen for vital genes or pathways upon hypoxic-reoxygenation stress, hepatopancreas gene expression profiles were investigated by using a strategy combining second and third generation sequencing. Five groups of samples, including hypoxia for 1 and 6 h with DO of 1.0 mg/L, reoxygenation for 1 and 12 h with DO of 6.8 mg/L, and the samples under normoxia condition, were used for transcriptome sequencing. Twenty Illumina cDNA libraries were prepared to screen for the differentially expressed genes (DEGs) among the 5 groups of samples. Based on the assembled reference full-length transcriptome, 389 and 533 significantly DEGs were identified in the groups under severe hypoxia treatment for 1 and 6 h, respectively. The top three enriched pathways for these DEGs were "protein processing in endoplasmic reticulum," "MAPK signaling pathway," and "endocytosis." Among these DEGs, hypoxia-inducible factor 1α (Hif-1α) and some Hif-1 downstream genes, such as Ugt-1, Egfr, Igfbp-1, Pk, and Hsp70, were significant differentially expressed when exposed to hypoxia stress. A series of antioxidant enzymes, including two types of superoxide dismutase (Cu/ZnSOD and MnSOD), catalase (CAT), and glutathione peroxidase (GPx), were identified to be differentially expressed during hypoxia-reoxygenation treatment, implying their distinct modulation roles on reoxygenation-induced oxidative stress. The full-length transcriptome and the critical genes characterized should contribute to the revelation of intrinsic molecular mechanism being associated with hypoxia/reoxygenation regulation and provide useful foundation for future genetic breeding of the red swamp crayfish.