Transcriptome Analysis of Crassostrea sikamea (♀) × Crassostrea gigas (♂) Hybrids Under Hypoxia in Occluded Water

Abstract

Hypoxia is considered to be one of the key factors affecting the survival of ocean organisms, it is necessary to parse the molecular processes involved in response to hypoxia. As a potential breeding species, the hybrid of Crassostrea sikamea (♀) × Crassostrea gigas (♂) shows valuable heterosis in survival and growth traits. Thus, RNA de novo was deployed in this study to analyze the molecular processes in the hybrids under hypoxia stress. The hybrids were cultured in occluded water, then the dissolved oxygen was gradually consumed by oysters, and the gill tissue of hybrids was sampled at the very beginning and the lowest respiration point in the experiment. In the current study, 901 significant differentially expressed genes (DEGs) were identified under hypoxia compared to normoxia, among which 432 DEGs were downregulated, and the other 469 DEGs were upregulated. A total of 27 GO terms were significantly enriched, such as an integral component of membrane, extracellular region, immune response, tumor necrosis factor receptor binding, and neurotransmitter: sodium symporter activity. Besides, 19 KEGG pathways were significantly enriched, such as apoptosis, Th1 and Th2 cell differentiation, complement, and coagulation cascades, antigen processing and presentation, notch signaling pathway, and cytokine–cytokine receptor interaction. The current results showed that the TRAIL genes were downregulated, but the HSP70 and LIGHT genes were upregulated, which indicated the inhibition of Apoptosis, and the activity of innate immunity in oysters under hypoxia. This study provides preliminary insight into the molecular response to hypoxia in the gill of hybrids.