The Structure Analysis and mRNA Expression of CaV2 Gene Responding to Hypoxia Stress in Anadara granosa

The blood clam (Anadara granosa) is an economic bivalve that is relatively tolerant to hypoxia, but its molecular mechanism of hypoxia tolerance is unclear. We found that a significant decrease in extracellular Ca2+ concentration and a marked increase in intracellular Ca2+ concentration was observed in the blood clam through the fluorescence probe method, under hypoxic conditions at 0.5 mg/L. Concomitantly, there was a downward trend in the expression level of CaV2 mRNA, whereas NFAT (nuclear factor of activated T cells) expression increased by qRT-PCR. These findings suggest that the elevated intracellular Ca2+ concentration may activate negative transcription factors of NFAT, which subsequently suppresses the transcription of CaV2, leading to its decreased expression. Then, the NFAT RNA interference experiments supported this hypothesis. Sequence analysis and 3D structure prediction revealed conserved and mutated residue sites in blood clam compared to other bivalves. Hypoxia-induced changes in intracellular and extracellular Ca2+ concentrations, activating transcription factor NFAT and suppressing CaV2 expression. This study highlights the key roles of CaV2 and NFAT in hypoxia adaptation, paving the way for further exploration of hypoxia tolerance mechanisms in mollusca.