Molecular and physiological characterizations of razor clam (Sinonovacula constricta) aquaporin genes AQP4 and AQP10 in response to low-salinity tolerance.

Aquaporins (AQPs) are a family of membrane proteins responsible for the selective transport of water molecules and other neutral metabolic substances across cell membranes. These proteins play a crucial role in osmoregulation, enabling marine bivalves to accommodate salinity fluctuations. However, the regulatory mechanism of AQPs in the razor clam (Sinonovacula constricta) under salinity stress remain unclear. In this study, we investigated the roles of two classical AQP genes, Classical aquaporins ScAQP4 and aquaglyceroporin ScAQP10, in response to hypotonic stress in S. constricta. ScAQP4 and ScAQP10 are hydrophobic proteins with six transmembrane domains and a highly conserved MIP structural motif. Upon acute hyposaline challenges, the expression of ScAQP4 and ScAQP10 in gills exhibited a significant increase in responses to low-salinity stress initially, followed by a gradual osmotic rebalance. To further investigate their biological functions, we conducted dsRNA interference to knockdown the expression levels of ScAQP4 and ScAQP10 in gill tissues and assessed the following physiological alternations. The knockdown of ScAQP4 and ScAQP10 resulted in a significant increase in heart rate and apoptosis and severe cellular damage of gills. These findings highlighted the critical roles of ScAQP4 and ScAQP10 in maintaining the osmotic balance of S. constricta. Collectively, these results propose a mechanism by which S. constricta regulates the expression of AQPs to accommodate salinity variations in the natural habitat.