Classical aquaporins from Pacific white shrimp (Litopenaeus vannamei): Molecular characterization and expression analysis in hypersalinity

Aquaporins (AQPs) are major intrinsic proteins that facilitate the transport of water, small solutes, and ions through membranes. In mammals, the classical aquaporin AQP4 plays a central role in the preservation of central nervous system (CNS) water homeostasis. Litopenaeus vannamei is a typical euryhaline crustacean, with a salinity tolerance range of 0.5-78. Compared to those reared at low-salinity, shrimps cultured at high-salinity have better taste and qualities, but slower growth, lower product yield, and higher mortality. Thus, there is an urgent need to research the osmoregulation of L. vannamei under high-salinity. Previous studies mainly focus on the osmoregulation of gill and hepatopancreas, whereas there is a lack of research on the osmoregulatory roles of CNS in L. vannamei. In the current study, we first presented another two classical AQPs from L. vannamei, of which the arthropod-specific big brain aquaporin (LvBib) was expressed as C-terminal splice variants (LvBib_L and LvBib_S), and the aquaporin-like protein (LvAqpl) was a new type of aquaporin in crustaceans. Tissue distribution revealed that LvAqp4, LvAqpl, and LvBib_L were mostly expressed in the CNS of brain and thoracic ganglion. Then, the expression pattern of aquaporins in brain and thoracic ganglion were examined under both acute and chronic high-salinity stresses. The LvAqpl was found to be down-regulated in both tissues in the two experiments; LvAqp4 was elevated in both tissues under acute stress, whereas it was decreased in the thoracic ganglion during early periods of adaption to high-salinity; LvBib_L was up-regulated in brain but down-regulated in thoracic ganglion under acute stress, whereas it showed the opposite expression pattern during chronic stress. The results suggest that these aquaporins have an important role in the CNS response to high-salinity challenge. Our study provides a base for future mechanistic studies on the role of classical aquaporins in osmoregulation.