Atlantic halibut aquaporins: molecular characterization and role during oocyte hydration

Abstract

Recent studies have revealed a novel role for the teleost aquaporin-1b (Aqp1b) in mediating water influx during oocyte hydration of marine fish. Such hydration occurs during meiotic maturation providing a water reservoir for the embryo before organs associated with active osmoregulation are developed, and it causes the egg to float. To further understand the role of aquaporins in the hydration process, we cloned and characterized Aqp1a and -1b in Atlantic halibut, which spawns one of the largest pelagic eggs known (> 3 mm). These analyses revealed that Aqp1a is ubiquitously distributed, whereas Aqp1b is expressed almost exclusively in the ovary. Surprisingly, we found that Aqp1a is functional in Xenopus oocytes, whereas Aqp1b is retained in the oocyte cytoplasm. However, in vivo experiments showed that native Aqp1b is readily inserted into the halibut oocyte plasma membrane during meiotic maturation. These findings suggest that Aqp1b may play a role during oocyte hydration in Atlantic halibut as in Perciformes, although the specific intracellular regulation of Aqp1b trafficking is yet unknown