Aquaporin Biology of Spermatogenesis and Sperm Physiology in Mammals and Teleosts

Abstract

Fluid homeostasis is recognized as a critical factor during the development, maturation, and function of vertebrate male germ cells. These processes have been associated with the presence of multiple members of the aquaporin superfamily of water and solute channels in different cell types along the reproductive tract as well as in spermatozoa. We present a comparative analysis of the existing knowledge of aquaporin biology in the male reproductive tissues of mammals and teleosts. Current data suggest that in both vertebrate groups, aquaporins may have similar functions during differentiation of spermatozoa in the germinal epithelium, in the concentration and maturation of sperm in the testicular ducts, and in the regulation of osmotically induced volume changes in ejaculated spermatozoa. Recent studies have also provided insight into the possible function of aquaporins beyond water transport, such as in signaling pathways during spermatogenesis or the sensing of cell swelling and mitochondrial peroxide transport in activated sperm. However, an understanding of the specific physiological functions of the various aquaporins during germ cell development and sperm motility, as well as the molecular mechanisms involved, remains elusive. Novel experimental approaches need to be developed to elucidate these processes and to dissect the regulatory intracellular pathways implicated, which will greatly help to uncover the molecular basis of sperm physiology and male fertility in vertebrates.

Molecular cloning and expression analysis of the aqp1aa gene in half-smooth tongue sole (Cynoglossus semilaevis)

“…The mRNA expression of aqp1aa was detected in testicular germ cells, including spermatozoon and spermatid, using in situ hybridization (Fig 3), which is identical to that in gilthead seabream [39, 45]. Furthermore, regarding its expression levels in gonads, aqp1aa was highly expressed in male and pseudo-male testis (Fig 3D, 3E, 3G and 3H), while it was hardly expressed in the ovary (Fig 3F and 3I), which is identical to the results obtained using qPCR.…”

“…In marine teleosts, aqp1aa mainly expressed in spermatozoa, especially located flagellum of the spermatozoa in the gilthead seabream ( Sparus aurata ) [38]. Besides, the aqp1aa is involved in the sperm motility activation by mediating the water efflux during hyperosmotic shock [38, 39, 43, 45]. However, the function of aqp1aa in C .…”

“…In mammals, AQP1 has been recognized in the testis and is involved in the early stage of spermatogenesis [35–36], where it may play a role in the secretion of tubule liquid to achieve the luminal changes required for sperm concentration transition and maturation [12, 37]. In marine teleosts, two AQP1 paralogous genes ( aqp1aa and aqp1ab ) are reported [20, 38–45]. The aqp1ab predominately expressed in ovary and involved in the hydration of the oocyte [40–41, 46–48], while aqp1aa mainly expressed in spermatozoa, especially located flagellum of the spermatozoa in marine teleost ( Sparus aurata ) [38].…”

“…The aqp1ab predominately expressed in ovary and involved in the hydration of the oocyte [40–41, 46–48], while aqp1aa mainly expressed in spermatozoa, especially located flagellum of the spermatozoa in marine teleost ( Sparus aurata ) [38]. Besides, the aqp1aa is involved in the sperm motility activation by mediating the water efflux during hyperosmotic shock [38–39, 43, 45, 49]. Although the cloning of aqp1aa gene in tongue sole has been published [40], its function in tongue sole is still unclear.…”

The cellular localization and redistribution of multiple aquaporin paralogs in the spermatic duct epithelium of a maturing marine teleost

“…; Arrighi, ; Boj et al. ). The aquaporins are small hydrophobic integral membrane proteins that allow the bidirectional movement of water and other small, uncharged solutes (i.e.…”