Evidence for the Involvement of Aquaporins in Sperm Motility Activation of the Teleost Gilthead Sea Bream (Sparus aurata)1

Abstract

The expression of aquaporins in the spermatozoa of the marine teleost gilthead sea bream (Sparus aurata) and their involvement in the motility activation process were investigated. Sperm motility was activated by a hyperosmotic shock, but it was completely inhibited by 10 microM HgCl(2), such inhibition being partially recovered by beta-mercaptoethanol (ME). Conventional RT-PCR using primers specific for S. aurata aquaglyceroporin (glp) and aquaporin 1a (aqp1a) demonstrated the presence of both mRNAs in spermatozoa. Heterologous expression in Xenopus laevis oocytes showed that 10 and 100 microM HgCl(2) equally inhibited water and solute transport through S. aurata aquaporin 1a and S. aurata aquaglyceroporin, but treatment with ME only recovered aquaporin 1a-mediated water permeability. Western blot analysis using isoform-specific antisera on protein extracts from spermatozoa revealed bands that corresponded to the predicted molecular mass of S. aurata aquaglyceroporin (31 kDa) and S. aurata aquaporin 1a (28 kDa). The antisera also demonstrated that both aquaporins were localized in the head and flagellum of the spermatozoa. However, the immunoreaction at the plasma membrane of the spermatozoa head was more intense after the hyperosmotic activation, suggesting the translocation of both aquaporin 1a and aquaglyceroporin into the plasma membrane after the osmotic shock. This study therefore provides the first direct demonstration for the presence of aquaporins in fish sperm. The different sensitivities of S. aurata aquaporin 1a and S. aurata aquaglyceroporin to ME may explain the failure of this reducing agent to fully recover the mercurial inhibition of sperm motility, suggesting that these aquaporins may play different physiological roles during the activation and maintenance of sperm motility in sea bream.

Mechanism of action of mercury on sperm morphology, adenosine triphosphate content, and motility in Perca fluviatilis (Percidae; Teleostei)

“…On receiving the osmotic signal, ion channels and aquaporins regulate exchange of ions and water through the plasma membrane, respectively, which lead to the initiation of sperm motility [35][36][37]. Zilli et al [37] observed that HgCl 2 at 10 mM completely inhibited sperm activation in gilthead sea bream (Sparus aurata). Their study showed the existence of aquaporins in fish spermatozoa that are detected at the surface of the spermatozoa, both head and flagella.…”

Subcellular Localization of Selectively Permeable Aquaporins in the Male Germ Line of a Marine Teleost Reveals Spatial Redistribution in Activated Spermatozoa1

“…To date, only a single study has shown that aquaporin proteins are expressed in the spermatozoa of a marine teleost, the gilthead seabream (Sparus aurata) [7]. This study revealed that the water-specific channel aquaporin-1aa (Aqp1aa) and the glycerol-, urea-, and water-transporting channel Aqp10b are both present in the head and flagellum of ejaculated spermatozoa, and that mercury, an inhibitor of Aqp1aa and -10b water transport [7][8][9][10], blocks sperm motility in seawater [7].…”

Involvement of redox- and phosphorylation-dependent pathways in osmotic adaptation in sperm cells of euryhaline tilapia

“…Water may be transported by aquaporins in the plasma membrane (King and Agre, 1996;Verkman, 2002). Sperm of the marine teleost sea bream (Sparus aurata) express aquaporin 1a and aquaglyceroporin, which are localised to the plasma membrane of the head and flagellum (Zilli et al, 2009). In tilapia sperm, it seems reasonable that redoxdependent signal cascades are involved in the regulation of osmotic tolerance and motility.…”