Immunolocalization of Aquaporin-1, −5, and −7 in the Avian Testis and Vas Deferens

Abstract

Thirteen mammalian aquaporin (AQP) isoforms have been identified, and they have a unique tissue-specific pattern of expression. AQPs have been found in the reproductive system of both male and female humans, rats, and mice. However, tissue expression and cellular and subcellular localization of AQPs have been poorly investigated in the male reproductive system of birds. The localization of AQP subtypes (AQP1, 2, 3, 4, 5, 7, 8, 9, and 11) in the goose testis and vas deferens has been studied through immunohistochemistry and immunobloting. Interestingly, the testicular and deferential tissues were positive for AQP1, -5, and -7 but not the others. AQP1 immunoreactivity was detected in the capillary endothelial cells of testis and vas deferens. AQP5 was localized in the interstitial tissue of the testis, including Leydig cells, as well as in the basal cells of vas deferens. Double-labeling confocal microscopy revealed coexpression of AQP5 with capillary AQP1 in the testis. AQP7 was expressed in elongated spermatid and spermatozoa tails in the testis, as well as spermatozoa tails in the vas deferens. These results suggest that several subtypes of AQPs are involved in the regulation of water homeostasis in the goose male reproductive system.

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

“…In line with this notion is the observation that Aqp1aa is the only aquaporin found abundantly distributed along the entire flagella of ejaculated spermatozoa. Such a pattern of aquaporin expression in the male germ cells of seabream is similar to that described in tetrapods, since in these species AQP1 and -7 are localized in round and/or elongated spermatids [21,23,24,64,66]. However, in mammals, it is quite likely that species-specific differences in AQP8 localization in germ cells exist, including restriction to certain spermatogenic cell types or to all germ cells, or even exclusive expression in Sertoli cells [3].…”

“…The presence of these orthologs in seabream Sertoli and Leydig cells is conserved with respect to mammals since this has been previously reported in rats (Rattus norvegicus) [12-14, 19, 61], although the expression of AQP9 was undetectable in the testis of the dog (Canis lupus familiaris), fruit-eating bat (Artibeus lituratus), mouse (Mus musculus), and human [47,[62][63][64]. Mammalian Sertoli and Leydig cells also express the AQP8 and -0 orthologs, respectively [12,16,65], and in avian species AQP5, which is not conserved in the zebrafish genome [32], is specifically found in Leydig cells [66]. Although Aqp8b protein expression could not be demonstrated in seabream Sertoli cells, it is still possible that other Aqp8 paralogs, such as Aqp8aa, which is phylogenetically closer to the tetrapod AQP8 than to Aqp8b [30], are present in these cells.…”

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

“…Different evolutionary statuses of aqp1aa suggest different functions of aqp1aa in teleosts and mammals. In mammals, in addition to being involved in cell migration and neural signal transduction [17, 34], AQPs also play a role in the early stages of spermatogenesis through the secretion of tubule liquid to achieve water homeostasis in the lumen, for sperm concentration transition and maturation [37]. In marine teleosts, aqp1aa mainly expressed in spermatozoa, especially located flagellum of the spermatozoa in the gilthead seabream ( Sparus aurata ) [38].…”

“…Aquaporins (AQPs) are transmembrane water channel proteins that allow water and some small molecules to pass through the plasma membrane of cells in animals [17]. To date, a diversity of the aquaporin gene superfamily have been discovered in prokaryotic and eukaryotic organisms [18–29].…”

“…Aquaporin 1 (AQP1) is the first isoform identified on the cell membrane of erythrocytes [30], its monomers contain water pores but associate in the membrane as tetramers, each monomer typically contains six transmembrane α-helices with the N- and C-termini both located on the cytoplasmic side of the membrane [31–32], and its role in cells has been extensively studied and well understood as a water-selective channel. However, subsequent studies have revealed that AQP1 has other roles in living organisms, including cell migration, spermatogenesis and neural signal transduction [17, 33–34]. 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].…”