Immunolocalization of a mammalian aquaporin 3 homolog in water-transporting epithelial cells in several organs of the clawed toad Xenopus laevis

Abstract

Nucleotide sequences of cDNA were used to construct antibodies against an aquaporin (AQP) expressed in the clawed toad, Xenopus laevis, viz., Xenopus AQP3, a homolog of mammalian AQP3. Xenopus AQP3 was immunolocalized in the basolateral membrane of the principal cells of the ventral skin, the urinary bladder, the collecting duct and late distal tubule of the kidney, the absorptive epithelial cells of the large intestine, and the ciliated epithelial cells of the oviducts. Therefore, we designated this AQP as basolateral Xenopus AQP3 (AQP-x3BL). The intensity of labeling for AQP-x3BL differed between the ventral and dorsal skin, with the basolateral membrane of the principal cells in the ventral skin showing intense labeling, whereas that in the dorsal skin was lightly labeled. AQP-x3BL was also immunolocalized in the basolateral membrane of secretory cells in the small granular and mucous glands of the skin. As AQP-x5, a homolog of mammalian AQP5, is localized in the apical membrane of these same cells, this provides a pathway for fluid secretion by the glands. Although Hyla AQP-h2 is translocated from the cytoplasm to the apical membrane of the Hyla urinary bladder in response to arginine vasotocin (AVT), AQP-h2 immunoreactivity in Xenopus bladder remains in the cytoplasm and barely moves to the apical membrane, regardless of AVT stimulation. AQP-x3 is localized in the basolateral membrane, even though the AVT-stimulated AQP-h2 does not translocate to the apical membrane. These findings provide new insights into AQP function in aquatic anurans.

Gene expression and localization of two types of AQP5 inXenopus tropicalisunder hydration and dehydration

“…9, B-D). AQP-xt5b was not found in the apical plasma membrane of flattened cells located in the intermediate region between the acinus and excretory duct of mucous glands, unlike X. laevis AQP-x5(b) (26,30). These findings are summarized in Fig.…”

“…10, C and D). Because AQP3 is expressed in the granular cells of the luminal epithelium (30,40,41), AQP-xt5a-positive cells are considered to be the granular cells. After dehydration, the number of AQP-xt5a-positive cells increased, and labels were observed in the apical membrane and cytoplasm of most granular cells (Fig.…”

“…Another two glands are observed in the X. laevis skin: the small granular (granulated) gland and the NP gland in the nuptial pad of the male forelimb (17). Immunohistochemistry and immunoelectron microscopy with an antibody raised against AQP-x5 revealed that AQP-x5 is present in the apical plasma membrane of acinar cells of the small granular glands (30).…”

Dynamic regulation of aquaglyceroporin expression in erythrocyte cultures from cold‐ and warm‐acclimated cope's gray treefrog, Hyla chrysoscelis

“…One route for transmembrane transport of glycerol is via aquaporin/aquaglyceroporin (AQP/GLP) members of the MIP family of transmembrane proteins (Thomas et al, 2002). Several amphibian orthologs of mammalian aquaporins have been identified, including members of both the AQP and GLP functional classes (Ma et al, '96; Tanii et al, 2002; Virkki et al, 2002; Kubota et al, 2006; Akabane et al, 2007; Ogushi et al, 2007; Zimmerman et al, 2007; Mochida et al, 2008; Suzuki and Tanaka, 2009). In addition, two anuran‐specific aquaporin types appear to have evolved to support physiologic responses to changes in the external environment, including those that occur during metamorphosis and the transition from an aquatic to a terrestrial environment (Suzuki et al, 2007; Suzuki and Tanaka, 2009; Ogushi et al, 2010; Suzuki and Tanaka, 2010).…”

Renal responses to salinity change in snakes with and without salt glands

“…Water then exits the cell via the basolaterally located AQP3 (Kinne and Zeidel, 2009;Sugiura et al, 2008). Although renal expression of AQP3 is restricted to the basolateral membranes of collecting duct cells in mammals and birds, its distribution among amphibians appears to extend into the distal tubules (Akabane et al, 2007;Mochida et al, 2008) and among fishes the localization of AQP3 remains equivocal . As reviewed by Dantzler (Dantzler, 1976), the permeability of the distal tubule to water is quite variable among reptiles (and can also vary considerably with hydration status within a given species).…”