Aquaporin (AQP) Channels in the Spiny Dogfish, Squalus acanthias I: Characterization of AQP3 and AQP15 Function and Expression, and Localization of the Proteins in Gill and Spiral Valve Intestine

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology
• Main Authors: Cutler, Christopher P., Murray, Debra, Ojo, Tolulope, Harmon, Sheena, MacIver, Bryce, Cramb, Gordon, Zeidel, Mark L.
• Format: Text
• Language: unknown
• Published: Digital Commons@Georgia Southern 2021
• Subjects: Aquaporin water and small solute channels; Elasmobranchs; Spiny dogfish (Squalus acanthias); Western blotting; Immunohistochemistry; Salinity acclimation; Oocyte functional expression; Biochemistry; Biophysics; and Structural Biology; Biology; spiny dogfish; Squalus acanthias
• Online Access: https://digitalcommons.georgiasouthern.edu/biology-facpubs/260; https://doi.org/10.1016/j.cbpb.2021.110702

Complementary DNAs (cDNAs) for two aquaporin water channel genes (AQP3 and AQP15) were amplified cloned and sequenced to initiate this study. Northern blot analysis was carried out to confirm the mRNA sizes of these AQP genes with AQP3 mRNA bands exhibiting sizes of 1.2 and 1.6 k bases and AQP15 had a mRNA band of 2.1 k bases. Northern blot analysis was also performed on kidney and esophagus total RNA samples from fish acclimated to 75%, 100% or 120% seawater (SW). The level of AQP15 mRNA expression was shown to significantly decrease following salinity acclimation from 100 to 120% SW. An opposite but non-significantly different trend was observed for AQP3 mRNA levels. Full length cDNAs were then used to generate AQP3 and AQP15 mRNAs for microinjection into Xenopus oocytes. Both AQP3- and AQP15- microinjected oocytes exhibited significantly elevated apparent water permeability compared to control oocytes at neutral pH. The apparent water permeability was mercury-inhibitable, significantly so in the case of AQP3. AQP3 microinjected oocytes showed pH sensitivity in their apparent water permeability, showing a lack of permeability at acidic pH values. The Carboxyl-terminal derived amino acid sequences of AQP3 and AQP15 were used to generate rabbit affinity-purified polyclonal antibodies. Western blots with the antibodies showed a band of 31.3 kDa for AQP3 in the kidney, with minor bands at 26, 24 and 21 kDa. For AQP15 a band of 26 kDa was seen in gill and kidney. Fainter bands at 28 and 24 kDa were also seen in the kidney. There was also some higher molecular weight banding. None of the bands were seen when the antibodies were pre- blocked with their peptide antigens. Immunohistochemical localization studies were also performed in the gill and spiral valve intestine. In the gill, AQP15 antibody staining was seen sporadically in the membranes of surface epithelial cells of the secondary lamellae. Tyramide amplification of signals was employed in the spiral valve intestine. Tyramide-amplified AQP3 antibody staining ...