title: Expression of a mammalian aquaporin 3 homolog in the anterior pituitary gonadotrophs of the tree frog, Hyla japonica.
abstract: Aquaporins (AQPs) are a family of water channel proteins that play a major role in maintaining water homeostasis in various organisms. Several AQPs have been identified in the tree frog, Hyla japonica. Of these, AQP-h3BL, which is expressed in the basolateral membrane of the epithelial cells, is a homolog of mammalian AQP3. Using immunohistochemistry and in situ RT-PCR, we have demonstrated that AQP-h3BL is expressed in the anterior pituitary gonadotrophs of the tree frog but not in the other hormone-producing cells of the anterior pituitary. In gonadotrophs labeled for luteinizing hormone subunit-β (LHβ), AQP-h3BL protein was found to reside in the plasma membrane, the nuclear membrane and the cytoplasm. Double-labeling of AQP-h3BL mRNA and LHβ protein revealed that AQP-h3BL mRNA is expressed in the gonadotrophs. Following stimulation by gonadotropin-releasing hormone (GnRH), the label for AQP-h3BL localized in the plasma membrane became more intense, concomitant with the transport of LHβ-positive materials to the plasma membrane. These developments coincided with a decrease in the labeling density in the cytoplasm and near the nuclear membrane, suggesting that the latter localizations may function as "storage area" for AQP-h3BL. Immunoelectron microscopy also confirmed these localizations of AQP-h3BL protein. Based on these results, we suggest that AQP-h3BL protein in the frog gonadotrophs is involved in the formation of secretory granules, the swelling and increase in the volume of the granules and exocytosis.
authors.affiliation: Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Ohya836, Suruga-ku, Shizuoka 422-8529, Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Sato
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakakura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ogushi
authors.forename: Gen
authors.initials: G
authors.lastname: Akabane
authors.forename: Shingo
authors.initials: S
authors.lastname: Kurabuchi
authors.forename: Masakazu
authors.initials: M
authors.lastname: Suzuki
authors.forename: Shigeyasu
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D001001:Anura / Q000033:anatomy & histology* / Q000378:metabolism*; D051400:Aquaporin 3 / Q000235:genetics / Q000378:metabolism*; D052681:Gonadotrophs / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008322:Mammals; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D020033:Protein Isoforms; D012333:RNA, Messenger; D051400:Aquaporin 3