[
International Worm Meeting,
2003]
Water movement across the cell membrane is a fundamental process for the maintenance of water homeostasis in many cell types. The aquaporin (AQP) water channels belong to the major intrinsic protein (MIP) superfamily and play a central role in water transport. AQPs are present in many forms of life including bacteria, yeast, plants, insects, and mammals. There are at least eleven AQPs (AQP0-AQP10) in mammals which functionally characterized in terms of the permeability of water and small solutes. The primary structures of AQPs are almost similar in size (250-290 amino acids). Six membrane-spanning domains and two highly conserved amino acid residues called NPA (asparagine-proline-alanine) boxes are the common features of AQP. The completion of genome sequence of the nematode Caenorhabditis elegans revealed the presence of eight MIPs in its genome. Of these MIPs, AQP-CE1 (C01G6.5) and AQP-CE2 (F40F9.9) have been characterized as water permeable channels when expressed in Xenopus oocytes. AQP-CE1 and CE2 correspond to AQP3 and AQP8 in mammals, respectively, from sequence homology and channel characteristics. The remaining "typical" MIPs in C. elegans are also thought to function as water channels, although physiological roles are still unknown. We have recently identified and characterized the novel type of aquaporin, AQP11 and AQP12 in mouse, which did not permeate water. We found two homologs in C. elegans genome, ZK525.2 (III) and ZK1321.3 (II). ZK525.2 encoded 290 amino acids and ZK1321.3 encoded 280 amino acids having homology with AQP11. When cRNAs were expressed in Xenopus oocyte, they did not permeate water as AQP11. To understand the physiological roles of new AQP genes in C. elegans, we investigated expression patterns and knock out phenotypes of ZK525.2 and ZK1321.3. Expression pattern of ZK525.2::GFP and ZK1321.3::GFP translational fusion constructs were almost similar; both were strongly expressed in intestine, and weakly in other minor tissues. RNAi of ZK525.2 or ZK1321.3 resulted in no obvious phenotype when it was done solely. Since AQP11 was expressed in small intestine in mouse, ZK525.2 and ZK1321.3 products may have redundant roles in C. elegans intestine. We are now trying to observe clear phenotype by double RNAi. We will also present the progress on expression and RNAi analysis for typical MIPs in C. elegans.