title: Temporal and spatial expression of distinct troponin T genes in embryonic/larval tail striated muscle and adult body wall smooth muscle of ascidian.
abstract: During development of the ascidian Halocynthia roretzi, the tadpole larva hatched from the tailbud embryo metamorphoses to the adult with a body wall muscle. Although the adult body wall muscle is morphologically nonsarcomeric smooth muscle, it contains a troponin complex consisting of three subunits (T, I, and C) as do vertebrate striated muscles. Different from vertebrate troponins, however, the smooth muscle troponin promotes actin-myosin interaction in the presence of high concentration of Ca2+, and this promoting property is attributable to troponin T. To address whether the embryonic/larval tail striated muscle and the adult smooth muscle utilize identical or different regulatory machinery, we cloned troponin T cDNAs from each cDNA library. The embryonic and the adult troponin Ts were encoded by distinct genes and shared only < 60% identity with each other. These isoforms were specifically expressed in the embryonic/larval tail striated muscle and the adult smooth muscle, respectively. These results may imply that these isoforms regulate actin-myosin interaction in different manners. The adult troponin T under forced expression in mouse fibroblasts was unexpectedly located in the nuclei. However, a truncated protein with a deletion including a cluster of basic amino acids colocalized with tropomyosin on actin filaments. Thus, complex formation with troponin I and C immediately after the synthesis is likely to be essential for the protein to properly localize on the thin filaments.
authors.affiliation: Department of Biology, Faculty of Science, Chiba University, Japan. tendo@cuphd.nd.chiba-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Endo
authors.forename: K
authors.initials: K
authors.lastname: Matsumoto
authors.forename: T
authors.initials: T
authors.lastname: Hama
authors.forename: Y
authors.initials: Y
authors.lastname: Ohtsuka
authors.forename: G
authors.initials: G
authors.lastname: Katsura
authors.forename: T
authors.initials: T
authors.lastname: Obinata
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018507:Gene Expression Regulation, Developmental; D007814:Larva / Q000254:growth & development; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000196:embryology*; D009130:Muscle, Smooth / Q000196:embryology*; D011817:Rabbits; D014162:Transfection; D014336:Troponin / Q000737:chemistry / Q000235:genetics*; D020107:Troponin T; D014561:Urochordata / Q000196:embryology*
chemical_list: D014336:Troponin; D020107:Troponin T