title: Characterization of mammalian synemin, an intermediate filament protein present in all four classes of muscle cells and some neuroglial cells: co-localization and interaction with type III intermediate filament proteins and keratins.
abstract: Using a monoclonal antibody, we have detected a high molecular weight muscle protein, co-localized and co-isolating with desmin. Searching a human cDNA database with partial amino acid sequences of the protein, we found a cDNA clone encoding a 1565-amino-acid polypeptide, identified as a mammalian (human) synemin, a member of the intermediate filament (IF) protein family. Immunoblotting showed the presence of a 180-kDa polypeptide in skeletal muscle and 180- and 200-kDa polypeptides in cardiac and smooth muscles. Interestingly, synemin was also found in myoepithelial cells, which have keratin filaments instead of desmin. Moreover, synemin was also found in astrocytes of optic nerves and non-myelin-forming Schwann cells, together with glial fibrillary acidic protein (GFAP) and vimentin. Blot overlays pointed to molecular interactions of synemin with desmin, vimentin, GFAP and keratin 5 and 6, but not with keratin 14. The experimental data also suggested a possible link with nebulin, a skeletal muscle protein. Purified synemin was coassembled with desmin in different molar ratios, and at 1:25, as typically found in vivo, IFs were formed which were comparable in length to desmin filaments. However, at molar ratios of 3:25 and 6:25, much shorter and irregular shaped filamentous polymers were generated. The fact that synemin is present in all four classes of muscle cells and a specific type of glial cells is indicative of important functions. Its incorporation may give structural and functional versatility to the IF cytoskeleton.
authors.affiliation: Unit of Biosystems, Graduate School of Human Informatics, Nagoya University, Nagoya, Japan. Hirako_Y@klinik.uni-wuerzburg.de
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Hirako
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yamakawa
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tsujimura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nishizawa
authors.forename: Masayo
authors.initials: M
authors.lastname: Okumura
authors.forename: Jiro
authors.initials: J
authors.lastname: Usukura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Jackson
authors.forename: Katsushi
authors.initials: K
authors.lastname: Owaribe
authors.forename: Osamu
authors.initials: O
authors.lastname: Ohara
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism; D000941:Antigens / Q000276:immunology / Q000378:metabolism; D003893:Desmin / Q000648:ultrastructure; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000032:analysis* / Q000235:genetics / Q000276:immunology; D007633:Keratins / Q000032:analysis* / Q000378:metabolism; D009124:Muscle Proteins / Q000032:analysis* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000737:chemistry; D009130:Muscle, Smooth / Q000737:chemistry; D009132:Muscles / Q000737:chemistry*; D009206:Myocardium / Q000737:chemistry; D009457:Neuroglia / Q000737:chemistry*; D011817:Rabbits; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D000941:Antigens; D003893:Desmin; D007381:Intermediate Filament Proteins; D009124:Muscle Proteins; C430456:desmuslin; C035620:nebulin; D007633:Keratins