title: The importance of subfragment 2 and C-terminus of myosin heavy chain for thick filament assembly in skeletal muscle cells.
abstract: In skeletal muscle cells, myofibrillar proteins are highly organized into sarcomeres in which thick filaments interdigitate with thin filaments to generate contractile force. The size of thick filaments, which consist mainly of myosin molecules, is strictly controlled. However, little is known about the mechanisms by which myosin molecules assemble into thick filaments. Here, we assessed the ability of each domain of myosin heavy chain (Myh) to form thick filaments. We showed that exogenously expressed subfragment 2 (S2) + light meromyosin (LMM) of Myh was efficiently incorporated into thick filaments in muscle cells, although neither solely expressed S2 nor LMM targeted to thick filaments properly. In nonmuscle COS7 cells, S2+LMM formed more enlarged filaments/speckles than LMM. These results suggest that Myh filament formation is induced by S2 accompanying LMM. We further examined the effects of Myh C-terminus on thick filament assembly. C-terminal deletion mutants were incorporated not into entire thick filaments but rather into restricted regions of thick filaments. Our findings suggest that the elongation of myosin filaments to form thick filaments is regulated by S2 as well as C-terminus of LMM.
authors.affiliation: Animal Products Research Division, Institute of Livestock and Grassland Science, NARO, Tsukuba, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Ojima
authors.forename: Mika
authors.initials: M
authors.lastname: Oe
authors.forename: Ikuyo
authors.initials: I
authors.lastname: Nakajima
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shibata
authors.forename: Susumu
authors.initials: S
authors.lastname: Muroya
authors.forename: Koichi
authors.initials: K
authors.lastname: Chikuni
authors.forename: Akihito
authors.initials: A
authors.lastname: Hattori
authors.forename: Takanori
authors.initials: T
authors.lastname: Nishimura
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism* / Q000502:physiology*; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology*; D050505:Mutant Proteins / Q000378:metabolism; D015879:Myosin Subfragments / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012518:Sarcomeres; D024744:Skeletal Muscle Myosins / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D015879:Myosin Subfragments; D024744:Skeletal Muscle Myosins
keywords: myofibril; myofibrillogenesis; sarcomere; skeletal muscle; thick filament