title: Expression of myosin heavy chain isoforms in the postnatal mouse masseter muscle.
abstract: We investigated the properties of the masseter muscle in mice from five to seven weeks of age. Myosin heavy chain (MyHC) isoforms were measured in the masseter muscle. The three types of muscle fibers (Type I, strong reaction; Type IIA, intermediate reaction; and Type IIB, weak reaction) were all present in the masseter muscle in five-weeks-old mice and seven-weeks-old mice, the three types could be clearly distinguished by their enzyme activity. The percentage of Type IIB fibers (above 50%) was the highest among all fiber types both 5- and 7-weeks-old mice. The mRNA levels for myosin slow and myosin IIb increased significantly between 5 and 7 weeks. These observations suggest that muscle fiber size, muscle fiber types and mRNA levels of the MyHC isoforms all contribute to the diminished functional adaptability of enzyme activity in the masseter muscle.
authors.affiliation: Department of Anatomy, School of Dentistry at Tokyo, Nippon Dental University, 1-9-20 Fujimi Chiyoda-Ku, Tokyo, Japan 102-8159.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Miwa
authors.forename: Masataka
authors.initials: M
authors.lastname: Sunohara
authors.forename: Iwao
authors.initials: I
authors.lastname: Sato
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D008297:Male; D008406:Masseter Muscle / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D018995:Myosin Heavy Chains / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D024507:Nonmuscle Myosin Type IIA / Q000378:metabolism; D024501:Nonmuscle Myosin Type IIB / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D009243:NAD; D024507:Nonmuscle Myosin Type IIA; D024501:Nonmuscle Myosin Type IIB; D018995:Myosin Heavy Chains