The Mr 165,000 M-protein myomesin: a specific protein of cross-striated muscle cells.

Abstract

The tissue specificity of chicken 165,000 M-protein, tentatively named "myomesin," a tightly bound component of the M-line region of adult skeletal and heart myofibrils, was investigated by immunological techniques . Besides skeletal and heart muscle, only thymus (known to contain myogenic cells) was found to contain myomesin . No myomesin could, however, be detected in smooth muscle or any other tissue tested . This result was confirmed in vitro on several cultured embryonic cell types. Only skeletal and heart muscle cells, but not smooth muscle or fibroblast cells, showed the presence of myomesin . When the occurrence and the distribution of myomesin during differentiation of breast muscle cells in culture were studied by the indirect immunofluorescence technique, this protein was first detected in postmitotic, nonproliferating myoblasts in a regular pattern of fluorescent cross-striations . In electron micrographs of sections through young myotubes, it could be shown to be present within the forming H-zones of nascent myofibrils . In large myotubes the typical striation pattern in the M-line region of the myofibrils was observed . Synthesis of myomesin measured by incorporation of [31S] methionine into immunoprecipitable protein of differentiating cells increased sharply after -48 h in culture, i .e ., at the time when the major myofibrillar proteins are accumulated . No significant amounts of myomesin were, however, found in cells prevented from undergoing normal myogenesis by 5'-bromodeoxyuridine .The results indicate that myomesin (a) is a myofibrillar protein specific for cross-striated muscle, (b) represents a highly specific marker for cross-striated muscle cell differentiation, and (c) might play an important role in myofibril assembly and/or maintenance.The temporal appearance of myofibrillar proteins as well as the composition and organization of myofibrils in differentiating muscle cells have been subjects of intense studies in recent years (for review, see references 1, 5, 11, 13, 17, 19, 24, and 30) . Investigations of the properties of a number ofnewly detected, so-called minor components of the myofibrillar compartment (12,14,25,28,31,48,53) have provided a better insight into the molecular organization of the unit of contractility, the sarcomere . There is, however, still considerable lack of knowledge regarding the sequence of appearance and organization of the myofibrillar structures during development (1,13,19,37,49). One of the major transverse structures in a mature cross-striated muscle fiber, the Z-band, has been described as the initial site of myofibrillogenesis (19), whereas the second one, the so-called M-line, has only recently been found to play a role in the organization of the assembly of the myofibrillar structure (10,12,16,43 Our own investigations on the structure and function of the M-line region ofchicken skeletal and heart muscle indicate the presence of two major protein components: the muscle type isoprotein of creatine kinase (MM-CK) (48, 50, 52) and the 165...

The M-band: an elastic web that crosslinks thick filaments in the center of the sarcomere

“…By contrast, myomesin which was first discovered as a copurifying component in M-protein preparations [12,13], is found in all types of vertebrate striated muscle investigated so far [25] as well as in the first sarcomeres assembled in the developing heart [3]. The importance of myomesin is further supported by the observation that myomesin seems to be expressed at a fixed ratio to myosin in different muscle types [26].…”

“…The C-termini of titin molecules also overlap there [11] (Box 1). In addition, the M-band contains two principal candidates for the role of M-bridges, originally named myomesin [12,13] (myomesin-1 in RefSeq database) and M-protein [14] lines missing), whereas the slowest fibers have a four-line pattern (M1 line missing), and fibers of intermediate speed have variations of a fiveline pattern [23,65,66]. Accordingly, the M-band appearance changes during differentiation of slow fibers of the rat [23] and correlates with the beating rate in the heart of different species [21].…”

Postnatal suppression of myomesin, muscle creatine kinase and the M-line in rat extraocular muscle

“…While myomesin may be an integral component of myofibrils even in the absence of a structurally visible M-line (Strehler et al, 1980), suggesting that EH-based myofilament linkages might be present in eye muscle, it is not yet clear what adaptive value EH-myomesin 1 may serve in a muscle that lacks the stereotypical structural connections between adjacent myosin filaments. Prior studies Eppenberger et al, 1981;Van der Ven et al, 1999;Yang et al, 2000) have shown that an M-line appears within H-zones of forming myofibrils and that myomesin 1 accumulation is coordinated with that of other myofibrillar proteins. By contrast, myomesin 2 is known to accumulate several days later and thus may not be essential for initial sarcomeric organization (Carlsson et al, 1990;Grove et al, 1985Grove and Thornell, 1988).…”

Low-Level Expression of a Mutant Coxsackieviral cDNA Induces a Myocytopathic Effect in Culture

“…Twentyfour to 96 hours after infection, the myocytes were fixed and immunostained with both a rabbit anti-CVB3 antibody 28 and a mouse monoclonal anti-myomesin antibody. 29 There was disruption of myofilaments and evidence of a direct cytopathic effect 48 hours after infection in cells that stained positive for CVB3 (Figure 1). In addition, there was release of infectious progeny virus and LDH into the extracellular medium of infected cells (data not shown).…”

“…28 Myofilament architecture was assessed by staining of myocytes with a monoclonal mouse anti-myomesin antibody (generous gift from J.C. Perriard 29 ). ␤-Galactosidase-expressing cells were identified by a monoclonal antibody (Promega).…”