Independent Assembly of 1.6 .MU.m Long Bipolar MHC Filaments and I-Z-I Bodies.

Holtzer, H.; Hijikata, Takao; Lin, Zhenwu; Zhang, Zhiqian; Holtzer, S.; Protasi, Feliciano; Franzini‐Armstrong, Clara; Sweeney, H. Lee

doi:10.1247/csf.22.83

Cited by 125 publications

(144 citation statements)

References 28 publications

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“…At day 3, s-␣-actinin was observed as punctuated pattern, i.e. the I-Z-I bodies, in emerging growth tips where de novo synthesized myofibrillar proteins are assembled into sarcomere structures (14,33) (Fig. 3A, bracket), and Z-band striations were seen in the shaft of the same myotubes (Fig.…”

Section: Transcription Of the P94 Gene During Myofibrillogenesis-ex-mentioning

confidence: 99%

Myogenic Stage, Sarcomere Length, and Protease Activity Modulate Localization of Muscle-specific Calpain

Ojima

Ono

Doi

et al. 2007

Journal of Biological Chemistry

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p94/calpain 3 is a Ca2؉ -binding intracellular protease predominantly expressed in skeletal muscles. p94 binds to the N2A and M-line regions of connectin/titin and localizes in the Z-bands. Genetic evidence showing that compromised p94 proteolytic activity leads to muscular dystrophy (limb-girdle muscular dystrophy type 2A) indicates the importance of p94 function in myofibrils. Here we show that a series of p94 splice variants is expressed immediately after muscle differentiation and differentially change localization during myofibrillogenesis. We found that the endogenous N-terminal (but not C-terminal) domain of p94 was not only localized in the Z-bands but also directly bound to sarcomeric ␣-actinin. These data suggest the incorporation of proteolytic N-terminal fragments of p94 into the Z-bands. In myofibrils localization of exogenously expressed p94 shifted from the M-line to N2A as the sarcomere lengthens beyond ϳ2.6 and 2.8 m for wild-type and proteaseinactive p94, respectively. These data demonstrate for the first time that p94 proteolytic activity is involved in responses to muscle conditions, which may explain why p94 inactivation causes limb-girdle muscular dystrophy. p94/calpain 3 is a member of the calpain family of intracellular Ca 2ϩ -requiring Cys proteases, which cleave substrates at specific and limited sites to modulate their structure and function. In contrast to the conventional -and m-calpains, which are ubiquitously expressed in almost all cells (1, 2), p94 is predominantly expressed in skeletal muscle with lesser amounts of several differentially spliced variants in skeletal muscle and nonmuscle cells (3). The human p94 gene, CAPN3, was identified as responsible for limb-girdle muscular dystrophy type 2A (or "calpainopathy") (4). In mice transgenic overexpression of a protease-inactive form of p94, p94:C129S, and p94 gene knockout caused a mild myopathy and muscular dystrophy, respectively (5-7). Furthermore, a defect in the proper proteolytic activity of p94 is a common feature of limb-girdle muscular dystrophy type 2A pathogenic mutations (8). These findings indicate that p94 protease activity is essential to maintain healthy condition of skeletal muscle. However, the specific physiological functions of p94 as a protease in skeletal muscle remain largely unknown.Skeletal muscles contain highly organized sarcomere structures that consist of systematically expressed myofibrillar proteins. One of the earliest myofibrillar proteins expressed in vertebrate myogenic cells is connectin/titin (9), which is the largest protein molecule known and is abundantly expressed in striated muscles where it constitutes an intrasarcomeric filament (10, 11). During sarcomere assembly, connectin is considered a key molecule for integration of thin filament/Z-band precursors (I-Z-I bodies) and the thick filaments, which are independently assembled in growth tips of elongating myotubes. The N terminus of connectin is located in both I-Z-I body and mature Z, and the C terminus is in the M-line of the thick fil...

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Section: Transcription Of the P94 Gene During Myofibrillogenesis-ex-mentioning

confidence: 99%

Myogenic Stage, Sarcomere Length, and Protease Activity Modulate Localization of Muscle-specific Calpain

Ojima

Ono

Doi

et al. 2007

Journal of Biological Chemistry

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“…Titin is also present during this step; its N-terminus assembles early in myofibrillogenesis with α-actinin and actin while its C-terminus assembles with myosin filaments that integrate later in assembly [20,21]. It has long been known that muscle myosin filaments assemble separately from nascent Z-bodies and actin filaments [35]. Recent studies have shown that nascent myosin filaments are associated with the chaperone proteins Hsc70 and Hsp90 before incorporation into sarcomeres [36] ( figure 10, step 2).…”

Section: Krp1 Promotes Lateral Fusion Of Myofibril Assembly Intermedimentioning

confidence: 99%

Krp1 (Sarcosin) promotes lateral fusion of myofibril assembly intermediates in cultured mouse cardiomyocytes

Greenberg

Connelly

Daniels

et al. 2008

Experimental Cell Research

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Krp1, also called sarcosin, is a cardiac and skeletal muscle kelch-repeat protein hypothesized to promote the assembly of myofibrils, the contractile organelles of striated muscles, through interaction with N-RAP and actin. To elucidate its role, endogenous Krp1 was studied in primary embryonic mouse cardiomyocytes. While immunofluorescence showed punctate Krp1 distribution throughout the cell, detergent extraction revealed a significant pool of Krp1 associated with cytoskeletal elements. Reduction of Krp1 expression with siRNA resulted in specific inhibition of myofibril accumulation with no effect on cell spreading. Immunostaining analysis and electron microscopy revealed that cardiomyocytes lacking Krp1 contained sarcomeric proteins with longitudinal periodicities similar to mature myofibrils, but fibrils remained thin and separated. These thin myofibrils were degraded by a scission mechanism distinct from the myofibril disassembly pathway observed during cell division in the developing heart. The data are consistent with a model in which Krp1 promotes lateral fusion of adjacent thin fibrils into mature, wide myofibrils and contribute insight into mechanisms of myofibrillogenesis and disassembly.

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“…Four major hypotheses seeking to explain the mechanism of myofibril formation have been recently reviewed by Sanger et al (2005). These hypothetic models can be summarized as following: (1) template model that considers stress fiber-like structures as templates or scaffolds for assembly of myofibrils (Dlugosz et al 1984); (2) the "stitching" model in which the actin filaments and Z-bands assemble independently from myosin filaments (Schultheiss et al 1990;Holtzer et al 1997;Ojima et al 1999); (3) premyofibril model assuming the formation of premyofibrils as immediate structural precursors of myofibrils (Rhee et al 1994;Du et al 2003;Sanger 2005), and (4) direct assembly of myofibrils without any intermediate structures [for literature see Ehler et al (1999Ehler et al ( , 2004]. …”

Section: Introductionmentioning

confidence: 99%

Early incorporation of obscurin into nascent sarcomeres: implication for myofibril assembly during cardiac myogenesis

Borisov

Martynova

Russell

2008

Histochem Cell Biol

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Obscurin is a recently identified giant multidomain muscle protein whose functions remain poorly understood. The goal of this study was to investigate the process of assembly of obscurin into nascent sarcomeres during the transition from non-striated myofibril precursors to striated structure of differentiating myofibrils in cell cultures of neonatal rat cardiac myocytes. Double immunofluorescent labeling and high resolution confocal microscopy demonstrated intense incorporation of obscurin in the areas of transition from non-striated to striated regions on the tips of developing myofibrils and at the sites of lateral fusion of nascent sarcomere bundles. We found that obscurin rapidly and precisely accumulated in the middle of the A-band regions of the terminal newly assembled half-sarcomeres in the zones of transition from the continuous, non-striated pattern of sarcomeric α-actinin distribution to cross-striated structure of laterally expanding nascent Z-discs. The striated pattern of obscurin typically ended at these points. This occurred before the assembly of morphologically differentiated terminal Z-discs of the assembling sarcomeres on the tips of growing myofibrils. The presence of obscurin in the areas of the terminal Z-discs of each new sarcomere was detected at the same time or shortly after complete assembly of sarcomeric structure. Many non-striated fibers with very low concentration of obscurin were already immunopositive for sarcomeric actin and myosin. This suggests that obscurin may serve for organization and alignment of myofilaments into the striated pattern. The comparison of obscurin and titin localization in these areas showed that obscurin assembly into the A-bands occurred soon after or concomitantly with incorporation of titin. Electron microscopy of growing myofibrils demonstrated intense formation and integration of myosin filaments into the "open" half-assembled sarcomeres in the areas of the terminal Z-I structures and at the lateral surfaces of newly formed, terminally located nascent sarcomeres. This process progressed before the assembly of the second-formed, terminal Z-discs of new sarcomeres and before the development of ultrastructurally detectable mature M-lines that define the completion of myofibril assembly, which supports the data of immunocytochemical study. Abundant non-aligned sarcomeres in immature myofibrils located on the growing tips were spatially separated and underwent the transition to the registered, aligned pattern. The sarcoplasmic reticulum, © Springer-Verlag 2008 aborisov@umich.edu. This paper is dedicated to the memory of Professor Pavel P. Rumyantsev (1927Rumyantsev ( -1988, a pioneer in studies of cardiac muscle differentiation, who is a lasting inspiration to all who worked with him. the organelle known to interact with obscurin, assembled around each new sarcomere. These results suggest that obscurin is directly involved in the proper positioning and alignment of myofilaments within nascent sarcomeres and in the establishment of the registered ...

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Independent Assembly of 1.6 .MU.m Long Bipolar MHC Filaments and I-Z-I Bodies.

Cited by 125 publications

References 28 publications

Myogenic Stage, Sarcomere Length, and Protease Activity Modulate Localization of Muscle-specific Calpain

Myogenic Stage, Sarcomere Length, and Protease Activity Modulate Localization of Muscle-specific Calpain

Krp1 (Sarcosin) promotes lateral fusion of myofibril assembly intermediates in cultured mouse cardiomyocytes

Early incorporation of obscurin into nascent sarcomeres: implication for myofibril assembly during cardiac myogenesis

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