Myonuclear domain in skeletal muscle fibers. A critical review (original) (raw)
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ADDITION OF NEW MYONUCLEI IS A PRE-REQUISITE FOR SKELETAL MUSCLE GROWTH
Skeletal muscles have the ability to grow, develop and regenerate in response to physiological demands. They grow mostly by increase in size and in some cases by increasing the number of myofiber. Regeneration and adaptation of new fiber size are dependent on satellite cells proliferative capacity and the number of myonuclei. When a stimulus is applied on skeletal muscles, there is satellite cell proliferation which induces more myonuclei. Myonuclei are the memory cells of skeletal muscles, which provide the genetic machinery for synthesis of contractile protein according to demands resulting in muscle growth. Different studies have demonstrated that increase in number of myonuclei is directly proportional to increase in fiber size. The myonuclear domain remains same as myonuclei increase their number in case of hypertrophy and decrease their number in case of atrophy. Some protein supplements along with resistance training act as growth stimulus which enhance the effects of functional or resistance training and results in augmentation in number of myonuclei and skeletal muscle growth. In acute stage, rate of myonuclei addition is more; if same intensity of stimulus applied for longer period of time; myonuclear number stabilized and there will be a slow increment in myonuclei number. The satellite cell proliferation gradually declines with advancing age while number of myonuclei seems to have no such effect of advancing age on their proliferation. In this review, it will be discussed that myonuclei are the prerequisite for skeletal muscles growth, satellite cell, myofiber size and myonuclei are positively correlated. Also the affects of different variables like training, detraining and supplementation on the skeletal muscle growth and myonuclear domain will be evaluated.
Myonuclear domain size varies along the lengths of maturing skeletal muscle fibers
International Journal of Developmental Biology, 2002
In a skeletal muscle fiber, each myonucleus is responsible for gene expression in its surrounding cytoplasm. The region of cytoplasm associated with an individual myonucleus is termed myonuclear domain. However, little is known about domain size variation within individual muscle fibers. This study tests the hypothesis that myonuclear domains expressing neonatal myosin within end regions of maturing fibers will be smaller than domains elsewhere in the fibers. The model used is chicken pectoralis, where we have previously shown that during development repression of neonatal myosin radiates from the central region towards the fiber ends. Samples excised from birds aged nine through to 115 days after hatching were sectioned transversely. Using computer image analysis and immunocytochemistry, fiber profiles were classified as neonatal, transforming or adult. Each profile was also located in an adjacent dystrophin-labelled section, where myonuclei were visualized using haematoxylin and b...
The FASEB Journal, 2012
Muscle force is typically proportional to muscle size, resulting in constant force normalized to muscle fiber cross-sectional area (specific force). Mice over-expressing insulin like growth factor-1 (IGF-1) exhibit a proportional gain in muscle force and size, but not the myostatin deficient mice. In an attempt to explore the role of the cytoplasmic volume supported by individual myonuclei (myonuclear domain size, MND) on functional capacity of skeletal muscle, we have investigated specific force in relation to MND and the content of the molecular motor protein, myosin, at the single muscle fiber level from myostatin knock-out (Mstn -/-) and IGF-1 overexpressing (mIgf1 +/+ ) mice. We hypothesize that the addition of extra myonuclei is a prerequisite for maintained specific force during muscle hypertrophy. A novel algorithm was used to measure individual MNDs in 3D along the length of single muscle fibers from the fast-twitch EDL and the slow-twitch soleus muscle. A significant impact of the size of individual myonuclear domains in hypertrophic muscle fibers on both specific force and myosin content was observed. This effect was muscle cell type specific and suggested there is a critical volume individual myonuclei can support efficiently. The large MNDs found in fast muscles of Mstn -/mice were correlated with the decrement in specific force and myosin content in Mstn -/muscles. Thus, myostatin inhibition may not be able to maintain the appropriate myonuclear domain for optimal function. Short title: Myonuclear domain size, force production and muscle hypertrophy
Nature Communications, 2020
Mammalian cells exhibit remarkable diversity in cell size, but the factors that regulate establishment and maintenance of these sizes remain poorly understood. This is especially true for skeletal muscle, comprised of syncytial myofibers that each accrue hundreds of nuclei during development. Here, we directly explore the assumed causal relationship between multinucleation and establishment of normal size through titration of myonuclear numbers during mouse neonatal development. Three independent mouse models, where myonuclear numbers were reduced by 75, 55, or 25%, led to the discovery that myonuclei possess a reserve capacity to support larger functional cytoplasmic volumes in developing myofibers. Surprisingly, the results revealed an inverse relationship between nuclei numbers and reserve capacity. We propose that as myonuclear numbers increase, the range of transcriptional return on a per nuclear basis in myofibers diminishes, which accounts for both the absolute reliance devel...
Cell Tissue Res, 1996
The relationship between myonuclear number, cellular size, succinate dehydrogenase activity, and myosin type was examined in single fiber segments (n = 54; 9 _+ 3 mm long) mechanically:gdissected from soleus and plantaris muscles of adult rats. One end of each fiber segment was stained for DNA before quantitative photometric analysis of succinate dehydrogenase activity; the other end was double immunolabelled with fast and slow myosin heavy chain monoclonal antibodies. Mean _+ S,D. cytoplasmic volume/myonucleus ratio was higher in fast and slow plantaris fibers (112 _+ 69 vs. 34 _+ 21 x 103 gm 3) than fast and slow soleus fibers (40 _+ 20 vs. 30 + 14 x 103 i, tm3), respectively. Slow fibers always had small volumes/myonucleus, regardless of fiber diameter, succinate dehydrogenase activity, or muscle of origin. In contrast, smaller diameter (< 70 gm) fast soleus and plantaris fibers with high succinate dehydrogenase activity appeared to have low volumes/myonucleus while larger diameter (> 70 gm) fast fibers with low succinate dehydrogenase activity always had large volume/myonucleus. Slow soleus fibers had significantly greater numbers of myonuclei/mm than did either fast soleus or fast plantaris fibers (116 _+ 51 vs. 55 + 22 and 44 _+ 23), respectively. These data suggest that the myonuclear domain is more limited in slow than fast fibers and in the fibers with a high, compared to a low, oxidative metabolic capability.
Regulation of skeletal muscle fiber size, shape and function
Journal of Biomechanics, 1991
There is convincing evidence that the cross-sectional ama, the type of myosin expressed. the potential for oxidative phosphorylation and the number of myonucki of a skektal musck fiber a closely intertkpcndent. Each of these vtiables. as well as the shape of the fiber. has idcntifiabk physiological consequences. Further. it is suggested that the cytoplasmic 10 myonuckus ratio is a function of the myosin type and Ihe amount and/or mh of protein synthesis and dcgradadon. Although the neuromuscular activity (ekctromyogmphic activity) as well as the associated mechanical and meb&olic events have significant regulatory influenceson pnwein metabolism ~ICIX am other importon regulatory factors independent of these activity-rclatcd events. Both the activity and non-activity ~kted~ulatorymcchPnisnrsprobablyoccurviaac~adeofcellulirrcv~u.Thespccificcombinrtionsofallular responses that occur may define ihc natu= of the modulatory effects on specifc proteins. In spite of the compkxily of Ihe regulatory mechanisms of protein modularion and how thcx responses arc structumlly integrated into or removed from functional fibers. it is suggestcd'that con~rolkdstudiaofhuman neuromuscular function can be more accumtcly defined and intcrpmted when fiber and muscle size and shape anz considered.
Developmental effects on myonuclear domain size of rat diaphragm fibers
Journal of Applied Physiology, 2008
During early postnatal development in rat diaphragm muscle (Diam), significant fiber growth and transitions in myosin heavy chain (MHC) isoform expression occur. Similar to other skeletal muscles, Diam fibers are multinucleated, and each myonucleus regulates the gene products within a finite volume: the myonuclear domain (MND). We hypothesized that postnatal changes in fiber cross-sectional area (CSA) are associated with increased number of myonuclei so that the MND size is maintained. The Diam was removed at postnatal days 14 (P-14) and 28 (P-28). MHC isoform expression was determined by SDS-PAGE. Fiber CSA, myonuclear number, and MND size were measured using confocal microscopy. By P-14, significant coexpression of MHC isoforms was present with no fiber displaying singular expression of MHCNeo. By P-28, singular expression was predominant. MND size was not different across fiber types at P-14. Significant fiber growth was evident by P-28 at all fiber types (fiber CSA increased by ...
Ageing influences myonuclear domain size differently in fast and slow skeletal muscle of rats
Acta Physiologica, 2009
In multinucleated skeletal muscle, a myonuclear domain is the region of cytoplasm governed by one nucleus, and myofibres are mosaics of overlapping myonuclear domains. Association of ageing and myonuclear domain is important in the understanding of sarcopenia and with prevention or combating age-related muscle declines. This study examined the effects of age, fibre type and muscle on nucleo-cytoplasmic (N/C) relationships as reflecting myonuclear domain size. Methods: The N/C was compared in fibre types of soleus and plantaris muscles from young (n = 6) and ageing (n = 8) male Fisher 344 rats. Results: There were no significant differences in fibre type composition or cross-sectional area of the soleus across ages. The old soleus had significantly more myonuclei, resulting in a significantly smaller myonuclear domain size. The plantaris muscle showed a higher percentage of slow fibres in old compared with young fibres. There were no differences in the number of myonuclei or in myonuclear domain size between young and older animals. Conclusion: We found muscle-specific differences in the effects of ageing on myonuclear domain, possibly as a result of reduced efficiency of the myonuclei in the slow muscles.
Myonucleus-Related Properties in Soleus Muscle Fibers of mdx Mice
Cells Tissues Organs, 2010
Distribution and total number of myonuclei in single soleus muscle fibers, sampled from tendon to tendon, were analyzed in mdx and wild-type (WT) mice. Apoptotic myonuclei and the microscopic structure around the myonuclei were also analyzed. Three types of muscle fibers of mdx mice with myonuclear distribution at either central, peripheral, or both central and peripheral regions were observed in the longitudinal analyses. All of the myonuclei were located at the peripheral region in WT mice. The total number of myonuclei counted in the whole length of fibers with peripheral myonuclei only was 17% less in mdx than in WT mice (p < 0.05). But the total myonuclear numbers in mdx mouse fibers with different distribution (peripheral vs. central) of myonuclei were identical, and the peripheral nucleus was noted where the central nucleus was missing. Myonuclei located between the center and peripheral regions were also seen in the cross-sectional analyses of muscle fibers. The cross-sec...