Muscle development

Figure 1. Muscle development. A skeletal muscle fiber is formed by the fusion of many single cells (myoblasts) into a multinucleated myotube. Myotubes then develop into the muscle fiber (see text). Sarcomeres form in longitudinal structures called myofibrils. The repeating structure of the sarcomere contains interdigitating thick and thin filaments.

Leibovitch, S. A., Lenormand, J. L., Leibovitch, M. P., Guiller, M., Mallard, L., and Harel, J. (1990). Rat myogenic c-mos cDNA cloning sequence analysis and regulation during muscle development. Oncogene 5 1149-1157. 

Endo, T. and Nidal-Ginard, B. (1988) SV40 large T antigen induces reentry of terminally differentiated myotubes into the cell cycle. In Kedes, L.H. and Stockdale, F.E. (eds) Cellular and Molecular Biology of Muscle Development. Alan R. Liss, New York, pp. 95-104. 

Page, A.P. and Winter, A.D. (1998) A divergent multi-domain cyclophilin is highly conserved between parasitic and free-living nematode species and is important in larval muscle development. Molecular and Biochemical Parasitology 95, 215-227. 

Vincent, J.B. (2003) The potential value and potential toxicity of chromium picolinate as a nutritional supplement, weight-loss agent and muscle development agent, Sports Med., 33, 213-230. Vincent, J.B. (2004) Recent advances in the nutritional biochemistry of trivalent chromium, Proc. Nutr. Soc., 63, 41-47. 

Apart from this HDACs are also associated with a number of other epigenetic repression mechanisms including histone methylation, polycomb group of proteins and DNA methylation (discussed later). The class II HDACs have been found to be involved in muscle development, particularly HDAC 5 and 9 knockouts or mutants show evidence of cardiac hypertrophy in a age or stress dependent manner (Zhang et al, 2002 Chang et al, 2004). 

Provided that blood supply and innervation remain intact, skeletal muscle heals well after injury or disease. Damage to fibres causes endothelial cells to secrete general growth factors (e.g. fibroblast growth factor, insulin-like growth factors) and growth factors specific to muscle development which stimulate proliferation of satellite cells. These then migrate to the site of injury to form myotubes, as in foetal development. If, however, the number of satellite cells is... 

Steroids that aid in muscle development are called anabolic steroids. They are synthetic derivatives of testosterone, thus have the same muscle-building effect as testosterone. There are more than 100 different anabolic steroids which, vary in structure, duration of action, relative effects and toxicities. Androstenedione, stanozolol and dianabol are anabolic steroids. They are used to treat people suffering from traumas accompanied by muscle deterioration. The use of anabolic steroid can lead to a number of dangerous side-effects, including lowered levels of high density lipoprotein cholesterol, which benefits the heart, and elevated levels of harmful low density lipoprotein, stimulation of prostate tumours, clotting disorders and liver problems. 

Muscle, whose structure and function are discussed in Chapter 19, develops in response to four members of the myoD family. These include myoD, myogenin, myf5, and MRF4.417-419 All are muscle-specific transcription factors of the basic helix -loop -helix class. An unusual aspect of muscle development is formation of multinucleate myotubes (muscle fibers p. 1096)420 Apoptosis plays an important role in muscle development and can present significant complications in damaged cardiac muscle.421 Defects in several developmental control genes are responsible for congenital heart diseases.422... 

T-type calcium channels play critical roles in shaping the electrical and plastic properties of neurons and are also implicated in hormone secretion, differentiation and muscle development (Huguenard, 1996 Perez-Reyes, 2003). In thalamic reticular and relay neurons, T-type channels contribute to rhythmic rebound burst firing and spindle waves associated with slow-wave sleep. T-type channels also play crucial roles in dendritic integration and calcium-mediated spiking in hippocampal pyramidal cells, and in synaptic release at olfactory dendrodendritic... 

Dangain, J., and Vrbova, G., 1984, Muscle development in mdx mutant mice, Muscle Nerve, 7, pp 700-704. 

Raghu P. and Hasan G. (1995) The inositol 1,4,5-triphosphate receptor expression in Drosophila suggests a role for IP3 signalling in muscle development and adult chemosensory functions. Dev. Biol. 171, 564-577. 

Caspase-8 Embryonic lethality Impaired heart muscle development, decreased hematopoietic precursors Defects in Fas- and TNF-initiated cell death Myocardial thinning, reduced trabeculation [65, 66]... 

In females Androgens can cause masculinization with acne, growth of facial hair, deepening of the voice, male pattern baldness, and excessive muscle development. Menstrual irregularities may also occur. Testosterone should not be used by pregnant women, because of the possible virilization of the female fetus. 

Some of the responses by the body to anaerobic exercise are visually obvious. Greater strength, speed, and muscle development are reasons that athletes emphasize anaerobic training. However, research has shown that these results are not easily predicted, and even the effects on the amouit of muscle mass are not entirely clear (9). The effects of these short-duration exercises on cardiopulmonary function and on nutritional requirements are minimal. 

Though the amount of muscle protein gained per day during weight training does not justify an increased protein intake, many athletes believe that high levels of protein are essential to stimulate maximum muscle development. However, as shown in Fig. 1, intakes of protein above the requirement produce no stimulation of protein synthesis. By feeding different levels of protein to rodents, we found that maximum muscle mass and the maximum rate of protein synthesis were achieved at relatively low levels of dietary protein and intakes two or three times this level produced no additional stimulation (16). 

Bechtel, P.J. (1986). Muscle development and contractile proteins. In P.J. Bechtel eAI), Muscle as Food. Academic Press, Orlando, pp. 1-35. 

Plate 17 A mutant mouse basic helix-loop-helix domain bHLH) of a Myo D protein (residues 102-166. with cysteine 135 replaced by serine). The bHI H domain is complexed with 5 -deoxy-P-TCAACAGCTT(3A-3 DNA. The HLH homodimer is presented. One HLH-motif is in blue and the other is in pink. Members of the Myo D family of proteins are transcriptional activators, that play a central role in muscle development and in the formation Of specific muscle cells. (The ribbon structure was reconstructed with permission of the authors and Cell from data in ref. 20 of Chapter 9). 

Bevan, S., Steinbach, J.H. (1977). The distribution of a-bungar-otoxin binding sites on mammalian skeletal muscle developing in vivo. J. Physiol. (Land.) 261 195-213. 

FIGURE 45.1. (A) Schematic presentation of the stages of muscle development and (B) reproduction of these stages under in vitro... 

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