Myogenic proteins

Knockout mice and Drosophila mutants have been used to explore the roles of MRF and MEF proteins in conferring myogenic specificity in intact animals, extending the work in cell culture. These experiments demonstrated the importance of three of the MRF proteins and of MEF proteins for distinct steps in muscle development (see Figure 22-14). The function of the fourth myogenic protein, Mrf4, is not entirely clear It may be expressed later and help maintain differentiated muscle cells and by combinatorial control to ensure that only muscle-specific genes are activated. 

Neurogenesis In Drosophila depends upon a set of four neu rogenic bHLH proteins that are conceptually and stmcturaUy similar to the vertebrate myogenic proteins (see Figure 22-18). 

Gu, W., Schneider, J.W., Condorelli, G., Kaushal, S., Mahdavi, V. and Nadal-Ginard, B. (1993) Interaction of myogenic factors and the retinoblastoma protein mediates muscle cell commitment and differentiation. Cell 72, 309-324. 

Li, L., Zhou, J., James, G., Heller-Harrison, R, Czech, M.P. and Olson, E.N. (1992) FGF inactivates myogenic helix-loop-helix proteins through phosphorylation of a conserved protein kinase C site in their DNA-binding domains. Cell 71, 1182-1194. 

Polyacrylamide gel electrophoresis (PAGE) and cellulose acetate membrane electrophoresis (CAME) were applied to distinguish escolar and oilfish from 27 commercial fish based on muscle protein differences (Ochiai et al., 1984). Myogen fractions from the muscles were subjected... 

Baudier J, Bergeret E, Bertacchi N, Weintraub H, Gagnon J, Garin J. 1995. Interactions of myogenic bHLH transcription factors with calcium-binding calmodulin and SlOOa (alpha alpha) proteins. Biochemistry 34(24) 7834-7846. 

Molkentin, J.D., B.L. Black, J.F. Martin, and E.N. Olson (1995). Cooperative activation of muscle gene expression by MEF2 and myogenic bHLH proteins. Cell 83 1125-1136. 

Benjamine, I.J., S. Horie, M.L. Greenberg, R.J. Alpern and R.S. Williams (1992). Induction of stress proteins in cultured myogenic cells Molecular signals for the activation of heat shock transcription during ischemia. J. Clin. Invest. 89 1685-1689. 

A period in the United States in 1939 as a Rockefeller Fellow in the Harvard laboratory of E. J. Cohn widened his experience of proteins and knowledge of their physical chemistry and led to his first crystallization of a muscle jirotein, a myogen from rabbit muscle which was later shown hy other workers to be identical with triosephosphate dehydrogenase. 

Czok, R., and Buecher, T. 1960. Crystallized enzymes from the myogen of rabbit skeletal muscle. Adv. Protein Chem. 15 315-415. 

Caldesmon is a cytoplasmic protein with two isoform classes, one of which is found predominantly in smooth muscle cells and other cell types with partial myogenic differentiation. High-molecular-weight isoforms with molecular weights between 89 and 93 kD are capable of binding to actin, tropomyosin, calmodulin, myosin, and phospholipids, and they function to counteract actin-tropomyosin-activated myosin adenosine triphosphatase (ATPase). As such, they are mediators for the inhibition of calcium-dependent smooth muscle contraction." ... 

Certain markers with specificity for muscle differentiation may be useful in recognizing leiomyomas, beyond desmin, caldesmon, and muscle-associated actins, but their application in diagnostic immunohistopathology is not generally considered routine. Smooth muscle myosin and Z-band protein have been advocated by some, particularly when either the histologic pattern is unusual (such as myxoid or hyalinized lesions) or the interpretation of a myogenous lesion is not corroborated by other stains. 

Immunohistochemical analyses of AAM have revealed reactivity for actin and often for desmin but not S-100 protein, suggesting a myogenic or myofi-broblastic pattern of differentiation.Ultrastructural... 

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