ABSTRACT Skeletal muscle fibers are surrounded by an extracellular matrix. The extracellular matrix forms a complex dynamic architecture and is composed of glycoproteins, collagen, and proteoglycans. Proteoglycans have been suggested to play an important functional role in tissue differentiation. Proteoglycans affect the myogenic process by regulating collagen fibrillogenesis, modulating cell growth and the response to growth factors. The extracellular matrix communicates information back to the cell through integrin receptors. Integrins are heterodimeric transmembrane glycoproteins that contain extracellular, transmembrane, and cytoplasmic domains. During myogenesis, integrins play a role in both cell ahesion to the extracellular matrix and sarcomere formation. Therefore, the regulation of myoblast integrin temporal and spatial expression is critical in the formation of differentiated muscle. Although specific extracellular matrix components have been identified as being essential in myogenesis, the exact functions of these macromolecular proteins as they relate to muscle formation and growth is still not well understood.
Implications
Why should the domestic animal industries be concerned about the extracellular matrix? Selection for growth rate and muscling alters muscle fiber proportions, and likely the amount of extracellular matrix space. The extracellular matrix functions in tissue water-holding capacity, elasticity, growth factor regulation, and cellular growth properties. Both the swine and turkey industries in recent years have experienced a meat quality problem termed pale, soft, and exudative (PSE). When cooked, meat from animals with the PSE condition has a soft texture, poor juiciness, and increased yield losses. Proteoglycans are a major determinant in tissue water-holding capacity but have not been studied with regard to PSE. If the amount of proteoglycans have been reduced in animals selected for growth rate and muscling, the reduced water-holding capacity would directly affect the juiciness and drip loss. Therefore, domestic animal industries should consider how the extracellular matrix is affected by selection.
Key Words: Connective Tissue, Muscles, Proteoglycans
© 2002, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 80(E-Suppl. 2):E8-E13
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