ALTERATIONS IN SARCOMERE STRUCTURE, COLLAGEN ORGANIZATION, MITOCHONDRIAL ACTIVITY, AND PROTEIN-METABOLISM IN THE AVIAN LOW SCORE NORMAL MUSCLE WEAKNESS

Skeletal muscle fibers are surrounded by an extracellular matrix. The extracellular matrix is composed of glycoproteins, collagen, and prote oglycans. Proteoglycans have been suggested to play an important funct ional role in tissue differentiation. However, an understanding of how the extracellular matrix affects skeletal muscle development and func tion is largely unknown. In the avian genetic muscle weakness, low sco re normal (LSN), a late embryonic increase in the expression of decori n is followed by a subsequent increase in collagen crosslinking. The s arcomere organization, collagen fibril diameter and organization were investigated using transmission electron microscopy. Measurements were made at 20 days of embryonic development and 6 weeks posthatch. These studies showed changes in sarcomere organization and deterioration of muscle fibril structure in the LSN pectoral muscle. In vitro satellit e cell cultures were developed and assayed for mitochondrial activity, and protein synthesis and degradation. In these analyses, mitochondri al activity from LSN satellite cells was significantly higher than tho se from normal pectoral muscle satellite cells. Protein synthesis rate s between the normal and LSN satellite cell-derived myotubes were simi lar, but protein degradation rates were higher in the LSN cultures. Ba sed on the reported functions of decorin as a regulator of cell prolif eration and collagen fibril organization, it is possible that the late embryonic increase in decorin may be influencing the alterations in L SN sarcomere and collagen organization.