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Scanning electron microscopical study of skeletal muscle fiber ends in normal and dystrophic mice
1Department of Anatomy, Ehime University School of Medicine, Japan.
Abstract:
Muscle fiber ends at myotendinous junctions were examined by scanning electron microscopy after removal of tendon connective tissue components by HCl hydrolysis in the extensor digitorum longus muscle of 30-, 60- and 120-day-old normal and dystrophic (dy) mice. A remarkable morphological difference between normal and dystrophic mice was observed. In normal 30-day-old mice, muscle fiber ends had already assumed a complicated three-dimensional morphology with many thin cytoplasmic processes and lateral longitudinal clefts. On the other hand, in dystrophic animals at the 60th day, muscle fiber ends were characterized by a simple conical form with a rather smooth surface in which existed a number of pit-like sarcolemmal invaginations, and short and narrow longitudinal slits, possibly an indication of developmental immaturity. Thereafter, the slits increased in number and in length, although the linear elongation of the slits seems to be caused by the fusion of adjacent pits to one another and to existing slits. From these findings, the fiber ends in the adult (120-day-old) dystrophic mouse are suggested to retain a preceding state of their unique structural differentiation.
Insights
Dystrophic mouse muscle fiber ends show delayed development, retaining immature structures into adulthood. This contrasts with normal mice, where complex fiber end morphology develops early.
Area of Science:
- Muscle Biology
- Developmental Biology
- Pathology
Background:
- The myotendinous junction (MTJ) is crucial for force transmission.
- Understanding MTJ development in muscular dystrophy is vital for therapeutic strategies.
Purpose of the Study:
- To investigate morphological differences in muscle fiber ends at the MTJ between normal and dystrophic mice during development.
- To characterize the structural maturation of muscle fiber ends in the context of muscular dystrophy.
Main Methods:
- Scanning electron microscopy was used to examine muscle fiber ends.
- Extensor digitorum longus muscles from mice of different ages (30, 60, 120 days) were analyzed.
- Tendon connective tissue was removed via HCl hydrolysis.
Main Results:
- Normal mice at 30 days exhibited complex, three-dimensional muscle fiber ends with cytoplasmic processes and clefts.
- Dystrophic mice at 60 days displayed simpler, conical fiber ends with smooth surfaces, invaginations, and short slits, suggesting developmental delay.
- In adult dystrophic mice (120 days), fiber ends retained immature features, with slits appearing to form from fused pits.
Conclusions:
- Muscle fiber ends in dystrophic mice exhibit a unique structural differentiation characterized by delayed maturation.
- The observed morphology in adult dystrophic mice suggests a persistence of an earlier developmental state.