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Development of chequerboard pattern in human foetal skeletal muscle
Insights
Human skeletal muscle development shows no distinct fiber types before innervation. Early myogenesis reveals uniform enzyme activity, with differences emerging later due to developmental stage, not inherent metabolic distinctions.
Area of Science:
- Developmental Biology
- Histochemistry
- Muscle Physiology
Background:
- Human skeletal muscle development is a complex process.
- Understanding early myogenesis is crucial for identifying potential developmental anomalies.
Purpose of the Study:
- To investigate the histochemical and electron microscopic development of human myogenesis.
- To identify early metabolic or structural differences in skeletal muscle fibers.
Main Methods:
- Histochemical analysis of enzyme activity (ATPase, oxidative enzymes, phosphorylase).
- Electron microscopy to observe ultrastructural changes.
- Examination of human fetal muscle tissue from 9 to 26 weeks of gestation.
Main Results:
- Primitive myotubes form by the 9th week, with ATPase activity reflecting myoblast fusion differences.
- Early myotubes exhibit high oxidative enzyme activity and lack phosphorylase.
- Fiber maturation begins between 20-24 weeks, showing uniform enzyme activity resembling intermediate fibers.
- A mosaic pattern of enzymatic activity appears around 26 weeks.
- Observed enzymatic differences are attributed to varying fiber developmental stages, not inherent type distinctions.
Conclusions:
- No significant morphological or metabolic differences exist between individual human skeletal muscle fibers before metabolic differentiation.
- Metabolic differentiation into fiber types occurs post-innervation.
- Early observed variations in enzyme activity are transient and stage-dependent.
Abstract:
The study was undertaken to race the histochemical and electron microscopic development patterns of human myogenesis from the 9th to the 26th week of foetal life. Particular attention was paid to the possibility of appearance of metabolic or structural differences between individual skeletal muscle fibres in early periods of myogenesis. The 9th week of foetal life is the period when primitive myotubes are formed. Irregular distribution of the ATPase (pH 9-4) activity observed at this time is due to differences in the structure of fusing myoblasts. The early myotubes show a high activity of the oxidative enzymes and lack of phosphorylase. Conversion of immature muscle cells into structurally mature fibres begins between the 20th and the 24th week. The latter fibres exhibit a uniform activity of all the studied enzymes and thus resemble the intermediate type of fibres of mature muscles. From about the 26th week on the typical mosaic pattern of the enzymatic activity is observed. All the differences in enzymatic activity which appear in fibers prior to their full morphologicaal maturity result from differences in developmental stages of the fibres at the given moment. The present study also suggests that there are no morphological or metabolic differences between individual humanskeletal muscle fibres prior to their metabolic differentiation into types which occurs after their innervation.