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Distribution of fiber types in embryonic chick limb muscles innervated by foreign motoneurons
Abstract:
The differentiation of distinct myotube fiber types in chick limb muscle development is coincident with innervation. The role of motoneurons in influencing fiber type differentiation was analyzed by causing chick hind limb muscles to be innervated by inappropriate motoneurons and then examining experimental muscles for changes in the distribution of myosin ATPase fiber types. Motoneuron innervation of limb muscles was altered by performing either limb shifts, limb reversals, or large spinal cord reversals on early neural tube or limb bud stage chick embryos. The distribution of fiber types was then analyzed in muscles from stage 36 (E10) to stage 45 (E20) embryos after processing hind limb sections for myosin ATPase histochemistry. In the majority of experimental muscles examined (267/312), the distribution of myosin ATPase fiber types was unaltered. In the remaining experimental muscles (14%), alterations in the distribution of myosin ATPase fiber types occurred, indicating that in some cases, foreign innervation may alter the developmental program of differentiating myotubes. The results suggest that myotubes differentiate myosin ATPase staining characteristics according to an intrinsic program and that these differentiating myotubes are selectively innervated by motoneurons of the appropriate type under most conditions including normal development. Under exceptional circumstances of motoneuron-muscle fiber type mismatch, embryonic motoneurons can alter fiber type expression.
Insights
Motoneuron innervation influences chick muscle fiber type, but myotubes primarily follow an intrinsic program. In rare cases of innervation mismatch, motoneurons can alter fiber type expression.
Area of Science:
- Developmental Biology
- Neuroscience
- Muscle Physiology
Background:
- Myotube fiber type differentiation in chick limb muscles occurs alongside innervation.
- The precise role of motoneurons in dictating these fiber types is not fully understood.
Purpose of the Study:
- To investigate the influence of motoneurons on myotube fiber type differentiation.
- To determine if altering innervation patterns affects myosin ATPase fiber type distribution in chick hind limb muscles.
Main Methods:
- Altering motoneuron innervation by performing limb/spinal cord reversals in chick embryos.
- Analyzing myosin ATPase fiber type distribution in hind limb muscles from stage 36 to 45 embryos using histochemistry.
Main Results:
- In most experimental muscles (86%), fiber type distribution remained unchanged despite altered innervation.
- A minority of muscles (14%) showed altered myosin ATPase fiber types, indicating foreign innervation can impact differentiation.
- Myotubes appear to follow an intrinsic program for differentiation, with selective innervation by appropriate motoneurons under normal conditions.
Conclusions:
- Chick myotubes primarily differentiate fiber types based on an intrinsic program.
- Motoneuron innervation typically matches the appropriate fiber type.
- Exceptional cases of motoneuron-muscle fiber type mismatch can lead to altered fiber type expression.