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Structure and function of embryonic growth plate in the absence of functioning skeletal muscle
1Orthopaedic Research Laboratories, University of Michigan, Ann Arbor 48109-0486, USA.
Insights
Functioning fetal skeletal muscle is essential for normal bone development. Muscle activity stimulates chondrocyte proliferation in the growth plate, crucial for long bone growth.
Area of Science:
- Skeletal biology
- Developmental biology
- Chondrogenesis
Background:
- Normal skeletal development relies on active fetal skeletal muscle.
- Muscle contraction influences bone growth, but the precise mechanisms are unclear.
Purpose of the Study:
- To investigate if functioning muscle stimulates long bone growth by affecting chondrocyte proliferation, differentiation, and hypertrophy.
- To determine the role of muscle activity in skeletal development using a chick embryo model.
Main Methods:
- Chemical paralysis and muscle atrophy were induced in midgestation chick embryos.
- Bromodeoxyuridine uptake was measured to assess chondrocyte proliferation.
- Chondroepiphysis and tibial growth plate zones were analyzed for cell proliferation and hypertrophy.
Main Results:
- Paralysis did not affect overall long bone development or growth plate organization.
- Bromodeoxyuridine uptake was reduced by 27-55% in paralyzed chicks, indicating decreased chondrocyte proliferation.
- The proliferative zone size and cell number were reduced; hypertrophic chondrocyte size was largely unaffected.
Conclusions:
- Functioning fetal muscle primarily stimulates skeletal growth by promoting the recruitment or proliferation of immature chondrocytes.
- Muscle activity plays a critical role in regulating chondrocyte dynamics within the growth plate.
- These findings highlight the interdependence of muscle and bone development during the fetal period.
Abstract:
Normal growth and development of the skeleton require the presence of viable, actively contracting skeletal muscle throughout the fetal period. A chick embryo model of midgestation chemical paralysis and secondary muscle atrophy was used to test the hypothesis that functioning muscle stimulates the growth of long bones by influencing the proliferation, differentiation, and hypertrophy of chondrocytes in cartilage of the epiphysis and growth plate. Paralysis did not alter the overall developmental stage of the long bone or the organization of the growth plate. Compared with controls, however, uptake of bromodeoxyuridine in the paralyzed chick was reduced by 27-55% in the chondroepiphysis and uppermost zone of the tibial growth plate, indicating reduced proliferation of chondrocytes. A specific reduction in the size of the proliferative zone and a reduced number of proliferating cells were also observed. By contrast, in the second, post-proliferative zone of the growth plate, the height of the zone was unchanged and its area was only slightly reduced compared with controls. Finally, median hypertrophic cell profile area, a measure of cell size, was not significantly affected by paralysis, although frequency analysis revealed modest numerical reductions in the population of the largest hypertrophic chondrocytes in the paralyzed group. These data suggest that the role of functioning fetal muscle in maintaining proper skeletal growth may be mediated primarily through specific stimulation of the recruitment or proliferation of immature chondrocytes, or of both.