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Centrioles are lost as embryonic myoblasts fuse into myotubes in vitro
Abstract:
Embryonic chick myoblasts possess an extensive network of cytoplasmic microtubules which emanate from a single, perinuclear centrosome containing a microtubule-organizing center (MTOC) and the centrioles. However, after myoblasts fuse into myotubes the centrosome is no longer apparent, and instead long parallel arrays of microtubules are seen. From ultrastructural studies on developing muscle tissue, it has been proposed that centrioles are present in myoblasts but are absent from fused muscle fibers. We have examined this hypothesis in vitro in cultures of chick embryonic muscle cells using sera which specifically label centrioles. Almost all (90-97%) mononucleated cells in these cultures, including myoblasts aligned just prior to fusion, contain a pair of centrioles in close proximity to the nucleus. However, in newly fused multinucleated myotubes as well as in older myotubes that had developed myofibrils, centrioles were rarely found (1-10% positive cells). This study thus provides direct evidence for a loss of centrioles from muscle cells soon after they fuse to form myotubes.
Insights
Embryonic chick muscle cells lose centrioles upon fusion into myotubes. This study confirms the absence of centrioles in fused muscle fibers, impacting microtubule organization.
Area of Science:
- Cell Biology
- Developmental Biology
- Muscle Development
Background:
- Embryonic chick myoblasts feature a prominent centrosome with centrioles and a microtubule-organizing center (MTOC).
- Upon fusion into myotubes, the centrosome becomes less apparent, with microtubules forming parallel arrays.
- Previous ultrastructural studies suggested centrioles are lost in fused muscle fibers.
Purpose of the Study:
- To investigate the hypothesis that centrioles are lost from chick muscle cells after fusion into myotubes.
- To provide direct evidence for the presence or absence of centrioles in myoblasts and myotubes in vitro.
Main Methods:
- Culturing embryonic chick muscle cells in vitro.
- Utilizing sera that specifically label centrioles for immunofluorescence.
- Quantifying the percentage of mononucleated myoblasts and multinucleated myotubes containing centrioles.
Main Results:
- Nearly all (90-97%) mononucleated myoblasts, including those nearing fusion, possessed centrioles.
- Centrioles were rarely detected (1-10%) in newly fused and mature multinucleated myotubes.
- This indicates a significant loss of centrioles during the myoblast fusion process.
Conclusions:
- The study provides direct experimental evidence for the loss of centrioles in chick muscle cells post-fusion.
- This loss likely contributes to the altered microtubule organization observed in multinucleated myotubes.
- The findings challenge previous assumptions and clarify the fate of centrioles during muscle fiber formation.