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Published on: April 29, 2011
Mitogen stimulation affects contractile protein mRNA abundance and translation in embryonic quail myocytes
1Department of Biology, University of Virginia, Charlottesville 22901.
Abstract:
In cultures of differentiated, fusion-blocked muscle cells obtained from embryonic Japanese quail (Coturnix coturnix japonica), mitogen stimulation leads to an immediate reduction in the rates of synthesis of skeletal muscle myosin heavy chain (MHC) and alpha-actin. The molecular mechanisms responsible for this downregulation were examined. The cellular abundances of the alpha-actin and MHC mRNAs were affected differently by mitogen stimulation; alpha-actin mRNA abundance declined by an amount which quantitatively accounted for the observed decrease in alpha-actin synthesis, whereas MHC mRNA abundance remained virtually unchanged during the first 6 h following mitogen stimulation, a period during which MHC synthesis declined by more than 70%. MHC mRNA abundance did decline between 6 and 12 h after mitogen stimulation. Downregulation of MHC synthesis therefore involves an initial block in mRNA translation combined with a later loss of MHC mRNA from the cytoplasma, while alpha-actin synthesis is regulated at the level of mRNA abundance. These observations are consistent with the hypothesis that, in addition to transcriptional activation of muscle-specific genes, skeletal muscle differentiation normally involves cell cycle-dependent modulations in cellular factors which control message stability and message translation.
Insights
Mitogen stimulation in quail muscle cells rapidly reduces skeletal muscle myosin heavy chain (MHC) and alpha-actin synthesis. This occurs via translational control for MHC and mRNA abundance for alpha-actin during muscle differentiation.
Area of Science:
- Molecular Biology
- Developmental Biology
- Cell Biology
Background:
- Skeletal muscle differentiation involves complex gene regulation.
- Understanding the control of muscle-specific protein synthesis is crucial for developmental biology.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the downregulation of myosin heavy chain (MHC) and alpha-actin synthesis following mitogen stimulation in differentiated muscle cells.
- To differentiate between translational and transcriptional regulation of these proteins.
Main Methods:
- Primary cell cultures of embryonic Japanese quail (Coturnix coturnix japonica) differentiated muscle cells.
- Mitogen stimulation and subsequent analysis of protein synthesis rates.
- Quantification of alpha-actin and MHC mRNA abundance over time.
Main Results:
- Mitogen stimulation caused an immediate decrease in both MHC and alpha-actin synthesis.
- Alpha-actin synthesis reduction was proportional to its mRNA level decrease.
- MHC synthesis decreased significantly within 6 hours, while MHC mRNA levels remained stable initially, declining later.
Conclusions:
- MHC synthesis downregulation involves an initial translational block followed by mRNA degradation.
- Alpha-actin synthesis is primarily regulated at the mRNA abundance level.
- Muscle differentiation involves cell cycle-dependent regulation of mRNA stability and translation.
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