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Histochemical and biochemical analysis of myosin heavy chain expression during cardiogenesis in the rat
1Department of Anatomy, Loyola University, Stritch School of Medicine, Maywood, IL 60153.
Insights
Myosin heavy chain (HC) expression in rat hearts shows distinct patterns in atria and ventricles during development. Ventricles shift from fetal HC beta to adult HC alpha, while atria consistently express HC alpha.
Area of Science:
- Cardiovascular Biology
- Developmental Biology
- Molecular Cardiology
Background:
- Tissue-specific myosin heavy chain (HC) expression is crucial for myocardial function but poorly understood during mammalian heart development.
- Adult myosin HC isoforms correlate with myocardial functional capacity, highlighting the importance of studying their developmental regulation.
Purpose of the Study:
- To analyze myosin HC isoform expression in atrial and ventricular myocardia during fetal cardiogenesis in the rat.
- To investigate the tissue-specific patterns and developmental modulation of myosin HC expression in the developing heart.
Main Methods:
- Separation of cardiac HCs by electrophoresis under denaturing conditions.
- Immunohistochemical localization of myosin HC alpha using a specific monoclonal antibody (R 37).
Main Results:
- Myosin HC isoform expression exhibited distinct tissue-specific patterns during rat heart development.
- Atrial myocytes consistently expressed HC alpha throughout development.
- Fetal ventricles predominantly expressed HC beta, with minor amounts of HC alpha, while adult ventricles exclusively expressed HC alpha. HC alpha expression patterns in fetal ventricles suggested roles in both conduction system and working myocardial cells.
Conclusions:
- Myosin isoform expression is developmentally modulated in a tissue-specific manner during fetal cardiogenesis.
- This modulation involves differential expression of HC beta and HC alpha, and potentially a third distinct myosin HC isoform in fetal hearts.
Abstract:
Little is known about the tissue-specific expression of contractile proteins during cardiogenesis in the mammalian heart. Since the myosin heavy chain (HC) isoform expressed in the adult correlates with myocardial functional capacity, we undertook an analysis of myosin HC expression in atrial and ventricular myocardia during fetal cardiogenesis in the rat heart. Cardiac HCs were separated by electrophoresis under denaturing conditions. The expression of the predominant adult isoform HC alpha was localized within developing fetal cardiac chambers by immunohistochemistry with a specific monoclonal antibody (R 37). Results demonstrated that myosin HC isoform expression followed tissue-specific patterns during cardiogenesis in the rat. Atrial myocytes expressed HC alpha throughout development. The ventricles expressed exclusively HC alpha in the adult, but HC beta expression predominated in fetal ventricles. Fetal ventricles also expressed minor amounts of HC alpha, whose amount and distribution varied with developmental stage. HC alpha was initially confined to tracts of cells in the trabeculae, suggestive of future conduction system cells. A more extensive population of HC alpha-expressing cells appeared several days before birth in a pattern which could represent the prenatal initiation of HC alpha expression in working myocardial cells. These results indicate that there is tissue-specific developmental modulation of myosin isoform expression during fetal development. Results also demonstrated that this modulation may include expression of a third electrophoretically distinct myosin HC in fetal hearts.