Related Experiment Videos
Characterization of cardiotin, a structural component in the myocard
G Schaart1, P F van der Ven, F C Ramaekers
1Department of Molecular Cell Biology & Genetics, Cardiovascular Research Institute Maastricht (CARIM), University of Limburg, The Netherlands.
Insights
Cardiotin, a novel structural protein (>300 kDa) in cardiac and skeletal muscle, exhibits a unique filamentous distribution independent of other sarcomeric proteins. Its expression begins postnatally, suggesting a crucial role in mature heart muscle development.
Area of Science:
- Muscle biology
- Protein biochemistry
- Cellular and subcellular structures
Background:
- Cardiotin is a high molecular mass protein (>300 kDa) identified as a structural component of striated muscle.
- Its presence and distribution within muscle tissues were previously uncharacterized.
Purpose of the Study:
- To characterize cardiotin, a novel structural protein.
- To determine its subcellular localization within striated muscle.
- To investigate its expression pattern during muscle development.
Main Methods:
- Monoclonal antibody production and characterization.
- Immunofluorescence microscopy (confocal scanning laser microscopy).
- Subcellular fractionation and biochemical solubility assays.
Main Results:
- Cardiotin is localized between myofibrils in a filamentous pattern, distinct from other sarcomeric proteins.
- Filaments are approximately 2.3 microns apart and oriented perpendicularly to sarcomeric cross-striations, spanning multiple sarcomeres.
- Cardiotin is insoluble in detergents and high salt concentrations, indicating a structural role.
- Expression is detected in adult cardiac and skeletal muscle but not in smooth muscle or embryonic hearts, initiating postnatally.
Conclusions:
- Cardiotin is a unique structural protein of striated muscle with a distinct filamentous localization.
- Its insolubility suggests a significant role in myofibril organization and cardiac muscle structure.
- Cardiotin expression is developmentally regulated, appearing after birth.
Abstract:
The characterization and subcellular distribution of cardiotin, a structural component of striated muscle, is described using a monoclonal antibody. This high molecular mass component (> 300 kDa) is expressed in the myocard of several species and to a lesser extent also in skeletal muscle. Cardiotin is not found in smooth muscle tissues, other mesenchymal or epithelial tissues. The cardiotin distribution pattern is independent of other sarcomeric components, such as desmin, myosin, actin, titin, nebulin, and desmoplakin, and shows a longitudinal filamentous localization between myofibrils. The average distance between parallel running cardiotin filaments is approximately 2.3 microns, as concluded from confocal scanning laser microscopic analysis of double-immunolabeled muscle preparations. The cardiotin filamentous staining reaction is oriented perpendicularly to the typical cross-striations observed with antibodies to desmin, spanning several sarcomeres and showing a length between 12 to 80 microns in frozen sections. Its localization pattern suggests a possible link with the sarcoplasmic reticulum. We have never observed cardiotin filaments to cross the intercalated disks, stained by antibodies to desmoplakins or desmin. Cardiotin cannot be solubilized from cardiac muscle by nonionic detergents of high concentrations of KCl or KI, suggesting a structural role in the myocard. The protein could so far not be detected in developing embryonic heart, but expression seems to be initiated after birth, depending on the species examined.