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Striated muscle tropomyosin-enriched microfilaments of developing muscles of chicken embryos
1Department of Anatomy, College of Medicine, National Taiwan University, Taipei.
Abstract:
The striated muscle tropomyosin-enriched microfilaments were isolated from developing muscles in ovo by the previously described method with a monoclonal antibody against striated muscle isoforms of tropomyosin (Lin & Lin, 1986). Two-dimensional gel analysis of the isolated microfilaments from developing heart, thigh and breast muscles revealed the coexistence of non-muscle isoforms of tropomyosin and actin throughout all stages of embryogenesis. A small but significant amount of skeletal muscle isoforms (alpha, beta) of tropomyosins and their phosphorylated forms was detected in the microfilaments isolated from hearts of 6-15-day-old embryos. These skeletal isoforms of tropomyosins disappeared after this stage of embryogenesis. In addition, we also detected both embryonic and adult isoforms of troponin T in early developing hearts. In developing thigh and breast muscles, the presence of non-muscle tropomyosin isoforms 2, 3a and 3b in the isolated microfilaments was apparent. The contents of tropomyosin isoform 2 were decreased with development and this non-muscle isoform completely disappeared at the 15th day of embryogenesis. On the other hand, the non-muscle tropomyosin isoforms 3a and 3b were present throughout all stages of development. Double-label immunofluorescence microscopy with monoclonal CH1 (anti-striated muscle isoforms of tropomyosin) and CG beta 6 (anti-non-muscle isoforms of tropomyosin) on the isolated, glycerinated skeletal and cardiac muscle cells of 10-day-old or 13-day-old embryos confirmed the colocalization of muscle and non-muscle isoforms of tropomyosins within the same cells. These results suggest that different isoforms of actin and tropomyosin can assemble into a class of microfilaments (i.e. striated muscle tropomyosin-enriched microfilaments) in ovo, which may transform into the thin filaments of mature muscle cells.
Insights
Developing muscle cells contain both muscle and non-muscle tropomyosin isoforms, suggesting these proteins assemble into microfilaments that may form mature muscle thin filaments.
Area of Science:
- Muscle biology
- Cellular and molecular biology
- Developmental biology
Background:
- Tropomyosin isoforms play crucial roles in muscle structure and function.
- Understanding tropomyosin expression during embryonic development is key to muscle formation.
- Microfilaments are essential components of the muscle cytoskeleton.
Purpose of the Study:
- To investigate the presence and co-localization of different tropomyosin isoforms in developing avian muscles.
- To determine the developmental dynamics of non-muscle and striated muscle tropomyosin isoforms.
- To explore the potential assembly of these isoforms into functional microfilaments in ovo.
Main Methods:
- Isolation of tropomyosin-enriched microfilaments from embryonic heart, thigh, and breast muscles.
- Two-dimensional gel electrophoresis for protein analysis.
- Double-label immunofluorescence microscopy using specific monoclonal antibodies.
Main Results:
- Coexistence of non-muscle and striated muscle tropomyosin isoforms in developing muscles throughout embryogenesis.
- Detection of skeletal muscle tropomyosin isoforms (alpha, beta) in embryonic hearts (6-15 days), which later disappeared.
- Presence of non-muscle tropomyosin isoforms 2, 3a, and 3b in developing thigh and breast muscles, with isoform 2 decreasing and disappearing by day 15.
- Confirmation of co-localization of muscle and non-muscle tropomyosin isoforms within the same developing muscle cells.
Conclusions:
- Different tropomyosin isoforms, alongside actin, can assemble into striated muscle tropomyosin-enriched microfilaments in ovo.
- These microfilaments may represent precursors to the thin filaments found in mature muscle cells.
- The dynamic expression and co-localization of tropomyosin isoforms highlight their complex roles in muscle development.