Alpha-sarcomeric actins are assembled preferentially into striated myofibrils in developing muscle cells compared to cytoskeletal actins, although both can be incorporated.
This in vitro study demonstrates that while both cytoskeletal and sarcomeric actins can incorporate into myofibrils, sarcomeric alpha-actins are preferentially assembled during muscle cell development.
Monoclonal antibodies (McAb) to actin were prepared to analyze the assembly of actin isoforms in developing muscle cells in vitro. One of the antibodies (SkA-06) was specific for alpha-sarcomeric actin isoforms in skeletal and cardiac muscles, while the others recognized cytoskeletal (beta, gamma) actin isoforms in smooth muscle and non-muscle tissues as well as the sarcomeric (alpha) actins. Using SkA-06 and a polyclonal antibody (PcAb) specific for cytoskeletal actins, the subcellular localization of the actin isoforms was examined by immunocytochemical methods. While in developing young myotubes, cytoskeletal and sarcomeric actins were co-localized in nascent myofibrils or stress-fiber-like structures, sarcomeric actins predominated in striated myofibrils in more developed myotubes. When FITC-labeled cytoskeletal and sarcomeric actins were introduced into young myotubes by a microinjection method, the latter became detectable in striated structures sooner than the former but they were finally incorporated into striated myofibrils. These results suggest that alpha-actin(s) as well as beta- and gamma-actins can be incorporated into myofibrils, but alpha-actin(s) is assembled preferentially into myofibrils in developing muscle cells.
Hayakawa et al. (Thu,) conducted a other in Developing skeletal muscle cells in vitro. Microinjection of FITC-labeled cytoskeletal and sarcomeric actins was evaluated on Subcellular localization and assembly of actin isoforms. Alpha-sarcomeric actins are assembled preferentially into striated myofibrils in developing muscle cells compared to cytoskeletal actins, although both can be incorporated.