Mechanism of Incorporation of Newly Synthesized Myosin Alkali Light Chain into Myofibril

Abstract

Objectives: The present work was designed to study the incorporation of newly synthesized myosin alkali light 
chain (MLC) molecules into myofibris. 
Materials and Methods: cDNA of fast skeletal muscle type of MLC tagged with green fluorescence protein (LC3f
GFP) was transfected into cultured chicken cardiomyocytes, and the assembly of expressed LC3f-GFP was observed 
in living cells under a fluorescence microscope equipped with a cooled CCD camera. 
Results: At 14-16 hours after transfection, LC3f-GFP was diffusely distributed in the cytoplasm of cardiomyocytes. 
In some cells, however, intense fluorescence spots of LC3f-GFP were found along myofibrils with a periodically of 
1.2 µm. Confocal microscopy of such cells, stained with rhodamine-labeled phalloidin, revealed the fluorescence 
spots of LC3f-GFP localized at both ends of A-bond. When these cells were further incubated, LC3f-GFP came to 
be localized at all levels of the A-bands by 26 hours after transfection.  
Conclusion: These results indicate that myosin filaments are not replaced with newly synthesized myosin molecules 
at once along their length, but molecules in filaments are replaced individually from their ends.