Dabiri G A, Turnacioglu K K, Sanger J M, Sanger J W
Department of Cell and Developmental Biology and Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058, USA.
Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):9493-8. doi: 10.1073/pnas.94.17.9493.
Myofibril formation was visualized in cultured live cardiomyocytes that were transfected with plasmids expressing green fluorescent protein (GFP) linked to the Z-band protein, alpha-actinin. The expression of this fluorescent protein provided an in vivo label for structures containing alpha-actinin. The GFP-alpha-actinin fusion protein was incorporated into Z-bands, intercalated discs, and attachment plaques, as well as into the punctate aggregates, or Z-bodies, that are thought to be the precursors of Z-bands. Observations of live cells over several days in culture permitted us to test aspects of several theories of myofibril assembly that had been proposed previously based on the study of fixed cells. Fine fibrils, called premyofibrils, that formed de novo at the spreading edges of cardiomyocytes, contained punctate concentrations of alpha-actinin, termed Z-bodies. The punctate Z-bodies grew and aligned with Z-bodies in adjacent fibrils. With increasing time, adjacent fibrils and Z-bodies appeared to fuse and form mature myofibrils and Z-bands in cytoplasmic regions where the linear arrays of Z-bodies had been. These new myofibrils became aligned with existing myofibrils at their Z-bands to form myofibrils that spanned the length of the spread cell. These results are consistent with a model that postulates that the fibrils that form de novo near the cell membrane are premyofibrils-i.e., the precursors of mature myofibrils.
在转染了表达与Z带蛋白α-辅肌动蛋白相连的绿色荧光蛋白（GFP）的质粒的培养活心肌细胞中，观察到了肌原纤维的形成。这种荧光蛋白的表达为含有α-辅肌动蛋白的结构提供了体内标记。GFP-α-辅肌动蛋白融合蛋白被整合到Z带、闰盘和附着斑中，以及被认为是Z带前体的点状聚集体（即Z小体）中。在培养的几天内对活细胞进行观察，使我们能够检验先前基于对固定细胞的研究提出的几种肌原纤维组装理论的各个方面。在心肌细胞伸展边缘处新形成的称为前肌原纤维的细纤维，含有α-辅肌动蛋白的点状聚集物，称为Z小体。点状Z小体生长并与相邻纤维中的Z小体对齐。随着时间的推移，相邻的纤维和Z小体似乎融合，在Z小体线性排列的细胞质区域形成成熟的肌原纤维和Z带。这些新的肌原纤维在其Z带处与现有的肌原纤维对齐，形成跨越伸展细胞长度的肌原纤维。这些结果与一个模型一致，该模型假定在细胞膜附近新形成的纤维是前肌原纤维，即成熟肌原纤维的前体。
