伴肌动蛋白标尺并不决定细肌丝的长度。
A nebulin ruler does not dictate thin filament lengths.
作者信息
Castillo Angelica, Nowak Roberta, Littlefield Kimberly P, Fowler Velia M, Littlefield Ryan S
机构信息
Department of Forensic Science, Chaminade University, Honolulu, Hawaii, USA.
出版信息
Biophys J. 2009 Mar 4;96(5):1856-65. doi: 10.1016/j.bpj.2008.10.053.
To generate force, striated muscle requires overlap between uniform-length actin and myosin filaments. The hypothesis that a nebulin ruler mechanism specifies thin filament lengths by targeting where tropomodulin (Tmod) caps the slow-growing, pointed end has not been rigorously tested. Using fluorescent microscopy and quantitative image analysis, we found that nebulin extended 1.01-1.03 mum from the Z-line, but Tmod localized 1.13-1.31 mum from the Z-line, in seven different rabbit skeletal muscles. Because nebulin does not extend to the thin filament pointed ends, it can neither target Tmod capping nor specify thin filament lengths. We found instead a strong correspondence between thin filament lengths and titin isoform sizes for each muscle. Our results suggest the existence of a mechanism whereby nebulin specifies the minimum thin filament length and sarcomere length regulates and coordinates pointed-end dynamics to maintain the relative overlap of the thin and thick filaments during myofibril assembly.
为了产生力量，横纹肌需要等长的肌动蛋白丝和肌球蛋白丝相互重叠。有一种假说认为，伴肌动蛋白的尺子机制通过确定原肌球蛋白（Tmod）封端慢速生长的尖端的位置来指定细肌丝的长度，但这一假说尚未得到严格验证。通过荧光显微镜和定量图像分析，我们发现，在七种不同的兔骨骼肌中，伴肌动蛋白从Z线延伸1.01 - 1.03微米，但原肌球蛋白位于距Z线1.13 - 1.31微米处。由于伴肌动蛋白不会延伸到细肌丝的尖端，所以它既不能定位原肌球蛋白的封端，也不能指定细肌丝的长度。相反，我们发现每条肌肉的细肌丝长度与肌联蛋白同工型大小之间存在很强的对应关系。我们的结果表明存在一种机制，通过该机制伴肌动蛋白指定细肌丝的最小长度，肌节长度调节并协调尖端动力学，以在肌原纤维组装过程中维持细肌丝和粗肌丝的相对重叠。
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