Burkeen A K, Maday S L, Rybicka K K, Sulcove J A, Ward J, Huang M M, Barstead R, Franzini-Armstrong C, Allen T StC
Biology Department, Oberlin College, Oberlin, Ohio 44074-1097, USA.
Biophys J. 2004 Feb;86(2):991-1001. doi: 10.1016/S0006-3495(04)74174-0.
Caenorhabditis elegans strains mutant for the unc-27 gene show abnormal locomotion and muscle structure. Experiments revealed that unc-27 is one of four C. elegans troponin I genes and that three mutant alleles truncate the protein: recessive and presumed null allele e155 terminates after nine codons; semidominant su142sd eliminates the inhibitory and C-terminal regions; and semidominant su195sd abbreviates the extreme C-terminus. Assays of in vivo muscular performance at high and low loads indicated that su142sd is most deleterious, with e155 least and su195sd intermediate. Microscopy revealed in mutant muscle a prevalent disorder of dense body positioning and a less well defined sarcomeric structure, with small islands of thin filaments interspersed within the overlap region of A bands and even within the H zone. The mutants' rigid paralysis and sarcomeric disarray are consistent with unregulated contraction of the sarcomeres, in which small portions of each myofibril shorten irregularly and independently of one another, thereby distorting the disposition of filaments. The exacerbated deficits of su142sd worms are compatible with involvement in vivo of the N-terminal portion of troponin I in enhancing force production, and the severe impairment associated with su195sd highlights importance of the extreme C-terminus in the protein's inhibitory function.
unc-27基因发生突变的秀丽隐杆线虫品系表现出异常的运动能力和肌肉结构。实验表明，unc-27是秀丽隐杆线虫四个肌钙蛋白I基因之一，三个突变等位基因会使该蛋白截短：隐性且可能为无效等位基因e155在九个密码子后终止；半显性的su142sd缺失抑制性区域和C末端区域；半显性的su195sd缩短了极端C末端。在高负荷和低负荷下对体内肌肉性能的测定表明，su142sd的危害最大，e155最小，su195sd居中。显微镜检查显示，突变肌肉中致密体定位普遍紊乱，肌节结构不太明确，在A带的重叠区域甚至H区内散布着细肌丝小岛。突变体的僵硬麻痹和肌节紊乱与肌节不受控制的收缩一致，即每个肌原纤维的小部分不规则且相互独立地缩短，从而扭曲了细丝的排列。su142sd线虫更严重的缺陷与肌钙蛋白I的N末端部分在增强力量产生中的体内参与有关，而与su195sd相关的严重损伤突出了极端C末端在该蛋白抑制功能中的重要性。
