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Biophysical Journal 86:991-1001 (2004)
© 2004 The Biophysical Society

Disruption of Caenorhabditis elegans Muscle Structure and Function Caused by Mutation of Troponin I

A. K. Burkeen *, S. L. Maday *, K. K. Rybicka {dagger}, J. A. Sulcove *, J. Ward {dagger}, M. M. Huang {ddagger}, R. Barstead {ddagger}, C. Franzini-Armstrong, {dagger} and T. StC. Allen *

* Biology Department, Oberlin College, Oberlin, Ohio; {dagger} Pennsylvania Muscle Institute and Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania; and {ddagger} Oklahoma Medical Research Foundation, Program in Molecular Biology, Oklahoma City, Oklahoma

Correspondence: Address reprint requests to Taylor Allen, Biology Department, Oberlin College, 119 Woodland St., Oberlin, OH 44074-1097. Tel.: 440-775-8324; Fax: 440-775-8960; E-mail: taylor.allen{at}oberlin.edu.

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.




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