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J. Cell Biol.,
Volume 143, Number 5, November 30, 1998 1201-1213
* University of Pennsylvania, Department of Cell and Developmental Biology, Pennsylvania Muscle Institute, School of
Medicine, Philadelphia, Pennsylvania 19104-6058; We have investigated the functions of troponin T (CeTnT-1) in Caenorhabditis elegans embryonic
body wall muscle. TnT tethers troponin I (TnI) and
troponin C (TnC) to the thin filament via tropomyosin
(Tm), and TnT/Tm regulates the activation and inhibition of myosin-actin interaction in response to changes
in intracellular [Ca2+]. Loss of CeTnT-1 function causes
aberrant muscle trembling and tearing of muscle cells
from their exoskeletal attachment sites (Myers, C.D.,
P.-Y. Goh, T. StC. Allen, E.A. Bucher, and T. Bogaert. 1996. J. Cell Biol. 132:1061-1077). We hypothesized
that muscle tearing is a consequence of excessive force
generation resulting from defective tethering of Tn
complex proteins. Biochemical studies suggest that
such defective tethering would result in either (a) Ca2+-independent activation, due to lack of Tn complex
binding and consequent lack of inhibition, or (b) delayed reestablishment of TnI/TnC binding to the thin
filament after Ca2+ activation and consequent abnormal duration of force. Analyses of animals doubly
mutant for CeTnT-1 and for genes required for Ca2+
signaling support that CeTnT-1 phenotypes are dependent on Ca2+ signaling, thus supporting the second
model and providing new in vivo evidence that full
inhibition of thin filaments in low [Ca2+] does not require TnT.
University of Washington, Department of Microbiology, Seattle, Washington
98195-7740; § Oberlin College, Department of Biology, Oberlin, Ohio 44074-1082
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