A Nebulin Ruler Does Not Dictate Thin Filament Lengths

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 fluores...

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Bibliographic Details
Published in:Biophysical journal 2009-03, Vol.96 (5), p.156
Main Authors: Castillo, Angelica, Nowak, Roberta, Littlefield, Kimberly P, Fowler, Velia M, Littlefield, Ryan S
Format: Article
Language:English
Subjects:
Biophysics
Fluorescence
Microscopy
Musculoskeletal system
Proteins
Rabbits
Online Access:Get full text
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Summary: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 ...m from the Z-line, but Tmod localized 1.13...1.31 ...m 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. (ProQuest: ... denotes formulae/symbols omitted.)
ISSN:0006-3495
1542-0086