Thin filaments (red) become elongated when nebulin is lost. Titin (blue) and thick filaments (green) are unaffected.
Muscle physiology depends on the precise alignment, length, and overlap of thin (actin) and thick (myosin) filaments. Capping proteins such as Tmod stop the growing and shrinking of dynamic thin filaments but lack the innate ability to know when to do so. The new results show that the capping proteins know when to act because of nebulin, a giant protein that spans the length of thin filaments.Nebulin's size varies by muscle cell type, and the variation correlates with thin filament length. McElhinny et al. removed nebulin from cultured heart muscle cells by RNAi and found that the actin filaments became unruly. Their pointed ends (which overlap with thick...
