Publication
The nebulin SH3 domain is dispensable for normal skeletal muscle structure but is required for effective active load bearing in mouse
Publisher:
The Company of Biologists
Date:
2013
DOI:
10.1242/JCS.137026
Abstract: Nemaline myopathy (NM) is a congenital myopathy with an estimated incidence of 1∶50.000 live births, caused by mutations in thin filament components, including nebulin, accounting for about 50% of the cases. The identification of NM cases with nonsense mutations resulting in loss of the extreme C-terminal SH3 domain of nebulin suggests an important role of the nebulin SH3 domain, which is further supported by the recent demonstration of its role in IGF-1-induced sarcomeric actin filament formation through targeting of N-WASP to the Z-line. To provide further insights into the functional significance of the nebulin SH3 domain in the Z-disk and understand the mechanisms by which truncations of nebulin lead to NM, we took two approaches: 1) an affinity-based proteomic screening to identify novel interaction partners of the nebulin SH3 domain and 2) generation and characterization of a novel knock-in mouse model with a premature stop codon in the nebulin gene, eliminating its C-terminal SH3 domain (NebΔSH3 mouse). Surprisingly, detailed analyses of NebΔSH3 mice revealed no structural or histological skeletal muscle abnormalities and no changes in gene expression or localization of interaction partners of the nebulin SH3 domain, including myopalladin, palladin, zyxin, and N-WASP. Also, no significant effect on peak isometric stress production, passive tensile stress, or Young's modulus was found. However, NebΔSH3 muscle displayed a slightly altered force-frequency relationship and was significantly more susceptible to eccentric contraction-induced injury, suggesting that the nebulin SH3 domain plays a role in bearing high active stress and perhaps in fine-tuning the excitation-contraction coupling mechanism.