Although my muscles fail me if I try to pick up anything that weighs more than three pounds, I’m appreciative of their health and relative youth. With so many complicated structures required for one single muscle to function properly, it is no wonder there is a long list of myopathies, or muscular diseases, that make life difficult for countless folks. Thankfully, many biologists are here to help us understand muscle structure and function.
Muscles fibers are made of long chains of sarcomeres, the basic units of a muscle, which contract to allow for muscle function. Costameres are structures that connect sarcomeres to the muscle cell’s plasma membrane, called the sarcolemma. The disruption of this physical connection can cause several different myopathies. A recent paper describes the role for a protein called obscurin in sarcolemma and costamere integrity. According to Randazzo and colleagues, mice that were deficient in obscurin had altered localization of a muscle-specific adaptor protein called ankyrin isoform ankB at the M-line of sarcomeres, as well as an altered localization of the costamere-specific protein dystrophin at costameres. The microtubule network at the sarcolemma was also disrupted in mice lacking obscurin. These results are consistent with sarcolemma instability and reduced muscle exercise tolerance seen in these mutant mice. In the images above, muscle fibers in mice lacking obscurin (bottom row) have reduced levels of dystrophin (red, left column) at costameres, while another costamere protein called β-dystroglycan (β-DG, red, middle column) appears unchanged. The microtubule cytoskeleton (red, right column) in these mutant fibers is also disrupted. (Z-disk protein α-actinin is in green in all images.)
Randazzo, D., Giacomello, E., Lorenzini, S., Rossi, D., Pierantozzi, E., Blaauw, B., Reggiani, C., Lange, S., Peter, A., Chen, J., & Sorrentino, V. (2013). Obscurin is required for ankyrinB-dependent dystrophin localization and sarcolemma integrity originally published in the Journal of Cell Biology, 200 (4), 523-536 DOI: 10.1083/jcb.201205118