Zhan, H. et al. Nat. Commun. 5, 4974 (2014).

Technical issues make it difficult to track single molecules in a living organism despite the development of super-resolution imaging techniques that improve light microscope resolution to a few nanometers. Zhan et al. now show that complementation-activated light microscopy (CALM) can be used to follow individual voltage-dependent calcium channels in the muscle cells of living adult roundworms. CALM relies on fusing a protein of interest to a nonfluorescing GFP that lacks a single β-strand, which can be added back at low levels for complementation and sparse molecular labeling; it does not need photobleaching or low protein levels. The authors used dystrophin-mutant worms as models for human Duchenne muscular dystrophy and discovered that dystrophin modulates calcium-channel positional organization in muscle cell membranes and neuromuscular synapses by transducing changes in muscle tension.