How is muscle phenotype controlled by nerve activity?

Motor neurons are known to affect muscle growth and fiber type profile (fas t/slow, oxidative/glycolytic) by regulating muscle gene expression. However , the mechanism by which the information contained in specific action poten tial patterns is decoded by the transcriptional machinery of muscle fiber n uclei remains to be established. This is a basic issue in nerve/muscle biol ogy, which has major implications in neurology, sport medicine and aging. W e describe here a general strategy aimed at identifying the signal transduc tion pathways mediating the effects of nerve activity. This approach is bas ed on the overexpression of constitutively active or dominant negative tran sduction factors in regenerating skeletal muscle.