Muscle LIM protein is upregulated in fast skeletal muscle during transition toward slower phenotypes

protein is upregulated in fast skeletal muscle during transi-tion toward slower phenotypes. Am J Physiol Cell Physiol 280: C273–C279, 2001.—Muscle LIM protein (MLP) is con-stitutively expressed in slow, but undetectable in fast, mus-cles of the rat. Here we show that MLP was upregulated at both the mRNA and protein levels under experimental con-ditions leading to transitions from fast to slower phenotypes. Chronic low-frequency stimulation and mechanical overload-ing by synergist removal both induced fast-to-slow shifts in myosin heavy chain (MHC) isoforms and expression of MLP in fast muscles. High amounts of MLP mRNA and protein were also present in fast muscles of the myotonic, hyperac-tive ADR mouse. Hypothyroidism evoked shifts in myosin composition toward slower isoforms and increased the MLP protein content of soleus (SOL) muscle but failed to induc