Differential expression of slow and fast skeletal muscle troponin C. Slow skeletal muscle troponin C is expressed in human fibroblasts.

We have isolated and sequenced the cDNAs for human slow and fast skeletal muscle troponin C (TnC). Each cDNA is encoded by one of the two TnC genes in the human genome. The fast skeletal muscle TnC gene appears to be expressed exclusively in skeletal muscle. Only the slow TnC gene is expressed in human cardiac ventricle. The slow skeletal TnC gene is also expressed in skeletal muscle and, surprisingly, in several human fibroblast cell lines. Thus, at least one of the three proteins of the troponin complex appears to be expressed in non-muscle cells of higher vertebrates. The relative steady-state amounts of the slow and fast skeletal TnC mRNAs in various adult and embryonic striated muscles are similar to the expected amounts of the corresponding protein, suggesting that the expression of TnC genes is controlled predominantly by the production or accumulation of mRNA rather than by translational or post-translational mechanisms.