Expression of calpastatin isoforms in muscle and functionality of multiple calpastatin promoters

Calpastatin is the specific endogenous inhibitor of calpain proteinase that is encoded by a single gene. Transient transfection assays in both a non-fusing skeletal muscle and non-muscle cell-line demonstrated that the putative porcine calpastatin promoter regions 5 ′ to exons 1xa, 1xb, and 1u were functional. Both real-time quantitative and semi-quantitative RT-PCR on porcine skeletal muscle total RNA indicated that steady-state expression of Type I and III mRNAs containing exons 1xa and 1u, respectively, was at equivalent levels whilst the expression of Type II mRNA containing exon 1xb was significantly less ( p