A novel isoform of delta-sarcoglycan is localized at the sarcoplasmic reticulum of mouse skeletal muscle.

The sarcoglycan-sarcospan complex (alpha-, beta-, gamma-, delta-, epsilon-, and zeta-SG-SSPN), a component of the dystrophin-associated glycoprotein complex (DAGC), is located at the sarcolemma of muscle fibers where it contributes to maintain cell integrity during contraction-relaxation cycles; gamma- and delta-SG are also expressed in the sarcoplasmic reticulum (SR). In this study, we report the identification of a novel isoform of murine delta-SG produced by alternative splicing that we named delta-SG3. This isoform is present at transcript level in several tissues, with its highest expression in skeletal and cardiac muscle. The delta-SG3 protein lacks the last 122 amino acids at the C-terminal, which are replaced by 10 new amino acids (EGFLNMQLAG). Interestingly, double immunofluorescence analysis for delta-SG3 and the dihydropyridine receptor (DHPR) shows a close localization of these two proteins. We propose the subcellular distribution of this novel delta-SG3 isoform at the SR and its involvement in intracellular calcium concentration regulation.