TISSUE-SPECIFIC AND DEVELOPMENTALLY-REGULATED ALTERNATIVE SPLICING INMOUSE SKELETAL-MUSCLE RYANODINE RECEPTOR MESSENGER-RNA

The ryanodine receptor is a channel for Ca2+ release from intracellula r stores. By PCR analysis, we identified two alternatively spliced reg ions in mRNA of the mouse skeletal muscle ryanodine receptor (sRyR). T he splice variants were characterized by the presence or absence of 15 bp (ASI) and 18 bp (ASII) exons. The exclusion of these exons results in the absence of the regions corresponding to Ala(3481)-Gln(3485) an d Val(3865)-Asn(3870) respectively, of rabbit sRyR; these amino acid s equences exist in the modulatory region, where sites for phosphorylati on and binding of Ca2+, calmodulin and ATP are postulated to be. We al so detected sRyR in brain and heart as well as in skeletal muscle, and the splicing patterns were found to be tissue-specific. Only the ASII -lacking isoform was detected in heart, whereas in other tissues the A SII-containing isoform was predominant. The splicing patterns were als o found to change during development. In skeletal muscle, the ASI-cont aining isoform increased gradually from embryo to adult. The ASII-lack ing isoform abruptly increased upon birth, but the ASII-containing iso form increased steadily afterwards. In cerebrum, the ratio of the ASII -containing isoform to the ASII-lacking one increased abruptly during embryonic days 14 and 18. These findings suggest that the alternative splicing of ASI and ASII, by affecting the modulatory region, generate s functionally different sRyR isoforms in a tissue-specific and develo pmentally regulated manner.