Alternative processing of the sarco/endoplasmic reticulum Ca2+-ATPase transcripts during muscle differentiation is a specifically regulated process

Expression of the muscle-specific 2a isoform of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) requires activation of an otherwise inefficient splice process at the 3´-end of the primary gene transcript. We provide evidence that SERCA2 splicing is a specifically regulated process, rather than the result of an increase in general splice efficiency or a decrease in polyadenylation efficiency at the 5´-most polyadenylation site. This is indicated by the fact that changes in general splice and polyadenylation efficiency, as observed during B-cell maturation, did not affect SERCA2 splicing. Furthermore, expression and overexpression studies did not support the hypothesis that changes in the level of the alternative splice factor ASF/SF2 or other arginine and serine rich proteins are sufficient to obtain the regulation of muscle- and neuronal-specific splicing.