CELF1 and myotonic dystrophy type 1: Thus, in adult DM1 tissues inactivation of MBNL1 function by intranuclear sequestration in foci (53–56) and a concomitant increased stability of CUG-BP1 due to PKC-dependent phosphorylation in most affected tissues (24,28) drives the production of normally embryonically expressed splicevariants.