Mediates pre-mRNA alternative splicing regulation. Acts either as activator or repressor of splicing on specific pre-mRNA targets. Inhibits cardiac troponin-T (TNNT2) pre-mRNA exon inclusion but induces insulin receptor (IR) pre-mRNA exon inclusion in muscle. Antagonizes the alternative splicing activity pattern of CELF proteins. RNA-binding protein that binds to 5'ACACCC-3' core sequence, termed zipcode, within the 3'UTR of ITGA3. Binds to CUG triplet repeat expansion in myotonic dystrophy muscle cells by sequestering the target RNAs. Together with RNA binding proteins RBPMS and RBFOX2, activates vascular smooth muscle cells alternative splicing events (By similarity). Regulates NCOR2 alternative splicing (By similarity). Seems to regulate expression and localization of ITGA3 by transporting it from the nucleus to cytoplasm at adhesion plaques. May play a role in myotonic dystrophy pathophysiology (DM). {ECO:0000250|UniProtKB:F2Z3T4, ECO:0000269|PubMed:15257297, ECO:0000269|PubMed:16273094, ECO:0000269|PubMed:16946708}. This is the function of Ensembl gene identifier ENSG00000139793 (MBNL2, muscleblind like splicing regulator 2).