RNA-binding protein implicated in the regulation of pre-mRNA alternative splicing. Mediates exon inclusion and/or exclusion in pre-mRNA that are subject to tissue-specific and developmentally regulated alternative splicing. Specifically activates exon 5 inclusion of TNNT2 in a muscle-specific splicing enhancer (MSE)-dependent manner. Promotes also exon exclusion of INSR pre-mRNA. Expressed mainly in kidney, brain and testis and present in other tissues albeit at lower levels. Also expressed in fetal kidney. Belongs to the CELF/BRUNOL family.