| MBNL2 is an RNA binding member of the muscleblind like protein family that regulates alternative pre mRNA splicing and other post transcriptional processes and shows prominent expression in brain, heart, and skeletal muscle, where it contributes to developmental and tissue specific RNA programs. The protein contains four C3H type zinc finger RNA binding domains arranged in two tandem pairs and recognizes YGCY enriched sequence motifs such as 5′ ACACCC 3′ in introns and 3′UTRs, which allows position dependent activation or repression of exon inclusion and regulation of mRNA localization and stability. MBNL2 binds pre mRNAs co transcriptionally and controls alternative splicing of numerous targets, acting as a splicing repressor on some transcripts and an activator on others; in muscle cells it inhibits inclusion of specific cardiac troponin T exons while promoting inclusion of defined insulin receptor exons, and in vascular smooth muscle cells it cooperates with RBPMS and RBFOX2 to drive a contractile type splicing program. MBNL2 functions in a partially redundant and partially specialized manner with MBNL1 and MBNL3; all three paralogs bind similar YGCY motifs but show different binding affinities, splicing potencies, and mobility on CUG expanded RNA, so that MBNL2 contributes distinct quantitative and qualitative effects to the overall MBNL dependent splicing network. Transcriptome wide analyses identify MBNL proteins, including MBNL2, as regulators of developmentally programmed splicing switches that convert embryonic patterns to adult isoforms in muscle and brain by repositioning exons encoding regulatory motifs in ion channels, cytoskeletal proteins, and signaling molecules, and MBNL dependent regulation also extends to mRNA localization in neurites and to 3′UTR processing. In myotonic dystrophy type 1 and related microsatellite expansion disorders, expanded CUG or CCUG repeat RNAs form nuclear foci that bind and sequester MBNL proteins, including MBNL2, which causes loss of normal MBNL2 activity, disruption of developmentally regulated splicing of many pre mRNAs, and re expression of fetal isoforms associated with muscle weakness, cardiac conduction abnormalities, and CNS manifestations. MBNL2 also participates in DNA damage and stress responses; induction of MBNL2 under hypoxic and genotoxic conditions stabilizes the CDK inhibitor p21 transcript and influences cell cycle arrest and survival, linking MBNL2 dependent RNA control to checkpoint pathways and stress adaptation. Altered MBNL2 expression impacts metastasis and epithelial–mesenchymal transition, with MBNL2 regulating cancer cell migration and invasion through modulation of PI3K/Akt linked EMT regulators and through broader changes in splicing networks that affect adhesion, cytoskeletal dynamics, and signaling components. |
