RBM20 isoform regulation by independent transcription start sites adapts alternative splicing in development and disease.

Summary

This study discovers an alternative transcription start site for RBM20 that produces a conserved, functional isoform lacking exon 1, predominantly translated from exon 2. Isoform ratios shift during disease, with hypertrophic cardiomyopathy showing RBM20 upregulation largely via the alternative isoform, revealing a second axis of RBM20 control beyond phosphorylation-dependent localization.

Key Findings

• Discovery of an alternative RBM20 transcription start site between exon 1 and 2 producing a shorter, functional isoform.
• Ribosome profiling identifies an internal exon 2 ATG as the predominant translation start site for the isoform.
• Isoform ratios are tightly perinatally regulated and shift in disease; RBM20 upregulation in hypertrophic cardiomyopathy is largely via the alternative isoform.

Clinical Implications

Although preclinical, isoform-specific modulation of RBM20 could enable precision control of cardiomyopathy-associated splicing programs and inform biomarker development distinguishing hypertrophic vs dilated remodeling.

Limitations

• Predominantly preclinical without interventional modulation of isoform ratios in vivo patients.
• Functional impact on clinical phenotypes and outcomes remains to be prospectively validated.

Future Directions

Define regulators of RBM20 alternative TSS usage, develop isoform-specific modulators, and test whether shifting isoform ratios rescues cardiomyopathy phenotypes in translational models.