Ptbp1 Condensates With Phase Separation‐Like Features in Cardiomyocyte Nuclei Regulate Splicing of Proliferative Genes in Neonatal Cardiomyocytes

ABSTRACT Cardiovascular diseases remain the leading cause of morbidity and mortality worldwide; however, effective clinical therapies that achieve myocardial regeneration are still lacking, underscoring the urgent need for novel therapeutic strategies. In this study, we identified an RNA‐binding protein Ptbp1, a key component of RNA metabolism, as a critical regulator of cardiomyocyte proliferation via the formation of biomolecular condensates. We found that Ptbp1 exhibits granule‐like structures in cardiomyocyte nuclei during fetal to early postnatal stages. These Ptbp1 foci are phase‐separated liquid droplets formed via its multivalent RNA binding domains. Functional analyses revealed that Ptbp1 is essential for cardiomyocyte proliferation in neonatal mouse primary culture assays. Furthermore, proximity labeling using a primary antibody‐based approach combined with RIP‐seq in highly purified cardiomyocyte populations demonstrated that these condensates are enriched with multiple proliferation‐associated factors. Our findings identify a novel phase‐separated condensate in cardiomyocytes and provide a new potential therapeutic target for cardiac regeneration.