LSM4 is an RNA-binding protein that functions as a core component of the spliceosome and mRNA decay machinery. As part of the heptameric LSM2-8 complex, LSM4 binds specifically to the 3'-terminal U-tract of U6 snRNA and participates in U4/U6-U5 tri-snRNP complex assembly and spliceosomal B complex formation, essential for pre-mRNA splicing 1. Beyond splicing, LSM4 localizes to P-bodies where its C-terminal RGG domain, when symmetrically dimethylated at arginine residues by PRMT5, promotes processing body formation and mRNA decay 23. This posttranslational modification enhances LSM4 binding to the SMN protein, facilitating tri-snRNP biogenesis 3. LSM4 also exhibits moonlighting functions in cell volume regulation through plasma membrane association and interaction with ICln 4. Under physiological conditions, LSM4 undergoes liquid-liquid phase separation in vitro, suggesting involvement in RNA processing organization 5. Clinically, LSM4 dysregulation associates with cancer pathogenesis: reduced LSM4 expression correlates with abnormal spermatogenesis, elevated LSM4 levels are observed in breast cancer and non-small cell lung cancer with poor prognostic implications, and LSM4 upregulation in melanoma correlates with reduced overall survival 6789.