ISY1 is a spliceosomal protein with dual roles in pre-mRNA splicing and miRNA biogenesis. As a component of the spliceosome C complex, ISY1 participates in the catalytic steps of pre-mRNA splicing 1. In miRNA processing, ISY1 works with the endonuclease CPSF3 to generate progenitor-miRNA intermediates from pri-miR-17∼92, licensing selective production of five miRNAs from this cluster while excluding miR-92 2. During embryonic stem cell (ESC) differentiation, ISY1 expression dynamically regulates the transition from naive to primed pluripotency by controlling miRNA biogenesis. Gain- and loss-of-function studies demonstrate that ISY1 promotes exit from the naive state and establishes a "poised" pluripotent state characterized by specific miRNA and mRNA signatures 3. Beyond splicing and miRNA processing, ISY1 functions as a regulator of base excision repair by enhancing apurinic/apyrimidinic endonuclease 1 (APE1) activity, establishing a connection between DNA damage repair and splicing 4. Clinical relevance includes ISY1 mutations identified in neonatal hypoxic-ischemic encephalopathy cases 5, and altered ISY1 expression patterns observed in cervical cancer proteomics studies 6. These diverse functions position ISY1 as a multifunctional regulator integrating RNA processing with developmental and DNA repair pathways.