CTC1 is a core component of the CST (CTC1-STN1-TEN1) complex, a single-stranded DNA-binding protein that functions as a specialized replication factor essential for telomere maintenance and genome stability 1. The CST complex executes two critical functions at telomeres: it recruits and regulates DNA polymerase α/primase (Polα/primase) to synthesize the complementary C-rich strand through fill-in reactions 21, and it inhibits telomerase to prevent telomere overelongation and maintain telomere length homeostasis 1. Beyond telomeres, CTC1 regulates double-strand break (DSB) repair pathway choice by suppressing DNA end resection through distinct mechanisms that block both EXO1 and BLM-DNA2 nuclease activities, thereby promoting non-homologous end joining over homologous recombination 34. CTC1 also facilitates replication fork recovery and G-quadruplex resolution through cooperation with helicase RECQ4 5, and promotes ATR activation during replication stress by stabilizing TopBP1 6. Pathogenic CTC1 variants cause Coats plus, a telomere biology disorder characterized by pathological telomere shortening and disease mechanisms involving disrupted protein-protein interactions critical for telomere maintenance 7. Enhanced CTC1 expression promotes radioresistance in melanoma by maintaining telomere length 8, highlighting its therapeutic potential as a cancer treatment target.