Diverse Roles of Cohesin in Chromosome Dynamics and Stem Cells

The cohesin complex is a highly conserved, ring-shaped protein assembly that plays fundamental roles in chromosome biology. Originally identified as the molecular glue that holds sister chromatids together from DNA replication until cell division, cohesin has since been recognized as a pleiotropic regulator of genome organization, gene expression, DNA repair, and cell fate determination. In embryonic stem cells (ESCs), cohesin's functions extend beyond canonical sister chromatid cohesion to include the maintenance of three-dimensional (3D) chromatin architecture through DNA loop extrusion, regulation of pluripotency-associated transcriptional programs, and facilitation of homologous recombination-mediated DNA repair during the prolonged S phase. Recent discoveries have revealed that meiosis-specific cohesin components, particularly the α-kleisin subunit REC8 and its interacting partner STAG3, are expressed and functionally active in mitotic ESC chromosomes, where they contribute to chromosomal organization and sister chromatid cohesion in concert with mitotic RAD21-containing cohesin. Furthermore, the interplay between cohesin and condensin complexes at shared genomic binding sites has emerged as a critical determinant of chromosome topology, with cohesin depletion leading to aberrant condensin accumulation and chromosome hypercompaction. Importantly, perturbations in cohesin function not only impair ESC self-renewal but also direct lineage-specific differentiation, linking cohesin to stem cell fate determination. Germline mutations in cohesin and its regulators underlie a spectrum of developmental disorders termed cohesinopathies, while somatic mutations are frequently observed in various cancers. This review provides a comprehensive overview of the diverse roles of cohesin in chromosome structure, cell cycle regulation, and stem cell biology, with particular emphasis on recent findings in ESCs that illuminate the complex interplay between mitotic and meiotic cohesin complexes.