Chromosome Architecture Defined by the Meiosis-Specific Cohesin in Mammalian Germ Cells

Sister chromatid cohesion, established by the cohesin complex, is indispensable for accurate chromosome segregation in both mitosis and meiosis. Whereas mitosis relies predominantly on the canonical cohesin complex composed of SMC1α, SMC3, RAD21, and STAG1/2, meiosis employs specialized variants, including SMC1β, REC8, RAD21L, and STAG3. These meiosis-specific cohesins impart unique structural and regulatory properties essential for gametogenesis. They form the chromosome axis and organize chromatin loops, thereby providing the framework for homolog recognition, synapsis, and crossover control. At centromeres, meiotic cohesins secure proper kinetochore orientation and enable the stepwise release of cohesion across successive divisions. A striking feature of cohesins in oocytes is their extraordinary stability, persisting from fetal stages until adulthood, which underpins female reproductive longevity. Progressive loss of cohesin integrity with age contributes to aneuploidy, infertility, and congenital disorders, highlighting their clinical significance. This review synthesizes recent advances in defining the molecular composition, dynamics, and functions of meiotic cohesins in mammals. We emphasize their multifaceted roles in shaping chromosome architecture, examine mechanisms that link cohesin maintenance to reproductive aging, and outline key unresolved questions that may shed light on both the evolutionary innovations of meiosis and the origins of human reproductive disorders.