Specialized functions of cohesins STAG1 and STAG2 in 3D genome architecture

Cohesin is a complex conserved in evolution that entraps DNA. Originally identified for its role in sister chromatid cohesion, it is currently considered a key player in 3D genome organization. In vertebrates, two paralog genes encode two versions of the SA/STAG subunit of cohesin, STAG1 and STAG2. While the existence of two variant complexes has been largely ignored in many cohesin studies, the high frequency of STAG2 mutations in cancer has stirred up the interest in dissecting the unique properties that the STAG proteins confer on cohesin. In this review, we summarize recent progress in our understanding of the functional specificity of cohesin-STAG1 and cohesin-STAG2 with particular emphasis on their contributions to genome organization and gene regulation.