Schematic representation illustrating the distinct chromosomal localization patterns of Scc1- and Rec8-cohesin in oocytes, and how these complexes contribute to two independent functions of cohesin. (A) While Rec8-cohesin (orange) localizes between the two sister chromatids and is essential for chromosome cohesion, Scc1-cohesin (green) localizes onto the chromatid axis and contributes to loop and TAD formation. In wild-type oocytes, Wapl continuously removes Scc1-cohesin from chromatin, and in Wapl^Δ/Δ oocytes, these cohesin complexes accumulate onto the chromatid axis. The differences in higher-order chromatin structure observed between Wapl^fl/fl and Wapl^Δ/Δ oocytes were very mild, possibly due to the existence of a physical constraint in oocytes that prevents the Scc1-cohesin–dependent loops to be extended in the absence of Wapl. We propose that in the absence of Wapl, the accumulation of Scc1-cohesin onto chromatin leads to extrusion of loops within loops, that when extruded to the maximum lead to accumulation of Scc1 onto the chromatid axis (vermicelli). (B) Chromosome organization and cohesion are mediated by distinct cohesin complexes in fully grown mouse oocytes: Rec8-cohesin (orange) mediates chromosome cohesion and Scc1-cohesin (green) mediates loop extrusion.