The Drosophila RAD21 cohesin persists at the centromere region in mitosis

'Cohesin' is a highly conserved multiprotein complex thought to be the prim ary effector of sister-chromatid cohesion in all eukaryotes. Cohesin comple xes in budding yeast hold sister chromatids together from S phase until ana phase, but in metazoans, cohesin proteins dissociate from chromosomes and r edistribute into the whole cell volume during prophase, well before sister chromatids separate (reviewed in [1,2]). Here we address this apparent anom aly by investigating the cell-cycle dynamics of DRAD21, the Drosophila orth ologue of the Xenopus XRAD21 and Saccharomyces cerevisiae Scc1p/Mcd1p cohes ins [3]. Analysis of DRAD21 in S2 Drosophila tissue culture cells and live embryos expressing a DRAD21-green fluorescent protein (GFP) fusion revealed the presence of four distinct subcellular pools of DRAD21: a cytoplasmic p ool; a chromosome-associated pool which dissociates from chromatin as chrom osomes condense in prophase; a short-lived centrosome-associated pool prese nt during meta phase-ana phase; and a centromere-proximal pool which remain s bound to condensed chromosomes, is found along the junction of sister chr omatids between kinetochores, and persists until the meta phase-anaphase tr ansition. We conclude that in Drosophila, and possibly all metazoans, a min or pool of cohesin remains bound to centromere-proximal chromatin after pro phase and maintains sister-chromatid cohesion until the meta ph ase-anaphas e transition.