Fig 4. Interphase cohesion between sister chromatids following cohesin knockdown does not require the presence of a homolog.

(A) Cartoon showing theoretical interactions between chromosomes. Homologs and sister chromatids can be held together by a combination of homolog-homolog and sister-sister interactions (left) or just homolog-homolog interactions that indirectly hold sister chromatids together (middle, right). (B) Karyotype of Clone 8 cells, which have two copies of the autosomes (long arrows) and a single X chromosome (arrowhead). Scale bar = 5 μm. (C) Clone 8 cells following Rad21 knockdown (top row, immunofluorescence; bottom row, FISH). GFP serves as a marker for cells transfected with dsRNA, while Cyclin B (CycB) indicates cells in the G2 stage of the cell cycle. The cell marked by the arrow is in G2 and depleted for cohesin, but FISH indicates that sister chromatid cohesion is unperturbed, both for an autosome (dodeca, 3rd Chr.) and for the X chromosome (16E). Scale bar = 5 μm. (D) Quantification of results for experiment illustrated in (C) showing percentages of nuclei with a single FISH signal at dodeca and 16E. Means represent three independent trials; error bars = SD; n≥40 per trial per knockdown. Differences between control and Rad21 knockdown cells were not significant by Fisher’s exact test (P = 0.0654 and P = 0.7992 for dodeca and 16E, respectively).