Sister chromatid cohesion is mediated by individual cohesin complexes

Eukaryotic genomes are organized by loop extrusion and sister chromatid cohesion, both mediated by the multimeric cohesin protein complex. Understanding how cohesin holds sister DNAs together, and how loss of cohesion causes age-related infertility in females, requires knowledge as to cohesin’s stoichiometry in vivo. Using quantitative super-resolution imaging, we identify two discrete populations of chromatin-bound cohesin in post-replicative human cells. While most complexes appear dimeric, cohesin localized to sites of sister chromatid cohesion and associated with Sororin is exclusively monomeric. The monomeric stoichiometry of Sororin:cohesin complexes demonstrates that sister chromatid cohesion is conferred by individual cohesin rings, a key prediction of the proposal that cohesion arises from their co-entrapment of sister DNAs., Below is the information on how samples were stained and images acquired, sorted by microscopy technique.
Immunofluorescence staining
Cells were grown to 80% confluency on 22x22 mm #1.5H high-precision coverslips (thickness 0.170 ± 0.005 mm, Marienfeld Superior). Cells were washed in PBS, pre-extracted in ice-cold PBS 0.2% Triton X-100 (Sigma-Aldrich) for 1.5 min on ice and fixed in 4% formaldehyde for 15 min. For non-pre-extracted samples, cells were fixed and subsequently permeabilized in PBS 0.2% Triton X-100 for 5 min. Primary and secondary antibodies were diluted in antibody diluent (DMEM medium containing 10% FBS, 0.05% sodium azide, sterile filtered 0.2 mm). Samples were incubated in primary antibody for 1.5 h and for 1 h in secondary antibody solution supplemented with 4’,6’-diamidino-2-phenylindole-dyhydrochloride (DAPI, 0.5 mg/ml). In between primary and secondary antibody staining, samples were washed 3x in PBS 0.2% Tween. After secondary antibody incubation, samples were was..., , # **Sister chromatid cohesion is mediated by individual cohesin complexes**

\[Access this dataset on Dyrad] (DOI:10.5061/dryad.3r2280gpg)

Eukaryotic genomes are organized by loop extrusion and sister chromatid cohesion, both mediated by the multimeric cohesin protein complex. Understanding how cohesin holds sister DNAs together, and how loss of cohesion causes age-related infertility in females, requires knowledge as to cohesin’s stoichiometry *in vivo*. Using quantitative super-resolution imaging, we identify two discrete populations of chromatin bound cohesin in post-replicative human cells. While most complexes appear dimeric, cohesin localized to sites of sister chromatid cohesion and associated with sororin is exclusively monomeric. The monomeric stoichiometry of sororin:cohesin complexes demonstrates that sister chromatid cohesion is conferred by individual cohesin rings, a key prediction of the proposal that cohesion arises from their co-entrapment of sister DNAs.

### Descript...