ESR1 and breast cancer: To determine whether the changes in gene expression seen in the 16p11.2 RER region also correspond to altered large-scale chromatin compaction, we performed FISH using probes located at the boundaries of the two ~400 kb subregions defined in Fig. 5a on nuclei of the luminal ER+ MCF7 and basal-type ER− MDAMB231 breast cancer cell lines [20] (subregions 2 and 3).