Figure 1. Complete assembly of ROBs.

A) Working model for ROB formation depending on recombination between SST1 repeats (pink triangles) located in PHRs (colored bands) on the short arms of human chromosomes 13, 14, and 21. The adjacent 45S rDNA arrays, also called NORs, facilitate 3D proximity by co-locating in nucleoli. B) Schematic representation of the main SST1 arrays and flanking sequences in acrocentric chromosomes from CHM13. This region is similar on chromosomes 13 and 21, but inverted on chromosome 14. C-E) Representative images of ROBs from each cell line are shown. The left top panels display chromosomes labeled with an SST1 probe (magenta) and whole chromosome paints as indicated. The middle panels show chromosomes labeled with an SST1 probe (magenta) and centromeric satellite probes for CenSat 14/22 (orange) and CenSat 13/21 (green). DNA was counterstained with DAPI. The magnified inset (right) demonstrates SST1 localization between the two centromere arrays. Scale bar is 1 μm. The plot on the right shows averaged intensity profiles of lines drawn through the centromeres of at least 10 ROBs. Intensity profiles were aligned to the peak of the Gaussian of the SST1 signal and normalized to the maximum intensity of each channel. Error bars denote standard deviations. The lower panels show a synteny plots comparing the assembled ROB to CHM13. The structure of each fused region is shown in detail.