Design of FISH assays to detect genomic CRLF2 rearrangements. (A-B) The 3 BAC clones flanking the CRLF2 locus and 1 centromeric to IGH@ on chromosome 14, respectively. The red arrow in panel A highlights the PAR1 region involved in the deletions that join P2RY8 to CRLF2. The colors and names of the BAC probes used to perform FISH in panels C to H are shown in the lower left of each panel. (C-D) Results from the IGH and the CRLF2 break-apart assays, respectively. Arrows indicate the split signals. (E-F) The IGH-CRLF2 fusion probes on interphase and metaphase cells, respectively. Arrows in panel E highlight the fusion signal, whereas arrows in panel F indicate normal signals from X, Y, and 14 as well as the fusion signal on der14. (G) The loss of 261P4 in 1 sample resulting from PAR1 deletion. (H) The same sample shows that the signal is regained when a more centromeric BAC (74L17) is used, and 2 normal fusion signals are seen. Areas of cellular debris and nuclei lacking red/green signals in the same focal plane as the other cells were masked during image capture.