Figure 1.
Molecular characterization of CPSF6-RARG fusions. (A) May-Grünwald-Giemsa staining showing hypergranular promyelocytes with Auer rods in the diagnostic BM aspirate from patient 1. Black arrow points to Auer rods. Original magnification ×1000. (B) Interphase FISH using the PML-RARA dual-color, dual-fusion translocation probe revealed absence of PML-RARA for patient 1. (C) Karyotypic analysis performed on the diagnostic BM revealed tetraploidy karyotype of 92, XXXX[2] for patient 1. (D) May-Grünwald-Giemsa staining showing hypergranular promyelocytes in the diagnostic BM aspirate from patient 2. Black arrow points to Auer rods. Original magnification ×1000. (E) Interphase FISH using the RARA dual-color break-apart probe showing 2 yellow signals corresponding to an intact RARA gene for patient 2. (F) Karyotypic analysis performed on the diagnostic BM revealed del(12)(p12)[2]/46,XX[18] for patient 2. (G) Whole-genome sequencing analysis results revealed that the breakpoint (red arrow) in 12q15 was located at intron 4 of the CPSF6 gene in both patients. There are 2 breakpoints (red arrow) in RARG gene, which are located at intron 3 and the 5′ untranslated region. The 3′ region of the RARG gene (from exon 1 or exon 4 to exon 9) was reversed and fused in-frame with the 5′ region of the CPSF6 gene (from exon 1 to exon 4) in both patients. (H) Electrophoresis of RT-PCR products from 2 patients showed 2 types of CPSF6-RARG fusion transcripts. (I) Partial nucleotide sequences surrounding the junctions of the 2 types of CPSF6-RARG fusion transcripts. The fusion transcript from patient 1 was a fusion between exon 4 of the CPSF6 gene with exon 4 of the RARG gene. The fusion transcript from patient 2 was a fusion between exon 4 of the CPSF6 gene with exon 1 of the RARG gene. (J) Schematic diagram of CPSF6, RARG, CPSF6-RARG-S, and CPSF6-RARG-L fusion proteins. CPSF6-RARG-L harbored a point mutation from 805G to C in patient 2, resulting in a change of glycine to arginine at 269. The breakpoint is indicated by a red line. UTR, untranslated region.