Aberrant nuclear-staining pattern of NUP98/NSD1-positive samples. Immunofluorescence of leukemic cells with antibodies directed against the N-terminus of NUP98 (green) and the C-terminus of NSD1 (red) is shown for a NUP98/NSD1-positive (A) and a NUP98/NSD1-negative patient sample (B). Patient 3397 shows a pattern of nuclear speckles for NUP98 staining as well as NSD1 staining, indicating accumulation of the NUP98/NSD1 fusion protein in aggregates in the nucleus, in contrast to patient 4576. DAPI indicates 4,6-diamidino-2-phenylindole.