In situ hybridization of human bone marrow cryosections. Sections of human bone marrow were incubated with DIG-labeled-cRNA sense (a) or antisense probe (b). Bound cRNA probes were detected with anti-digoxigenin-alkaline phosphatase Fab fragments, followed by incubation with NBT/BCIP color solution. The megakaryocytes observed in sections incubated with the PCI-cRNA antisense probe showed dark blue precipitates (b). Control sections incubated with the sense probe yielded negative results (a). (Original magnification × 1,000.)