Silver bands in chronic granulocytic leukemia. II. The Philadelphia chromosome

To test if rRNA gene activity in the Philadelphia (Ph) chromosome nucleolar organizing regions (NOR) differs from other NOR we scored silver banding patterns in leukemic cells of 32 patients (one patient was sampled twice) in the chronic phase of chronic granulocytic leukemia. The average number of bands per NOR in banded cells of these patients was 0.40 +/- 0.06 for the Ph NOR, not significantly different from the 0.41 +/- 0.02 per D chromosome NOR or the 0.41 +/- 0.04 per G. Across the 33 cases, the number of different Ph NOR banded in at least one cell (23 of 33, 70%) was also closely similar to the cumulative maximum number of chromosome D NOR banded per cell (137 of 198 banded, 69%) and G NOR banded (67 of 99, 67%). We conclude that the activity of rRNA genes in Ph NOR is closely similar to that of the other nine NOR in each CGL cell. In situ hybridization of 3H-labeled complementary rRNA to NOR of two patients revealed that the mean number of Ph NOR grains fell within the range of the other NOR. Also, grain distributions across the NOR of leukemic cells closely matched those of stimulated lymphocytes. Thus, a limited sampling has shown no evidence for consistent differences or changes in the rRNA gene number of Ph NOR.