NUCLEAR LAMIN EXPRESSION REVEALS A SURPRISINGLY HIGH GROWTH FRACTION IN CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS

In an attempt to better characterize leukemic bone marrow cells of chi ldren with ALL in G(0)/G(1), we studied the variation of the nuclear p rojection area (NPA) during the cell cycle. Approximately half of the increase of the nuclear volume during the cell cycle occurred before D NA synthesis. Next, we assessed by in situ hybridization (ISH) the exp ression of nuclear envelope type A/C and type B lamins in leukemic lym phoblast and unstimulated as well as stimulated normal peripheral bloo d mononuclear cells (PBMC). It was found that 82.0+/-16.0% of the ALL cells expressed B-type and 5.8+/-3.1% A/C-type lamins. The in vitro (3 )HdT pulse-labeling index ((3)HdT LI) of ALL cells varied from 1.3 to 16.8%. Of unstimulated PBMC 2.9 and 1.2% expressed lamin type B and A/ C, respectively. The (3)HdT LI was 0.8%. In conA-stimulated PBMC, the corresponding values were 95.3 and 74.8% and 31.0%, respectively. In v iew of the current concepts regarding G(1) events and regulation of ce ll proliferation, we considered B-type lamin expression an early marke r for the commitment to proliferation and used it for growth fraction (GF) determinations. By this method, a surprisingly high GF was found in ALL cell populations; there was no correlation between GF and the ( 3)HdT LI, as seen in normal cells.