Correlation of Egr3 expression with HSPC proliferation. (A) Egr3 expression in normal LKS⁺ cells in leukemic and nonleukemic microenvironments. Normal cells (CD45.1) were isolated from leukemia day 14 and transplanted into nonleukemic recipients. LKS⁺ cells were sorted 1 to 4 weeks after reconstitution. Data are represented as the mean ± SD (n = 3). (B) Flow plots (left panel) and histogram (right panel) of the cell cycle status of donor LKS⁺ cells from primary recipients (control [Cntrl] vs day 14). Data are represented as the mean ± SD (n = 6). (C) Egr3 expression in LKS⁺ cells from leukemic and control spleen. Data are represented as the mean ± SD (n = 6). (D) Coculture of LKS⁺ cells with BM plasma. Normal LKS⁺ cells were cultured with BM plasma obtained from control and day 14 leukemic mice. The proliferation of LKS⁺ cells was markedly suppressed by the leukemic BM plasma. Data are represented as the mean ± SEM (n = 6; 2 independent experiments). (E) LKS⁺ cells were treated as indicated in Figure 6D. Egr3 expression is shown. Data are represented as the mean ± SEM (n = 6; 2 independent experiments). **P < .01; ***P < .001.