Sipa1 is expressed in BM mesenchymal cells and downregulated in the stromal cells from patients with MPN. (A-B) Microarray analysis showed SIPA1 gene expression in native and culture-expanded BM MSCs of healthy donors (A) and mice (B). The data on SIPA1 expression in human MSCs were extracted from 2 independent experiments previously done on the freshly sorted CD45⁻CD235A⁻CD31⁻CD44⁻ cells and the culture-expanded MSCs. The data on Sipa1 expression in the Ebf2⁺ MSCs were from 3 independent experiments. The expression in mouse cells was normalized to 4 housekeeping genes, including Gapdh, β-Actin, Transferrin Receptor, Pyruvate Carboxylase, in mouse cells and to 3 housekeeping genes, including GAPDH, β-Actin, ISGF-3 (STAT1), in human cells by DNA-Chip analyzer (dChip) analysis, as described.^27,28  (C) FACS profiles showing the gating strategy for sorting of SCA1⁺CD51⁺ MSCs, SCA1⁻CD51⁺ MPCs, and the more mature SCA1⁻CD51⁻ stromal cells from young adult mouse BM. The cells were first gated within CD45⁻TER119⁻CD31⁻CD44⁻ cells, and then the CD31⁺ endothelial cells and the CD44⁺ mature stromal cells were gated within the CD45⁻TER119⁻ cells as indicated. (D) qPCR analysis of Sipa1 messenger RNA (mRNA) expression in the BM stromal cell subsets. Data are mean ± standard error of the mean (SEM), from 5 independent experiments. Hprt was used to normalize the expression. P values were calculated by unpaired Student t test. (E) qPCR analysis revealed downregulation of SIPA1 expression in the BM endothelial cells and MSCs of newly diagnosed patients with CML, CNL, and CMML. P values between the patients and the age-matched healthy controls were tested by unpaired Mann-Whitney U test. HPRT was used to normalize the expression. Red dot indicates CMML and CNL samples.