MT1-MMP gene deletion causes myelosuppression. (A-C) The number of (A) WBCs, (B) platelets (PLT), and (C) RBCs in the PB of 14-day-old mice was counted (n = 8). (D) Images of mouse femurs (bars, 1 mm). (E) Total BM cell number per femur. (F) The percentage of PDGFRα⁺Sca1⁺ cells (MSCs) was determined by flow cytometry (n = 2). (G) (left panel) Representative MicroCT scan images, and (right panel) quantification of the relative BM area within the BM femur shaft are presented (n = 3). (H) H&E-stained femur sections. Right panel shows the quantification of the BM area per femur. B indicates bone, (bars, 200 μm). (I) Megakaryocyte number (n = 5). (J-K) Real-time PCR analysis of MT1-MMP expression in (J) BM nuclear cells (BMNCs), Lin⁺, Lin⁻, and BM stroma cells, and (K) in MS-5, NIH3T3, FOB, and BMEC-1 cells. (L-M) The (L) absolute number of CFU-C per 10⁵ BM cells and (M) frequency and absolute number/femur of CFU-S, CMP, GMP, MEP, CD34-KSL cells, and competitive repopulating units (CRU) in wild-type and knockout BM cells (n = 3). For CRU determination, freshly isolated BM cells of different cell concentration were transplanted into recipients (n = 10). Four months posttransplantation, the repopulating unit (RU) with trilineage engraftment (> 1% of donor-derived cells) was calculated. The absolute number of CRU was calculated based on the observed number of BM cells per femur. Errors in bar graphs are SEM; *P < .05, **P < .01. CFU-C indicates CFU cells; CFU-S, CFU-spleen; CMP, common myeloid progenitor; GMP, granulocyte/macrophage lineage-restricted progenitor; and MEP, megakaryocyte/erythrocyte lineage-restricted progenitor.