Deletion of pitpα and pitpα/pitpß in MKs results in decreased HSC and HPC numbers in the BM. BM was collected from WT littermate control (n = 5), pitpα^−/− (n = 4), or pitpα^−/−/β^−/− (n = 3) mice and analyzed for HSC and HPC numbers. (A) The number of LT-HSCs (Ai), ST-HSCs (Aii), and MEPs (Aiii) per femur was determined by flow cytometry. (B) Progenitor cell numbers and function were analyzed utilizing a functional HPC colony assay examining CFU-GMs (Bi), BFU-Es (Bii), and CFU-GEMMs (Biii) per femur. (C) The percentage of CFU-GMs (Ci), BFU-Es (Cii), and CFU-GEMMs (Ciii) in the S phase of the cell cycle was determined using the high-specific-activity tritiated thymidine kill technique. For the colony assays, each mouse was plated in triplicate. All data are presented as mean ± SEM. *P < .05, **P < .005, and ***P < .0005 when compared with WT as determined by Student t tests.