ARNT deletion results in reduced LT-HSC numbers. (A) Methylcellulose colony-forming assays were performed on single-cell preparations from BM and spleen, showing increased frequency of colony-forming cells in KO BM and spleen. Colony counts for specific cell types for BM (B) and spleen (C) (n = 4 ctrl, 4 KO). (D) Representative FACS plots for LSK-SLAM to resolve hematopoietic progenitor cell populations show relative changes in hematopoietic progenitor cell populations of KO mice. Absolute numbers of hematopoietic progenitors are altered in KO mice and quantified in (E) (n = 6 ctrl, 6 KO). Numbers are based on populations present in 1 femur and 1 tibia. (F) Limiting-dilution analysis demonstrates decreased frequency of HSCs in KO mice, with absolute frequencies of 1in 23 320 and 1 in 56 156 for the control and KO mice, respectively, P < .05. (Donor n = 6 ctrl, n = 6 KO. Recipient n = 33 ctrl, n = 32 KO). *P < .05, **P < .01.