Conditional deletion of Jam3 in HSPCs before leukemic onset exacerbates imbalanced hematopoiesis in an iMLL-AF9 mouse model. (A) Scheme illustrating the experimental procedure used for generation and analysis of conditional Jam3–deficient leukemic mice (iMLL Jam3^ko/ko), wild-type leukemic mice (iMLL Jam3^fl/fl), or nonleukemic control wild-type mice. (B) Graph showing the mean of fluorescence intensity (MFI) of JAM-C on indicated hematopoietic subsets isolated from the BM at end point. Results are shown for nonleukemic (filled circles), leukemic Jam3-proficient (empty squares), and Jam3-deficient animals (filled squares). (C) Graph showing the fold change in transcriptional expression of actin (Actb) and Jam3, 9 days after the last poly (I:C) injection at the time of leukemia induction with DOX. (D) Graph showing evolution of WBC in indicated group of animals. Time scale is normalized to end point. (E) Graph showing evolution of red cell distribution width (RDW) in indicated group of animals. (F-I) Graphs showing the relative frequencies of LSKs (F), LT-HSCs (G), ST-HSCs (H), and GMPs (I) isolated from the BM of nonleukemic (filled circles), leukemic Jam3-proficient (empty squares), and Jam3-deficient animals (filled squares). (J) UMAP projection of Lin⁻/c-Kit⁺/Sca-1^+/− cells isolated from nonleukemic (left panel), iMLL Jam3^fl/fl (middle panel), or iMLL Jam3^ko/ko mice (right panel). Cell populations are color coded according to fluorescence-activated cell sorting gating and downsampling is adjusted to 2907 cells in all panels. Data are represented with mean ± SEM; ns, not significant; ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. CMP, common myeloid progenitor; MEP, megakaryocyte-erythrocyte progenitor; MPP, multipotent progenitor.