Ex vivo profiling of MKs by flow cytometry and scRNA-seq demonstrates that the bone marrow is the leading site of megakaryopoiesis in mice. (A) Representative dot plots of HSPCs, MKPs, and MKs. (B) Absolute LT-HSC cell counts across tissues. (C) Absolute counts of MKPs across tissues. (D) Absolute counts of MKs across tissues. Blue, fetal liver; red, bone marrow; green, spleen; and light blue, lung. Bone marrow, spleen, and lung (n = 5 animals) and fetal liver (n = 3 animals). Data are shown as mean ± standard error of the mean. Statistics were performed with 1-way analysis of variance with Tukey multiple comparisons test at 95% confidence interval (CI). (E) Uniform manifold approximation and projection (UMAP) projection of scRNA-seq data sets of murine lung and bone marrow CD41⁺ cells (Yeung et al⁶). Plots are colored based on the sampling tissue (top) or cluster identity (bottom). (F) Bubble plot showing expression of common murine hematopoiesis markers across clusters. The red box highlights canonical MK markers. (G) Scatterplot showing gating strategy used to select CD41⁺CD42⁺ cells based on RNA expression. (H) Bubble plot showing MK and immune-related markers expression on CD41⁺CD42⁺ cells across clusters. (I) Average expression of genes from a proplatelet formation (PPF) signature on CD41⁺CD42⁺ cells.