Megakaryocytic colonies developed in contact with PDPN-expressing arteriolar pericytes in the BM. (A-B) Representative images of longitudinal (A) and transverse (B) femurs with anti-PDPN and DAPI staining. (C-E) Representative images of BM vasculature ensheathed in PDPN⁺ stromal cells staining with PDPN/Sca-1/DAPI (C), PDPN/CD31/DAPI (D), and PDPN/CD31/Sca-1 (E). (F) Representative IHC images of the CLEC-2 WT and CLEC-2 cKO BM staining with CD41, PDPN, and DAPI. In CLEC-2 WT BM, CD41⁺ megakaryocyte clusters located adjacent to PDPN⁺ stromal cells at periarteriolar sites in the BM. (G) Percentage of megakaryocytes and megakaryocytic colonies which associated with PDPN⁺ stromal cells at periarteriolar space in the CLEC-2 WT and cKO BM. CD41⁺ nucleated cells and colonies localizing within 10 μm distance from PDPN⁺ stromal cells were defined as the megakaryocytes or immature megakaryocytic colonies associated with arteriole. Data were obtained using frozen BM sections from 3 individual CLEC-2 WT or CLEC-2 cKO mice. Scale bars, 100 μm for A and B; 50 μm for C, D, and F; 10 μm for E and magnified image in panel F. A, arteriole; B, bone; CV, central vein; S, sinusoid.