Rs26-Confetti expression in the platelet lineage reveals megakaryocyte clustering in the bone marrow. (A-C) Analysis of megakaryocytes (MK) in bone marrow whole mounts from von Willebrand factor (vWF)-Cre and PF4-Cre dependent Rs26-Confetti reporter mice. (A) Representative micrographs showing YFP, CFP, RFP and GFP overlay, arrows: MK, scale bar: 50 µm. Of note, vWF is expressed early during megkaryopoiesis in pluripotent platelet biased hematopoietic stem cells, leading to vWF-Credriven expression of Confetti in a large proportion of small, multi-lineage bone marrow cells in addition to large MK. (B) Quantification of color expression n=3 mice per group, t-test; (C) detailed analysis of color expression. (D) Confetti fluorescence (YFP, RFP, GFP and CFP) and Gp1b (DyLight647) staining of representative single/grouped cells. Image was cropped from Figure 1B and shown at higher magnification. Compare Figure 1B and E percentage of single and grouped MK, n=10 bones, ANOVA. (F) Mean distance of Confetti positive cells in the bone marrow of PF4-cre (n=50) and vWF-cre (n=157) dependent Rs26-Confetti reporter mice from CD144+ blood vessels. Analyzed in n=3 bones from individual mice per group, t-test. YFP: yellow fluorescent protein; GFP: green fluorescent protein; RFP: red green fluorescent protein; CFP: cyan green fluorescent protein.