Fig. 7. Abnormal hematopoiesis in runx1-mo embryos. Two-color in situ hybridization for flk-1 (purple) and scl (red) expression (A,B,E,F,I,J,M,N) and single hybridization with the myb riboprobe (O,P). Lateral views of the posterior (A,B,I,J,M,N) and anterior (E,F) embryo regions, and whole embryos (O,P); anterior towards the left. (M,N) Higher magnification of the ICM regions. Histological cross-sections of the tail (C) and trunk (G,K). Cytology of cells collected from ICM collections (D) and vitelline vessels (H,L). All are 48 hpf, except A,B, which are 24 hpf. Controls are indicated. (A,B) scl-positive cells (red arrow) accumulate in the ICM of runx1-mo embryo. (E,F) Lack of scl expression in circulation (red arrowhead) in runx1-mo embryo. (I) Cells that accumulate in the tail maintain scl expression (red arrowhead). In A,E,I, axial vessels (purple arrows) and intersegmental vessels (purple arrowheads) are poorly formed when compared with controls (B,F,J). (M,N) scl-positive cells (red arrow) predominate in runx1-mo embryo when compared with the predominantly flk-1-positive population in control (purple arrows). (C) Large immature cells (arrow) mixed with necrotic cells (arrowhead). (D) Blast-like morphology of accumulated cells with a mitotic figure (arrow). (G, arrow; H) Erythroid cells with delayed maturation compared with normal in K,L. (O,P) Reduction in myb expression in the aorta of runx1-mo embryo compared with control (arrowheads). Scale bars: 
10 µm.
