Embryonic sites of Runx1 expression. Diagrams of the mouse conceptus at embryonic day 7.5 (E7.5), E8.5, and E10.5 showing representative Runx1 expression patterns. Runx1 expression (blue) is measured by β-galactosidase activity in histologic sections of Runx1^LacZ/+ embryos¹⁹  in which the LacZ knockin results in a Runx1 knockout allele or by immunostaining with a Runx1-specific antibody. Hematopoietic sites and cells expressing Runx1 are shown below each embryo. Runx1 expression patterns were taken from previous studies.^{19,28,45,60,62,64,66,67}  ab, allantoic bud; bi, blood islands; BL-CFC, blast colony-forming cells; c, chorion; pl and PL, placenta; vc, vessel of confluence; ys and YS, yolk sac.