Expression of TEK in the AGM region. (A) Mouse embryo at 10.5 dpc was whole-mount–stained with TEK MoAb by immunohistochemistry. The AGM region (arrow) and vitelline artery (arrowhead) were strongly stained. hl, hind limb; h, heart; fl, fore limb. (B) FACS analysis showed that ∼5% of 10.5 dpc AGM cells were TEK⁺. Most TEK⁺ cells coexpressed CD34 and c-Kit.