The majority of Etv2-EYFP-expressing cells at E8.5-E9.5 arise from Mesp1-Cre+ cells.
A, whole-mount images of Mesp1-Cre; Rosa-TdTomato; Etv2-EYFP compound embryos at E9.5. Scale bar = 200 μm. B, FACS analysis of lineage-traced Mesp1-Cre+ cells and Etv2-EYFP+ cells at E8.5 and (C) E9.5 in both the yolk sac and embryo. D, total EYFP+ cells (percent) and TdTomato+ in the total Etv2-EYFP+ population (percent) at E8.5 and E9.5. Note that 95.6% of Etv2-EYFP+ cells at E8.5 and 87.2% of Etv2-EYFP+ cells at E9.5 are derived from cells that have expressed Mesp1-Cre. Note that, in the yolk sac, 98% of Etv2-EYFP+ cells at E8.5 and E9.5 are descendants from Mesp1-Cre+ cells (n = 4). E, immunostaining of EYFP (green, left panel) and TdTomato (red, center panel) in the Mesp1-Cre;Rosa-TdTomato;Etv2-EYFP embryo. The coexpression of EYFP and TdTomato is shown as the overlay (yellow, right panel). The arrows indicate double-positive cells, and the arrowheads point to GFP single positives. sc, spinal cord; da, dorsal aorta; lb, limb bud. The section is at the forelimb level.