Figure 3

Embryonic yolk sac-derived cells give rise to macrophages in the embryo. Cells were isolated from the blood of EGFP⁺ embryos at 3 days of development (HH16 to HH17), prior to the onset of definitive hematopoiesis (which occurs around HH17 to HH19 [26]), and injected into the yolk sac circulation of age-matched non-transgenic recipients. The images are representative whole mounts at different times and locations during subsequent development of separate individual birds. (A) Day 6 yolk sac blood vessels; note the extensive infiltration of the yolk sac by the transferred cells. (B) Day 10 eye. (C) Day 7 inter-digit region. (D) Day 8 foot. (E) EGFP⁺ microglial cells in the brain of a chick on the day of hatch. (F) Ubiquitous expression of EGFP in seminiferous tubules of a 16-week-old male recipient demonstrates successful establishment of germ cell chimerism from donor primordial germ cells. In the same animal, there were no detectable EGFP cells in any other location viewed as a whole mount. Scale bars A = 200 μm, B = 500 μm, C = 200 μm, D = 500 μm, E = 100 μm, F = 100 μm.