Fig. 4. Mobilization of CECs/EPCs in parabiosis (part 1). (A) An E13 chick wing immediately after a wound: the limb is on the CAM (^*) and the size of the wound is delimited by two hemorrhagic dots (arrowheads). (B) The wound (arrowhead) 1 day later, after the shortening of feather buds. Scale bar: 5 mm. (C) Transverse section of an E14 wounded wing showing elongated QH1⁺ECs (arrows) in the interstitium and integrated in a vessel (^*) as well as round QH1⁺ HCs (arrowheads). In a contralateral E14 wing (D), QH1⁺ECs (arrow) and QH1⁺HCs (arrowheads) are less numerous. Scale bar: 100 µm. (E,F) Sections of chick CAM from parabiosis 1 day after wounding. (E) After wounding of veins, there are numerous QH1⁺ECs (arrows) and QH1⁺HCs (arrowheads). (F) After wounding of arteries, QH1⁺ECs (arrows) and HCs (arrowheads) are more rare; ^*, vessel. Scale bar: 40 µm. (G,H) QH1/TUNEL double staining illustrating that QH1⁺CECs/EPCs (arrow in G) and QH1⁺HCs (arrowhead in G) are TUNEL^-, while apoptotic nuclei are present in the CAM ectoderm (arrowheads in H). Scale bar: 35 µm. (I) Chick wing (W) 6 days after grafting onto the CAM of a `parabiotic' chick embryo. (J) Chick lung (L) 9 days after grafting onto the CAM of a `parabiotic' chick embryo. Scale bar: 3 mm. (K) Transverse section of a grafted limb showing QH1⁺ECs (arrows) and QH1⁺HCs (arrowheads) around the cartilage (ca). (L) transverse section of a grafted lung with a QH1⁺EC (arrow) integrated in a vessel endothelium (^*) and QH1⁺HCs (arrowheads) in the mesenchyme surrounding a parabronchius (p). Scale bar: 100 µm. (M-O) BrdU incorporation in an E15 parabiosis 9 days after grafting of a chick limb bud onto the chick CAM. (M) In a feather bud of the grafted limb, numerous nuclei are BrdU⁺ (brown dots); however, QH1⁺ECs (arrows) present in the pulp are BrdU^-. Scale bar: 70 µm. (N) In the corresponding `parabiotic' host chick heart, BrdU is incorporated into the myocardium (brown dots), but QH1⁺ECs (arrows) and QH1⁺HCs (arrowhead) are BrdU^-. Scale bar: 35 µm. (O) A double stained QH1⁺/BrdU⁺EC in a myocardiac capillary (c), the brown nucleus (^*) is surrounded by the dark blue QH1 staining. Scale bar: 15 µm.