Fig. 2. Identification of quail ECs and HCs in chick CAM after parabiosis. (A-C) Sambucus nigra lectin (SAMB)/QH1 double staining. (A) The endothelium (arrow) of a chick vessel (v) stained by SAMB. Scale bar: 25 µm. (B,C) One isolated interstitial quail SAMB⁺/QH1⁺EC. Scale bar: 15 µm. (D,E) QH1/VEGFR2 double staining: a QH1⁺EC expresses VEGFR2 transcripts (arrow); a QH1⁺HC does not (arrowhead). Scale bar: 25 µm. (F-H) LEP/QH1 double staining: an elongated LEP^-/QH1⁺EC (white arrow) surrounded by chick (LEP⁺/QH1^-, white arrowheads) and quail (LEP⁺/QH1⁺, blue arrowheads) macrophages. Scale bar: 25 µm. (I-L) LEA/QH1 double staining: (I-K) two quail LEA^-/QH1⁺ECs (white arrows) present in the vicinity of a chick LEA⁺/QH1^- macrophage (white arrowhead) and a round quail LEA^-/QH1⁺HC (blue arrow). Scale bar: 25 µm. (L) One quail (LEA⁺/QH1⁺, blue arrowhead) and one chick (LEA⁺/QH1^-, white arrowhead) macrophage are present. Scale bar: 15 µm. (M-O) GRL2/QH1 double staining: an elongated GRL2^-/QH1⁺EC (white arrow) identified among chick (GRL2⁺/QH1^-, white arrowheads) and quail (GRL2⁺/QH1⁺, blue arrowhead) hematopoietic precursors, and a quail GRL2^-/QH1⁺ macrophage (blue arrow). Scale bar: 10 µm. (P-T) QH1⁺HC distribution. QH1⁺HCs are found in muscle as extravasated cells (P, arrowheads) or in the bone marrow as osteoclasts (Q, arrowheads). Scale bar: 80 µm. BM, bone marrow; ca, cartilage; mu, muscle. (R-T) QH1/SMA double staining shows that QH1⁺HCs never reach vessel walls. ^*, vessel lumen. Scale bar: 70 µm.