Figure 5.

Streak to RBI quail-chick chimera transplants and Sox17 expression. ISH (Sox17, blue), and immunochemistry with anti-QCPN antibody (brown). Anterior to the top, (D, F) 50 μm gelatin sections, with level indicated by arrowheads. (A) Schematic of experiment. Donor quail tissue from rostral or caudal streak transplanted to rostral blastoderm isolate (RBI). (B) Rostral quail streak explanted into RBI for 4–6 hours has Sox17 expression in host RBI (B') and most of the donor QCPN positive cells (B"). (C) Similarly, when caudal streak cells are explanted into the RBI, the RBI has endogenous expression of Sox17 in area opaca (C') and most of the QCPN positive transplanted cells express Sox17 within 4–6 hours (C", C"'). C"' is the same section as C" taken without Hoffman contrast optics with lines to 10× magnification inset images to aid visualization. The central grafted quail cells are QCPN positive/Sox17 negative (inset left image has QCPN cell nuclei surrounded by Sox17 negative cytoplasm; also shown by whole mount images of Sox17 expression at stages 3c-4+ in which the node is clearly unlabeled; Figure 1) and the outer quail cells are QCPN and Sox17 positive (right inset image has QCPN positive nuclei surrounded by Sox17 positive blue cytoplasm). Note cells double labeled for Sox17 and QCPN (arrow) in B" and C". (D) Following overnight incubation only the endogenous RBI expression remains (D'), with the quail explant now negative for Sox17 expression (D"). (E) Overnight incubation of a caudal explant reveals that Sox17 is expressed only in endogenous chick cells (E'), whereas the QCPN positive cells have downregulated Sox17 expression (E").