Transplanted donor cells divide within host embryos. A, Double labeling of transplanted quail cells that incorporated BrdU after transplantation. The host embryo received BrdU 64 hr after transplantation and was fixed at 72 hr. Transplanted donor cells are red (QC/PN, arrow), and host cells that divided are green (anti-BrdU,star). Double-labeled cells are yellow(arrowheads). Arrow indicates a transplanted donor cell with a morphology characteristic for Schwann cells. Scale bar, 10 μm. B, Division of donor cells after transplantation. BrdU was injected into host embryos 16, 40, or 64 hr after transplantation, and the embryos were fixed 8 hr later. Both dorsal and ventral cells continue to divide 1 and 2–3 d after transplantation.