Hematopoietic potential of CD31-expressing cells in the murine yolk sac. (A-D) Confocal image of a 9.5-dpc murine yolk sac demonstrating the expression of CD31 (red, A) and c-kit (green, B). (C) Merged image. Hollow arrowheads indicate CD31 and c-kit double-positive cells, solid arrows indicate c-kit single-positive cell, and * indicates a CD31 single-positive cell. (D) Merged image with isotype controls and 4′6-diamidino-2-phenylindole 2HCl (DAPI)–labeled nuclei (scale bar, 50 μm). (E) Sorted cells from 8.5- and 9.5-dpc yolk sac (2000/dish) were plated in triplicate, and combined data obtained from 2 experiments are shown (ND indicates not detected). (F) In vivo hematopoietic potential of CD31-expressing cells in the 9.5-dpc yolk sac. Sublethally ablated newborn mice received transplants of 1000 sorted cells and were analyzed 6 months after transplantation for the presence of donor-derived Gpi-1A cells. Only mice that received transplants of CD31⁺ c-kit⁺ cells demonstrated multilineage donor-derived hematopoiesis (n = 5 mice; error bars indicate SEM).