Isolation and characterization of AGM-derived endothelial cells. (A) A day-11 murine embryo highlighting (rectangle) the AGM region that was dissected and used as a source for CD34⁺endothelial cells. (B) Transverse section through 11-day murine embryo AGM region stained with anti-CD34 antibody. Note the positively stained endothelium and adherent hematopoietic progenitor cells attached to the dorsal aorta (arrow), similar to those previously observed in the blood islands of the yolk sac and the AGM region of murine and human embryos.18-21 (C) Dissected AGM region stained with anti-CD34 antibody. Note the positively stained endothelial cells and adherent hematopoietic progenitor cells attached to the dorsal aorta (arrow). (D) A progenitor DAS 104 cell line was generated by polyoma virus middle-T transformation and was stained with anti-CD34 antibody. The CD34⁺ cells were isolated by FACS sorting. (E) DAS 104-4 and DAS 104-8 cell lines were stained with anti-CD34 antibody and analyzed by FACS. Note that both cell lines are positive for the CD34 antigen. Morphology of DAS 104-4 and DAS 104-8 cell lines showing typical flattented, endothelial-like structures.