Extramedullary origin of the uterine hemangioblast. BM-uterine tracking study. First, we reconstituted the BM of lethally irradiated wild-type (C57BL/6) mice with unfractionated BMCs from GFP⁺ donors (A). GFP⁺ cells were mobilized to the uterus after reconstitution (B; insets show GFP⁺ cells at higher magnification). CD34⁺/c-kit⁻ BMCs were isolated from the recipient uterus and cultured in MethoCult media. No colony-forming units (GFP⁺ or GFP⁻) were observed at day 7 (C; insets show GFP⁺ cell at higher magnification). White arrows indicate GFP⁺ cells. We reconstituted the BM of a second set of lethally irradiated C57BL/6 mice with whole (unselected) uterine cells (UCs) isolated from the primary recipient (combined with C57BL/6 BM helper cells) (D). At 12 weeks after the secondary reconstitution, no GFP⁺ cells were detected in the BM, blood, or spleens of the secondary recipients (by FACS).