Reversibility of hematopoietic stem cell direction (not 'commitment') as influenced by the microenvironment.
The 7-day colony types (E vs. G) formed in irradiated recipient spleens and bones by donor cells from adult bone marrow and spleen and early fetal liver were examined. Both direct and sequential transplant (retransplantation shortly after lodgment) experiments were carried out. It was found that recipient spleen receiving donor bone marrow, spleen or fetal liver developed significantly higher E/G ratios in that order, but that the E/G for colonies in recipient bones remained around 1. This led to the following conclusions concerning differences in the proportion of E or G colonies formed in recipient spleens and bones: (1) selective lodgment of 'committed' CFU-S does not occur; (2) selected repression or stimulation of 'committed' CFU-S does not occur; and (3) the findings are best explained by a condition of reversible directedness present in many or all transplantable pluripotent stem cells.
D000818:Animals; D016026:Bone Marrow Transplantation; D003114:Colony-Forming Units Assay; D005260:Female; D005333:Fetus / Q000166:cytology; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D008099:Liver / Q000166:cytology; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D008810:Mice, Inbred C57BL; D011247:Pregnancy; D013154:Spleen / Q000637:transplantation