The radial distribution of fibroblastic colony-forming units in mouse femoral marrow.

The distribution of fibroblastic colony forming units (CFU-F) in mouse femoral marrow was investigated using a method which separates bone marrow cells into two regional fractions of varying size. It is shown that the concentration of CFU-F decreases almost linearly from the femoral axis (800-1,000 CFU-F per 10(7) bone marrow cells) to the bone surface (300 CFU-F per 10(7) cells). When irradiated axial or marginal cells were added into cultures as feeder cells, the colony numbers produced by both axial or marginal CFU-F were increased by about 50% and the higher concentration in the axial regions remained. The survival curve for CFU-F in both regions was characterised by a Do value of 1.54 +/- 0.11 Gy and an extrapolation number of 2.60 +/- 0.38. The results are compared to the distributions of haemopoietic stem cells and committed progenitor cells.