Radiosensitivity of the Colony-Forming Cells of the Mouse Bone Marrow

Summary

Using the tritiated thymidine suicide technique to identify the proportion of a cell population in S, the prior observation that colony-forming cells of adult mouse bone marrow are predominantly in a quiescent state (G₀) was confirmed. When bone marrow was assayed 24 hr after bleeding, up to 43% of colony-forming units had entered S but their overall radiosensitivity was unchanged. However, survivors of the thymidine suicide among CFC had a significantly lower radiosensitivity, indicating that the CFC in S are more radiosensitive than in G₀. Moreover, cells in either G₁ or G₂ must have a lessened radiosensitivity to account for the maintenance of an unchanged D ₀ of the cell population that had entered the multiplication cycle following bleeding and from which cells in S had not been eliminated.