Mouse oocyte killing by neutrons: target considerations

Highly radiosensitive primordial mouse oocytes, the principal cells at genetic risk in the female, have been studied using 0.43 MeV neutrons. Analysis of the survival curve (D37 = 0.055 Gy) indicates that the diameter of the radiosensitive target (assumed spherical and of unit density) is larger than that of the nucleus but not of the oocyte, implicating a non-nuclear but sub-cellular target. This is consistent with results from the 3H-thymidine incorporated in DNA. Efforts to identify the extraordinarily radiosensitive lethality target in these primordial oocytes suggest it is the plasma membrane. Monte Carlo calculations for 0.43 MeV neutrons show that at the D37 only a single proton recoil will traverse the plasma membrane, consistent with the observed exponential survival curve. A highly sensitive non-DNA target for mouse oocyte killing may importantly influence interpretations of genetic mutation data from mice and their use in estimating genetic risk in humans. (author)