The in vivo but not the in vitro am3 revertant frequencies increase linearly with increased ethylnitrosourea doses in spleen of mice transgenic for phiX174 am3, cs70 using the single burst assay.

摘要

The am3 revertant frequencies (RF) in spleens from male mice transgenic for phiX174 am3, cs70 were analyzed 14 weeks after ethylnitrosourea (ENU) treatment, both by the single burst assay (SBA) and the mixed burst assay (MBA). The mean in vivo (burst size >30/assay plate) revertant frequency (MRF) for the vehicle control was 2.6x10(-7). The ENU induced in vivo RF were linear over the dose range 0-150mg/kg, (r(2)=0.999). The concomitant in (burst size G transitions. Sequence analysis of in vivo revertants from ENU treated animals revealed revertants that were 17% A-->G transitions and 83% A-->T transversions, the latter being consistent with the reported A:T base pair alterations induced by ENU. No A-->C transitions were seen. This suggests the occurrence of an ENU-induced O(2) ET-dT lesion leading to a dT base mismatch. The observations in this report both confirm and validate the use of the SBA for distinguishing between in vivo mutations that are fixed in the animal and in vitro mutations that arise from other sources. The ability of the SBA to distinguish the in vivo from the in vitro origin of mutations has increased the specificity, sensitivity and utility of the phiX transgenic system.