Mutations arise in the germline by errors of replication, recombination and
repair, and the movement of transposable elements. Transgenic mice bearing
reporter genes such as lacZ have proven useful for measurements of spontan
eous and induced mutation frequencies, as well as studies of the effects of
ageing. In this study, testicular DNA from lacZ transgenic mice was examin
ed for age-related effects on mutation frequency and type. The recovered tr
ansgene was tested for simple substitutions and rearrangements including tr
ansposition of endogenous mobile elements. There was no evidence for either
an age-related accumulation of mutations, or for the insertion of retrotra
nsposons into the lacZ reporter gene in the testis. We conclude that the fr
equency of retrotransposition of several mouse mobile elements into the lac
Z reporter gene is less than 3.73 x 10(-8). This is significantly less than
the known frequency of similar to 7% of all spontaneous mutations in the m
ouse being due to retrotransposition of these elements. (C) 2001 Elsevier S
cience Ireland Ltd. All rights reserved.