ENU induces mutations in the heart of lacZ transgenic mice

The use of transgenic mouse models as somatic mutation assays allows determ ination of mutation in all tissues of the mouse, including non-dividing tis sues. In this regard, these models can be used to study the possibility tha t mutations can be induced in mitotically quiescent organs such as the hear t. Mutations are generally thought to be associated with mitotic processes of DNA replication. Mutations, however, are also postulated to occur in the absence of mitosis as the result of DNA repair. Tn order to determine whet her or not mutations could he induced in the heart, we analyzed the mutant frequency in the hearts of F-1 (Muta(TM) Mouse X SWR) mice that had been tr eated acutely with 250 mg/kg ENU and sampled at days 10, 35, and 70 post-tr eatment. A significant increase in mutant frequency at day 70 shows that mu tations can be induced in the heart. Since the heart contains small numbers of non-muscle cells, additional mechanisms that could explain these result s were also considered. The effect of ENU-induced cell proliferation or a s ub-population of rapidly dividing cells is ruled out by C-14-thymidine upta ke studies which showed minimal proliferation. By the same token, the influ ence of ex vivo mutations (i.e., DNA adducts fixed as mutations during repl ication in the bacteria) is ruled out by the observed time course of mutati ons, as well as experimental evidence showing that such mutations are not d etected in the lacZ assay. (C) 2000 Elsevier Science B.V. All rights reserv ed.