N-ETHYL-N-NITROSOUREA PREDOMINANTLY INDUCES MUTATIONS AT AT BASE-PAIRS IN PRE-MEIOTIC GERM-CELLS OF DROSOPHILA MALES

Molecular mutation spectra induced by N-ethyl-N-nitrosourea have been obtained in several organisms and test systems, frequently showing dif ferent results, In Drosophila melanogaster this spectrum has been anal yzed in postmeiotic stages, resulting in good agreement between the ad duct spectrum and mutational events, the majority being GC-->AT transi tions (61%). However, when collecting data about in vivo ENU-induced m utations in mouse germ cell stages mostly damage at A:T sites (89%) wa s observed. In this work we analyze the molecular spectrum induced wit h ENU in pre-meiotic repair-active male germ cells of D.melanogaster, using the specific locus test (SLT),vith the vermilion locus as target . Results show that the most mutagenic sites in spermatogonial stem ce lls of Drosophila are A:T pairs (85%), with AT-->TA transversions (50% ) and AT-->GC transitions (35%) as the most frequent mutations. Differ ences from the post-meiotic spectrum may be explained by the active re pair of some adducts, such as O-6-ethylguanine and N-alkyl-induced aba sic sites. In addition, these results show the relevance of the minor lesions O-4-ethylthymine and O-2-ethylthymine in the production of mut ations, as a consequence of their poor repair. Finally, since there is a striking similarity to the ENU-induced mutation spectrum in mouse, these results reveal that Drosophila continues to be an excellent mode l system.