N-Ethyl-N-nitrosourea predominantly induces mutations at AT base pairs in pre-meiotic germ cells of Drosophila males

Abstract

Molecular mutation spectra induced by N-ethyl-N-nitrosourea have been obtained in several organisms and test systems, frequently showing different results. In Drosophila melanogaster this spectrum has been analyzed in post-meiotic stages, resulting in good agreement between the adduct spectrum and mutational events, the majority being GC→AT transitions (61%). However, when collecting data about in vivo ENU-induced mutations in mouse germ cell stages mostly damage at A:T sites (89%) was observed. In this work we analyze the molecular spectrum induced with ENU in pre-meiotic repair-active male germ cells of D.melanogaster, using the specific locus test (SLT) with the vermilion locus as target. Results show that the most mutagenic sites in spermatogonial stem cells of Drosophila are A:T pairs (85%), with AT→TA transversions (50%) and AT→GC transitions (35%) as the most frequent mutations. Differences from the post-meiotic spectrum may be explained by the active repair of some adducts, such as O6-ethylguanine and N-alkyl-induced abasic sites. In addition, these results show the relevance of the minor lesions O4-ethylthymine and O2-ethylthymine in the production of mutations, 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 model system.