Genetic damage by bifunctional agents in repair-active pre-meiotic stages of Drosophila males.
Most of our understanding of germline mutagenesis in Drosophila is based on the DNA repair-inactive, haploid post-meiotic stages. The diploid, repair-active pre-meiotic stages are more relevant to the situation encountered in somatic cells. DNA mono-adducts induced by agents like methyl methanesulphonate (MMS) and ethylene oxide (EO) are well repaired in the pre-meiotic cell stages, and these agents show therefore, no or considerable lower mutagenic activity in these stages. In contrast, in this study the two bifunctional nitrogen mustards chlorambucil (CAB) and mechlorethamine (MEC) show significantly elevated mutant frequencies of both post- and pre-meiotic germ cells. Results were similar for the X-chromosomal and the autosomal (2nd) recessive lethal (RL) test. CAB and MEC were also active in stem cells, but in comparison with post-stem cell stages they seem to be better protected. The germ cell specific response in post- and pre-meiotic cell stages was for both nitrogen mustards comparable to mutagenic activity patterns observed in the specific locus test in the mouse. It was reported that for diepoxybutane (DEB), another cross-linking agent, the ratio of the RL frequency for the 2nd- and the X-chromosome was increased from 2.1 for post-meiotic stages to 9.5 for pre-meiotic stages. In own experiments aiming to confirm this observation, a high ratio was indeed found. The induction of large deletions by DEB could be the reason for this difference, since such lesions might include both a sex-linked lethal and a vital gene required for the development of spermatocytes into mature sperm. Similar differences were expected for CAB and MEC since they are also inducers of large deletions. But unexpectedly, no differences in 2nd/X RL ratio between post- and pre-meiotic cell stages were found for the nitrogen mustards. Possible causes such as distinct proportions of multi-locus deletions (MLDs), mitotic recombination and the formation of persistent lesions, are discussed.
Wijen
J P
JP
Department of Radiation Genetics and Chemical Mutagenesis, MGC, Sylvius Laboratories, Leiden University Medical Centre, Wassenaarseweg 72, 2300 RA Leiden, The Netherlands.
Nivard
M J
MJ
Vogel
E W
EW
D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D002699:Chlorambucil / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects / Q000235:genetics; D018736:DNA Adducts / Q000187:drug effects / Q000235:genetics; D004249:DNA Damage; D004260:DNA Repair; D004330:Drosophila / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D005260:Female; D007814:Larva / Q000187:drug effects / Q000235:genetics; D008297:Male; D008466:Mechlorethamine / Q000494:pharmacology*; D008540:Meiosis; D016296:Mutagenesis; D009152:Mutagenicity Tests / Q000379:methods; D009154:Mutation; D013090:Spermatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
D018906:Antineoplastic Agents, Alkylating; D018736:DNA Adducts; D002699:Chlorambucil; D008466:Mechlorethamine; D004247:DNA