Evaluation of the database on mutant frequencies and DNA sequence alterations of vermilion mutations induced in germ cells of Drosophila shows the importance of a neutral mutation detection system

The vermilion gene in Drosophila has extensively been used for the molecula r analysis of mutations induced by chemicals in germ cells in vivo. The gen e is located on the X-chromosome and is a useful target for the study of mu tagenesis since all types of mutations are generated. We have critically ev aluated this system with respect to sensitivity for mutation induction and selectivity for different types of mutations, using a database of more than 600 vermilion mutants induced in postmeiotic male germ cells by 18 mutagen s. From most of these mutants the mutation has been analysed. These data sh owed 336 base substitutions, 96 intra-locus DNA rearrangements and 78 multi -locus deletions (MLD). Mutants containing a MLD were either heterozygous s terile or homozygous and hemizygous lethal. The distribution of both basepa ir (bp) changes and intra-locus rearrangements over the coding region of th e vermilion gene was uniform with no preferences concerning 5' or 3' region s, certain exons, splice sites, specific amino acid changes or nonsense mut ations. Possible hotspots for base substitutions seem to be related to the type of DNA damage rather than to the vermilion system. Gene mutations othe r than bp changes were examined on sequence characteristics flanking the de letion breakpoints. Induction frequencies of vermilion mosaic mutants were, in general, higher than those of vermilion complete mutants, suggesting that persistent lesion s are the main contributors to the molecular spectra. Comparison of inducti on frequencies of vermilion mutants and sex-linked recessive lethal (SLRL) mutants for the 18 mutagens showed that the sensitivity of the vermilion ge ne against a mutagenic insult is representative for genes located on the X- chromosome. The effect of nucleotide excision repair (NER) on the formation of SLRL mutants correlated with an increase of transversions in the vermil ion spectra under NER deficient conditions. Furthermore, the clastogenic po tency of the mutagens, i.e., the efficiency to induce chromosomal-losses vs . SLRL forward mutations, shows a positive correlation with the percentage of DNA deletions in the molecular spectra of vermilion mutants. (C) 1999 El sevier Science B.V. All rights reserved.