Recovery and characterization of hybrid dysgenesis-induced mei-9 and mei-41 alleles of Drosophila melanogaster.

X-Linked methyl methanesulfonate (MMS)-sensitive mutations were induced with hybrid dysgenesis using four P strains: pi 2, Harwich, T-007 and OK-1. Mutations were identified after two generations of backcrosses to M strain females to replace the autosomes. Among 51,471 X-chromosomes examined 10 carried stable MMS-sensitive mutations representing 8 independent events. Males of the mutant strains failed to induce gonadal dysgenesis in crosses to Oregon-R females at 28.5 degrees C. Complementation tests showed that 3 of the induced mutations were mei-9 alleles, 2 were mei-41 alleles, 1 was a mus102 allele, and 2 were alleles at a newly identified MMS-sensitive locus, mus112 (map position: 1-32.8). As assayed by in situ hybridization on polytene chromosomes, each X-chromosome had no more than four P element insertions. 4 of the 8 mutations recovered in this study proved to have P element insertions at or very close to sites to which MMS sensitivity has been mapped. Hybrid dysgenesis-induced reversion of 2 mutants, mei-9RT1 and mei-41RT2, is associated with the loss of the P element from regions 4B and 14C respectively.

Specific reduction of N,N-dimethylnitrosamine mutagenicity in Drosophila melanogaster by dimethyl sulfoxide.

Dimethyl sulfoxide (DMSO) used as a solvent has been observed to complicate mutagenicity screens by interacting with tested chemicals to yield false positives or negatives. We have used DMSO as a solvent in the Drosophila melanogaster recessive sex-linked lethal mutation assay and find that it reduces, but does not abolish, the detectable mutagenicity of N,N-dimethylnitrosamine (DMN). Its use as a solvent with procarbazine, another promutagen, shows no effect on mutagenicity in Drosophila. DMSO does not exhibit a general inhibitory action on microsome activity when ecdysone 20-monooxygenase activity is used as a measure of cytochrome P-450 activity. We were unable to detect the low DMN demethylase activity in the strain used. Hence, the inhibitory effect of DMSO in Drosophila at both the physiological and biological level appears to be limited and not general in action. Because DMN and DMSO are similar in structure, it is possible that DMSO is interacting with a DMN demethylase in Drosophila. This might lead to a reduction in the conversion of DMN to a mutagen. Consequently, from the results of this study and others DMSO should be used cautiously as a solvent in Drosophila mutagen screening.

Cytogenetic characterization of the 4BC region on the X chromosome of Drosophila melanogaster: localization of the mei-9, norpA and omb genes.

Thirty genetic alterations, which involve the 4BC region of the Drosophila X chromosome, have been induced by ionizing radiation or by an endogenous mutator element. These mutations were recovered by screening for reversion of the dominant mutants Oce and Qd or for induction of the recessive mutants bi and rb. Among the 23 mutants generated by ionizing radiation, 20 have proven to be cytologically detectable chromosomal aberrations. Seven additional unique aberrations were generated in the Uc mutator strain. In total, 22 cytologically detectable deficiencies, 3 translocations, 1 inversion, 1 transposition, and 3 cytologically normal mutants have been recovered. Complementation analysis has permitted the cytogenetic localization of eight genes in the 4BC region. The mei-9 locus has been assigned to region 4B4-6, because this function is carried by Df(1)rb41 but not by Df(1)biD1. The norpA locus has been placed in the 4B6-C1 region based on its location between the distal breakpoints of Df(1)biD2 and Df(1)rb41. The genes lac, Qd, bi, and omb are localized to bands 4C5,6, rb to 4C6 and amb to 4C7,8. With one exception the complementation analysis has also permitted a determination of the linear sequence of these genes. This cytogenetic localization of these loci will facilitate the cloning and molecular analysis of genes controlling a key function in DNA repair and recombination (mei-9), and two fundamental neural functions (norpA and omb).

The induction of chromosome aberrations by cis-platinum(II) diamminodichloride in Drosophila melanogaster.

We have determined the in vivo effects of cis-platinum(II)diamminodichloride (cis-PDD) treatment on the induction of chromosome aberrations in Drosophila melanogaster germ cells. cis-PDD treatment induces significant increases in chromosome breakage in all stages of spermatogenesis in a battery of test systems using ring or rod-X males and repair-proficient or deficient females. Since no increase in nondisjunction was induced by cis-PDD in either male or female germ cells, any aneuploidy inducing effects of this compound should result from its clastogenic action. We also find that mei-9 excision repair function is involved in the repair of cis-PDD-induced DNA lesions in a manner that provides additional evidence that partial and ring chromosome losses are not completely homologous.