The repair-deficient mei-9 alpha Drosophila female potentiates chromosome loss induced in the parenteral genome by diethylnitrosamine

Following matings of DEN-treated Xc2/BSYy+ males with repair-deficient mei-9 alpha females and ordinary females, significant increases in complete and partial sex chromosome loss as well as dramatic shifts in sex ratio were found with mei-9 alpha but not ordinary females. Accordingly, the mei-9 alpha female enhances the detection of chromosome lesions leading to chromosome loss induced in the male genome by DEN. To date, the 4 compounds tested in this way (DMN, DEN, MMS and procarbazine) exhibit strong potentiation of chromosome loss with mei-9 alpha females suggesting the possibility that a protocol involving treatment (or not) or Xc2/BSYy+ males mated with mei-9 alpha females may hold promise as an alternative to traditional tests for chromosome loss using repair-proficient females. Comparison with published translocation data on the 4 compounds indicated above suggests an overall greater sensitivity of the described mei-9 alpha chromosome-loss test compared with the traditional translocation test in the detection of chemically induced chromosome lesions.     

Genetic study on the effects of the repair-deficient mutant females mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 of Drosophila on spontaneous and X-ray-induced chromosome loss in the paternal genome

The repair-deficient mutants mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 in Drosophila melanogaster were investigated regarding their effects on spontaneous and X-ray-induced chromosome loss in postmeiotic cells. Each mutant was incorporated singly into XC2, and the ring-X male provided with BSYy+. From matings of males carrying mus101D1, mus302D1 or mei-41D5, mutants identifying a caffeine-sensitive (CAS) postreplication-repair pathway, with corresponding mutant females, and non-mutant males to non-mutant females, overall frequencies of spontaneous partial loss and spontaneous complete loss were significantly increased in each mutant cross except for spontaneous complete loss with mus302 where an increase was noted only in brood 2. Similar findings were noted when males carrying the excision-repair mutant mei-9a were mated with mei-9a females. Males carrying the mutant mus104D1, identifying a caffeine-insensitive (CIS) postreplication-repair pathway, tested with mus104D1 females, produced results that were not significantly different from non-mutant controls. When males were given 3000 rad X-irradiation, frequencies of induced partial loss were significantly higher with mus101D1, mus302D1, mei-41D5 and mei91, and not significantly higher with mus101D1, mus302D1, mei41D5 and mei-9a, and not significantly different from controls with mus104D1. It was suggested that the functional CAS postreplication-repair pathway primarily promotes repair of breaks while an alternative pathway(s) not defined by mus104 promotes misrepair. Therefore, the significant increases in both spontaneous and induced partial loss with the excision-repair-deficient mutant mei-9a suggests the possibility that (a) the excision-repair-pathway may not function in misrepair and (b) the undefined misrepair pathway may be dominant pathway for postreplication repair in Drosophila since mei-9a females presumably have functional postreplication repair and misrepair capacity. The suggestion that the CAS postreplication-repair pathway and the excision-repair pathway function primarily in repair, and an undefined pathway in misrepair is in line with the finding that with mus104D1, no significant increase was found in spontaneous complete loss, but with mus101D1, mus302D1, mei-41D5 and mei-9a significant increases were observed. Results on induced complete loss, with the exception of those with mei-41D5, show a poor correlation with other classes of loss of each of the mutants. Possible explanations for this discrepancy are discussed.     

O-alkylation in DNA does not correlate with the formation of chromosome breakage events in D. melanogaster

Postmeiotic cell stages of repair-proficient ring-X (RX) males were treated with methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), diethylnitrosamine (DEN) or ethylnitrosourea (ENU) and then mated to either repair-defective (mei-9L1) or to repair-competent females (mei-9+). Absence of the mei-9+ function resulted in a hypermutability effect to all alkylating agents (AAs) when they were assayed for their ability to induce chromosomal aberrations (chromosome loss; CL), irrespective of marked differences in distribution of DNA adducts brought about by these AAs. This picture is different from that described previously for the induction of point mutations (Vogel et al., 1985a). There, evidence was presented indicating that reduction in DNA excision repair does not affect point mutation induction (recessive lethals) by those AAs most efficient in ring-oxygen alkylation such as ENU, DEN, N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), and isopropyl methanesulfonate (iPMS): the order of hypermutability of AAs with mei-9L relative to mei-9+ was MMS greater than MNU greater than DMN = EMS greater than iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9L1 females were plotted against those determined for mei-9+ females, straight lines of following slopes were obtained: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4, and iPMS = ENU = DEN = ENNG = 1. Those findings, together with the recent observation that AAs do not split into two groups when assayed for their ability to cause CL, point to the involvement of different DNA alkylation products in ENU- and DEN-induced chromosome loss vs. that of point mutations. It is concluded that with ENU and DEN chromosomal loss results from N-alkylation products whereas point mutations (SLRL) are the consequence of interactions with oxygen-sites in DNA. Thus, as a consequence of a very dominating role of O-ethylguanine (and possibly O4-alkylation of thymine), N-alkylation in DNA does not contribute measurably to mutation induction in the case of ENU-type mutagens while O-alkylation, very clearly, does not show a positive correlation with the formation of chromosome breakage events in Drosophila. Conversely, it appeared that with MMS-type mutagens (MMS; dimethyl sulfate, DMS; trimethyl phosphate, TMP), alkylation products such as 7-methylguanine and 3-methyladenine, if unrepaired or misrepaired, are potentially mutagenic lesions causing both mutations and chromosomal aberrations.     

The relationship between reaction kinetics and mutagenic action of monofunctional alkylating agents in higher eukaryotic systems. IV. The effects of the excision-defective mei-9L1 and mus(2)201D1 mutants on alkylation-induced genetic damage in Drosophila

Repair-defective mutants of Drosophila melanogaster which identify two major DNA excision repair loci have been examined for their effects on alkylation-induced mutagenesis using the sex-linked recessive lethal assay as a measure of genotoxic endpoint. The alkylating agents (AAs) chosen for comparative analysis were selected on the basis of their reaction kinetics with DNA and included MMS, EMS, MNU, DMN, ENU, DEN and ENNG. Repair-proficient males were treated with the AAs and mated with either excision-defective mei-9L1 or mus(2)201D1 females or appropriate excision-proficient control females. The results of the present work suggest that a qualitative and quantitative relationship exists between the nature and the extent of chemical modification of DNA and the induction of of genetic alterations. The presence of either excision-defective mutant can enhance the frequency of mutation (hypermutability) and this hypermutability can be correlated with the Swain-Scott constant S of specific AAs such that as the SN1 character of the DNA alkylation reaction increases, the difference in response between repair-deficient and repair-proficient females decreases. The order of hypermutability of AAs with mei-9L1 relative to mei-9+ is MMS greater than MNU greater than DMN = EMS greater than iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9L1 females are plotted against those determined for control females, straight lines of different slopes are obtained. These mei-9L1/mei-9+ indices are: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4 and iPMS = ENU = DEN = ENNG = 1. An identical order of hypermutability with similar indices is obtained for the mus(2)201 mutants: MMS(7.3) greater than MNU (5.4) greater than EMS(2.0) greater than ENU(1.1). Thus, absence of excision repair function has a significant effect on mutation production by AAs efficient in alkylating N-atoms in DNA but no measurable influence on mutation production by AAs most efficient in alkylating O-atoms in DNA. The possible nature of these DNA adducts has been discussed in relation to repair of alkylated DNA. In another series of experiments, the effect on alkylation mutagenesis of mei-9L1 was studied in males, by comparing mutation induction in mei-9L1 males vs. activity in Berlin K (control). Although these experiments suggested the existence of DNA repair in postmeiotic cells during spermatogenesis, no quantitative comparisons could be made.(ABSTRACT TRUNCATED AT 400 WORDS)     

Review of the current status of the mei-9a test for chromosome loss in Drosophila melanogaster: An assay with radically improved detection capacity for chromosome lesions induced by methyl methanesulfonate (MMS), dimenthylnitrosamine (DMN), and especially diethylnitrosamine (DEN) and procarbazine

A review of previous findings as well as new data are included in the present paper on recent invetigations by Zimmering and co-workers regarding a radical improvement in the detection capacity of the conventional test for chromosome loss to assay for induced chromosome lesions/breakage. The improvement has been achieved through the use of mei-9^a repair-deficient P1 females to which treated males are mated. 4 compounds have been tested including MMS, DMN, DEN and procarbazine. Not only the mei-9^a test yielded significantly higher frequencies of induced chromosome loss with MMS and DMN than the conventional test, preliminary data, in fact, providing evidence of a positive response in the mei-9^a test at a concentration one order of magnitude below that producing no effect in the conventional test, but, more critically, it has permitted detection of highly significant increases in induced chromosome loss with DEN and procarbazine, compounds proving negative in the conventional tests for chromosome loss and heritable traslocations at all concentrations employed including those producing substantial to high frequencies of recessive lethal.     

High frequency of spontaneous Minute mutations detected in the F1 progeny of interstrain matings between a recombination-defective mei-9L1 and the y w m f/sc8(y+) Y BS; dp strain of Drosophila melanogaster

The yield of spontaneous Minute mutations was recorded in the F1 progeny of interstrain (reciprocal) and intrastrain matings between a recombination- and excision repair-defective mei-9L1 (mei-9) strain and the y w m f/sc8(y+) Y BS; dp (ywmf-2) strain of Drosophila melanogaster. As a comparison, interstrain matings between a postreplication repair-defective st mus(3)302D1 (mus(3)) strain and the ywmf-2 strain were also studied for Minute mutations. The results show that: (1) a strikingly high frequency of Minute mutations is observed in the progeny of mei-9 female X ywmf-2 male crosses, but not in that of ywmf-2 females X mei-9 males; (2) no such difference exists in the progeny of intrastrain matings; and (3) there exists no marked inequality of Minute frequencies in the progeny of reciprocal crosses of mus(3) and ywmf-2 strains.     

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.     

A genetic study of the effects of the repair-deficient mei-9 mutation in drosophila on spontaneous and X-ray-induced paternal sex chromosome loss

The repair-deficient mutant, mei-9^a in Drosophila melanogaster was investigated regarding its effect on spontaneous and X-ray-induced chromosome loss in male postmeiotic cells. From matings of males carrying a mei-9^a or an ordinary ring-X and a doubly marked Y chromosome (B^SYy⁺) with mei-9^a or ordinary females, the spontaneous frequencies of complete loss, partial loss, and inferred ring-X loss (based on shifts in sex ratio female:male) were significantly higher with mei-9^a than with non-mei-9^a. When males were given 3000 rad X-irradiation, frequencies of induced partial loss, inferred ring-X loss and the reduction in the number of progeny per female were significantly greater with mei-9^a than with non-mei-9^a. The results provide evidence that the mei-9^a is a potentiator of both spontaneous and X-ray-induced chromosome lesions in sperm of the Drosophila male. Evidence is presented which implicates the presence of mei-9^a in the P₁ female and not the male as (at least) largely responsible for the characteristic mei-9^a effects.     

Analysis of hexamethylphosphoramide (HMPA)-induced genetic alterations in relation to DNA damage and DNA repair in Drosophila melanogaster

This paper reports the results of a study on the mutagenic profile of HMPA in Drosophila melanogaster. HMPA produced all types of genetic damage tested for in post-meiotic cells of treated males; at the concentrations used, recessive lethals and ring-X losses were induced at significant rates while 2–3 translocations, entire and partial Y-chromosome losses only occurred at low rates. From a comparison with alkylation-induced mutational spectra, we note a number of peculiarities of HMPA mutagenesis:

1. (1) there is no storage effect on HMPA-induced translocations;

2. (2) the ratio of F₂-lethals: F₃-lethals varies from 6 : 1 to 9 : 1, indicating a low capacity of HMPA for delayed mutations;

3. (3) the use of the DNA-repair-deficient mei-9^L1 females instead of an excision-proficient control strain has no influence on the recovery of mutations )recessive lethals) induced in males;

4. (4) the high frequencies of chromosome loss (CL) induced by HMPA, which are mostly due to ring-X loss, leads us to speculate that one (or more) of its metabolites acts as a DNA-crosslinking agent. In experiments on maternal effects with mei-9^L1 females, there is a 20–40% reduction in the rates of induced CL. Conversely, with mei-41^D5 females, there is a weak increase in CL frequencies.

5. (5) HPLC analysis of DNA reacted with [¹⁴C]HMPA exhibits no methylation at the O⁶ or the N-7 of guanine. This finding, together with the observed inactivity of hexaethylphosphoramide (HEPA) in the recessive lethal assay, suggests that the formation of DNA-bound forms from HMPA may not be the result of simple methylation reactions. This conclusion is supported by the genetic data, i.e., the lack of a storage effect on HMPA-induced chromosome rearrangements.

Consistent with a hypothesis by Brodberg et al. (1983) to explain the action of cisplatin in Drosophila, comparisons of the spectra of genetic alterations produced by HMPA, A 139 (bifunctional) and Thio-TEPA (trifunctional) in the assay for chromosome loss suggest the involvement of two distinct mechanisms in the formation of ring-X loss by crosslinking agents. One pathway concerns induction of chromosome loss as a consequence of sister-chromatid exchanges (SCEs). The second mechanism may be due to DNA adducts or a single adduct responsible for both a fraction of CL and for induced partial Y-loss (PL). Inactivation of the mei-9⁺ function has two consequences: SCE-mediated ring-X loss frequency is lowered in mei-9 females in comparison to the repair-proficient control strain, while the opposite effect is indicated for that fraction of ring-X loss generated by the second mutational pathway. Additional complicating factors include the observation of a dual role of storage in our study: the proportion of SCE-related chromosome losses decreases with increasing time of storage, but that produced by the alternative pathway increases. Thus, the CL frequencies actually recorded under the heading ‘chromosome loss’ appear as the net result of two mechanisms counteracting each other in their effects.     

Evaluation in Drosophila melanogaster of the mutagenic potential of furfural in the mei-9a test for chromosome loss in germ-line cells and the wing spot test for mutational activity in somatic cells.

The mutagenic potential of furfural was evaluated by means of the chromosome loss test in germ cells and the wing spot test in somatic cells of Drosophila melanogaster. The chromosome loss test was carried out employing repair-proficient as well as repair-deficient females. Males carried the compound Y chromosome, BSYy+. Two routes of administration were used: injection and feeding of adult males. Genetic damage was demonstrable after matings of treated males with females carrying the excision repair-deficient mutant mei-9a. The somatic mutation and recombination test was carried out treating 72-h transheterozygous mwh+/+flr3 larvae. Acute treatment of larvae was chosen as the method of exposure. Evidence indicates that furfural induces somatic damage as measured in the wing spot test.     

X-ray-induced mutation spectra of different germ-cell stages of Drosophila males with a double marked Y-chromosome and either a normal X-or a ring-X-chromosome (author's transl)

Different germ-cell stages of Drosophila males with a double marked Y-chromosome and either a normal X- or a ring-X chromosome were irradiated with X-rays, inducing the following aberrations: chromosome loss, chromosome gain (XYX-females), partial Y loss and isochromosomes of the Y-chromosome.Doses of 520 rad in spermatocytes and spermatids and 2600 rad in sperm, produced the same effect in these stages with regard to the chromosome loss in the males with a normal X, and the following results were obtained: (a) The partial Y loss in postmeiotic stages is small in comparison with spermatocytes in both stocks. This could mean that in spermatocytes this aberration is determined by exchange processes which can only be induced and/or detected in premeiotic stages. (b) In spermatocytes and mature sperm of males with a ring-X chromosome, the chromosome loss was 2.9 times greater than in those with a normal X. In spermatids of the males with a ring-X the rate of loss was only 1.5 times greater. In spermatocytes of either males with a ring-X or a normal X a similar high rate of isochromosomes could be induced. However, in spermatids and mature sperm the rate of induction of isochromosomes was found to be very small. These results seem to indicate that in mature sperm the rejoining of breaks in the Y-chromosome takes place before, and in the X-chromosome usually after the replication. If in post-meiotic stages of Drosophila the X- and Y-chromosomes existed as chromatid-like subunits then in spermatids these should behave as a structural unit.In sperm we were able to induce similar frequencies of individuals with a single isochromosome type in all body cells as of individuals with two types of isochromosomes (isochromosome mosaics). This result seems to indicate that after irradiation of sperm one of the first two division nuclei is lethal in an proportion of the zygotes.     

Isolation and Characterization of X-Linked Mutants of DROSOPHILA MELANOGASTER Which Are Sensitive to Mutagens

Thirteen X-linked mutants have been isolated in Drosophila melanogaster which render male and homozygous female larvae sensitive to the mutagen methyl methanesulfonate. Their characterization and preliminary assignment to functional groups is described. Four of these mutants are alleles of mei-41 (Baker and Carpenter 1972). Like previously isolated alleles of this locus, these mutants reduce fertility and increase loss and nondisjunction of the X-chromosome in homozygous females. The remaining mutants have been tentatively assigned to six functional groups (two mutants to the mus(1)101 locus, two to mus(1)102 , two to mus(1)103, and one each to mus(1)104, mus(1)105 , and mus(1)106). Several of the complementation groups can be distinguished on the basis of nondisjunction and cross sensitivity to mutagens. Females homozygous for the mei-41, mus(1)101 and mus(1)102 mutants exhibit elevated levels of nondisjunction. Mutants belonging to complementation groups mei-41, mus(1)101, and mus(1)104 are sensitive to nitrogen mustard (HN2) in addition to their MMS sensitivity. Among these mutants there is currently a direct correlation between sensitivity to HN2, sensitivity to 2-acetylaminofluorene and a deficiency in post-replication repair ( Boyd and Setlow 1976). Only the mei-41 mutants are hypersensitive to UV radiation, although several of the mutants exhibit sensitivity to gamma-rays. Semidominance is observed in female larvae of the mei-41, mus(1)104, and mus(1)103 mutants after exposure to high concentrations of MMS. The properties of the mutants generally conform to a pattern which has been established for related mutants in yeast. Additional properties of these mutants are summarized in Table 9.     

Genetic analysis of X-linked mutagen-sensitive mutants of Drosophila melanogaster

Mutants at 2 new loci which control mutagen-sensitivity are described. Mutants at both loci are female-sterile and are hypersensitive to killing by MMS; neither increases the frequency of sex-linked recessive lethals. A screen of previously described female-sterile and meotic mutants has revealed that a number of these are also sensitive to mutagens. In addition, several new mutants have been identified on the basis of sensitivity to either HN2 or MMS. An anlysis of complementation data suggests that all of the X-linked genes controlling sensitivity to MMS may now have been identified. Among the new mei-41 alleles are mutants which show verly little meiotic nondisjunction or loss. Cytogenetic mapping of previously known mutants is also described. The mutants mus(1)104^D1 and mei-41^D5 are located in th eregion 14B13±?14D1,2 on the polytene chromosome map, and they map very close to each other genetically. Cytogenetically mus(1)101^D1 is between salivary chromosome bands 12A6,7 and 12D3, mus(1)103^D1 is between bands 12A1,2 and 12A6,7, and mus(1)-109^A1 is in section 8F3-9A2.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. VII. Effects of repair deficiency in males on X-ray-induced sex-linked recessive lethals in spermatozoa

The response of mature spermatozoa to the X-ray induction (500 R and 3000 R) of sex-linked recessive lethals was studied in Drosophila melanogaster males known to be deficient in excision- or post-replication repair of UV damage in somatic cells. The results show that the induced frequencies of recessive lethals in the excision-repair-deficient males (mei-9a and mei-9L1) are similar to those in the appropriate repair-proficient males (mei+ and Berlin-K). However, in the post-replication-repair-deficient males (w mus(1)101D1), these frequencies are significantly lower than in the comparable repair-proficient males (w) after 500 R, but not after 3000 R.     

Suppressing effect of vanillin on chromosome aberrations that occur spontaneously or are induced by mitomycin C in the germ cell line of Drosophila melanogaster.

In order to investigate the anticlastogenic effect of vanillin on ring-X loss, D. melanogaster females exposed to different vanillin concentrations were crossed with non-treated, MMC- or MMS-treated males. The results obtained with this in vivo investigation showed a significant inhibition of vanillin in the frequencies of spontaneous ring-X loss--59, 56, 38 and 36%--at the different concentrations used. In addition, vanillin treatment caused a significant suppression of MMC-induced ring-X loss. This decrease was observed only in the first 3 days after the interruption of vanillin treatment and at the concentrations of 0.5 and 1% of this flavoring agent. In contrast, vanillin did not show any effect on chromosome loss provoked by MMS. Therefore, the ring-X loss-decreasing effect of vanillin seemed to depend on the quality of DNA lesions and consequently on a specific enzymatic repair process present in the oocytes of D. melanogaster.     

DNA Repair Dependence of Somatic Mutagenesis of Transposon-Caused WHITE Alleles in DROSOPHILA MELANOGASTER after Treatment with Alkylating Agents

DNA repair-defective alleles of the mei-9, mei-41, mus-104 and mus-101 loci of Drosophila melanogaster were introduced into stocks bearing the UZ and SZ marker sets. Males with the UZ marker set, z1 (zeste allele) and w+(TE) (genetically unstable white allele presumably caused by a transposable element), or the SZ marker set, z1 and w+R (semistable white allele caused by partial duplication of the w+ locus plus transposon insert), were exposed to EMS at the first instar. After emergence, adult males bearing red spots on lemon-yellow eyes were scored as flies with somatic reversions of w+(TE) or w+R. The relative mutabilities (relative values of reversion frequency at an equal EMS dose) of either w+(TE) or w+R in a repair-proficient strain and in mei-9, mei-41, mus-104 and mus-101 strains were 1: approximately 1.2:0.3:0.3:0.7, despite the fact that w+(TE) reverted two to three times as frequently as w+R under both the repair-proficient and repair-deficient genetic conditions. Similarly, after treatment with MMS, MNNG and ENNG, w+(TE) was somatically more mutable in the mei-9 strain and less mutable in the mei-41 and mus-104 strains than in the repair-proficient strain. From these results, we propose that mutagenic lesions produced in DNA by treatment with these chemicals are converted to mutant DNA sequences via the error-prone repair mechanisms dependent on the products of the genes mei-41+ (mei-41 and mus-104 being alleles of the same locus) and mus-101+, whereas they are eliminated by mei-9+-dependent excision repair. In contrast to the approximately linear responses of induced reversions of w+(TE) with ENNG in the repair-proficient, mei-9, and mei-41 strains, seemingly there were dosage insensitive ranges for induced reversion with MNNG in the repair-proficient and mei-41 strains, but not for reversion in the mei-9 strain; w+(TE) in the mus-104 strain was virtually nonmutable with MNNG and ENNG. These results suggest that O6-methylguanine (O6MeG) produced in DNA with MNNG, but not O6-ethylguanine produced with ENNG, is almost completely repaired in a low dose range by constitutive activity of DNA O6MeG transmethylase. From the distribution of clone sizes of spontaneous revertant spots and other data, we propose that both w+(TE) and w+R have a similar tendency to spontaneously revert more frequently at early rather than at later developmental stages probably reflecting a common property of their inserted transposons.     

Effects of DNA-repair-deficient mutants on somatic and germ line mutagenesis in the UZ system in Drosophila melanogaster

To analyze the underlying mechanisms of the UZ system in Drosophila melanogaster, i.e., the unstable white locus with an IS element included originally described by Rasmuson and Green (1974), the repair deficient mutants mei-9b and mei-4lD5 and the meiotic mutant mei-2l8 were introduced into X-chromosomes containing the UZ system. These strains were submitted to larval feeding of MMS to analyze differences occurring in mutation rate and survival. The mei-9b and mei-4l strains were markedly sensitive to MMS treatment, while mei-2l8 did not affect survival. Only the mutant mei-4l, which is lacking in post-replication repair, affected the somatic mutation rate of the UZ system, decreasing it by 50%. The spontaneous germ line mutation rate of UZ, on the other hand, was increased by introducing mei-4l or mei-9b, possibly as a result of the high frequency of unrepaired spontaneous chromosome breaks that occur in these mutants.     

Genetic characterization of the mei-41 locus in Drosophila melanogaster

Summary The mutagen-sensitive mutant mus(1)104 ^D1 of Drosophila melanogaster maps to a position on the X chromosome very close to the meiotic mutant mei-41 ^D5 . Both mutants have been characterized as mutagen-sensitive and defective in post-replication repair. In the present report we show by complementation studies that mus(1)104 and mus(1)103 are allelic with mei-41. In addition, two reported alleles of mus(1)104 lie between the mei-41 alleles A10 and D5. The size of the mei-41 locus is estimated to be about 0.1 centimorgans (cM). Because several alleles of mei-41 have been shown to reduce recombination and increase meiotic chromosome loss and nondisjunction, mus(1)104 ^D1 females were examined for defects in meiosis. Although there was no evidence for reduced recombination on the second chromosome in homozygous mus(1)104 ^D1 females, heterozygous mus(1)104 ^D1 /mei-41 ^>D5 and mus(1)104 ^D1 /deficiency females showed reduced levels of recombination. However, there was no evidence of an increase in nondijunction in these females.We dedicate this article to the memory of Larry Sandler, who passed away suddenly on February 7, 1987     

Studies on mutagen-sensitive strains of Drosophila melanogaster. IV. Modification of genetic damage induced by X-irradiation of spermatozoa and spermatids in N2 or O2 by mei-9a, mei-41D5 and mus(1)101D1

The influence of defects in DNA repair processes on X-ray-induced genetic damage in post-meiotic male germ cell stages of Drosophila melanogaster was studied using the 'maternal effects approach'. Basc males were irradiated in N2, air or O2 either as 48-h-old pupae (to sample spermatids) or as 3-4-day-old adults (to sample mature spermatozoa) and mated to females of 3 repair-deficient strains (mei-9a: excision-repair-deficient; mei-41D5: post-replication-repair-deficient; mus(1)101D1: post-replication-repair-deficient and impaired in DNA synthesis). Simultaneous controls involving mating of males to repair-proficient females (mei+) were run. The frequencies of sex-linked recessive lethals and of autosomal translocations were determined following standard genetic procedures. The responses elicited in the different crosses with repair-deficient females were compared with those in mei+ crosses. The main findings are the following: with mei-9 females, the frequencies of recessive lethals are higher after irradiation of spermatids in N2, but not after irradiation in air of O2 (relative to those in the mei+ crosses); this result is different from that obtained in earlier work with spermatozoa, in which cell stage, higher yields of recessive lethals were obtained after irradiation of males in either N2 or air; in the mei-9 crosses, there are no significant differences in response (relative to mei+) after irradiation of either spermatozoa or spermatids in O2; the translocation frequencies in the mei-9 crosses are similar to those in the mei+ crosses, irrespective of the treated germ cell stage or the irradiation atmosphere; irradiation of either spermatozoa or spermatids in N2, air or O2 does not result in any differential recovery of recessive lethals in the mei-41 relative to mei+ crosses; irradiation of spermatids in N2 and of spermatozoa in air leads to a higher recovery of translocations in the mei-41 crosses; and after irradiation of spermatids or spermatozoa in any of the gaseous atmospheres, the frequencies of recessive lethals and of translocations are lower in the mus-101 crosses. The differences in responses (between cell stages, in different gaseous atmospheres and with different repair-deficient females) are explained on the basis of both qualitative and quantitative differences in the composition of the initial lesions and the extent to which their repair may be affected by the defects present in the different repair-deficient females. Several discrepancies between expectations based on biochemical results and the genetic results are pointed out.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hypersensitivity of Drosophila mei-41 mutants to hydroxyurea is associated with reduced mitotic chromosome stability

6 mutant alleles of the mei-41 locus in Drosophila melanogaster are shown to cause hypersensitivity to hydroxyurea in larvae. The strength of that sensitivity is directly correlated with the influence of the mutant alleles on meiosis in that: alleles exhibiting a strong meiotic effect (mei-41D2, mei-41D5, mei-41D7) are highly sensitive; alleles with negligible meiotic effects (mei-41(104)D1, mei-41(104)D2) are moderately sensitive and an allele which expresses meiotic effects only under restricted conditions (mei-41D9) has an intermediate sensitivity. This sensitivity is not a general feature of strong postreplication repair-deficient mutants, because mutants with that phenotype from other loci do not exhibit sensitivity (mus(2)205A1, mus(3)302D1, mus(3)310D1). The observed lethality is not due to hypersensitivity of DNA synthesis in mei-41 larvae to hydroxyurea as assayed by tritiated thymidine incorporation. Lethality is, however, potentially attributable to an abnormal enhancement of chromosomal aberrations by hydroxyurea in mutant mei-41 larvae. Both in vivo and in vitro exposure of neuroblast cells to hydroxyurea results in an increase in 3 types of aberrations which is several fold higher in mei-41 tissue. Since hydroxyurea disrupts DNA synthesis, these results further implicate the mei-41 locus in DNA metabolism and provide an additional tool for an elucidation of its function. The possible existence of additional genes of this nature is suggested by a more modest sensitivity to hydroxyurea which has been detected in two stocks carrying mutagen-sensitive alleles of alternate genes.