Comparison of Somatic Reversions between the Ivory Allele and Transposon-Caused Mutant Alleles at the White Locus of DROSOPHILA MELANOGASTER after Larval Treatment with X Rays and Ethyl Methanesulfonate

Somatic reversion of strains with the ivory (wi) allele, a mutation associated with a tandem duplication of a DNA sequence at the white locus, increased with the age of larvae at the time of X-irradiation as expected from the increase in the number of target cells. In contrast, two independently isolated strains with unstable w+ loci associated with insertion of transposable elements showed higher reversion frequencies after treatment with X rays or ethyl methanesulfonate (EMS) at early larval stages than at late stages. Nevertheless, both the wi strain and the two unstable w+ strains reverted at nearly equal rates after treatment with X rays or EMS at early larval stages. Possible similarity in "hot spot" structure for the high reversibility of the two types of mutations is discussed in relation to production of presumed "mutator-type" cofactors specific to the transposon-caused mutations at early larval stages.     

Isolation and Characterization of Sex-Linked Female-Sterile Mutants in DROSOPHILA MELANOGASTER with Special Attention to Eggshell Mutants

To study genes that function mainly or exclusively during oogenesis, we have isolated and analyzed female-sterile mutations, with special emphasis on those that affect eggshell formation. Following treatment that induced 61 to 66% lethals, 8.1% of the 1071 X chromosomes tested carried recessive female sterility mutations (87 isolates), and 8.0% carried partial female-sterile mutations (86 isolates), respectively. In addition, three dominant female steriles were recovered. Some of the mutants had very low fecundity, and others laid morphologically normal eggs that failed to develop. A third category included 29 mutants that laid eggs with morphological abnormalities: 26 were female steriles, two were partial female steriles and one was fertile. Mutants of this third category were characterized in some detail and compared with 40 previously isolated mutants that laid similarly abnormal eggs. Approximately 28–31 complementation groups with morphological abnormalities were detected, some of which were large allelic series (11, 9, 7, 6 and 5 alleles). Twenty-four groups were mapped genetically or cytogenetically, and 21 were partially characterized by ultrastructural and biochemical procedures. Of the latter, one group showed clear deficiency of yolk proteins, and nine showed prominent ultrastructural defects in the chorion (at least eight accompanied by deficiencies in characterized chorion proteins). At least six groups with clear-cut effects were found at loci not previously identified with known chorion structural genes.     

Meiosis in Male DROSOPHILA MELANOGASTER I. Isolation and Characterization of Meiotic Mutants Affecting Second Chromosome Disjunction

Two second chromosome, EMS-induced, meiotic mutants which cause an increase in second chromosome nondisjunction are described. The first mutant is recessive and causes an increase in second chromosome nondisjunction in both males and females. It causes no increase in nondisjunction of the sex chromosomes in either sex, nor of the third chromosome in females. No haplo-4-progeny were recovered from either sex. Thus, it appears that this mutant, which is localized to the second chromosome, affects only second chromosome disjunction and acts in both sexes.-The other mutant affects chromosome disjunction in males and has no effect in females. Nondisjunction occurs at the first meiotic division. Sex chromosome disjunction in the presence of this mutant is similar to that of sc(4)sc(8), with an excess of X and nullo-XY sperm relative to Y and XY sperm. In some lines, there is an excess of nullo-2 sperm relative to diplo-2 sperm, which appears to be regulated, in part, by the Y chromosome. A normal Y chromosome causes an increase in nullo-2 sperm, where B(s)Y does not. There is also a high correlation between second and sex chromosome nondisjunction. Nearly half of the second chromosome exceptions are also nondisjunctional for the sex chromosomes. Among the double exceptions, there is an excess of XY nullo-2 and nullo-XY diplo-2 gametes. Meiotic drive, chromosome loss and nonhomologous pairing are considered as possible explanations for the double exceptions.     

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.     

A Genetic and Biochemical Analysis of the Temperature Sensitive, Normal-Winged Alleles of the Rudimentary Locus of DROSOPHILA MELANOGASTER

The genetic and biochemical characteristics of a particular class of mutants at the rudimentary locus are described. The mutants are pyrimidine auxotrophs, like classical rudimentary alleles, but they are unique in that they do not alter the size or shape of the wing (Falk and Nash 1974b). Aspartate transcarbamylase and dihydroorotase activities have been measured in seven different normal-winged mutants, and the results indicate that these strains are enzymologically "leaky" mutants. Previous studies have shown that three genetic functions (corresponding to the first three enzymes of pyrimidine synthesis) are associated with the rudimentary locus. Four of the seven mutants appear to affect all three of these functions. Each of the four is temperature sensitive, and a biochemical analysis of the temperature sensitivity of one of these mutants, (r)pyr1-3, suggests that a process affecting the synthesis or assembly of these enzymes is altered at high temperatures.     

Resolution of an Equivocal Genetic Element in DROSOPHILA MELANOGASTER: Organization of the Maroon-like Locus

Despite extensive prior study, an understanding of the genetic organization of the maroon-like locus (ma-l:1–64.8) has been elusive. A large-scale, three-point fine structure recombination experiment is described, whose results provide documentation for an inescapable argument that maroon-like is a single element rather than a polycistronic system.     

Spontaneous and Ethyl Methanesulfonate-Induced Mutations Controlling Viability in DROSOPHILA MELANOGASTER. I. Recessive Lethal Mutations

The efficiency of the adult feeding method for EMS treatment in Drosophila melanogaster was studied by measuring the frequency of induced recessive lethals on the second chromosome. The treatment was most effective when mature spermatozoa or spermatids were treated and was much less effective on earlier stages. The number of mutations induced was proportional to the concentration except at the highest doses. The recessive lethal rate was estimated to be about 0.012 per second chromosome per 10(-4) M. In addition, about 0.004-0.005 recessive lethals per 10(-4) M were found in a later generation in chromosomes that had not shown the lethal effect in the previous generation. When the experiments are done in a consistent manner and gametes treated as mature sperm or spermatids are sampled, the results are highly reproducible. However, modifications of the procedure, such as starvation before EMS treatment, can considerably alter the effectiveness of the mutagen.     

Quantitative Genetics of DROSOPHILA MELANOGASTER. I. Sexual Dimorphism in Genetic Parameters for Wing Traits

Sexual dimorphism in genetic parameters is examined for wing dimensions of Drosophila melanogaster. Data are fit to a quantitative genetic model where phenotypic variance is a linear function of additive genetic autosomal variance (common to both sexes), additive genetic X-linked variances distinct for each sex, variance due to common rearing environment of families, residual environmental variance, random error variance due to replication, and variance due to measurement error and developmental asymmetry (left vs. right sides). Polygenic dosage compensation and its effect on genetic variances and covariances between sexes is discussed. Variance estimates for wing length and other wing dimensions highly correlated with length support the hypothesis that the Drosophila system of dosage compensation will cause male X-linked genetic variance to be substantially larger than female X-linked variance. Results for various wing dimensions differ, suggesting that the level of dosage compensation may differ for different traits. Genetic correlations between sexes for the same trait are presented. Total additive genetic correlations are near unity for most wing traits; this indicates that selection in the same direction in both sexes would have a minor effect on changing the magnitude of difference between sexes. Additive X-linked correlations suggest some genotype x sex interactions for X-linked effects.     

UV and Ethyl Methanesulfonate Effects in Hyperthermophilic Archaea and Isolation of Auxotrophic Mutants of Pyrococcus Strains

The lethal and mutagenic effects of ethyl methanesulfonate (EMS) and UV on nine archaeal strains belonging to each of the two described genera of Thermococcales, Pyrococcus and Thermococcus, were investigated. To test the efficiency of the EMS and UV mutagenesis under a variety of experimental conditions, we chose Pyrococcus abyssi strain GE5 as a model strain. We observed a strong induced mutagenicity in both cases, since the spontaneous mutation frequency (expressed as the frequency of resistance to 5-fluoroorotic acid) increased up to 150-fold with EMS and 400-fold with UV, after mutagen exposure. Although a heterogeneous response to the induced effects caused after EMS and UV exposures was detected for all the other sulfothermophilic archaea tested, an efficient mutagenicity of Pyrococcus-like isolates GE27, GE23, and GE9 was observed. Optimal procedures described for UV mutagenesis yielded a number of useful uracil auxotrophic mutant strains of Pyrococcus abyssi. Received: 2 May 1996 / Accepted: 3 July 1996     

Fine-Structure Analysis and Genetic Organization at the Base of the X Chromosome in DROSOPHILA MELANOGASTER

Genetic organization at the base of the X chromosome was studied through the analysis of X-ray-induced deficiencies. Deficiencies were recovered so as to have a preselected right end "anchored" in the centric heterochromatin to the right of the su(f) locus. "Free" ends of deficiencies occurred at any of 22 intervals in Section 20 and in the proximal portion of Section 19 of Bridges' (1938) polytene chromosome map. The distribution of 130 such free ends of deficiencies induced in normal, In(1)sc ⁸, and In(1)w^m4 chromosomes suggests that on the single section level, genes are flanked by "hot" or "cold" sites for X-ray-induced breaks, and that occurrence of the hot spots is dependent on their interaction with the fixed-end sites in the centric heterochromatin. In the light of these results, it is argued that long heterochromatic sequences separate the relatively few genes in Section 20, and thus endow it with several characteristics typical of heterochromatic regions. Section 20 is considered to be a transition region between the mostly heterochromatic and mostly euchromatic regions of the X chromosome; the differences between them are suggested as being merely quantitative.     

Genetic and Developmental Analysis of the Locus vnd in DROSOPHILA MELANOGASTER

Genetic and developmental analysis of an X-linked vital locus vnd was undertaken. Embryos hemizygous for the original allele vnd did not hatch and exhibited a disorganized ventral nervous system (VNS). The mutation maps in the region 1B6-7 to 1B9-10, a subregion of an area previously shown to be essential to normal neural development. In this paper, we report isolation of five new alleles at the locus vnd. Genetic complementation analysis of all mutations at the vnd locus, with lethal alleles at adjacent loci, indicates that all lesions at the locus vnd affect only one vital gene function in the region. Four of the five alleles are embryonic lethal; one allele is subvital and behaves like an hypomorphic mutation. Hemizygous embryos for three of the four embryonic lethal alleles were inspected in histological sections; all exhibited disorganized VNS similar to the original allele. The developmental analysis in gynandromorphic genetic mosaics shows that (1) vnd+ gene function is not essential in most imaginal-disc cell derivatives, (2) only about 30% of the mosaic zygotes survive as adults, (3) mosaic zygotes with mutant tissue close to the head cuticle are least likely to survive, and (4) mutant tissue in the thoracic ganglion in the adult is not necessarily lethal. The mosaic data are consistent with the vnd+ gene function being necessary in neural cells derived from the anterioventral region of the blastoderm.     

The Relationship between the Functional Complexity and the Molecular Organization of the ANTENNAPEDIA Locus of DROSOPHILA MELANOGASTER

The Antp locus is involved in the development of the thorax of the larval and adult Drosophila. The absence of Antp+ function during embryogenesis results in the larval mesothorax exhibiting characteristics of the prothorax and an ensuing lethality; the loss of Antp+ function in the development of the adult thorax causes specific portions of the leg, wing and humeral imaginal discs to develop abnormally. Every Antp mutation, however, does not cause all of these developmental defects. Certain mutant alleles disrupt humeral and wing disc development without affecting leg development, and they are not deficient for the wild-type function required during embryogenesis. Other Antp mutations result in abnormal legs, but do not alter dorsal thoracic development. Mutations of each type can complement to produce a normal adult fly, which suggests that there are at least two discrete functional units within the locus. This hypothesis is supported by the fact that each of the developmental defects arises from the alteration of a different physical region within the Antp DNA. These observations indicate that the complete developmental role of the Antp locus is defined by the spatial and temporal regulation of the expression of several individual functional units.     

Regulation of Ribosomal RNA and 5s RNA Synthesis in DROSOPHILA MELANOGASTER: I. Bobbed Mutants

Analysis of the rates and amounts of rRNA and 5s RNA synthesized in Drosophila melanogaster bobbed mutants was done by using acrylamide-gel electrophoresis. The results show that the amounts of rRNA synthesized are constant, although the rates of rRNA synthesis in bb's are reduced to 30% of the wild-type level. The rates of synthesis of 5s RNA were constant. The rate of synthesis of the two kinds of molecules that enter in equimolar amounts into the mature ribosome is non-coordinated.-The rates of rRNA synthesis were shown to be proportional to the length of the scutellar bristles, supporting the notion that in trichogen cells there is no developmental delay, but the size of the bristle depends directly on the rate of rRNA synthesis.