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At least 1,135 records · Page 63Linked to original sources
PubMed1994

Modification of the Drosophila heterochromatic mutation brownDominant by linkage alterations.

The variegating mutation brownDominant (bwD) of Drosophila melanogaster is associated with an insertion of heterochromatin into chromosome arm 2R at 59E, the site of the bw gene. Mutagenesis produced 150 dominant suppressors of bwD variegation. These fall into two classes: unlinked suppressors, which also suppress other variegating mutations; and linked chromosome rearrangements, which suppress only bwD. Some rearrangements are broken at 59E, and so might directly interfere with variegation caused by the heterochromatic insertion at that site. However, most rearrangements are translocations broken proximal to bw within the 52D-57D region of 2R. Translocation breakpoints on the X chromosome are scattered throughout the X euchromatin, while those on chromosome 3 are confined to the tips. This suggests that a special property of the X chromosome suppresses bwD variegation, as does a distal autosomal location. Conversely, two enhancers of bwD are caused by translocations from the same part of 2R to proximal heterochromatin, bringing the bwD heterochromatic insertion close to the chromocenter with which it strongly associates. These results support the notion that heterochromatin formation at a genetic locus depends on its location within the nucleus.

Animals↗
PubMed1994

Mosaic suppressor, a gene in Drosophila that modifies retrotransposon expression and interacts with zeste.

A newly identified locus in Drosophila melanogaster, Mosaic suppressor (Msu), is described. This gene modifies the expression of white-apricot (wa), which is a copia retrotransposon-induced allele of the white gene. In addition to suppressing wa in a mosaic fashion, this mutation suppresses or enhances the expression of several other retrotransposon induced white alleles. Mutations in Msu alter copia transcript abundance and may regulate the expression of several other retrotransposons. While each of the two Msu isolates is homozygous lethal, heteroallelic escapers occur at a low frequency. These escapers act not only as strong suppressors of wa, but also as a recessive enhancer of synaptic-dependent gene expression at white. The mutation described here suggests a connection between the regulation of specific transcriptional units such as retrotransposons and more global synapsis dependent regulatory effects.

Alleles↗
PubMed1994

Effects of the maleless mutation on X and autosomal gene expression in Drosophila melanogaster.

The mutational effect of the maleless (mle) gene in Drosophila has been reexamined. Earlier work had suggested that mle along with other male-lethal genes was responsible for hypertranscription of the X chromosome in males to bring about dosage compensation. Prompted by studies on dosage sensitive regulatory genes, we tested for effects of mlets on the phenotypes of 16 X or autosomal mutations in adult escapers of lethality. In third instar larvae, prior to the major lethal phase of mle, we examined activities of 6 X or autosomally encoded enzymes, steady state mRNA levels of 15 X-linked or autosomal genes and transcripts from two large genomic segments derived from either the X or from chromosome 2 and present in yeast artificial chromosomes. In contrast to the previously hypothesized role, we detected pronounced effects of mle on the expression of both X-linked and autosomal loci such that a large proportion of the tested genes were increased in expression, while only two X-linked loci were reduced. The most prevalent consequence was an increase of autosomal gene expression, which can explain previously observed reduced X:autosome transcription ratios. These observations suggest that if mle plays a role in the discrimination of the X and the autosomes, it may do so by modification of the effects of dosage sensitive regulatory genes.

Animals↗
PubMed1994

The original pink-eyed dilution mutation (p) arose in Asiatic mice: implications for the H4 minor histocompatibility antigen, Myod1 regulation and the origin of inbred strains.

Allelic variation of the mouse pink-eyed dilution (p) gene in common laboratory strains and wild mice was examined by Southern blot and by polymerase chain reaction. In these assays the original p mutation allele found in strains SJL/J, 129/J, B10.129(21m), P/J and FS/Ei most closely matches an Asian Mus musculus allele, confirming anecdotal accounts of the Asian origin of this mutation. In contrast, the wild-type allele found in other common laboratory strains was apparently derived from Mus domesticus. Analysis of chromosome 7 loci both proximal and distal to the p locus demonstrates that strains SJL/J, 129/J, B10.129(21M), P/J and FS/Ei contain DNA segments of varying length derived from M. musculus. Strains 129/J and B10.129(21M) contain the largest segment of M. musculus-derived DNA (about 5 cM), including the loci Myod1, p, three clustered GABAA receptor subunit loci (Gabrg3, Gabra5 and Gabrb3), and Snrpn. The difference in the species origin of genes from this region of chromosome 7 may underlie the basis of the antigenicity of the minor histocompatibility antigen H4, defined by the strain B10.129(21M), and may account for the enhanced Myod1 activity observed in SJL/J mice.

Alleles↗
PubMed1995

Genotypic effects, maternal effects and grand-maternal effects of immobilized derivatives of the transposable element mariner.

The baseline rate of spontaneous integration of the autonomous mariner element Mos1 into the germline of Drosophila melanogaster is estimated as 16 +/- 5% (mean +/- SE) among fertile G0 flies. However, the transformation rate is reduced approximately 20-fold in Mos1 constructs with exogenous DNA in the size range 5-12 kb inserted into the SacI site. To provide alternative Mos1 helper plasmids for transformation experiments, two types of Mos1-promoter fusions were constructed: hsp-70:Mos1 and hsp26-Sgs3:Mos1. The former has the Mos1 coding region driven by the hsp70 heat-shock promoter; the latter has it driven by the basal Sgs3 promoter under the control of the hsp26 female-germline specific transcriptional regulator. When introduced into D. melanogaster by P-element-mediated germline transformation, these elements are unable to transpose or excise in the presence of autonomous Mos1-related elements (they are "marooned") because the 5' inverted repeat of Mos1 is missing. As expected, the hsp26-Sgs3:Mos1 fusions exhibit a significantly greater rate of germline excision of a target mariner element than do the hsp70:Mos1 fusions. Unexpectedly, the rate of excision of target mariner elements induced by hsp26-Sgs3:Mos1 is the same in the male germline as in the female germline. Both hsp:Mos1 fusions show strong germline expression and a maternal effect of the mariner transposase. A significant grand-maternal effect of the hsp:Mos1 fusions was also detected as a result of a maternal effect on the germline of the F1 progeny. Among flies carrying the promoter fusions inherited maternally, about three-quarters of the overall rate of germline excision derives from the direct genotypic effect and about one-quarter results from the grand-maternal effect. Despite the strong somatic expression of the hsp:Mos1 fusions, mariner transformants carrying a white+ reporter gene at the SacI site remained stable in the soma.

Animals↗
PubMed1995

Conservation of brown gene trans-inactivation in Drosophila.

The mechanism underlying trans-inactivation associated with dominant position effect variegation (PEV) of the Drosophila melanogaster brown gene has been addressed by a comparison with its D. virilis homologue. This comparison revealed: 86% identity between conceptual translation products of the brown gene from these two species, functional homology, as the D. virilis gene rescues a D. melanogaster null brown mutation, and conservation of the sequences required for trans-inactivation, as the D. virilis gene in D. melanogaster is subject to dominant PEV. An extended region of sequence similarity upstream of the open reading frame is observed. As the D. virilis homologue is functionally interchangeable with the D. melanogaster gene, these genes must share regulatory sequences as well as protein coding homology. These results support a model in which trans-inactivation is mediated by a heterochromatin-sensitive transcription factor.

ATP-Binding Cassette Transporters↗
PubMed1996

Differences in crossover frequency and distribution among three sibling species of Drosophila.

Comparisons of the genetic and cytogenetic maps of three sibling species of Drosophila reveal marked differences in the frequency and cumulative distribution of crossovers during meiosis. The maps for two of these species, Drosophila melanogaster and D. simulans, have previously been described, while this report presents new map data for D. mauritiana, obtained using a set of P element markers. A genetic map covering nearly the entire genome was constructed by estimating the recombination fraction for each pair of adjacent inserts. The P-based genetic map of mauritiana is approximately 1.8 times longer than the standard melanogaster map. It appears that mauritiana has higher recombination along the entire length of each chromosome, but the difference is greates in centromere-proximal regions of the autosomes. The mauritiana autosomes show little or no centromeric recombinational suppression, a characteristic that is prominent in melanogaster. D. simulans appears to be intermediate both in terms of total map length and intensity of the autosomal centromeric effect. These interspecific differences in recombination have important evolutionary implications for DNA sequence organization and variability. In particular, mauritiana is expected to differ from melanogaster in patterns and amounts of sequence variation and transposon insertions.

Animals↗
PubMed1997

A Polycomb and GAGA dependent silencer adjoins the Fab-7 boundary in the Drosophila bithorax complex.

The homeotic genes of the Drosophila bithorax complex are controlled by a large cis-regulatory region that ensures their segmentally restricted pattern of expression. A deletion that removes the Frontabdominal-7 cis-regulatory region (Fab-7') dominantly transforms parasegment 11 into parasegment 12. Previous studies suggested that removal of a domain boundary element on the proximal side of Fab-7' is responsible for this gain-of-function phenotype. In this article we demonstrate that the Fab-7' deletion also removes a silencer element, the iab-7 PRE, which maps to a different DNA segment and plays a different role in regulating parasegment-specific expression patterns of the Abd-B gene. The iab-7 PRE mediates pairing-sensitive silencing of mini-white, and can maintain the segmentally restricted expression pattern of a BXD, Ubx/lacZ reporter transgene. Both silencing activities depend upon Polycomb Group proteins. Pairing-sensitive silencing is relieved by removing the transvection protein Zeste, but is enhanced in a novel pairing-independent manner by the zeste' allele. The iab-7 PRE silencer is contained within a 0.8-kb fragment that spans a nuclease hypersensitive site, and silencing appears to depend on the chromatin remodeling protein, the GAGA factor.

Alleles↗
PubMed1997

Chromatin insulator elements block the silencing of a target gene by the Drosophila polycomb response element (PRE) but allow trans interactions between PREs on different chromosomes.

Polycomb response elements (PREs) can establish a silenced state that affects the expression of genes over considerable distances. We have tested the ability of insulator or boundary elements to block the repression of the miniwhite gene by the Ubx PRE. The gypsy element and the scs element interposed between PRE and miniwhite gene protect it against silencing but the scs' is only weakly effective. When the PRE-miniwhite gene construct is insulated from flanking chromosomal sequences by gypsy elements at both ends, it can still establish efficient silencing in some lines but not others. We show that this can be caused by interactions in trans with PREs at other sites. PRE-containing transposons inserted at different sites or even on different chromosomes can interact, resulting in enhanced silencing. These trans interactions are not blocked by the gypsy insulator and reveal the importance of nonhomologous associations between different regions of the genome for both silencing and activation of genes. The similarity between the behavior of PREs and enhancers suggests a model for their long-distance action.

Animals↗
PubMed1998

Dominant defects in Drosophila eye pigmentation resulting from a euchromatin-heterochromatin fusion gene.

We have isolated a dominant mutation, pugilistDominant (pugD), that causes variegated reductions in pteridine and ommochrome pigmentation of the Drosophila eye. The effect of pugD on pteridine pigmentation is most dramatic: the only remaining pigment consists of a thin ring of pigment around the periphery of the eye with a few scattered spots in the center. The pugD mutation disrupts a gene that encodes a Drosophila homolog of the trifunctional enzyme methylenetetrahydrofolate dehydrogenase (MTHFD; E.C.1.5.1.5, E.C.3.5. 4.9, E.C.6.3.4.3). This enzyme produces a cofactor that is utilized in purine biosynthesis. Because pteridines are derived from GTP, the pigment defect may result from an impairment in the production of purines. The mutant allele consists of a portion of the MTHFD coding region fused to approximately 1 kb of highly repetitive DNA. Transcription and translation of both parts are required for the phenotype. The repetitive DNA consists of approximately 140 nearly perfect repeats of the sequence AGAGAGA, a significant component of centric heterochromatin. The unusual nature of the protein produced by this gene may be responsible for its dominance. The repetitive DNA may also account for the variegated aspect of the phenotype. It may promote occasional association of the pugD locus with centric heterochromatin, accompanied by inactivation of pugD, in a manner similar to the proposed mode of action for brownDominant.

Animals↗
PubMed1999

Pairing-dependent mislocalization of a Drosophila brown gene reporter to a heterochromatic environment.

We describe the precise positioning of a reporter gene within heterochromatin where it may be silenced. A transposition of the 59E-60A region into pericentric heterochromatin ensnares distal 59E-60A via somatic pairing. The frequency with which a brown (bw) reporter gene in 59E is silenced is influenced by chromosomal configurations. Silencing occurs only when the bw+ reporter is unpaired due to heterozygosity with a deficiency, where the frequency of bw+ reporter expression is correlated with the extent of bw gene and flanking sequence present. Surprisingly, the frequency of pairing between the transposition in heterochromatin and distal 59E observed cytologically is indistinguishable from the frequency of pairing of homologous chromosomes at 59E in wild-type larval brains, regardless of configuration. Therefore, bringing a susceptible reporter gene into close proximity with heterochromatin does not necessarily affect its expression, but local pairing changes resulting from altered chromosomal configurations can lead to silencing. We also find that an ensnared distal copy of bw that is interrupted by a heterochromatic insertion enhances silencing. This demonstrates that bw can be simultaneously acted upon by pericentric and distal blocks of heterochromatin.

ATP-Binding Cassette Transporters↗
PubMed2001

Genomic organization and characterization of the white locus of the Mediterranean fruitfly, Ceratitis capitata.

An approximately 14-kb region of genomic DNA encoding the wild-type white eye (w+) color gene from the medfly, Ceratitis capitata has been cloned and characterized at the molecular level. Comparison of the intron-exon organization of this locus among several dipteran insects reveals distinct organizational patterns that are consistent with the phylogenetic relationships of these flies and the dendrogram of the predicted primary amino acid sequence of the white loci. An examination of w+ expression during medfly development has been carried out, displaying overall similarity to corresponding studies for white gene homologues in Drosophila melanogaster and other insects. Interestingly, we have detected two phenotypically neutral allelic forms of the locus that have arisen as the result of an apparently novel insertion or deletion event located in the large first intron of the medfly white locus. Cloning and sequencing of two mutant white alleles, w1 and w2, from the we,wp and M245 strains, respectively, indicate that the mutant conditions in these strains are the result of independent events--a frameshift mutation in exon 6 for w1 and a deletion including a large part of exon 2 in the case of w2.

Alleles↗
PubMed1976

Organization of the rosy locus in Drosophila melanogaster: evidence for a control element adjacent to the xanthine dehydrogenase structural element.

From a collection of electrophoretic variants of XDH obtained from laboratory strains and natural populations, a stock was isolated that was associated with much greater than normal levels of XDH activity. Preliminary recombination experiments demonstrated that this character maps to the rosy locus. While a series of observations failed to relate this phenotype to alteration in the structure of the XDH polypeptide, kinetic and immunological experiments did succeed in associating this character with variation in number of molecules of XDH/fly. Large scale fine structure recombination experiments locate the genetic basis for this variation in number of molecules of XDH/fly to a site very close to, but definitely outside of, the genetic boundaries of the XDH structural information. Observations are described which eliminate the possibility that we are dealing with a tandem duplication of the XDH structural element. Turning to a regulatory role for this genetic element located adjacent to the XDH structural information, a simple experiment is described which demonstrates that it functions as a "cis-acting" regulator of the XDH structural element.

Animals↗
PubMed1979

Analysis of the albino-locus region of the mouse. III. Time of death of prenatal lethals.

The stage at which homozygotes die was determined for 28 mutations (general symbol c*) at the albino (c) locus, of which 26 had earlier been found to be probably prenatally lethal. Within each of the mutant stocks, the uterine contents of c*/c(ch) females, made pregnant either by c*/c(ch) males ("Ex" series) or by c(ch)/c(ch) males ("Co" series), were examined between 13 and 17 days postconception. Altogether, 743 females were dissected and 7197 corpora lutea (representing ovulations) counted. In selected stocks, an additional 40 and 13 females were dissected on days seven or nine, respectively.-In each of the 26 presumed prenatally lethal mutants, there was a deficiency of living fetuses in the Ex, as compared with the Co, group. Overall, this deficiency was 23.6% (expectation, 25% c*/c*). All meaningful excesses were in numbers either of moles (death shortly before, during, or just after implantation), or of early preimplantation losses. Homozygotes in none of the mutant stocks die between days nine and 19 postconception. Of 24 c-locus mutants known to be deficiencies since they lack the closely linked Mod-2, 13 clearly kill before implantation, ten around implantation, and one neonatally. The c and Mod-2 loci and the region between them are not needed for intrauterine survival.-There are indications that the distinction between early-preimplantation death and implantation death may, in a general way, be related to length of the deficiency.

Animals↗
PubMed1979

Spontaneous unequal exchange in the rosy region of Drosophila melanogaster.

A selective system for recovery of exchanges between trans mutations at adjacent loci, l(3)S12 and rosy, is described. In addition to the expected crossover and conversion classes, two exceptional types of offspring were recovered. Triploid offspring arose as 0.01% of all zygotes; the diploid chromosome set was apparently of maternal origin. Nine tandem duplications derived from unequal exchange between nonsister homologues were recovered among 2.25 x 10(6) zygotes screened. From considerations of the proportion of the genome that was assayed in this system, and on the assumption that the rate of unequal exchange observed is typical for the genome as a whole, it appears that one unequal exchange occurs per 500 female meioses in Drosophila.

Animals↗
PubMed1980

The influence of sexual and larval selection on the maintenance of polymorphism at the sepia locus in Drosophila melanogaster.

Sexual selection is measured between two strains of Drosophila melanogaster: a wild strain and a strain mutant at the sepia locus. Frequency-dependent male mating was found to successful, whereas the female genotype exerted no influence. The rarer the male genotype becomes, the greater is its mating success. A selection model is build for this behavior characteristic in which selection operates differently in the two sexes. The genetic consequencies of this odel upon the maintenance of genetic polymorphism at the sepia locus are compared to experimental data from previous population cage studies. The fit obtained with this sexual selection model is compared to that of the larval selection model previously investigated. A model composed of both sexual and larval components of fitness is presented. The role that each major selection component is expected to play in experimental populations as the gene frequency changes is discussed. Sexual selection leads to an equilibrium level higher than larval selection, and the combined model is very close to the experimental values.

Animals↗
PubMed1994

Cloning of MITF, the human homolog of the mouse microphthalmia gene and assignment to chromosome 3p14.1-p12.3.

The mouse microphthalmia (mi) gene encodes a basic-helix-loop-helix-zipper protein whose mutations may lead to loss of pigmentation in the eye, inner ear and skin, and to reduced eye size and early onset deafness. Mice with mutations at mi serve as models for human pigment disturbances in skin and eye that may be combined with sensorineural deafness. We have now obtained cDNA and genomic clones of the human homolog of mouse mi, identified a restriction fragment length polymorphism in the gene, and mapped the gene by somatic cell hybrid and fluorescence in situ hybridization techniques to a region of human chromosome 3 that shows a disrupted syntenic conservation with the region on mouse chromosome 6 to which mi maps. These studies will help to verify if any of the hereditary pigment disturbances in humans are due to mutations in this gene.

Amino Acid Sequence↗