The effect of modifiers of position-effect variegation on the variegation of heterochromatic genes of Drosophila melanogaster.

Abstract Dominant modifiers of position-effect variegation of Drosophila melanogaster were tested for their effects on the variegation of genes normally located in heterochromatin. These modifiers were previously isolated as strong suppressors of the variegation of euchromatic genes and have been postulated to encode structural components of heterochromatin or other products that influence chromosome condensation. While eight of the modifiers had weak or no detectable effects, six acted as enhancers of light (lt) variegation. The two modifiers with the strongest effects on lt were shown to also enhance the variegation of neighboring heterochromatic genes. These results suggest that the wild-type gene products of some modifiers of position-effect variegation are required for proper expression of genes normally located within or near the heterochromatin of chromosome 2. We conclude that these heterochromatic genes have fundamentally different regulatory requirements compared to those typical of euchromatic genes.

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Cis-effects of heterochromatin on heterochromatic and euchromatic gene activity in Drosophila melanogaster.

Genetics ◽

10.1093/genetics/140.3.1033 ◽

1995 ◽

Vol 140 (3) ◽

pp. 1033-1045

Author(s):

M Howe ◽

P Dimitri ◽

M Berloco ◽

B T Wakimoto

Keyword(s):

Chromosomal Rearrangements ◽

Position Effect ◽

Position Effect Variegation ◽

Regulatory Requirements ◽

Molecular Studies ◽

Effect Variegation ◽

Novel Method ◽

In Cis ◽

Derivatives Of ◽

Heterochromatic Genes

Abstract Chromosomal rearrangements that juxtapose heterochromatin and euchromatin can result in mosaic inactivation of heterochromatic and euchromatic genes. This phenomenon, position effect variegation (PEV), suggests that heterochromatic and euchromatic genes differ in their regulatory requirements. This report describes a novel method for mapping regions required for heterochromatic genes, and those that induce PEV of a euchromatic gene. P transposase mutagenesis was used to generate derivatives of a translocation that variegated for the light+ (lt+) gene and carried the euchromatic white+ (w+) gene on a transposon near the heterochromatin-euchromatin junction. Cytogenetic and genetic analyses of the derivatives showed that P mutagenesis resulted in deletions of several megabases of heterochromatin. Genetic and molecular studies showed that the derivatives shared a euchromatic breakpoint but differed in their heterochromatic breakpoint and their effects on seven heterochromatic genes and the w+ gene. Heterochromatic genes differed in their response to deletions. The lt+ gene was sensitive to the amount of heterochromatin at the breakpoint but the heterochromatic 40Fa gene was not. The severity of variegated w+ phenotype did not depend on the amount of heterochromatin in cis, but varied with local heterochromatic environment. These data are relevant for considering mechanisms of PEV of both heterochromatic and euchromatic genes.

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Suppressors of position-effect variegation in Drosophila melanogaster affect expression of the heterochromatic gene light in the absence of a chromosome rearrangement

Genome ◽

10.1139/g98-041 ◽

1998 ◽

Vol 41 (4) ◽

pp. 495-503 ◽

Cited By ~ 20

Author(s):

N J Clegg ◽

B M Honda ◽

I P Whitehead ◽

T A Grigliatti ◽

B Wakimoto ◽

...

Keyword(s):

Drosophila Melanogaster ◽

Chromosomal Rearrangements ◽

Position Effect ◽

Centromeric Heterochromatin ◽

Position Effect Variegation ◽

Gene Products ◽

Affect Expression ◽

Effect Variegation ◽

Heterochromatic Genes ◽

Var Gene

Suppressors of position-effect variegation (Su(var)s) in Drosophila melanogaster are usually studied in the presence of chromosomal rearrangements, which exhibit variegated expression of euchromatic genes moved near to, or heterochromatic genes moved away from, centromeric heterochromatin. However, the effects of Su(var) mutations on heterochromatic gene expression in the absence of a variegating re-arrangement have not yet been defined. Here we present a number of results which suggest that Su(var) gene products can interact to affect the expression of the light gene in its normal heterochromatic location. We initially observed that eye pigment was reduced in several Su(var) double mutants; the phenotype resembled that of light mutations and was more severe when only one copy of the light gene was present. This reduced pigmentation could be alleviated by a duplication for the light gene or by a reduction in the amount of cellular heterochromatin. In addition, the viability of most Su(var) double mutant combinations tested was greatly reduced in a genetic background of reduced light gene dosage, when extra heterochromatin is present. We conclude that Su(var) gene products can affect expression of the heterochromatic light gene in the absence of any chromosomal rearrangements. However, it is noteworthy that mutations in any single Su(var) gene have little effect on light expression; we observe instead that different pairings of Su(var) mutations are required to show an effect on light expression. Interestingly, we have obtained evidence that at least two of the second chromosome Su(var) mutations are gain-of-function lesions, which also suggests that there may be different modes of interaction among these genes. It may therefore be possible to use this more sensitive assay of Su(var) effects on heterochromatic genes to infer functional relationships among the products of the 50 or more known Su(var) loci.Key words: heterochromatin, chromatin, gene interactions.

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The role of heterochromatin in the expression of a heterochromatic gene, the rolled locus of Drosophila melanogaster.

Genetics ◽

10.1093/genetics/134.1.277 ◽

1993 ◽

Vol 134 (1) ◽

pp. 277-292 ◽

Cited By ~ 8

Author(s):

D F Eberl ◽

B J Duyf ◽

A J Hilliker

Keyword(s):

Drosophila Melanogaster ◽

Chromosomal Rearrangements ◽

Position Effect ◽

Centromeric Heterochromatin ◽

Position Effect Variegation ◽

Position Effects ◽

Major Function ◽

Effect Variegation ◽

Heterochromatic Genes

Abstract Constitutive heterochromatic regions of chromosomes are those that remain condensed through most or all of the cell cycle. In Drosophila melanogaster, the constitutive heterochromatic regions, located around the centromere, contain a number of gene loci, but at a much lower density than euchromatin. In the autosomal heterochromatin, the gene loci appear to be unique sequence genes interspersed among blocks of highly repeated sequences. Euchromatic genes do not function well when brought into the vicinity of heterochromatin (position-effect variegation). We test the possibility that the blocks of centromeric heterochromatin provide an environment essential for heterochromatic gene function. To assay directly the functional requirement of autosomal heterochromatic genes to reside in heterochromatin, the rolled (rl) gene, which is normally located deep in chromosome 2R heterochromatin, was relocated within small blocks of heterochromatin to a variety of euchromatic positions by successive series of chromosomal rearrangements. The function of the rl gene is severely affected in rearrangements in which the rl gene is isolated in a small block of heterochromatin, and these position effects can be reverted by rearrangements which bring the rl gene closer to any large block of autosomal or X chromosome heterochromatin. There is some evidence that five other 2R heterochromatic genes are also affected among these rearrangements. These findings demonstrate that the heterochromatic genes, in contrast to euchromatic genes whose function is inhibited by relocation to heterochromatin, require proximity to heterochromatin to function properly, and they argue strongly that a major function of the highly repeated satellite DNA, which comprises most of the heterochromatin, is to provide this heterochromatic environment.

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HISTONE GENE MULTIPLICITY AND POSITION EFFECT VARIEGATION IN DROSOPHILA MELANOGASTER

Genetics ◽

10.1093/genetics/105.2.327 ◽

1983 ◽

Vol 105 (2) ◽

pp. 327-344

Author(s):

Gerald D Moore ◽

Donald A Sinclair ◽

Thomas A Grigliatti

Keyword(s):

Drosophila Melanogaster ◽

Sex Chromosome ◽

Current Knowledge ◽

Position Effect ◽

Histone Gene ◽

Position Effect Variegation ◽

Chromosome 2 ◽

Gene Complex ◽

Position Effects ◽

Effect Variegation

ABSTRACT The histone genes of wild-type Drosophila melanogaster are reiterated 100–150 times per haploid genome and are located in the segment of chromosome 2 that corresponds to polytene bands 39D2-3 to E1-2. The influence of altered histone gene multiplicity on chromatin structure has been assayed by measuring modification of the gene inactivation associated with position effect variegation in genotypes bearing deletions of the 39D-E segment. The proportion of cells in which a variegating gene is active is increased in genotypes that are heterozygous for a deficiency that removes the histone gene complex. Deletions that remove segments adjacent to the histone gene complex have no effect on the expression of variegating genes. Suppression of position effect variegation associated with reduction of histone gene multiplicity applies to both X-linked and autosomal variegating genes. Position effects exerted by both autosomal and sex-chromosome heterochromatin were suppressible by deletions of the histone gene complex. The suppression was independent of the presence of the Y chromosome. A deficiency that deletes only the distal portion of the histone gene complex also has the ability to suppress position effect variegation. Duplication of the histone gene complex did not enhance position effect variegation. Deletion or duplication of the histone gene complex in the maternal genome had no effect on the extent of variegation in progeny whose histone gene multiplicity was normal. These results are discussed with respect to current knowledge of the organization of the histone gene complex and control of its expression.

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Mutational Analysis of a Histone Deacetylase in Drosophila melanogaster: Missense Mutations Suppress Gene Silencing Associated With Position Effect Variegation

Genetics ◽

10.1093/genetics/154.2.657 ◽

2000 ◽

Vol 154 (2) ◽

pp. 657-668 ◽

Cited By ~ 2

Author(s):

Randy Mottus ◽

Richard E Sobel ◽

Thomas A Grigliatti

Keyword(s):

Drosophila Melanogaster ◽

Histone Deacetylase ◽

Transcriptional Activity ◽

Mutational Analysis ◽

Position Effect ◽

Transcriptional Regulator ◽

Position Effect Variegation ◽

Missense Mutations ◽

Effect Variegation ◽

New Mutations

Abstract For many years it has been noted that there is a correlation between acetylation of histones and an increase in transcriptional activity. One prediction, based on this correlation, is that hypomorphic or null mutations in histone deacetylase genes should lead to increased levels of histone acetylation and result in increased levels of transcription. It was therefore surprising when it was reported, in both yeast and fruit flies, that mutations that reduced or eliminated a histone deacetylase resulted in transcriptional silencing of genes subject to telomeric and heterochromatic position effect variegation (PEV). Here we report the first mutational analysis of a histone deacetylase in a multicellular eukaryote by examining six new mutations in HDAC1 of Drosophila melanogaster. We observed a suite of phenotypes accompanying the mutations consistent with the notion that HDAC1 acts as a global transcriptional regulator. However, in contrast to recent findings, here we report that specific missense mutations in the structural gene of HDAC1 suppress the silencing of genes subject to PEV. We propose that the missense mutations reported here are acting as antimorphic mutations that “poison” the deacetylase complex and propose a model that accounts for the various phenotypes associated with lesions in the deacetylase locus.

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Recombinogenic Effects of Suppressors of Position-Effect Variegation in Drosophila

Genetics ◽

10.1093/genetics/160.2.609 ◽

2002 ◽

Vol 160 (2) ◽

pp. 609-621

Author(s):

Thomas Westphal ◽

Gunter Reuter

Keyword(s):

Chromatin Structure ◽

Position Effect ◽

Heterochromatic Region ◽

Crossing Over ◽

Position Effect Variegation ◽

Chromosome 2 ◽

Additive Effects ◽

Suppressor Mutations ◽

Effect Variegation ◽

Meiotic Nondisjunction

Abstract Compact chromatin structure, induction of gene silencing in position-effect variegation (PEV), and crossing-over suppression are typical features of heterochromatin. To identify genes affecting crossing-over suppression by heterochromatin we tested PEV suppressor mutations for their effects on crossing over in pericentromeric regions of Drosophila autosomes. From the 46 mutations (28 loci) studied, 16 Su(var) mutations of the nine genes Su(var)2-1, Su(var)2-2, Su(var)2-5, Su(var)2-10, Su(var)2-14, Su(var) 2-15, Su(var)3-3, Su(var)3-7, and Su(var)3-9 significantly increase in heterozygotes or by additive effects in double and triple heterozygotes crossing over in the ri-pp region of chromosome 3. Su(var)2-201 and Su(var) 2-1401 display the strongest recombinogenic effects and were also shown to enhance recombination within the light-rolled heterochromatic region of chromosome 2. The dominant recombinogenic effects of Su(var) mutations are most pronounced in proximal euchromatin and are accompanied with significant reduction of meiotic nondisjunction. Our data suggest that crossing-over suppression by heterochromatin is controlled at chromatin structure as well as illustrate the possible effects of heterochromatin on total crossing-over frequencies in the genome.

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Competition Between Different Variegating Rearrangements for Limited Heterochromatic Factors in Drosophila melanogaster

Genetics ◽

10.1093/genetics/145.4.945 ◽

1997 ◽

Vol 145 (4) ◽

pp. 945-959

Author(s):

Vett K Lloyd ◽

Donald A Sinclair ◽

Thomas A Grigliatti

Keyword(s):

Drosophila Melanogaster ◽

Chromosome Rearrangement ◽

Position Effect ◽

Position Effect Variegation ◽

Euchromatic Region ◽

Single Chromosome ◽

Mosaic Expression ◽

Effect Variegation ◽

Protein Components

Position effect variegation (PEV) results from the juxtaposition of a euchromatic gene to heterochromatin. In its new position the gene is inactivated in some cells and not in others. This mosaic expression is consistent with variability in the spread of heterochromatin from cell to cell. As many components of heterochromatin are likely to be produced in limited amounts, the spread of heterochromatin into a normally euchromatic region should be accompanied by a concomitant loss or redistribution of the protein components from other heterochromatic regions. We have shown that this is the case by simultaneously monitoring variegation of a euchromatic and a heterochromatic gene associated with a single chromosome rearrangement. Secondly, if several heterochromatic regions of the genome share limited components of heterochromatin, then some variegating rearrangements should compete for these components. We have examined this hypothesis by testing flies with combinations of two or more different variegating rearrangements. Of the nine combinations of pairs of variegating rearrangements we studied, seven showed nonreciprocal interactions. These results imply that many components of heterochromatin are both shared and present in limited amounts and that they can transfer between chromosomal sites. Consequently, even nonvariegation portions of the genome will be disrupted by re-allocation of heterochromatic proteins associated with PEV. These results have implications for models of PEV.

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