scholarly journals Live Analysis of Position Effect Variegation Reveals Different Modes of Action for HP1 and Su(var)3-9

2021 ◽  
Author(s):  
Keith Andrew Maggert ◽  
Farah J Bughio
Keyword(s):  
Gene Silencing ◽  
Developmental Trajectories ◽  
Position Effect ◽  
Epigenetic Inheritance ◽  
S Phase ◽  
Position Effect Variegation ◽  
Cell Clones ◽  
Effect Variegation ◽  
Random Patterns ◽  
Eukaryotic Genomes

Position Effect Variegation (PEV) results from the juxtaposition of euchromatic and heterochromatic components of eukaryotic genomes, silencing genes near the new euchromatin/heterochromatin junctions. The degree of silencing is itself heritable through S-phase, giving rise to distinctive random patterns of cell clones expressing the genes intermixed with clones in which the genes are silenced. Much of what we know about epigenetic inheritance in the soma stems from work on PEV aimed at identifying the components of the silencing machinery and its mechanism of inheritance. Despite identifying two central gene activities - the Su(var)3-9 histone H3-Lysine-9 methyltransferase and the Su(var)205/HP1 methyl-H3-Lysine-9 binding protein - their role in PEV has been inferred from terminal phenotypes, leaving considerable gaps in understanding how PEV behaves through development. Here, we investigate the phenotypes of Su(var)3-9 and Su(var)205/HP1 mutations in live developing tissues. We discovered that mutations in Su(var)205/HP1 compromise the initial establishment of PEV in early embryogenesis. Later gains of heterochromatin-induced gene silencing are possible, but are unstable and lost rapidly. In contrast, mutations in Su(var)3-9 exhibit robust silencing early in development, but fail to maintain it through subsequent cell divisions. Our analyses show that while the terminal phenotypes of these mutations may appear identical, they have arrived at them through different developmental trajectories. We discuss how our findings further challenge existing models for epigenetic inheritance of heterochromatin-induced gene silencing.

scholarly journals Replication of Heterochromatin and Structure of Polytene Chromosomes

2000 ◽  
Vol 20 (17) ◽  
pp. 6308-6316 ◽  
Author(s):  
Thomas J. Leach ◽  
Heather L. Chotkowski ◽  
Michael G. Wotring ◽  
Robert L. Dilwith ◽  
Robert L. Glaser
Keyword(s):  
Temporal Pattern ◽  
Position Effect ◽  
Polytene Chromosomes ◽  
S Phase ◽  
Parental Origin ◽  
Position Effect Variegation ◽  
Replication Forks ◽  
Satellite Sequences ◽  
Effect Variegation ◽  
Diploid Cells

ABSTRACT Heterochromatin is characteristically the last portion of the genome to be replicated. In polytene cells, heterochromatic sequences are underreplicated because S phase ends before replication of heterochromatin is completed. Truncated heterochromatic DNAs have been identified in polytene cells of Drosophila and may be the discontinuous molecules that form between fully replicated euchromatic and underreplicated heterochromatic regions of the chromosome. In this report, we characterize the temporal pattern of heterochromatic DNA truncation during development of polytene cells. Underreplication occurred during the first polytene S phase, yet DNA truncation, which was found within heterochromatic sequences of all fourDrosophila chromosomes, did not occur until the second polytene S phase. DNA truncation was correlated with underreplication, since increasing the replication of satellite sequences with thecycE 1672 mutation caused decreased production of truncated DNAs. Finally, truncation of heterochromatic DNAs was neither quantitatively nor qualitatively affected by modifiers of position effect variegation including the Y chromosome,Su(var)2052 , parental origin, or temperature. We propose that heterochromatic satellite sequences present a barrier to DNA replication and that replication forks that transiently stall at such barriers in late S phase of diploid cells are left unresolved in the shortened S phase of polytene cells. DNA truncation then occurs in the second polytene S phase, when new replication forks extend to the position of forks left unresolved in the first polytene S phase.

Different patterns of gene silencing in position-effect variegation

Genome ◽  
2003 ◽  
Vol 46 (6) ◽  
pp. 1104-1117 ◽  
Author(s):  
Vett K Lloyd ◽  
David Dyment ◽  
Donald A.R Sinclair ◽  
Thomas A Grigliatti
Keyword(s):  
Gene Silencing ◽  
Position Effect ◽  
Early Period ◽  
Cellular Level ◽  
Position Effect Variegation ◽  
Small Spot ◽  
Number Of Genes ◽  
Effect Variegation ◽  
Peak Sensitivity ◽  
Phenotypic Instability

Position-effect variegation (PEV) results when a fully functional gene is moved from its normal position to a position near to a broken heterochromatic-euchromatic boundary. In this new position, the gene, while remaining unaltered at the DNA level, is transcriptionally silenced in some cells but active in others, producing a diagnostic mosaic phenotype. Many variegating stocks show phenotypic instability, in that the level of variegation is dramatically different in different isolates or when out crossed. To test if this phenotypic instability was due to segregation of spontaneously accumulated mutations that suppress variegation, four different and well-characterized strains showing PEV for the white+ gene (wm4, wmMc, wm51b, and wmJ) and representing both large and small spot variegators were repeatedly out crossed to a strain free of modifiers, and the phenotypes of these variegators were monitored for 30 generations. Once free of modifiers, these variegating strains were then allowed to reaccumulate modifiers. The spontaneous suppressors of variegation were found to include both dominant and recessive, autosomal and X-linked alleles selected to reduce the detrimental effects of silencing white+ and adjacent genes. The time of peak sensitivity to temperature during development was also determined for these four variegators. Although large and small spot variegators have previously been attributed to early and late silencing events, respectively, the variegators we examined all shared a common early period of peak sensitivity to temperature. Once free of their variegation suppressors, the different variegating strains showed considerable differences in the frequency of inactivation at a cellular level (the number of cells showing silencing of a given gene) and the extent of variegation within the cell (the number of silenced genes). These results suggest that large and small spot variegation may be a superficial consequence of spontaneous variegation suppressors. The nature and number of these spontaneous variegation suppressors depends on the number of genes silenced in a given variegating rearrangement. These results are interpreted in the context of a model that proposes that the different underlying patterns of gene silencing seen in PEV can be attributed directly to the formation of heterochromatin domains possessing different properties of propagation during cell division.Key words: Drosophila melanogaster, position-effect variegation, spontaneous suppressors of variegation.

scholarly journals Position effect variegation in Drosophila melanogaster: relationship between suppression effect and the amount of Y chromosome.

Genetics ◽  
1989 ◽  
Vol 122 (4) ◽  
pp. 793-800 ◽  
Author(s):  
P Dimitri ◽  
C Pisano
Keyword(s):  
Drosophila Melanogaster ◽  
Y Chromosome ◽  
Position Effect ◽  
Chromosome Rearrangements ◽  
Position Effect Variegation ◽  
Position Effects ◽  
Suppression Effect ◽  
Genetic Nature ◽  
Cell Clones ◽  
Effect Variegation

Abstract Position effect variegation results from chromosome rearrangements which translocate euchromatic genes close to the heterochromatin. The euchromatin-heterochromatin association is responsible for the inactivation of these genes in some cell clones. In Drosophila melanogaster the Y chromosome, which is entirely heterochromatic, is known to suppress variegation of euchromatic genes. In the present work we have investigated the genetic nature of the variegation suppressing property of the D. melanogaster Y chromosome. We have determined the extent to which different cytologically characterized Y chromosome deficiencies and Y fragments suppress three V-type position effects: the Y-suppressed lethality, the white mottled and the brown dominant variegated phenotypes. We find that: (1) chromosomes which are cytologically different and yet retain similar amounts of heterochromatin are equally effective suppressors, and (2) suppression effect is positively related to the size of the Y chromosome deficiencies and fragments that we tested. It increases with increasing amounts of Y heterochromatin up to 60-80% of the entire Y, after which the effect reaches a plateau. These findings suggest suppression is a function of the amount of Y heterochromatin present in the genome and is not attributable to any discrete Y region.

scholarly journals Microwave influence on the position effect variegation in Drosophila melanogaster Meig.

2018 ◽  
Vol 23 ◽  
pp. 363-368
Author(s):  
L. D. Dyka ◽  
V. Yu. Strashnyuk
Keyword(s):  
Drosophila Melanogaster ◽  
Microwave Irradiation ◽  
Gene Silencing ◽  
Power Density ◽  
Position Effect ◽  
Pericentric Heterochromatin ◽  
Position Effect Variegation ◽  
Irradiation Intensity ◽  
Genetic Inactivation ◽  
Effect Variegation

Aim. The purpose of investigation was to study the effect of microwave irradiation of different intensity on the manifestation of the position effect variegation (PEV) in Drosophila melanogaster Meig. Methods. Experiments were carried out on mutant strain In(1)wm4, y. Microwave radiation with frequency 36.64 GHz and power density 0.01; 0.1 and 1 W/m2, was used. Exposure to microwaves was applied in early embryogenesis after 2-hour oviposition. Exposure time was 30 sec. PEV was examined in the irradiated and non-irradiated (control) flies. Results. In females, microwave irradiation at a power density of 1 W/m2 led to an enhance in the inactivation of the white+ gene transferred into a vicinity of pericentric heterochromatin in the X-chromosome. No effect was detected by irradiation intensity of 0.01 and 0.1 W/m2. In males, there was a suppression of genetic inactivation at a power density of 0.01 W/m2. Conclusions. Microwave irradiation can affect the size of heterochromatin blocks that cause gene silencing in PEV. The effect depends on the sex and intensity of the radiation. Keywords: Drosophila melanogaster Meig., position effect variegation, heterochromatin, gene silencing, non-ionising radiation.

scholarly journals Copy Number and Orientation Determine the Susceptibility of a Gene to Silencing by Nearby Heterochromatin in Drosophila

Genetics ◽  
1996 ◽  
Vol 142 (2) ◽  
pp. 447-458 ◽  
Author(s):  
Joy F Sabl ◽  
Steven Henikoff
Keyword(s):  
Gene Silencing ◽  
Copy Number ◽  
Chromosomal Rearrangement ◽  
Alternative Explanation ◽  
Position Effect ◽  
Phenotypic Selection ◽  
Position Effect Variegation ◽  
Transgene Copy Number ◽  
Mosaic Expression ◽  
Effect Variegation

Abstract The classical phenomenon of position-effect variegation (PEV) is the mosaic expression that occurs when a chromosomal rearrangement moves a euchromatic gene near heterochromatin. A striking feature of this phenomenon is that genes far away from the junction with heterochromatin can be affected, as if the heterochromatic state “spreads.” We have investigated classical PEV of a Drosophila brown transgene affected by a heterochromatic junction ~60 kb away. PEV was enhanced when the transgene was locally duplicated using P transposase. Successive rounds of P transposase mutagenesis and phenotypic selection produced a series of PEV alleles with differences in phenotype that depended on transgene copy number and orientation. As for other examples of classical PEV, nearby heterochromatin was required for gene silencing. Modifications of classical PEV by alterations at a single site are unexpected, and these observations contradict models for spreading that invoke propagation of heterochromatin along the chromosome. Rather, our results support a model in which local alterations affect the affinity of a gene region for nearby heterochromatin via homology-based pairing, suggesting an alternative explanation for this 65-year-old phenomenon.

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

Genetics ◽  
2000 ◽  
Vol 154 (2) ◽  
pp. 657-668 ◽  
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.

pitkinD, a Novel Gain-of-Function Enhancer of Position-Effect Variegation, Affects Chromatin Regulation During Oogenesis and Early Embryogenesis in Drosophila

Genetics ◽  
2001 ◽  
Vol 157 (3) ◽  
pp. 1227-1244 ◽  
Author(s):  
Steffi Kuhfittig ◽  
János Szabad ◽  
Gunnar Schotta ◽  
Jan Hoffmann ◽  
Endre Máthé ◽  
...  
Keyword(s):  
Germ Line ◽  
Position Effect ◽  
Early Embryogenesis ◽  
Position Effect Variegation ◽  
Chromatin Regulation ◽  
Gain Of Function ◽  
Position Effects ◽  
Dominant Female ◽  
Effect Variegation ◽  
Female Germ Line

Abstract The vast majority of the >100 modifier genes of position-effect variegation (PEV) in Drosophila have been identified genetically as haplo-insufficient loci. Here, we describe pitkinDominant (ptnD), a gain-of-function enhancer mutation of PEV. Its exceptionally strong enhancer effect is evident as elevated spreading of heterochromatin-induced gene silencing along euchromatic regions in variegating rearrangements. The ptnD mutation causes ectopic binding of the SU(VAR)3-9 heterochromatin protein at many euchromatic sites and, unlike other modifiers of PEV, it also affects stable position effects. Specifically, it induces silencing of white+ transgenes inserted at a wide variety of euchromatic sites. ptnD is associated with dominant female sterility. +/+ embryos produced by ptnD/+ females mated with wild-type males die at the end of embryogenesis, whereas the ptnD/+ sibling embryos arrest development at cleavage cycle 1-3, due to a combined effect of maternally provided mutant product and an early zygotic lethal effect of ptnD. This is the earliest zygotic effect of a mutation so far reported in Drosophila. Germ-line mosaics show that ptn+ function is required for normal development in the female germ line. These results, together with effects on PEV and white+ transgenes, are consistent with the hypothesis that the ptn gene plays an important role in chromatin regulation during development of the female germ line and in early embryogenesis.

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