Function of Insulators
Answer the questions below in an APA-style paper that is 1-3 pages in length (about 750 to 1000 words) about the Function of Insulators
1. Give a basic description of the process. Please include at least one figure/diagram/flowchart of your own design.
2. What is the purpose of the process? What function/benefit can it provide?
4. Are there any key individuals identified in the original research that lead to the current accepted theories/model describing this process?
5. Choose three research articles (from after 2017) that focus on the process. Explain the importance of results/analysis in each paper that led to a greater understanding of this process. What important fact(s)/idea(s) did the paper/research reveal?
6. List all of your references in a Bibliography, using proper in-text citations throughout your answer.
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 1/22
Published: 06 April 2005
Insulators are fundamental components of the eukaryotic
genomes
E Brasset & C Vaury
Heredity 94,571576(2005)
629 Accesses 47 Citations 3 Altmetric Metrics
Abstract
The properties of cis-regulatory elements able to influence gene transcription over large
distances have led to the hypothesis that elements called insulators should exist to limit
the action of enhancers and silencers. During the last decades, insulators have been
identified in many eukaryotes from yeast to human. Insulators possess two main
properties: (i) they can block enhancerpromoter communication (enhancer blocker
activity), and (ii) they can prevent the spread of repressive chromatin (barrier activity).
This review focuses on recent studies designed to elucidate the molecular mechanisms
of the insulator function, and gives an overview of the critical role of insulators in
nuclear organization and functional identity of chromatin.
Download PDF
Download PDF
nature heredity review article
Explore Journal info
javascript:;
javascript:;
https://www.nature.com/hdy
https://www.nature.com/articles/6800669/metrics
https://www.nature.com/articles/6800669.pdf
https://www.nature.com/articles/6800669.pdf
https://www.nature.com/
https://www.nature.com/hdy
https://www.nature.com/hdy/articles?type=review
https://www.nature.com/hdy
javascript:;
https://idp.nature.com/authorize/natureuser?client_id=grover&redirect_uri=https%3A%2F%2Fwww.nature.com%2Farticles%2F6800669
javascript:;
javascript:;
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 2/22
Introduction
Precise control over the expression of a gene is exerted through interactions between
the basic transcriptional machinery at the gene promoter and specific protein
complexes at enhancer or silencer elements. Enhancers and silencers exert long-
distance effects independently of their position and orientation. Nevertheless,
neighbouring genes potentially influenced by the presence of the same enhancer within
a defined chromosomal locus may display independent transcription profiles. A
fundamental question is then how to explain the limited range of the enhancer action.
The formation of independent domains of gene function may depend upon a class of
regulatory elements able to block the inappropriate action of enhancers or silencers.
Such regulatory elements are called insulators (Kuhn and Geyer, 2003). Insulators are
defined by two functional properties illustrated in Figure 1. First, an insulator is able to
block interaction between an enhancer and a promoter when positioned in-between
(Conte et al, 2002; Geyer and Corces, 1992; Kellum and Schedl, 1992). Second, an
insulator (also called barrier) prevents the advance of nearby condensed chromatin and
protects gene expression from positive or negative chromatin effects (Kellum and
Schedl, 1991; Roseman et al, 1993; Saitoh et al, 2000). In this review, we discuss recent
advances in our knowledge of the complexity of the mechanism underlying the insulator
function and its role in gene regulation.
Figure 1
https://www.nature.com/articles/6800669.pdf
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 3/22
Insulators possess two main properties: (a) they can block enhancerpromoter
communication (enhancer blocker activity), and (b) they can prevent the spread of
repressive chromatin (barrier activity).
What are the mechanisms of action of insulators?
Insulators are regulatory elements that can shelter genes from inappropriate regulatory
interactions. Transgenic assays have helped to dissect the exact sequences required for
insulation and have shown that short sequences if multimerized can reconstitute the
insulator effect (Scott et al, 1999). They have also helped to define the general
properties of insulators such as their enhancer-blocker and/or barrier functions.
However, we are at present unable to understand the molecular mechanisms underlying
these functions or to integrate into a general scheme additional observations such as:
(i) the enhancer-blocker and barrier activities are separable (Recillas-Targa et al, 2002);
(ii) insulator effectiveness is influenced by its structure, and by the nature of the
enhancer, promoter and genomic context (Scott et al, 1999; Walters et al, 1999); and
(iii) insulators are not permanent and impassable elements (Cai and Shen, 2001;
Muravyova et al, 2001). Two nonexclusive models are currently proposed: one of them
https://www.nature.com/articles/6800669/figures/1
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 4/22
is established according to a series of data reporting links between insulators and the
higher-order chromatin structures, and the other integrate data reporting connections
between the insulator properties and gene transcription.
Insulators and higher-order chromatin structures
A structural model proposes that the properties of the insulators result from their
relationship with the organization of higher-order chromatin structures (Labrador and
Corces, 2002). Experiments performed on a Drosophila insulator identified in a
retroelement called gypsy help to illustrate this model. This insulator was identified just
3 of the 5 long terminal repeat of gypsy. This is a 340-bp fragment, which contains a
cluster of 12 degenerate binding sites for a zinc-finger DNA protein, Su(Hw). This
insulator is able to block the interaction between enhancers and promoters, and to
protect a gene from nearby chromatin effects (van der Vlag et al, 2000). Both
properties depend on Su(Hw), which recruits the Mod(mdg4) protein. The gypsy
insulator is not specific to a single enhancer, but has been shown to act as enhancer-
blocker to more than 20 enhancers. Even so, this insulator does not establish an
impassable barrier. In certain conditions, the insulator is bypassed, the enhancer-
blocking effect is neutralized and enhancerpromoter communication is restored. Such
a bypass is observed when two gypsy insulators are placed between an enhancer and a
promoter. This loss of insulator activity has been proposed to result from
intrachromosomal pairing between the two gypsy insulators, causing chromatin to fold
and allowing the distal enhancer to contact the promoter. By extension, a single
intervening gypsy insulator would block enhancerpromoter communication by
interacting either with other insulators located at distant loci or at specific nuclear sites
(Cai and Shen, 2001; Muravyova et al, 2001). Evidence that the gypsy insulator
establishes chromatin domains is strengthened by the fact that Su(Hw) and Mod(mdg)4
associate with 500 sites in the Drosophila genome, but coalesce into only 25 large
structures. These structures, named insulator bodies, are proposed to establish
separate loop domains within the genome. The gypsy insulator sequences could then
be genomic sites where such interactions are favoured, and thus be responsible for the
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 5/22
generation of such loops. According to this model, Gerasimova et al (2000) have shown
that the nuclear positioning of a sequence can be altered. If tethered to the gypsy
insulator, this sequence is targeted to the nuclear periphery where the insulator bodies
are mostly detected.
Furthermore, recent experiments have shown that pairing between two heterologous
insulators such as the binding sites for the GAGA factor and the gypsy insulator may
also occur in the genome and be a possible means to bypass the insulator activity
(Melnikova et al, 2004).
Almost all vertebrate insulators described require binding of the regulatory protein
CTCF for their activity. Some recent results show that CTCF is copurified with a
nucleolar protein present at the nucleolar periphery, suggesting that it helps to displace
insulators to the periphery of the nucleole. These interactions may generate similar
loops described for the gypsy insulator element in Drosophila (Yusufzai et al, 2004).
Taken together with the fact that CTCF is also associated with the nuclear matrix, these
results suggest a functional connection between insulators, the nuclear matrix and
nuclear organization.
A connection between insulator activities and their interaction with some nuclear
structures is further supported by data obtained through a genetic screen performed in
yeast and specifically addressed to isolate genes involved in a possible link between
nuclear order and chromatin boundaries. Various proteins involved in nuclear-
cytoplasmic traffic, such as the exportins Cse1p or Mex67p, have been identified in this
screen and appear to block the propagation of heterochromatin by direct or indirect
tethering of the insulator element to the nuclear pore (Ishii et al, 2002) (Figure 2).
Figure 2
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 6/22
Boundaries interact with nuclear pore proteins by the nuclear pore complex (from
Ishii et al, 2002). Triangles S represent silencer elements, the white circles B
represent the boundary elements and the grey squares presumed unidentified
proteins. The boundary elements interact with nuclear pore proteins via the nuclear
pore complex (NPC). The authors propose that this nuclear organization allows the
gene located between both boundaries to be isolated from the silencing effect. Its
transcription is ON. The gene located outside the loop is not protected from the
silencer effect, and its transcription is OFF.
Faswb, a notch mutation in Drosophila, disrupts a boundary element, which results in an
alteration of the structural organization of the chromosome visualized by the elimination
of a band observed in the giant larval polytene chromosomes (Vazquez and Schedl,
2000).
Although all these examples implicate 3D loops in the insulator function, some results
do not fit well with a structural model as a unique model for insulation. As an example,
the first insulators identified, the Drosophila specialized chromatin structures, scs and
scs (Kellum and Schedl, 1991, 1992), are boundaries surrounding the 87A7 locus where
two hsp70 genes reside. As proposed above for the gypsy elements, interaction
between scs and scs could explain their insulator function; however, this interaction
https://www.nature.com/articles/6800669/figures/2
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 7/22
fails to explain why interaction between scs and scs is not a general property of these
elements but depends on sequences located outside the specific domain bearing the
insulator function (Kuhn et al, 2004). Additionally, Majumder and Cai have tested the
effect of pairing on enhancer-blocking activity of 11 homologous and heterologous
insulator combinations. The results have shown that, unlike the homologous pairing of
gypsy insulator or heterologous pairing of gypsy and binding sites for the GAGA factor
(Melnikova et al, 2004), heterologous combinations of gypsy and other insulators, as
well as homologous pairing with other boundary elements such as scs or SF1, do not
always reduce their enhancer-blocking activity (Majumder and Cai, 2003). Further,
some paired insulators exhibit a higher level of enhancer-blocking activity than either
single insulator alone, suggesting that they can function independently or additively
(Majumder and Cai, 2003).
Overall, the structural model proposes that insulators separate the chromatin fibre into
loops attached to a fixed perinuclear substrate, perhaps the nuclear lamin, which serves
as a scaffold to maintain the nuclear organization. However, if such 3D loops provoke
special localizations inside the nucleus, they can also be a means to prevent cis-
diffusion of some molecules necessary for the transcription machinery. Formation of
loops could then act as the primary step of the transcriptional model.
Insulators and gene transcription
The transcriptional model advances that insulators have direct consequences on
transcription (Geyer, 1997; Bell and Felsenfeld, 1999; Dorsett, 1999). Thus, this
transcriptional model depends on the prevailing models of enhancer function and may
be summarized in two different mechanisms. If it is assumed that a signal is propagated
along the chromatin fibre from the enhancer to the promoter, then insulators assembled
in nucleoprotein complexes might block the propagation of the enhancer signal along
the DNA. In this case, they act as physical barriers able to stop the activation of a gene
by its enhancer. Experiments performed on the transcription factor GAGA from
Drosophila melanogaster illustrate this model. GAGA can stimulate transcription by
linking an enhancer to its cognate promoter. It facilitates long-range activation by
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 8/22
providing a protein bridge that mediates enhancerpromoter communication. Insulators
could interfere with this property of GAGA, and restrict the recruitment of this factor to
the promoter (Mahmoudi et al, 2002).
If it is assumed that the enhancer advances as an obligatory propagated signal toward
the promoter, then an insulator could compete with the promoter for the enhancer, and
trap it into a nonproductive liaison (Geyer, 1997). Supporting this model is the fact that
a promoter has been detected within the scs and scs elements (Glover et al, 1995;
Avramova and Tikhonov, 1999), suggesting that these elements may not only be neutral
structural elements as proposed by the structural model, but rather their promoter may
titrate the enhancer function and keep it from activating transcription. A limit to the
transcriptional model is that it fails to explain why boundary elements have to be
between the enhancer and the promoter to function as enhancer blockers. In any case,
it fails to explain how an enhancer blocked on one side by an insulator can activate a
promoter on the other side. Thus, an alternative model involving proteins named
facilitators that bring the enhancer and the promoter close to each other can be
considered. Among these facilitators, the Drosophila Chip protein has been found to
interact with Su(Hw) (Morcillo et al, 1997). Genetic evidence has shown that Su(Hw)
becomes a more effective insulator when enhancerpromoter communication is
weakened by mutations in Chip. It is proposed that formation of ChipSu(Hw)
complexes breaks the chain of interaction between Chip and homeodomain proteins,
interfering with the process that brings the enhancer towards the promoter.
Recent analyses have shown that barrier elements might play a role in preserving the
separation between a silenced and an active chromatin state. Repressive chromatin has
been characterized by several molecular marks such as enrichment in methylation of
histone H3 lysine 9, hypoacetylation of histones H3 and H4 as well as the binding of
heterochromatin protein 1. On the other hand, transcriptionally active chromatin is
associated with hyperacetylation of H3 lysine 9 and 14. Several observations suggest
that barriers break the code of histone modifications necessary for the propagation of
silencing along the chromatin fibre. For example, methylated nucleosomes around the
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 9/22
HS4 insulator of the chicken -globin locus have been proposed to recruit Suv39H1 and
allow methylation of the adjacent nucleosomes. The 5HS4 insulator of the -globin
locus would acetylate the adjacent upstream nucleosomes, which prevents methylation
and thus terminates the propagation of the condensation signal (Burgess-Beusse et al,
2002). This modification state of nucleosomes within an insulated transgene suggests
that another model may account for the position effect protection of insulators.
Insulators might directly facilitate nucleosome acetylation. The resulting open chromatin
structure would bind factors protecting the gene against DNA methylation (Recillas-
Targa et al, 2002).
In conclusion, separate data obviously support one and/or the other of the structural
and transcriptional models. It is then possible that insulators may utilize several of these
mechanisms, although this remains to be demonstrated.
Role of insulators in nuclear function
From all the data reported so far, several roles can be attributed to insulators within the
cell.
Partition of distinct chromosomal regions
In addition, to play a structural role in the organization of DNA within the nucleus,
chromatin is also intimately involved in the regulation of eukaryotic gene expression
(Felsenfeld et al, 1996). Barriers are fundamental actors, keeping adjacent domains of
active and inactive chromatin distinct and preventing these regions from inappropriate
interactions (Figure 3).
Figure 3
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 10/22
Schematic model of the insulator function in the nuclear organization of chromatin.
Proteins (spheres) associated to insulators coalesce within the nucleus. These
structures named insulator bodies establish separate loop domains. Located within
such a loop, the enhancer E1 can activate transcription of a promoter located within
the same loop. However, it is unable to activate a promoter located outside in
another domain.
In the yeast Saccharomyces cerevisiae, a barrier is described at the junction between a
heterochromatic region with hypoacetylated lysines of all core histones and an active
euchromatic region with numerous acetylated histones (Kimura et al, 2002; Suka et al,
2002). These results suggest that insulators may establish a mark specifying the
functional identity of adjacent chromatin domains.
In chickens, a folate receptor gene is separated from the upstream -globin locus by a
16kpb region of silent chromatin. At the 5 boundary of the -globin locus, the
sequence 5HS4 marked by a constitutive DNAse I-hypersensitive site acts as a barrier
against the incursion of the repressive chromatin immediately upstream (Prioleau et al,
1999).
https://www.nature.com/articles/6800669/figures/3
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 11/22
Finally, in yeast telomeres, silent mating-type loci (HM) and rDNA repeats share many of
the features of heterochromatic genes. This characteristic together with the compact
organization of the genome suggests that yeast gene regulation has evolved efficient
mechanisms for insulating genes from each other. Some sequences named STAR
(subtelomeric antisilencing region) are able to counteract silencer-driven repression at
the mating-type HML locus and act with antisilencing properties against the spreading
of silenced chromatin (Singh and Klar, 1992; Fourel et al, 1999, 2001).
In all these cases, insulators would guarantee that transition from one domain to the
next occurs at a fixed position.
Insulators facilitates complex gene regulations
In the euchromatin, insulators are able to block external enhancers and silencers
(Akasaka et al, 1999). Thus, they play a fundamental role in blocking inappropriate
action of these regulatory sequences on a gene, and in isolating independent
transcriptional units from crossreaction with neighbouring regulatory sequences (Figure
4).
Figure 4
Connection between enhancer-blocking activity and imprinting: the mammalian
insulator ICR taken as an example. In females, the endodermal enhancer,
represented by a white circle E, is able to activate the H19 gene only because the
https://www.nature.com/articles/6800669/figures/4
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 12/22
CTCF binding site acts as an insulator able to block the enhancer effect on the
downstream Igf2 gene. In males, the ICR is methylated, which prevents the binding
of CTCF to its binding site. Activation of the Igf2 gene is then permitted. H19 is then
off potentially due methylation spreading from ICR. ON: when transcription of the
corresponding gene is allowed. OFF: when transcription of the corresponding gene
is blocked.
Another example taken from D. melanogaster concerns the Fab7 element. In the
bithorax complex, BX-C, an array of parasegment-specific regulatory domains is
separated by boundaries such as Fab7. These boundaries are responsible for the
autonomous activity of IAB-6 and IAB-7, which control expression of the Abd-B gene in
parasegments 11 and 12, respectively. Fab-7 is active in a wide range of tissues from
early embryogenesis through the adult stage. The Fab-7 boundary contains separable
regions that function at different stages of development (Schweinsberg and Schedl,
2004). This example illustrates how insulators can limit regulatory interactions at a
defined locus, but it also exemplifies how such insulator elements may exhibit
differential activities and orchestrate complex regulatory regions.
Finally, a connection between enhancer-blocking activity and imprinted loci has been
found, suggesting a role of insulators in the establishment of epigenetic marks in
chromatin. This function has been put forward through the analysis of the mammalian
insulator ICR (imprinted control region), a functional element found at the endogenous
locus IGF2/H19. Regulated by a parental-specific methylation, the insulator is implicated
in the imprinting of this locus. When present on the maternal chromosome, its insulator
function blocks access of the IGF2 promoter to endodermal enhancers, resulting in
exclusive H19 expression. When present on the paternal chromosome, the ICR is
methylated and impedes establishment of the insulation (Thorvaldsen et al, 1998;
Webber and Tilghman, 1998). ICR, then, has two antagonistic roles depending on its
parental origin: either it displays an insulator function or it is implicated in the
maintenance of a methylated state of the chromatin (Engel et al, 2004) (Figure 4).
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 13/22
Insulators and higher-order nuclear organization of chromatin within the nucleus
As described above, several data indicate that insulators are involved in chromatin
encroaching onto nuclear substructures. MARs (matrix attachment regions) have been
observed close to several regions defined as insulators. One such example is the
flanking MAR element of the human apoB gene locus presumed to represent the
anchorage site for a chromosomal loop (Antes et al, 2001). In chicken, an MAR element
was also identified at the 5 boundary of the lysozyme locus, which is thought to
mediate the organization of the lysozyme gene chromatin domain (Stief et al, 1989).
Thus, through their associated factors, insulators would play the fundamental cellular
role to recruit target genes to specific nuclear compartments as a way of maintaining a
tissue or development-restricted pattern of expression.
Insulators may promote the interaction between distant regulatory elements and promoters
A possible model explaining distant interactions between enhancers and promoters
implicates insulators. As reported above, two insulators may interact through complexes
bound to them. This interaction may generate the looping-out of sequences separating
an enhancer from its promoter, and bring enhancers and promoters in close proximity.
Insulators could then facilitate interactions over large distances.
Recent studies on the active -globin locus support this model. Indeed, they give
evidence for long-range gene regulation in vivo involving interaction between
transcriptional elements, with chromatin looping-out intervening. Additionally, the
murine -globin locus control region (LCR) is found in physical proximity to the active
globin genes, although this LCR is located 4060kb away. This interaction and looping-
out are only observed in expressing tissues and not in nonexpressing tissues (Tolhuis et
al, 2002). These data provide the additional evidence that involvement of the insulators
in such a regulation is a dynamic process that only occurs during transcription in vivo.
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 14/22
Conclusion
The prevalent mechanism leading to gene regulation operates via complex chromatin
structures. In this context, insulators are fundamental components of the eukaryotic
genomes because together with the chromatin structure, they act as crucial organizers
of the genome dynamic. Since they have been identified in many eukaryotic genomes,
they are supposed to have conserved roles in the organisms: they guarantee
specificities of enhancerpromoter interactions, and define autonomous domains for
transcription; they counteract regulatory communication between adjacent domains;
they facilitate interactions between distant enhancers and promoters; and they act as
genome organisers participating in nuclear organization. All these functions are not
static as previously thought, but act as dynamic functions adapted to the transcriptional
and/or developmental state of the cell. Thus, they provide the plasticity required to
respond to developmental and environmental cues. As expected, in light of all these
functions it is not surprising to find clear connections between insulator mutations and
human diseases as illustrated in a congenital form of myotonic dystrophy associated
with a loss of the function of the DM1 insulator (Filippova et al, 2001). Although all the
roles reported above have been clearly attributed to insulators, it is nevertheless
intriguing to find in some cases that deletion of some insulator sequences is not lethal
and sometimes has no obvious phenotype. Genomic redundancies can certainly explain
some of these results. Further, an as yet unsolved question is to understand why mutant
alleles of genes implicated in the insulator function of a large number of sequences
scattered in the genome, such as Su(Hw) for gypsy, are not lethal. It is obvious that
further analyses of these functional elements of the chromosomes and their associated
factors are necessary for the understanding of interactions linking large genomic
regions into one regulatory, organizational and evolutionary unit.
References
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 15/22
. Akasaka K, Nishimura A, Takata K, Mitsunaga K, Mibuka F, Ueda H et al (1999).
Upstream element of the sea urchin arylsulfatase gene serves as an insulator. Cell
Mol Biol (Noisy-le-grand) 45: 555565.
. Antes TJ, Namciu SJ, Fournier RE, Levy-Wilson B (2001). The 5 boundary of the
human apolipoprotein B chromatin domain in intestinal cells. Biochemistry 40:
67316742.
. Avramova Z, Tikhonov A (1999). Are scs and scs neutral chromatin domain
boundaries of the locus? Trends Genet 15: 138139.
. Bell AC, Felsenfeld G (1999). Stopped at the border: boundaries and insulators.
Curr Opin Genet Dev 9: 191198.
. Burgess-Beusse B, Farrell C, Gaszner M, Litt M, Mutskov V, Recillas-Targa F et al
(2002). The insulation of genes from external enhancers and silencing chromatin.
Proc Natl Acad Sci USA 99 (Suppl 4): 1643316437.
. Cai HN, Shen P (2001). Effects of cis arrangement of chromatin insulators on
enhancer-blocking activity. Science 291: 493495.
. Conte C, Dastugue B, Vaury C (2002). Coupling of enhancer and insulator
properties identified in two retrotransposons modulates their mutagenic impact on
nearby genes. Mol Cell Biol 22: 17671777.
. Dorsett D (1999). Distant liaisons: long-range enhancerpromoter interactions in
Drosophila. Curr Opin Genet Dev 9: 505514.
. Engel N, West AG, Felsenfeld G, Bartolomei MS (2004). Antagonism between DNA
hypermethylation and enhancer-blocking activity at the H19 DMD is uncovered by
CpG mutations. Nat Genet 36: 883888.
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 16/22
. Felsenfeld G, Boyes J, Chung J, Clark D, Studitsky V (1996). Chromatin structure
and gene expression. Proc Natl Acad Sci USA 93: 93849388.
. Filippova GN, Thienes CP, Penn BH, Cho DH, Hu YJ, Moore JM et al (2001). CTCF-
binding sites flank CTG/CAG repeats and form a methylation-sensitive insulator at
the DM1 locus. Nat Genet 28: 335343.
. Fourel G, Boscheron C, Revardel E, Lebrun E, Hu YF, Simmen KC et al (2001). An
activation-independent role of transcription factors in insulator function. EMBO
Rep 2: 124132.
. Fourel G, Revardel E, Koering CE, Gilson E (1999). Cohabitation of insulators and
silencing elements in yeast subtelomeric regions. EMBO J 18: 25222537.
. Gerasimova TI, Byrd K, Corces VG (2000). A chromatin insulator determines the
nuclear localization of DNA. Mol Cell 6: 10251035.
. Geyer PK (1997). The role of insulator elements in defining domains of gene
expression. Curr Opin Genet Dev 7: 242248.
. Geyer PK, Corces VG (1992). DNA position-specific repression of transcription by
a Drosophila zinc finger protein. Genes Dev 6: 18651873.
. Glover DM, Leibowitz MH, McLean DA, Parry H (1995). Mutations in aurora prevent
centrosome separation leading to the formation of monopolar spindles. Cell 81:
95105.
. Ishii K, Arib G, Lin C, Van Houwe G, Laemmli UK (2002). Chromatin boundaries in
budding yeast: the nuclear pore connection. Cell 109: 551562.
. Kellum R, Schedl P (1991). A position-effect assay for boundaries of higher order
chromosomal domains. Cell 64: 941950.
9/19/2020 Insulators are fundamental components of the eukaryotic genomes | Heredity
https://www.nature.com/articles/6800669 17/22
. Kellum R, Schedl P (1992). A group of scs elements function as domain boundaries
in an enhancer-blocking assay. Mol Cell Biol 12: 24242431.
. Kimura A, Umehara T, Horikoshi M (2002). Chromosomal gradient of histone
acetylation established by Sas2p and Sir2p functions as a shield against gene
silencing. Nat Genet 32: 370377.
. Kuhn EJ, Geyer PK (2003). Genomic insulators: connecting properties to
mechanism. Curr Opin Cell Biol 15: 259265.
. Kuhn EJ, Hart CM, Geyer PK (2004). Studies of the role of the Drosophila scs and
scs insulators in defining boundaries of a chromosome puff. Mol Cell Biol 24:
14701480.
. Labrador M, Corces VG (2002). Setting the boundaries of chromatin domains and
nuclear organization. Cell 111: 151154.
. Mahmoudi T, Katsani KR, Verrijzer CP (2002). GAGA can mediate enhancer
function in trans by linking two separate DNA molecules. EMBO J 21: 17751781.
. Majumder P, Cai HN (2003). The functional analysis of insulator interactions in the
Drosophila embryo. Proc Natl Acad Sci USA 100: 52235228.
. Melnikova L, Juge F, Gruzdeva N, Mazur A, Cavalli G, Georgiev P (2004).
Interaction between the GAGA factor and Mo
