Transcription through Intergenic Chromosomal Memory Elements of the Drosophila Bithorax Complex Correlates with an Epigenetic Switch

ABSTRACT The proteins of the trithorax and Polycomb groups maintain the differential expression pattern of homeotic genes established by the early embryonic patterning system during development. These proteins generate stable and heritable chromatin structures by acting via particular chromosomal memory elements. We established a transgenic assay system showing that the Polycomb group response elements bxd and Mcp confer epigenetic inheritance throughout development. With previously published data for the Fab7 cellular memory module, we confirmed the cellular memory function of Polycomb group response elements. In Drosophila melanogaster, several of these memory elements are located in the large intergenic regulatory regions of the homeotic bithorax complex. Using a transgene assay, we showed that transcription through a memory element correlated with the relief of silencing imposed by the Polycomb group proteins and established an epigenetically heritable active chromatin mode. A memory element remodeled by the process of transcription was able to maintain active expression of a reporter gene throughout development. Thus, transcription appears to reset and change epigenetic marks at chromosomal memory elements regulated by the Polycomb and trithorax proteins. Interestingly, in the bithorax complex of D. melanogaster, the segment-specific expression of noncoding intergenic transcripts during embryogenesis seems to fulfill this switching role for memory elements regulating the homeotic genes.

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The role of Polycomb-group response elements in regulation of engrailed transcription in Drosophila

Development ◽

10.1242/dev.014779 ◽

2008 ◽

Vol 135 (4) ◽

pp. 669-676 ◽

Cited By ~ 36

Author(s):

S. K. DeVido ◽

D. Kwon ◽

J. L. Brown ◽

J. A. Kassis

Keyword(s):

Polycomb Group ◽

Response Elements ◽

Group Response

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H3K27 modifications define segmental regulatory domains in the Drosophila bithorax complex

eLife ◽

10.7554/elife.02833 ◽

2014 ◽

Vol 3 ◽

Cited By ~ 69

Author(s):

Sarah K Bowman ◽

Aimee M Deaton ◽

Heber Domingues ◽

Peggy I Wang ◽

Ruslan I Sadreyev ◽

...

Keyword(s):

Drosophila Melanogaster ◽

Binding Protein ◽

Histone H3 ◽

Polycomb Group ◽

Homeotic Genes ◽

Bithorax Complex ◽

Body Segment ◽

Regulatory Domains ◽

Definition Of ◽

Identity Expression

The bithorax complex (BX-C) in Drosophila melanogaster is a cluster of homeotic genes that determine body segment identity. Expression of these genes is governed by cis-regulatory domains, one for each parasegment. Stable repression of these domains depends on Polycomb Group (PcG) functions, which include trimethylation of lysine 27 of histone H3 (H3K27me3). To search for parasegment-specific signatures that reflect PcG function, chromatin from single parasegments was isolated and profiled. The H3K27me3 profiles across the BX-C in successive parasegments showed a ‘stairstep’ pattern that revealed sharp boundaries of the BX-C regulatory domains. Acetylated H3K27 was broadly enriched across active domains, in a pattern complementary to H3K27me3. The CCCTC-binding protein (CTCF) bound the borders between H3K27 modification domains; it was retained even in parasegments where adjacent domains lack H3K27me3. These findings provide a molecular definition of the homeotic domains, and implicate precisely positioned H3K27 modifications as a central determinant of segment identity.

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Faculty Opinions recommendation of The role of Polycomb-group response elements in regulation of engrailed transcription in Drosophila.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1102354.558397 ◽

2008 ◽

Author(s):

Leonie Ringrose

Keyword(s):

Polycomb Group ◽

Response Elements ◽

Group Response

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A Polycomb and GAGA Dependent Silencer Adjoins the Fab-7 Boundary in the Drosophila Bithorax Complex

Genetics ◽

10.1093/genetics/146.4.1365 ◽

1997 ◽

Vol 146 (4) ◽

pp. 1365-1380 ◽

Cited By ~ 7

Author(s):

Kirsten Hagstrom ◽

Martin Muller ◽

Paul Schedl

Keyword(s):

Domain Boundary ◽

Expression Patterns ◽

Regulatory Region ◽

Polycomb Group ◽

Homeotic Genes ◽

Bithorax Complex ◽

Gaga Factor ◽

Independent Manner ◽

Specific Expression ◽

Restricted Pattern

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-71) dominantly transforms parasegment 11 into parasegment 12. Previous studies suggested that removal of a domain boundary element on the proximal side of Fab-71 is responsible for this gain-of-function phenotype. In this article we demonstrate that the Fab-71 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 zeste1 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.

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TheDrosophilaTrithorax protein is a coactivator required to prevent re-establishment of Polycomb silencing

Development ◽

10.1242/dev.129.10.2483 ◽

2002 ◽

Vol 129 (10) ◽

pp. 2483-2493 ◽

Cited By ~ 1

Author(s):

Sylvain Poux ◽

Béatrice Horard ◽

Christian J. A. Sigrist ◽

Vincenzo Pirrotta

Keyword(s):

Imaginal Discs ◽

Polycomb Group ◽

Active State ◽

Homeotic Genes ◽

Epigenetic Memory ◽

Gaga Factor ◽

Response Elements ◽

Active Gene ◽

Polycomb Response Elements

Polycomb group (PcG) and Trithorax (TRX) complexes assemble at Polycomb response elements (PREs) and maintain respectively the repressed and active state of homeotic genes. Although PcG and TRX complexes are distinct, their binding to some PRE fragments in vitro depends on GAGA motifs. GAGA factor immunoprecipitates with both complexes. In presence of a PRE, TRX stimulates expression and prevents the return of repression at later stages. When TRX levels are reduced, repression is re-established in inappropriate regions of imaginal discs, suggesting that TRX insufficiency impairs the epigenetic memory of the active state. Targeting a GAL-TRX fusion shows that TRX is a coactivator that stimulates expression of an active gene but cannot initiate expression by itself. Targeting a histone acetylase to a PRE does not affect embryonic silencing but causes a loss of memory in imaginal discs, suggesting that deacetylation is required to establish the memory of the repressed state.

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The Mcp Element From the Drosophila melanogaster Bithorax Complex Mediates Long-Distance Regulatory Interactions

Genetics ◽

10.1093/genetics/153.3.1333 ◽

1999 ◽

Vol 153 (3) ◽

pp. 1333-1356 ◽

Cited By ~ 2

Author(s):

Martin Muller ◽

Kirsten Hagstrom ◽

Henrik Gyurkovics ◽

Vincenzo Pirrotta ◽

Paul Schedl

Keyword(s):

Drosophila Melanogaster ◽

Polycomb Group ◽

Small Fragment ◽

Bithorax Complex ◽

Long Distance ◽

Response Elements ◽

Regulatory Interactions ◽

Homolog Pairing ◽

Polycomb Response Elements ◽

Trans Regulation

Abstract In the studies reported here, we have examined the properties of the Mcp element from the Drosophila melanogaster bithorax complex (BX-C). We have found that sequences from the Mcp region of BX-C have properties characteristic of Polycomb response elements (PREs), and that they silence adjacent reporters by a mechanism that requires trans-interactions between two copies of the transgene. However, Mcp trans-regulatory interactions have several novel features. In contrast to classical transvection, homolog pairing does not seem to be required. Thus, trans-regulatory interactions can be observed not only between Mcp transgenes inserted at the same site, but also between Mcp transgenes inserted at distant sites on the same chromosomal arm, or even on different arms. Trans-regulation can even be observed between transgenes inserted on different chromosomes. A small 800-bp Mcp sequence is sufficient to mediate these long-distance trans-regulatory interactions. This small fragment has little silencing activity on its own and must be combined with other Polycomb-Group-responsive elements to function as a “pairing-sensitive” silencer. Finally, this pairing element can also mediate long-distance interactions between enhancers and promoters, activating mini-white expression.

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Trithorax- and Polycomb-Group Response Elements within an Ultrabithorax Transcription Maintenance Unit Consist of Closely Situated but Separable Sequences

Molecular and Cellular Biology ◽

10.1128/mcb.19.7.5189 ◽

1999 ◽

Vol 19 (7) ◽

pp. 5189-5202 ◽

Cited By ~ 70

Author(s):

Sergei Tillib ◽

Svetlana Petruk ◽

Yurii Sedkov ◽

Alexander Kuzin ◽

Miki Fujioka ◽

...

Keyword(s):

Dna Sequences ◽

Protein Complexes ◽

Expression Patterns ◽

Regulatory Region ◽

Protein Product ◽

Polycomb Group ◽

Response Elements ◽

Complex Element ◽

Group Response

ABSTRACT In Drosophila, two classes of genes, thetrithorax group and the Polycomb group, are required in concert to maintain gene expression by regulating chromatin structure. We have identified Trithorax protein (TRX) binding elements within the bithorax complex and have found that within thebxd/pbx regulatory region these elements are functionally relevant for normal expression patterns in embryos and confer TRX binding in vivo. TRX was localized to three closely situated sites within a 3-kb chromatin maintenance unit with a modular structure. Results of an in vivo analysis showed that these DNA fragments (each ∼400 bp) contain both TRX- and Polycomb-group response elements (TREs and PREs) and that in the context of the endogenousUltrabithorax gene, all of these elements are essential for proper maintenance of expression in embryos. Dissection of one of these maintenance modules showed that TRX- and Polycomb-group responsiveness is conferred by neighboring but separable DNA sequences, suggesting that independent protein complexes are formed at their respective response elements. Furthermore, we have found that the activity of this TRE requires a sequence (∼90 bp) which maps to within several tens of base pairs from the closest neighboring PRE and that the PRE activity in one of the elements may require a binding site for PHO, the protein product of the Polycomb-group genepleiohomeotic. Our results show that long-range maintenance of Ultrabithorax expression requires a complex element composed of cooperating modules, each capable of interacting with both positive and negative chromatin regulators.

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