A Genetic Approach to the Recruitment of PRC2 at the HoxD Locus

Fabrice Daniel Darbellay, Denis Duboule, Nicolas Lonfat, Patrick Schorderet
Public Library of Science, 2013
Article

Polycomb group (PcG) proteins are essential for the repression of key factors during early development. In Drosophila, the polycomb repressive complexes (PRC) associate with defined polycomb response DNA elements (PREs). In mammals, however, the mechanisms underlying polycomb recruitment at targeted loci are poorly understood. We have used an in vivo approach to identify DNA sequences of importance for the proper recruitment of polycomb proteins at the HoxD locus. We report that various genomic re-arrangements of the gene cluster do not strongly affect PRC2 recruitment and that relatively small polycomb interacting sequences appear necessary and sufficient to confer polycomb recognition and targeting to ectopic loci. In addition, a high GC content, while not sufficient to recruit PRC2, may help its local spreading. We discuss the importance of PRC2 recruitment over Hox gene clusters in embryonic stem cells, for their subsequent coordinated transcriptional activation during development.

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Fabrice Daniel Darbellay, Denis Duboule, Nicolas Lonfat, Patrick Schorderet
Public Library of Science, 2013
Article

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https://infoscience.epfl.ch/record/190762?ln=fr

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Gène Hox

Les gènes Hox sont une catégorie particulière de gènes homéotiques ; ils sont parmi les gènes les plus longuement étudiés de la biologie évolutive. Les gènes homéotiques possèdent une séquence ADN qua

Facteur de transcription

vignette|upright=2.2|Schéma simplifié du mécanisme d'un activateur. Un facteur de transcription est une protéine nécessaire à l'initiation ou à la régulation de la transcription d'un gène dans l'ense

Protéine

redresse=1.36|vignette|Représentation d'une protéine, ici deux sous-unités d'une molécule d'hémoglobine. On observe les représentées en couleur, ainsi que deux des quatre molécules d'hème, qui sont l

Polycomb Recruitment and Targeting in Mammals

Patrick Schorderet

Polycomb- (PcG) and trithorax (trxG) group proteins are essential components in the regulation of multiple developmental regulators. In particular, during early stages, they act as chromatin modifiers in such a way as to set and maintain the transcriptional status of Hox genes. Little is known, in vertebrates, concerning the modalities of PcG binding to their target sites. One possibility is that they are recruited, in a synergistic manner, through their binding to specific DNA regulatory elements to control spatial and temporal restriction of Hox genes by trimethylating lysine 27 on histone 3 (H3K27me3). Whereas these DNA sequences, referred to as polycomb response elements (PREs), have been identified in Drosophila, their existence in mammals remains to be clearly demonstrated. In this work, we aim to decipher the means by which polycomb repressive complexes (PRCs) are recruited to PREs during early mouse development and focus on the HoxD cluster, a genomic segment that is amongst the most heavily covered by H3K27me3 marks in embryonic stem (ES) cells and where one of the few vertebrate PRE has been previously reporter. We describe relatively small DNA sequences lying within the HoxD locus that are necessary and sufficient for the tethering of polycomb to ectopic loci. These elements work synergistically to form a fully functional repressive domain. Moreover, we show that a sequence with high GC content, although not necessary for the initial recruitment of PRC per se, may stabilize the link between the complex and the underlying DNA. Finally, we propose a model for the evolution of polycomb targets and discuss the emergence of diverging recruitment mechanisms amongst Drosophila, mice and humans.

EPFL2013

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SV40 activates transcription from the transferrin receptor promoter by inducing a factor which binds to the CRE/AP-1 recognition sequence

Peter Martin Beard, Nicole Paduwat

During the course of lytic infection by simian virus 40 (SV40), expression of both the viral late genes and certain host cellular genes is induced. The promoter of the cellular transferrin receptor (TR) gene contains a DNA sequence which is similar to the AP-1- and AP-4-binding region in SV40 which has been implicated in the control of the viral late promoter. Expression of TR is needed for cells to enter S-phase and is therefore expected to be important for the SV40 lytic cycle. Here we show that the level of TR mRNA in vivo was increased by SV40 infection. A factor which activates transcription from the TR promoter in vitro was specifically induced in SV40-infected cells. Gel mobility shift assays with an oligonucleotide comprising this part of the TR promoter showed three nucleoprotein complexes to be formed with proteins from CV-1 cells. Following SV40 infection, one of the complexes was increased ten-fold. Formation of this complex was specifically reduced by competition with the phorbol ester-responsive element of the collagenase gene, implying that the factor is a member of the AP-1/Jun/Fos family. Cross-linking of the complex by ultraviolet light showed major DNA-binding components to be proteins of about 55 kD and 47 kD. Removal of this factor by adding the oligonucleotide to in vitro transcription reactions with the TR promoter, abolished the activation of TR transcription. The factor which binds to the TR promoter co-sedimented with SV40 chromosomes extracted late in infection. This suggests that similar transcriptional regulatory proteins are involved in controlling transcription from both the SV40 and the TR promoters, and that the virus can use a common mechanism to induce viral and host cellular transcription.

1991

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The mouse Hox-1.4 gene: primary structure, evidence for promoter activity and expression during development

Denis Duboule

This study reports the structure of the mouse homeobox-containing gene Hox-1.4 of the HOX-1 cluster, as well as its expression pattern during embryonic and fetal development. The overall structure of this gene includes two major exons, the second of which encodes the homeo-domain. The putative Hox-1.4 protein displays similarities with products of homologous genes located at the same relative positions in other HOX clusters. A fragment extending 360 base pairs (bp) upstream of a transcriptional start site was shown to be able to promote transcription in transfected cells. This fragment is GC-rich and contains binding sites for the Sp1 transcription factor. In situ hybridization studies revealed the Hox-1.4 expression pattern during development. As already reported for several other murine Hox genes, Hox-1.4 is expressed in the fetal central nervous system (CNS), in structures derived from somitic mesodermal condensations (sclerotomes, prevertebrae) as well as in several mesodermal components of various organs and structures such as lungs, gut, stomach, intestine and meso- and metanephros. This expression pattern is in good agreement with recent proposals concerning the involvement of such genes in the establishment of the vertebrate body plan as well as the relationship between the positions of these genes within their clusters and the anteroposterior restriction of their expression domains.

1989

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