Context-dependent enhancer function revealed by targeted inter-TAD relocation

Guillaume Andrey, Christopher Chase Bolt, Lucille Delisle, Denis Duboule, Aurélie Hintermann
NATURE PORTFOLIO, 2022
Journal paper

Abstract

Here the authors show that a strong enhancer sequence can be controlled by the chromatin environment provided by a topologically associated domain (TAD) located nearby. An enhancer relocated by homologous recombination takes all the hallmarks of its new neighboring enhancers located in the recipient TAD. The expression of some genes depends on large, adjacent regions of the genome that contain multiple enhancers. These regulatory landscapes frequently align with Topologically Associating Domains (TADs), where they integrate the function of multiple similar enhancers to produce a global, TAD-specific regulation. We asked if an individual enhancer could overcome the influence of one of these landscapes, to drive gene transcription. To test this, we transferred an enhancer from its native location, into a nearby TAD with a related yet different functional specificity. We used the biphasic regulation of Hoxd genes during limb development as a paradigm. These genes are first activated in proximal limb cells by enhancers located in one TAD, which is then silenced when the neighboring TAD activates its enhancers in distal limb cells. We transferred a distal limb enhancer into the proximal limb TAD and found that its new context suppresses its normal distal specificity, even though it is bound by HOX13 transcription factors, which are responsible for the distal activity. This activity can be rescued only when a large portion of the surrounding environment is removed. These results indicate that, at least in some cases, the functioning of enhancer elements is subordinated to the host chromatin context, which can exert a dominant control over its activity.

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Guillaume Andrey, Christopher Chase Bolt, Lucille Delisle, Denis Duboule, Aurélie Hintermann
NATURE PORTFOLIO, 2022
Journal paper

Abstract

Official source

https://infoscience.epfl.ch/record/295328?ln=en

About this result

Related concepts (18)

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Toward a mechanistic understanding of variable chromatin modules

Gerard Llimos Aubach

Our genome is a long sequence of DNA that contains all the information to be able to constitute a living organism like us, similarly to what the letters in a book do to create a story. This sequence, which is a stretch of molecules called nucleotides, is almost identical between organisms of the same species (>99.9% in humans), however it varies in a small percentage due to some nucleotides being different at specific positions of the genome. This variation in the DNA will therefore influence our traits and affect our susceptibility to a certain condition. Thus, their study is highly relevant in genetics and biomedicine since they allow not only to predict the predisposition to a disease, such as cancer, but also to understand the molecular and cellular mechanism behind a certain phenotype. The effect of a genetic variant on a phenotype is given by their capacity to modulate the expression of a gene, either by directly impacting its sequence and thus changing the protein, or by regulating its expression levels. Interestingly, more than 88% of the disease-associated genetic variants present in humans are located outside genes, on the so-called non-coding part of the genome. This poses a challenge to identify what gene the genetic variant affects and to understand how it does so. Genetic variants do not only influence gene expression but they also affect the epigenetics state of the DNA (i.e. DNA methylation, histone marks, transcription factor (TF) binding...) and its 3D conformation, consequently modifying the activity of gene regulatory elements like promoters and enhancers. Previously, it has been shown that some of these regulatory regions located in the same locus exhibit a high level of molecular coordination and interindividual variation, mostly affected by genetic variation or environmental effects. These regions were termed variable chromatin modules (VCMs) or cis-regulatory domains (CRDs) and are thought to be the manifestation of fine-grained regulatory units of the genome. Understanding how a VCM is formed and the molecular basis behind the cooperativity between regulatory elements is an outstanding question in the field. In this work, we aim at resolving part of this puzzle by mechanistically dissecting one VCM that is influenced by a non-coding germline variant in B cells. Using a set of tools such as genetic engineering, TF binding assays and chromosome conformation studies, we demonstrate that this variant creates a de novo binding site for the TF MEF2, which acts as a pioneering factor for dozens of other collaborating TFs. In turn, this actuates a cluster of enhancers spanning a region over 150 kilobases (kb) that regulates AXIN2 gene expression, and is associated with a global compaction of the chromatin. In addition, in line with the known tumor-suppressor properties of AXIN2, we found that this variant influences chronic lymphocytic leukemia (CLL) progression and predisposition. Together, the characterization of the AXIN2 VCM provides an unique example to the community of how a germline variant is able to switch on an entire genomic locus with high degree of cooperativity between regulatory elements, since it captures both the formation and transition behavior of a VCM. Furthermore, given the link with CLL, this focal variant could have translational potential by serving as a patient-stratifying or treatment diagnostic.

EPFL2021

Collinear expression of 5′ Hoxd genes during mammalian limb development is required to properly determine digits number and identity. We recently proposed a two-step model to account for the underlying regulatory mechanism, which involves an initial looping and recognition of the cluster by a complex of enhancer sequences, followed by a micro-scanning of nearby-located genes. This model could account for both the wild-type dosage of the various Hoxd transcripts, as well as for their quantitative variations in several mutant strains. Here, using the Chromosome Conformation Capture (3C) technique, we confirm the initial looping step by showing that the 5′ extremity of the HoxD cluster physically interacts with two previously identified, remote regulatory sequences displaying enhancer activity in developing digits. This spatial conformation is specific to presumptive digits and is not observed in tissues devoid of Hox gene transcription. The flexibility of these long-range interactions is illustrated by the ability of the enhancers to activate reporter transgenes inserted at various positions along the locus. To further define this regulatory landscape, we produced a large chromosomal inversion, separating the reporter transgene from the digit enhancers and HoxD cluster. Surprisingly, this configuration fails to abolish the transgene expression in developing digits, but leads to a major down-regulation of Hoxd genes in this domain, and concurrent morphological defects. These results suggest that the transcriptional activation of Hoxd genes requires the activity of additional and distant regulatory sequences, in addition to the enhancers identified so far by transgenic analysis.

Elsevier Science BV2009

, ,

Background: Four posterior Hoxd genes, from Hoxd13 to Hoxd10, are collectively regulated during the development of tetrapod digits. Besides the well-documented role of Hoxd13, the function of the neighboring genes has been difficult to evaluate due to the close genetic linkage and potential regulatory interferences. We used a combination of five small nested deletions in cis, involving from two to four consecutive genes of the Hoxd13 to Hoxd9 loci, in mice, to evaluate their combined functional importance. Results: We show that deletions leading to a gain of function of Hoxd13, via regulatory re-allocation, generate abnormal phenotypes, in agreement with the dominant negative role of this gene. We also show that Hoxd10, Hoxd11, and Hoxd12 all seem to play a genuine role in digit development, though less compelling than that of Hoxd13. In contrast, the nearby Hoxd9 contributed no measurable function in digits. Conclusions: We conclude that a slight and transient deregulation of Hoxd13 expression can readily affect the relative lengths of limb segments and that all posterior Hoxd genes likely contribute to the final limb morphology. We discuss the difficulty to clearly assess the functional share of individual genes within such a gene family, where closely located neighbors, coding for homologous proteins, are regulated by a unique circuitry and all contribute to shape the distal parts of our appendages. Developmental Dynamics 241:792-802, 2012. © 2012 Wiley Periodicals, Inc.

2012

Toward a mechanistic understanding of variable chromatin modules

Gerard Llimos Aubach

EPFL2021