Project description:Developmental genes are often controlled by large regulatory landscapes matching topologically associating domains (TADs). In various contexts, the associated chromatin backbone is modified by specific enhancer-enhancer and enhancer-promoter interactions. We used a TAD flanking the mouse HoxD cluster to study how these regulatory architectures are formed and deconstructed once their function achieved. We describe this TAD as a functional unit, with several regulatory sequences acting together to elicit a transcriptional response. With one exception, deletion of these sequences didn't modify the transcriptional outcome, a result at odds with a conventional view of enhancer function. The deletion and inversion of a CTCF site located near these regulatory sequences did not affect transcription of the target gene. Slight modifications were nevertheless observed, in agreement with the loop extrusion model. We discuss these unexpected results considering both conventional and alternative explanations relying on the accumulation of poorly specific factors within the TAD backbone.
Project description:In vertebrates, developmental genes are often controlled by large regulatory landscapes matching the dimensions of topologically associating domains (TADs). In various ontogenic contexts, the associated constitutive chromatin backbone is modified by fine-tuned specific variations in enhancer-enhancer and enhancer-promoter interaction profiles. In this work, we use a TAD flanking the HoxD gene cluster as a paradigm to address the question of how these complex regulatory architectures are formed and how they are de-constructed once their function has been achieved. We suggest that this TAD can be considered as a coherent functional unit in itself, with several regulatory sequences acting together to elicit a transcriptional response. With one notable exception, the deletion of each of these sequences in isolation did not produce any substantial modification in the global transcriptional outcome of the system, a result at odds with a conventional view of long-range enhancer function. Likewise, both the deletion and inversion of a CTCF site located in a region rich in such sequences did not affect transcription of the target gene. In the latter case, however, slight modifications were observed in interaction profiles in vivo in agreement with the loop extrusion model, despite no apparent functional consequences. We discuss these unexpected results by considering both conventional explanations and an alternative possibility whereby a rather unspecific accumulation of particular factors within the TAD backbone may have a global impact upon transcription.
Project description:In vertebrates, developmental genes are often controlled by large regulatory landscapes matching the dimensions of topologically associating domains (TADs). In various ontogenic contexts, the associated constitutive chromatin backbone is modified by fine-tuned specific variations in enhancer-enhancer and enhancer-promoter interaction profiles. In this work, we use a TAD flanking the HoxD gene cluster as a paradigm to address the question of how these complex regulatory architectures are formed and how they are de-constructed once their function has been achieved. We suggest that this TAD can be considered as a coherent functional unit in itself, with several regulatory sequences acting together to elicit a transcriptional response. With one notable exception, the deletion of each of these sequences in isolation did not produce any substantial modification in the global transcriptional outcome of the system, a result at odds with a conventional view of long-range enhancer function. Likewise, both the deletion and inversion of a CTCF site located in a region rich in such sequences did not affect transcription of the target gene. In the latter case, however, slight modifications were observed in interaction profiles in vivo in agreement with the loop extrusion model, despite no apparent functional consequences. We discuss these unexpected results by considering both conventional explanations and an alternative possibility whereby a rather unspecific accumulation of particular factors within the TAD backbone may have a global impact upon transcription.
Project description:In vertebrates, developmental genes are often controlled by large regulatory landscapes matching the dimensions of topologically associating domains (TADs). In various ontogenic contexts, the associated constitutive chromatin backbone is modified by fine-tuned specific variations in enhancer-enhancer and enhancer-promoter interaction profiles. In this work, we use a TAD flanking the HoxD gene cluster as a paradigm to address the question of how these complex regulatory architectures are formed and how they are de-constructed once their function has been achieved. We suggest that this TAD can be considered as a coherent functional unit in itself, with several regulatory sequences acting together to elicit a transcriptional response. With one notable exception, the deletion of each of these sequences in isolation did not produce any substantial modification in the global transcriptional outcome of the system, a result at odds with a conventional view of long-range enhancer function. Likewise, both the deletion and inversion of a CTCF site located in a region rich in such sequences did not affect transcription of the target gene. In the latter case, however, slight modifications were observed in interaction profiles in vivo in agreement with the loop extrusion model, despite no apparent functional consequences. We discuss these unexpected results by considering both conventional explanations and an alternative possibility whereby a rather unspecific accumulation of particular factors within the TAD backbone may have a global impact upon transcription.