Animal genomes are organized into topologically associated domains (TADs). TADs are thought to contribute to gene regulation by facilitating enhancer-promoter (E-P) contacts within a TAD preventing these contacts across TAD borders. However, the absolute difference in contact frequency across TAD boundaries is usually less than two-fold, even though disruptions of TAD borders can change gene expression by ten-fold. Existing models fail to explain this hypersensitive response. Here, we propose a futile cycle model of enhancer-mediated regulation that can exhibit hypersensitivity through bistability and hysteresis. Consistent with recent experiments, this regulation does not exhibit strong correlation between enhancer-promoter contact and promoter activity, even though regulation occurs through contact. Through mathematical analysis and stochastic simulation, we show that this system can create an illusion of enhancer-promoter biochemical specificity and explain the importance of weak TAD boundaries. It also offers a mechanism to reconcile apparently contradictory results from recent global TAD disruption with local TAD boundary deletion experiments. Together, these analyses advance our understanding of cis-regulatory contacts in controlling gene expression, and suggest new experimental directions.

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This is a theoretical and computational paper using published experimental data.

The following previously published data sets were used

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Author details

  1. Jordan Yupeng Xiao

    Program in Biophysics, Stanford University, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Antonina Hafner

    Department of Developmental Biology, Stanford University, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Alistair N Boettiger

    Department of Developmental Biology, Stanford University, Stanford, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-3554-5196


National Institutes of Health (U01 DK127419)

  • Alistair N Boettiger

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Job Dekker, University of Massachusetts Medical School, United States

Version history

  1. Received: October 25, 2020
  2. Accepted: June 25, 2021
  3. Accepted Manuscript published: July 9, 2021 (version 1)
  4. Version of Record published: August 9, 2021 (version 2)


© 2021, Xiao et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


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  1. Jordan Yupeng Xiao
  2. Antonina Hafner
  3. Alistair N Boettiger
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