Syntax compensates for poor binding sites to encode tissue specificity of developmental enhancers

Emma K. Farley, Katrina M. Olson, Wei Zhang, Daniel S. Rokhsar, Michael S. Levine

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

Transcriptional enhancers are short segments of DNA that switch genes on and off in response to a variety of intrinsic and extrinsic signals. Despite the discovery of the first enhancer more than 30 y ago, the relationship between primary DNA sequence and enhancer activity remains obscure. In particular, the importance of "syntax" (the order, orientation, and spacing of binding sites) is unclear. A high-throughput screen identified synthetic notochord enhancers that are activated by the combination of ZicL and ETS transcription factors in Ciona embryos. Manipulation of these enhancers elucidated a "regulatory code" of sequence and syntax features for notochord-specific expression. This code enabled in silico discovery of bona fide notochord enhancers, including those containing low-affinity binding sites that would be excluded by standard motif identification methods. One of the newly identified enhancers maps upstream of the known enhancer that regulates Brachyury (Ci-Bra), a key determinant of notochord specification. This newly identified Ci-Bra shadow enhancer contains binding sites with very low affinity, but optimal syntax, and thereforemediates surprisingly strong expression in the notochord. Weak binding sites are compensated by optimal syntax, whereas enhancers containing high-affinity binding affinities possess suboptimal syntax. We suggest this balance has obscured the importance of regulatory syntax, as noncanonical binding motifs are typically disregarded by enhancer detection methods. As a result, enhancers with low binding affinities but optimal syntax may be a vastly underappreciated feature of the regulatory genome.

Original languageEnglish (US)
Pages (from-to)6508-6513
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume113
Issue number23
DOIs
StatePublished - Jun 7 2016

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Enhancer
  • Enhancer grammar
  • Gene regulation
  • Regulatory principles
  • Transcription

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