Identification and Validation of Novel Hedgehog-Responsive Enhancers Predicted by Computational Analysis of Ci/Gli Binding Site Density

PLoS One. 2015 Dec 28;10(12):e0145225. doi: 10.1371/journal.pone.0145225. eCollection 2015.

Abstract

The Hedgehog (Hh) signaling pathway directs a multitude of cellular responses during embryogenesis and adult tissue homeostasis. Stimulation of the pathway results in activation of Hh target genes by the transcription factor Ci/Gli, which binds to specific motifs in genomic enhancers. In Drosophila, only a few enhancers (patched, decapentaplegic, wingless, stripe, knot, hairy, orthodenticle) have been shown by in vivo functional assays to depend on direct Ci/Gli regulation. All but one (orthodenticle) contain more than one Ci/Gli site, prompting us to directly test whether homotypic clustering of Ci/Gli binding sites is sufficient to define a Hh-regulated enhancer. We therefore developed a computational algorithm to identify Ci/Gli clusters that are enriched over random expectation, within a given region of the genome. Candidate genomic regions containing Ci/Gli clusters were functionally tested in chicken neural tube electroporation assays and in transgenic flies. Of the 22 Ci/Gli clusters tested, seven novel enhancers (and the previously known patched enhancer) were identified as Hh-responsive and Ci/Gli-dependent in one or both of these assays, including: Cuticular protein 100A (Cpr100A); invected (inv), which encodes an engrailed-related transcription factor expressed at the anterior/posterior wing disc boundary; roadkill (rdx), the fly homolog of vertebrate Spop; the segment polarity gene gooseberry (gsb); and two previously untested regions of the Hh receptor-encoding patched (ptc) gene. We conclude that homotypic Ci/Gli clustering is not sufficient information to ensure Hh-responsiveness; however, it can provide a clue for enhancer recognition within putative Hedgehog target gene loci.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Binding Sites / genetics
  • Chick Embryo
  • Computational Biology / methods*
  • DNA-Binding Proteins / metabolism*
  • Drosophila Proteins / genetics*
  • Drosophila Proteins / metabolism*
  • Drosophila melanogaster / embryology*
  • Drosophila melanogaster / genetics
  • Embryo, Nonmammalian / metabolism
  • Gene Expression Regulation, Developmental
  • Green Fluorescent Proteins / genetics
  • Hedgehog Proteins / genetics*
  • Hedgehog Proteins / metabolism
  • Neural Tube / metabolism
  • Oncogene Proteins / metabolism*
  • Regulatory Sequences, Nucleic Acid
  • Sequence Analysis, DNA
  • Signal Transduction / genetics
  • Trans-Activators / metabolism*
  • Transcription Factors / metabolism*
  • Wings, Animal / embryology
  • Zinc Finger Protein GLI1

Substances

  • DNA-Binding Proteins
  • Drosophila Proteins
  • Hedgehog Proteins
  • Oncogene Proteins
  • Trans-Activators
  • Transcription Factors
  • Zinc Finger Protein GLI1
  • ci protein, Drosophila
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins
  • hh protein, Drosophila