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Characterization of Dkk1 gene regulation by the osteoblast-specific transcription factor Osx

Chi Zhang1, Hui Dai, Benoit de Crombrugghe

  • 1Bone Research Laboratory, Texas Scottish Rite Hospital for Children, University of Texas Southwestern Medical Center, 2222 Welborn St., Dallas, TX 75219, USA. Chi5.Zhang@utsouthwestern.edu

Biochemical and Biophysical Research Communications
|March 31, 2012
PubMed

Insights

Osterix (Osx), a key factor in bone formation, directly regulates Dickkopf-1 (Dkk1) expression. This study reveals Osx targets the Dkk1 promoter, providing insights into bone development feedback mechanisms.

Area of Science:

  • Molecular Biology
  • Developmental Biology
  • Genetics

Background:

  • Bone formation relies on mesenchymal stem cell differentiation into osteoblasts.
  • Osterix (Osx) is a crucial transcription factor for osteoblast differentiation and bone development.
  • Osx's inhibition of Wnt signaling suggests feedback control in bone formation, involving Wnt antagonist Dickkopf-1 (Dkk1).

Purpose of the Study:

  • To elucidate the mechanism by which Osx regulates Dickkopf-1 (Dkk1) expression.
  • To determine if Dkk1 is a direct transcriptional target of Osx.
  • To identify the specific regulatory elements within the Dkk1 promoter involved in Osx-mediated activation.

Main Methods:

  • Quantitative real-time RT-PCR to assess Dkk1 expression in Osx-null and Osx-overexpressing cells.
  • siRNA-mediated inhibition of Osx in osteoblasts.
  • Reporter assays with Dkk1 promoter deletion mutants.
  • Quantitative chromatin immunoprecipitation (ChIP) assays.

Main Results:

  • Dkk1 expression was significantly downregulated in Osx-null mouse embryos and osteoblasts with inhibited Osx.
  • Overexpression of Osx led to increased Dkk1 expression.
  • A minimal region of 250bp in the Dkk1 promoter, containing two GC-rich binding sites, was identified as essential for Osx-mediated activation.
  • ChIP assays confirmed endogenous Osx binding to the native Dkk1 promoter in osteoblasts.

Conclusions:

  • Dickkopf-1 (Dkk1) is a direct transcriptional target of Osterix (Osx).
  • Osx binds to specific GC-rich sites within the proximal Dkk1 promoter to activate its expression.
  • These findings establish a direct regulatory link between Osx and Dkk1, contributing to understanding bone formation regulation.

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