A highly conserved Wnt-dependent TCF4 binding site within the proximal enhancer of the anti-myogenic Msx1 gene supports expression within Pax3-expressing limb bud muscle precursor cells

The product of the Msxl gene is a potent inhibitor of muscle differentiation. Msxl is expressed in muscle precursor cells of the limb bud that also express Pax3. It is thought that Msxl may facilitate distal migration by delaying myogenesis in these cells. Despite the role played by Msxl in inhibiting muscle differentiation, nothing is known of the mechanisms that support the expression of the Msxl gene within limb bud muscle precursor cells. In the present study we have used a combination of comparative genomics, mouse transgenic analysis, in situ hybridisation and inimunohistochemistry to identify a highly conserved and tissue-specific regulatory sub-domain within the previously characterised Msxl gene proximal enhancer element that supports the expression of the Msxl gene in Pax3-expressing mouse limb pre-muscle masses. Furthermore, using a combination of in situ hybridisation, in vivo ChIP assay and transgenic explant culture analysis we provide evidence that Msxl expression in limb bud muscle precursor cells is dependent on the canonical Wnt/TCF signalling pathway that is important in muscle shape formation. The results of these studies provide evidence of a mechanistic link between the Wnt/TCF and the Msxl/Pax3/MyoD pathways within limb bud muscle precursor cells. (C) 2007 Elsevier Inc. All rights reserved.