Expression of chickBarx-1 and its differential regulation by FGF-8 and BMP signaling in the maxillary primordia

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Abstract
The vertebrate face develops from a series of primordia surrounding the primitive mouth and is thought to be patterned by the differential expression of homeobox‐containing genes. Here we describe the isolation of the chick homologue of the homeobox‐containing gene, Barx‐1, and show its expression in the developing facial primordia, stomach, and appendicular skeleton. In the maxillary primordia, mesenchymal expression of Barx‐1 is complementary to that of Msx‐1, which correlate with overlying epithelial expression of Fgf‐8 and Bmp‐4, respectively. We show that epithelial signals are required to maintain Barx‐1 expression and that FGF‐8 can substitute for the epithelium. By contrast, BMPs reduce Barx‐1 expression and can antagonize FGF‐8 signaling. This suggests that in vivo, FGF‐8/BMP signaling may regulate Barx‐1 gene expression. This provides evidence that the differential expression of FGF‐8 and BMPs may determine homeobox‐containing gene expression and hence patterning of the facial primordia. Dev Dyn 1999;214:291–302.