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

The vertebrate face develops from a series of primordia surrounding the pri mitive mouth and is thought to be patterned by the differential expression of homeobox-containing genes. Here we describe the isolation of the chick h omologue of the homeobox-containing gene, Barx-1, and show its expression i n the developing facial primordia, stomach, and appendicular skeleton, In t he maxillary primordia, mesenchymal expression of Barx-1 is complementary t o that of Msx-1, which correlate with overlying epithelial expression of Fg f-8 and Bmp-4, respectively. We show that epithelial signals are required t o maintain Barx-1 expression and that FGF-8 can substitute for the epitheli um, By contrast, BMPs reduce Barx-1 expression and can antagonize FGF-8 sig naling. This suggests that in vivo, FGF-8/BMP signaling may regulate Barx-1 gene expression. This provides evidence that the differential expression o f FGF-8 and BMPs may determine homeobox-containing gene expression and henc e patterning of the facial primordia. Dev Dyn 1999;214:291-302. (C) 1999 Wi ley-Liss, Inc.