The homeobox genes MSX2 and MOX2 are candidates for regulating epithelial-mesenchymal cell interactions in the human placenta.

Homeobox genes of the Msx and Mox families are coexpressed in the vertebrate embryo in regions of epithelial-mesenchymal interactions. Here we show that a member of each family is expressed in extra-embryonic structures where epithelial and mesenchymal cell layers contact. In situ hybridization studies on first trimester human placental sections reveal that MSX2 and MOX2 are expressed predominantly in the cytotrophoblast cell layer. In term placenta, MSX2 and MOX2 are expressed in the syncytiotrophoblast. This is the first study to describe the expression of MOX2 in human tissues and to show that members of the Msx and Mox families of homeobox genes are expressed where epithelial and mesenchymal cell layers contact in the human placenta. A combinatorial code of homeobox genes that includes members of the Msx, Mox and Dlx families has been predicted to regulate epithelial-mesenchymal cell interactions in the vertebrate embryo. We have shown that MSX2, MOX2, DLX4 and the HB24 homeobox gene are expressed in the epithelial and mesenchymal cell types that form the placenta. We predict that this combination of homeobox genes is involved in regulating epithelial-mesenchymal cell interactions in extraembryonic tissues.