Rapid nasal pit formation in mouse embryos stimulated by ATP-containing medium.

The primary palate in the mouse is composed of epithelium and mesenchyme. Most studies on primary palate formation have concentrated on the role of the mesenchyme based upon the hypothesis that mesenchymal accumulation elevated the sides of the nasal placodes, thereby creating the depressed nasal pits. This study demonstrates that the epithelium is actively participating in formation of the nasal pits. Mouse heads from embryos of 14 to 24 paris of body somites were placed in medium 199 and photographed. The medium was replaced with medium containing 1.0 mM ATP and 0.05% Triton-X. Within 5 minutes, the placodes either thickened or invaginated. Control heads exposed to medium 199 containing only Triton-X or ATP did not show any invaginations. The rapid thickening and invagination stimulated by ATP-containing medium demonstrates that the epithelium is the dominant tissue in nasal put formation. Although mesenchymal accumulation certainly contributes to the formation of the primary palate, it is the placodal epithelial invagination that appears to shape the nasal pits.