Figure 5. αE-catenin is required for the epithelium-induced mesenchymal condensation during incisor development.

(a–d) In situ hybridization for Pax9 and Msx1 in control and Ctnna1^cKO. In control embryos, Pax9 and Msx1 are expressed in the mesenchyme of the tooth germ at E13.5. In Ctnna1^cKO, the expression of these genes is reduced or absent. (e,f) 3D reconstruction of control and Ctnna1^cKO tooth germs at E13.5 (epithelium is red and mesenchyme is green). The thickness of the mesenchyme is reduced in the absence of αE-catenin. (g) Quantification of thickness of the condensed mesenchyme around the incisor dental epithelium at E13.5 (mean±s.e.m., n=3, P<0.01). (h) Schematic illustration of the in vitro condensation assay. ED, embryonic day; PA, pharyngeal arch. (i,j) H2B-GFP labelled wild-type mesenchymal cells robustly condense around the dissected control epithelium in vitro (i) but fail to condense around the Ctnna1^cKO epithelium (j). White circles mark the position of GFP-negative epithelium. (k) Quantification of GFP-positive mesenchymal cells moving towards (IN) or away from (OUT) the epithelium shows Ctnna1^cKO epithelium is unable to retain mesenchymal cells in a condensed state (mean±s.e.m., n=4 in control, n=3 in Ctnna1^cKO, P<0.05). (l) The efficiency of mesenchymal cell movement (displacement over distance travelled) is not affected by αE-catenin deletion (mean±s.e.m., n=4 in control, n=3 in Ctnna1^cKO, P>0.05). All quantifications are analysed by using Student's t-test. *P<0.05, **P<0.01. Dotted lines outline the epithelium of the incisor tooth germ. Scale bar, 100 μm (a–d,i,j).