Fig. 8.

Model of frzb-1/crescent function in primary mouth formation. At neurula stages (stage 17-22), frzb-1 and crescent are expressed in a subset of cells that will form the primary mouth (purple). In these cells, frzb-1 and crescent inhibit Wnt signaling, which in turn prevents the continued synthesis of proteins Laminin and Fibronectin. Without such proteins, the basement membrane integrity is lost and by early tailbud stages (stage 24-26) it disappears. The dissolution of the basement membrane leads to subsequent stages of primary mouth development including cell death, invagination, thinning and finally perforation. frzb-1/crescent-expressing cells are colored purple; ectoderm, blue; endoderm, yellow. The basement membrane (BM) is indicated by a black line; cg, cement gland.