E-cadherin and P-cadherin comprise a critical cadherin threshold at the fusion site. (A) Optical slice of immunostained tissue sections shows decreased P-cadherin in Ctnnd1^f/f; Crect^Tg/0 mutants (n = 3) compared with controls (n = 3) at 5–7ts. Scale bar, 20 μm. (B) Immunofluorescence on sections of the prefusion junction detects decreased E-cadherin but not P-cadherin in 10ts Cdh1^f/f; Crect^Tg/0 mutants (n = 5) compared with controls (n = 5). MNP, medial nasal process; LNP, lateral nasal process. Scale bar, 20 μm. (C) Schematic of Cdh1/Cdh3 loci depicting Cdh3 mutations with linked Cdh1 alleles. Red triangles, loxP sites. (D)Cdh3^−/−; Cdh1^f/+ embryos appear similar to controls at E12.5. Scale bar, 500 μm. Immunofluorescence on sections of the fusion junction detects decreased P-cadherin but not E-cadherin in 20ts Cdh3^−/−; Cdh1^f/f mutants (n = 4) compared with control (n = 4). MNP, medial nasal process; LNP, lateral nasal process. Scale bars, 20 μm. (E) Cleft lip (white arrow) was detected in 4/9 E12.5 Cdh3^+/−; Cdh1^f/f; Crect^Tg/0 but not Cdh3^−/−; Cdh1^f/+; Crect^Tg/0 embryos. Cdh3^−/−; Cdh1^f/f; Crect^Tg/0 embryos at E10.5 exhibit dramatic dysmorphology. Scale bars, 500 μm.