Analysis of Cre mediated recombination. A, Solid triangles represent the loxP sites, and “E” represents the EcoRI restriction endonuclease site. Primers (arrows) F7 and B4 amplified the 600 bp wild-type allele; primers F6 and B6 amplified the 400 bp C/EBPαfl/fl allele; primers F4 and B4 amplified the 900 bp C/EBPα−/− allele. B, K14-Cre mice were mated with R26R transgenic mice and the first molars recovered by microdissection and subjected to β-galactosidase (lacZ) staining. Only epithelial cells (E) of the enamel organ, including the lingual enamel organ epithelia (open arrows) show positive reaction for lacZ staining while mesenchymal cells (M) are completely free of lacZ staining. C, Mandibles of newborn mice were used to produce frozen sections and subjected to lacZ staining to ascertain Cre recombination on a cell-by-cell basis. Occasional unstained ameloblast cells (arrow) were observed in the maturing region (d) and secretory region (e) of the incisor and in molars (f). M1, first molar; M2, second molar.