Figure 1. LacZ is strongly expressed during early tooth morphogenesis in Bmp4^lacZneo knock-in mice, while LacZ expression in transgenic mice harboring the 2.4-kb Bmp4 promoter LacZ (Bmp4 LacZ ^2.4p) construct is absent when evaluated at the same developmental stages. (A) Stage E11.5 whole-mount embryos from heterozygous Bmp4^lacZneo knock-in (left panel) and Bmp4LacZ^2.4p (right panel) mice were stained for β-galactosidase activity overnight. Note that expression signals in the somites are similar in Bmp4^lacZneo knock-in mice and Bmp4LacZ^2.4p mice, although the expression levels are different. A series of frozen sections from early incisor tooth buds from E12.5 (B), E13.5 (C), and E15.5 (D) embryos was stained with x-gal. A schematic construct map is displayed in the lower panels. Expression of LacZ in mice harboring the Bmp4^lacZneo knock-in construct, in which the NLS-LacZ-neo cassette replaces part of Exon3 in the mouse Bmp4 gene, is a sensitive indicator of endogenous Bmp4 expression. Abbreviations: E, epithelium; M, mesenchyme; DF, dental follicle; DO, dental organ; DP, dental papilla. The data shown are representative of three separate experiments in the same developmental stages.