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International audience; During development, Bone Morphogenetic Proteins (BMPs) can induce apoptosis, cell growth or differentiation. These different effects are mediated by dimers of two types of BMP-receptors (BMPRs). To identify the responding cells during tooth development and search for possible tissue-or stage-specificities in the receptors involved, the distribution patterns of BMPR-IA, -IB and -II were investigated in the mouse molar, from bud to bell stage. At the bud stage, BMP-2 was suggested to be involved in the formation of an epithelial signaling center, the primary enamel knot (PEK), while BMP-4 would mediate the condensation of the mesenchyme. Immunostaining showed the presence of BMPR-IA and -II in the epithelium instead of BMPR-IB and -II in the mesenchyme. At the cap stage, BMPR-IB was detected in the epithelium but not BMPR-II, suggesting the existence of another type II receptor to form a functional dimer. At the late cap stage in the epithelium, BMP-4, BMPR-IA and -II were restricted to the internal part of the PEK and the stalk: two apoptotic areas. The three proteins were detected in the mesenchyme, showing a strong staining where cusps were about to form. At the late bell stage, BMP-2 or -4 may induce cell differentiation. BMPR-IB and -II were detected in odontoblasts instead of BMPR-IA and -II in ameloblasts. These results provide the first evidence of multiple type I and type II BMP-receptors, expressed in the dental epithelium and mesenchyme at different stages of development, to signal different cellular activities in a time- and tissue-specific way.

International audience; Determination of the left-right (L-R) axis was shown recently to implicate several genes, among which TGFbeta-related molecules such as Activin betaB, lefty1 and 2 and Nodal. We show here that Bmp4 and its signal transduction pathway partners BMPR IA and Smad1 are transiently expressed on the right side of Hensen's node, when L-R polarity is being established. Moreover, Smad1 is expressed asymmetrically in the nascent notochord. These observations suggest a role for a BMP4-dependent autocrine or paracrine mechanism during early L-R determination.