Inhibition of apoptosis in the primary enamel knot does not affect specific tooth crown morphogenesis in the mouse

The enamel knot (EK), located in the center of cap-stage tooth germs, is a transitory duster of non-dividing epithelial cells, eventually linked to th e outer dental epithelium by the enamel septum (ES). It might act as a sign aling center providing positional information for tooth morphogenesis and c ould regulate the growth of tooth cusps through the induction of secondary signaling EKs. The EK undergoes apoptosis, which could constitute a mechani sm whereby the signaling functions of this structure are terminated. Recent ly, we demonstrated the segregation of 5-bromo-2'-deoxyuridine (BrdU) negat ive inner dental epithelial (IDE) cells of the EK into as many individual g roups of cells as cusps will form and suggested a morphogenetic role for th ese particular IDE cells. Using Z-VAD-fmk, a specific caspase inhibitor, ap optosis in the primary EK of first mouse lower cap-staged molars and lower incisors cultured in vitro was abrogated. No obvious histological alteratio ns were observed in the incisors, whereas a prominent EK and an ES connecti ng the outer dental epithelium (ODE) and the BrdU negative IDE cells cappin g cusp L2 were observed in the molars. EK specific transcription (Shh, Msx- 2, Bmp-2, Bmp4) was down-regulated in the body of these structures with the exception of the associated IDE cells. In these experimental conditions, s egregation of non-dividing transcriptionally active IDE cells occurred and a normal cusp pattern was expressed.