CULTURED INCISORS DISPLAY MAJOR MODIFICATIONS IN BASAL LAMINA DEPOSITION WITHOUT FURTHER EFFECT ON ODONTOBLAST DIFFERENTIATION

Matrix-mediated epithelio-mesenchymal interactions play a crucial role in the control of dental cytodifferentiations. Ultrastructural observ ation of the epithelio-mesenchymal junction in cultured embryonic mous e molars showed discrete zones with duplicated or multilayered basal l aminae. The use of synthetic peptides demonstrated that the process wa s RGD()-independent, did not involve the YIGSR(*) sequence present on laminin and could occur spontaneously. Cultured incisors showed a sim ilar but much more dramatic multiplication of the basal lamina. Furthe rmore, the deposition of multilayered basal laminae was specific for t he labial aspect of the tooth and could be detected after 6 h of cultu re. Despite these alterations, preodontoblasts differentiated and grad ients of differentiation were maintained, suggesting that among baseme nt membrane constituents, the basal lamina itself does not play a crit ical role. More important is the inner dental epithelium which may sti ll control odontoblast differentiation by means of diffusible molecule s able to reach surface receptors expressed by preodontoblasts or matr ix receptors underlying the basal lamina. Gradients of odontoblast dif ferentiation could result from a progressive acquisition of competence by preodontoblasts.