Putative role of basement membrane for dentinogenesis in the mesenchyme ofmurine dental papillae in vitro

In a new culture-conditioning system of agar-coated mesenchyme of isolated incisor dental papillae, dentinogenesis has been induced adjacent to an aga r substratum that functions as a foothold for cell immobilisation. To eluci date the role of the basement membrane (BM) in dentinogenesis, we have exam ined the way in which dentinogenesis depends upon BM components or transfor ming growth factor (TGF)-beta (1) in this system. At the mesenchymal-epithe lial junction of odontogenic organs (cut incisor tooth germs), TGF-beta (1) visibly increased in the BM during incubation. In isolated dental papillae , BM components were synthesised and deposited at aligned peripheral cells of the explants, together with an increasing amount of TGF-beta (1). These components were not assembled into extracellular matrix (ECM)-absorbed agar adjacent to explants, although dentinogenesis proceeded in the presence of pericellular BM components associated with TGF-beta (1). When signalling v ia TGF-beta type II receptors was blocked, neither ECM production nor denti nogenesis was observed but explants partially detached from the agar surfac e, presumably as a result of the suppressed production of ECM, since attach ment was retained by pre-coating explants with artificial matrices. Rescue experiments showed that TGF-beta (1) regulated dentinogenesis through ECM p roduction. With regard to BM components, inducible dentinogenesis was Arg-C ly-Asp (RGD)-dependent. Thus, pericellular BM components associated with TG F-beta (1) and an ECM-absorbed agar substratum, which affects dentinogenesi s, synergistically play a role similar to that of BM components in vivo. Th e BM therefore serves as a structural meshwork that acts as a foothold for cell immobilisation; its components act as ligands for RGD-dependent cell a dhesion and it stores TGF-beta (1), which regulates ECM production.