Colocalization of TGF-beta 1 and extracellular matrix proteins during rat tooth development

Recent studies suggest that TGF-beta 1 controls events in embryogenesis via its modulation of the extracellular matrix (ECM). During tooth development, histomorphogenetic and cytodifferentiation events are regulated by ECM-mediated epithelial-mesenchymal interactions. In this study, we have investigated the in vivo relationship of the localization of TGF-beta 1 to various ECM proteins, including glycosaminoglycans (GAGs), fibronectin, collagens I and III and to the enzyme alkaline phosphatase, at the early and late bell stages of rat molar tooth development. We have used polyclonal antibodies specific to peptides present in the precursor and processed forms of TGF-beta 1, fibronectin and Collagens I and III and immunohistochemical methods of detection. GAGs were stained with Alcian Blue GX and alkaline phosphatase was detected with the enzyme Naphthol-AS B1. Our results indicate that both the intracellular and extracellular forms of TGF-beta 1 are expressed in a site-specific manner, and that the growth factor colocalizes with alkaline phosphatase, fibronectin, collagens I and III and GAGs during the bell stages of tooth development. These data support the hypothesis that in tooth development, the actions of TGF-beta 1 may contribute to important qualitative changes in the composition and structure of extracellular matrices.