EXPRESSION AND LOCALIZATION OF LAMININ-5 SUBUNITS DURING MOUSE TOOTH DEVELOPMENT

Tooth morphogenesis is regulated by epithelial-mesenchymal interaction s mediated by the easement membrane (BM). Laminins are major glycoprot ein components of the BMs, which are involved in several cellular acti vities. The expression and localization of the alpha 3, beta 3, and ga mma 2 laminin-5 subunits have been analyzed by in situ hybridization a nd immunohistochemistry during mouse molar development, Initially (E12 ), mRNAs of all subunits were detected in the entire dental epithelium and the corresponding proteins were located in the BM. During cap for mation (E13-14), transcripts for the alpha 3 and gamma 2 subunits were localized in tile outer dental epithelium (ODE), whereas the beta 3 s ubunit mRNA was present in the inner dental epithelium (IDE). During t he early bell stage (E16), immunoreactivity for all subunits disappear ed from the BM along the IDE, although intense signals for beta 3 mRNA were detectable in cells of the IDE, Subsequently, when the dentinal matrix was secreted by odontoblasts (E18-19.5), mRNAs of all three sub units were re-expressed by ameloblasts, and the corresponding proteins were detected in ameloblasts and in the enamel matrix, Tissue recombi nation experiments demonstrated that when E16 IDE or ODE was associate d with E18 dental papilla mesenchyme, immunostaining for all laminin-5 subunits disappeared from the BM, whereas when cultured with non-dent al limb bud mesenchyme, they remained positive after 48 hr of culture, These results suggest that the temporospatial expression of laminin-5 subunits in tooth development, which appears to be differentially con trolled by the dental mesenchyme, might be related to the enamel organ histo-morphogenesis and the ameloblast differentiation. (C) 1998 Wile y-Liss, Inc.