Expression and localization of laminin-5 subunits during mouse tooth development

Abstract

Tooth morphogenesis is regulated by epithelial‐mesenchymal interactions mediated by the basement membrane (BM). Laminins are major glycoprotein components of the BMs, which are involved in several cellular activities. The expression and localization of the α3, β3, and γ2 laminin‐5 subunits have been analyzed by in situ hybridization and 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 formation (E13‐14), transcripts for the α3 and γ2 subunits were localized in the outer dental epithelium (ODE), whereas the β3 subunit mRNA was present in the inner dental epithelium (IDE). During the early bell stage (E16), immunoreactivity for all subunits disappeared from the BM along the IDE, although intense signals for β3 mRNA were detectable in cells of the IDE. Subsequently, when the dentinal matrix was secreted by odontoblasts (E18‐19.5), mRNAs of all three subunits were re‐expressed by ameloblasts, and the corresponding proteins were detected in ameloblasts and in the enamel matrix. Tissue recombination experiments demonstrated that when E16 IDE or ODE was associated with E18 dental papilla mesenchyme, immunostaining for all laminin‐5 subunits disappeared from the BM, whereas when cultured with non‐dental limb bud mesenchyme, they remained positive after 48 hr of culture. These results suggest that the temporo‐spatial expression of laminin‐5 subunits in tooth development, which appears to be differentially controlled by the dental mesenchyme, might be related to the enamel organ histo‐morphogenesis and the ameloblast differentiation. Dev. Dyn. 1998;211:164–176. © 1998 Wiley‐Liss, Inc.

Epigenetic Signals during Odontoblast Differentiation

“…A permanent remodeling of the BM is thus required to allow for the adequate maintenance of this structure with the progressive and coordinated evolution of both the IDE and pre-odontoblasts/odontoblasts. This remodeling has been documented (Osman and Ruch, 1981;Lesot et al, 1981;Mark et al, 1990;Thesleff et al, 1995;Yoshiba et al, 1998), and both the IDE and pre-odontoblasts contribute to the turnover of the BM (Ruch et al, 1995;Yoshiba et al, 1998).…”

“…The BM is a complex structure that includes the basal lamina and the lamina fibroreticularis (Merker, 1994). Collagen type IV, laminin 1, entactin/nidogen, and heparan sulfate are all present in the dental basal lamina (Lesot et al, 1981;Thesleff et al, 1981;Kubler et al, 1988;Yoshiba et al, 1998Yoshiba et al, , 2000. Heparan sulfate temporarily disappears from the BM during cap and bell formation, but later re-appears during odontoblast differentiation (Kogaya et al, 1990).…”

Phenotype and Variant Spectrum in theLAMB3Form of Amelogenesis Imperfecta

“…One hypothesis explaining the formation of multiple cusps is that mutated LAMB3 affects secondary enamel knot patterning, due to loss of normal function or a gain of toxic function. Interestingly, LAMB3 is expressed strongly in the enamel knot during the cap stage of tooth development, unlike the LAMA3 and LAMC2 subunits of LM332 (Yoshiba et al 1998a), potentially suggesting a role independent from the LM332 heterotrimer. If, as widely believed, each secondary enamel knot is associated with the development of 1 cusp (Thesleff et al 2001), disorganization or fragmentation of secondary enamel knots could lead to the formation of additional cusps.…”

Dental Epithelial Histomorphogenesisin vitro

“…3). The BM also showed a different composition when in contact with the IDE or ODE (Yoshiba et al, 1998;Nagai et al, 2001). The trypsin dissociation led to the hydrolysis of the BM and also affected the extracellular matrix in the mesenchyme and cell surfaces in both the epithelium and mesenchyme (Lesot et al, 1981;Osman and Ruch, 1981).…”