Expression and localization of laminin-5 subunits in the mouse incisor.

Laminin-5 is associated with several epithelial tissues and forms part of the anchoring filaments of hemidesmosomes. Recent data have shown that the expression of laminin-5 subunits is impaired in junctional epidermolysis bullosa (JEB), and, in these patients, enamel hypoplasia is commonly observed. Rodent incisors are continuously growing teeth with an asymmetry between their labial and lingual sides. Enamel matrix formation is restricted to the labial side. We have analyzed the changes in the expression and localization of laminin-5 subunits (alpha3, beta3, and gamma2) in lower incisors of the mouse. The apical loop located at the end of the labial side contained stem cells and showed expression for all laminin-5 subunits. In the anterior direction, the inner dental epithelial cells (IDE) transiently lost the immunoreactivity for all subunits, whereas the transcripts for the beta3 subunit remained in the IDE. All subunit mRNAs and proteins were expressed in ameloblasts facing predentine and also in secretory and maturation stage ameloblasts. Enamel matrix contained laminin-5. On the lingual side, the expression of laminin-5 subunits was continuous from the epithelial root sheath to the epithelial rests of Malassez in the periodontal ligament. These results suggest that spatial and temporal regulation of laminin-5 subunits correlates with the histogenesis of the dental organ, ameloblast differentiation, and enamel formation and also that laminin-5 plays a role in the adhesion between dental epithelial cells and the extracellular matrix (enamel or dentine) in areas where the dental basement membrane is absent.