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 ep idermolysis bullosa (JEB), and, in these patients, enamel hypoplasia i s commonly observed. Rodent incisors are continuously growing teeth wi th an asymmetry between their labial and lingual sides. Enamel matrix formation is restricted to the labial side. We have analyzed the chang es in the expression and localization of laminin-5 subunits (alpha 3, beta 3, and gamma 2) in lower incisors of the mouse. The apical loop l ocated at the end of the labial side contained stem cells and showed e xpression for all laminin-5 subunits. In the anterior direction, the i nner dental epithelial cells (LDE) transiently lost the immunoreactivi ty for all subunits, whereas the transcripts for the beta 3 subunit re mained in the IDE. All subunit mRNAs and proteins were expressed in am eloblasts 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 epithelia l root sheath to the epithelial rests of Malassez in the periodontal l igament. These results suggest that spatial and temporal regulation of laminin-5 subunits correlates with the histogenesis of the dental org an, ameloblast differentiation, and enamel formation and also that lam inin-5 plays a role in the adhesion between dental epithelial cells an d the extracellular matrix (enamel or dentine) in areas where the dent al basement membrane is absent.