Differential expression of laminin-5 subunits during incisor and molar development in the mouse

Rodent incisors are continuously growing teeth and enamel deposition is res tricted to the labial side. In the present study, the expression of laminin -5 subunits (alpha 3, beta 3 and gamma 2) has been analyzed by in site hybr idization in developing mouse lower incisors and compared to that reported in the molar. At the bud stage (E12), mRNAs for all subunits were detected in the whole epithelial thickening. At E14,when histogenesis had started,tr anscripts for a alpha 3 and gamma 2 subunits were restricted to the outer d ental epithelium (ODE), whereas the beta 3 subunit was intensely expressed in the inner dental epithelium (IDE). A transient expression for alpha 3 su bunit was seen in the enamel knot area and disappeared at E15. Subsequently , all laminin-5 subunit genes were re-expressed in differentiating amelobla sts on the labial side. Similar patterns of transcription were observed in incisor and molar, suggesting that the differential expression of laminin-5 subunits in the IDE might be involved in the histogenesis of the IDE and a meloblast differentiation. At E16.5, cells of the IDE at the anterior extre mity of the incisor and in the anterior part of the lingual IDE expressed t ranscripts for a3 and beta 3 but not for gamma 2 subunit. Similar expressio n patterns were observed in the enamel-free areas of the E18 molar. This sp ecific expression might thus be related to cells that do not differentiate as functional ameloblasts. Throughout incisor development, intense expressi on for all laminin-5 subunits was restricted to the labial side of the cerv ical loop. The asymmetrical expression of laminin-5 might be related to inc isor morphogenesis and to the differences in histogenesis and cytodifferent iation of the IDE that exist in the labial versus lingual aspect of the cer vical loop.