LAMININ GAMMA-2 EXPRESSION IS DEVELOPMENTALLY-REGULATED DURING MURINETOOTH MORPHOGENESIS AND IS INTENSE IN AMELOBLASTS

Mutations in the laminin gamma 2 gene cause junctional epidermolysis b ullosa, and enamel hypoplasias are frequently seen in these patients. Laminin gamma 2 is one of the three polypeptide chains forming the bas ement membrane glycoprotein laminin-5. We have localized the expressio n of the laminin gamma 2 gene by in situ hybridization during mouse to oth development from early morphogenesis to completion of crown develo pment. The expression was restricted to epithelial cells. During the e arly morphogenesis of the tooth germ, laminin gamma 2 was expressed by the outer dental epithelium and by the stellate reticulum cells. No e xpression was detected in the cells of the inner dental epithelium giv ing rise to ameloblasts. The pre-ameloblasts remained negative during the early bell stage, but, interestingly, expression was very prominen tly upregulated as the cells. differentiated into ameloblasts. This up regulation appeared to coincide with the start of enamel matrix secret ion. The ameloblasts expressed laminin gamma 2 intensely throughout th e period of active enamel deposition. The expression continued at a lo wer level in the maturation-stage ameloblasts covering the enamel surf ace. Immunolocalization of laminin-5 with polyclonal antibodies indica ted that the protein formed a continuous lining at the basal surfaces of the cells expressing the laminin gamma 2 transcripts. We suggest th at the role of laminin-5 during enamel formation may be to strengthen the anchorage of the ameloblasts to the enamel matrix, and that the pa thogenesis of enamel hypoplasias in cases of laminin-5 mutations could be associated with detachment of the ameloblast cell layer from the e namel surface.