Armed to the teeth with αvβ6 integrin

Tooth enamel is the hardest mineralised tissue in the body and is produced by cells called ameloblasts. During the secretory stage of amelogenesis, enamel proteins such as amelogenin are secreted into the enamel matrix, which is in direct contact with the ameloblast plasma membrane. In most cell types, integrins mediate cell–matrix adhesion and signalling, but the receptors that mediate ameloblast adhesion and matrix production are not well characterised. Hannu Larjava and colleagues (p. 732) hypothesised that integrin αvβ6, which might have a role in protection from periodontal disease, is expressed in ameloblasts where it regulates biomineralisation of enamel. The authors show that both human and mouse ameloblasts express β6 integrin mRNA and protein. In mice deficient in αvβ6 integrin (Itgb6^−/−), they found chalky rounded incisors, with a significantly reduced mineral-to-protein ratio, whereas the molars of these mice show reduced mineralisation and severe attrition. These phenotypes are rescued by the expression of Itgb6 under the control of the K14 promoter using a transgenic mouse approach. Interestingly, the abnormal accumulation of amelogenin-rich extracellular matrix the authors see in Itgb6^−/− teeth is primarily due to increased amelogenin synthesis rather than reduced removal of the matrix proteins. Larjava et al. conclude that integrin αvβ6 does indeed have a crucial role in regulating the deposition of amelogenin and subsequent enamel biomineralisation.