Radular teeth matrix protein 1 directs iron oxide deposition in chiton teeth

Abstract

Chitons deposit magnetite, a type of iron oxide, on the cusps of their radular teeth. The molecules that control the deposition of iron oxide on chiton teeth have not been identified. Using immunofluorescence staining, we found that chiton-specific radular teeth matrix protein 1 (RTMP1) is highly expressed in tooth epithelial cells prior to iron oxide deposition and preexists in the cusp at the site of iron oxide deposition. RTMP1 was found to be secreted from the elongated epithelial cells covering teeth and transported into teeth through microvilli. Moreover, recombinant RTMP1 exhibited the ability to form iron oxide. These results indicate that RTMP1 is a key molecule for iron oxide deposition in chiton teeth.