EXPRESSION AND LOCALIZATION OF FERRITIN MESSENGER-RNA IN AMELOBLASTS OF RAT INCISOR

At the maturation stage, the ameloblasts of the rat incisor incorporat e iron, supplied through the bloodstream, and deposit it into the surf ace layer of the enamel. In this unique iron transport system, ferriti n functions as a transient iron reservoir in the cells. Here the expre ssion of ferritin mRNA and its localization in the rat enamel organ wa s examined. Among various tissues, the enamel organ showed the highest expression for both ferritin Hand L-chain mRNA, as quantified by reve rse transcription-polymerase chain reaction. In situ hybridization usi ng digoxigenin-labelled cRNA probes for each chain demonstrated that b oth ferritin H- and L-chain mRNA were abundantly expressed in presecre tory and secretory ameloblasts, The intensity of the positive hybridiz ation signal gradually decreased toward the incisal direction. Differi ng from the mRNA localization, ferritin protein was immunologically un detectable in presecretory or secretory ameloblasts but was found in a meloblasts at the maturation stage, into which iron is known to be inc orporated from the bloodstream.Thus, the expression of ferritin mRNA p recedes the protein expression in the developmental stages of rat inci sor ameloblasts, and the translation of ferritin and its half-life are probably controlled by the iron entry, as has been reported for other cell types. (C) 1998 Elsevier Science Ltd. All rights reserved.