HEPATOCYTE GROWTH-FACTOR IS INVOLVED IN THE MORPHOGENESIS OF TOOTH GERM IN MURINE MOLARS

The patterns of gene expression for hepatocyte growth factor (HGF) and its receptor, c-Met, were revealed in the tooth germ of rat mandibula r molars using RT-PCR, In situ hybridization demonstrated that the HGF gene was expressed only in the cells of the dental papilla of the too th germ in vivo. The characteristic temporospatial distribution of HGF and c-Met during germ development was revealed using immunohistochemi cal studies in vivo, In order to demonstrate the functional role playe d by HGF in tooth development, HGF translation arrest by antisense pho sphorothioate oligodeoxynucleotide (ODN) was carried out in vitro, In the control experiment, explants of tooth germs from embryonic 14 day mice were cultured in a modification of Trowell's system under serum-f ree and chemically defined conditions for two weeks, Other explants we re cultured with 15mer antisense or sense ODN targeted to the HGF mRNA , Both the control and the sense-treated explants showed normal histol ogical structure, as observed in vivo, On the other hand, antisense-tr eated explants exhibited an abnormal structure in which the enamel org ans were surrounded by a thin layer of dentin and dental papilla, appe aring 'inside-out' compared to the control and sense-treated explants, although the cytodifferentiation of ameloblasts and odontoblasts was not inhibited, The explants treated with recombinant human HGF combine d with antisense ODN showed normal development, indicating that exogen ous HGF rescued the explants from the abnormal structure caused by ant isense ODN, The findings of a BrdU incorporation experiment suggested that the imbalance between the proliferation activity of the inner ena mel epithelium and that of the dental papilla caused by HGF translatio n arrest results in the abnormal structure of the tooth germ, These re sults indicate that HGF is involved in the morphogenesis of the murine molar.