title: A tuftelin-interacting protein (TIP39) localizes to the apical secretory pole of mouse ameloblasts.
abstract: Enamel biomineralization is a complex process that involves interactions between extracellular matrix proteins. To identify proteins interacting with tuftelin, a potential nucleator of enamel crystallites, the yeast two-hybrid system was applied to a mouse tooth expression library and a tuftelin-interacting protein (TIP) was isolated for further characterization. Polyclonal antibodies were prepared against two recombinant variants of this protein. Both antibodies identified a major protein product in tooth organs at 39 kDa, and this protein has been called TIP39. Northern analysis showed TIP39 messenger RNA in multiple organs, a pattern similar to that of tuftelin messenger RNA. In situ hybridization of mandibles of 1-day-old mice detected TIP39 RNA in secretory ameloblasts and odontoblasts. Immunolocalization of TIP39 and tuftelin in cultured ameloblast-like cells showed that these two proteins colocalize. Within the developing tooth organ, TIP39 and tuftelin immunolocalized to the apical pole of secretory ameloblasts (Tomes' processes) and to the newly secreted extracellular enamel matrix. TIP39 amino acid sequence appears to be highly conserved with similarities to proteins in species as diverse as yeast and primates. Available sequence data and the findings reported here suggest a role for TIP39 in the secretory pathway of extracellular proteins.
authors.affiliation: Center for Craniofacial Molecular Biology, University of Southern California School of Dentistry, Los Angeles, California 90033-1004, USA. paine@hsc.usc.edu
authors.forename: C T
authors.initials: CT
authors.lastname: Paine
authors.forename: M L
authors.initials: ML
authors.lastname: Paine
authors.forename: W
authors.initials: W
authors.lastname: Luo
authors.forename: C T
authors.initials: CT
authors.lastname: Okamoto
authors.forename: S P
authors.initials: SP
authors.lastname: Lyngstadaas
authors.forename: M L
authors.initials: ML
authors.lastname: Snead
mesh_terms: D000565:Ameloblasts / Q000378:metabolism* / Q000648:ultrastructure; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D016764:Cell Polarity; D003746:Dental Enamel Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009928:Organ Specificity; D000072260:RNA Splicing Factors; D012333:RNA, Messenger / Q000032:analysis; D016601:RNA-Binding Proteins; D016415:Sequence Alignment; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D003746:Dental Enamel Proteins; D009687:Nuclear Proteins; D000072260:RNA Splicing Factors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C485860:TFIP11 protein, human; C412229:Tfip11 protein, mouse; D033921:Vesicular Transport Proteins; C038456:tuftelin