title: Epithelial-specific knockout of the Rac1 gene leads to enamel defects.
abstract: The Ras-related C3 botulinum toxin substrate 1 (Rac1) gene encodes a 21-kDa GTP-binding protein belonging to the RAS superfamily. RAS members play important roles in controlling focal adhesion complex formation and cytoskeleton contraction, activities with consequences for cell growth, adhesion, migration, and differentiation. To examine the role(s) played by RAC1 protein in cell-matrix interactions and enamel matrix biomineralization, we used the Cre/loxP binary recombination system to characterize the expression of enamel matrix proteins and enamel formation in Rac1 knockout mice (Rac1(-/-)). Mating between mice bearing the floxed Rac1 allele and mice bearing a cytokeratin 14-Cre transgene generated mice in which Rac1 was absent from epithelial organs. Enamel of the Rac1 conditional knockout mouse was characterized by light microscopy, backscattered electron imaging in the scanning electron microscope, microcomputed tomography, and histochemistry. Enamel matrix protein expression was analyzed by western blotting. Major findings showed that the Tomes' processes of Rac1(-/-) ameloblasts lose contact with the forming enamel matrix in unerupted teeth, the amounts of amelogenin and ameloblastin are reduced in Rac1(-/-) ameloblasts, and after eruption, the enamel from Rac1(-/-) mice displays severe structural defects with a complete loss of enamel. These results support an essential role for RAC1 in the dental epithelium involving cell-matrix interactions and matrix biomineralization.
authors.affiliation: The Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA 90033, USA. zhanhuan@usc.edu
authors.forename: Zhan
authors.initials: Z
authors.lastname: Huang
authors.forename: Jieun
authors.initials: J
authors.lastname: Kim
authors.forename: Rodrigo S
authors.initials: RS
authors.lastname: Lacruz
authors.forename: Pablo
authors.initials: P
authors.lastname: Bringas
authors.forename: Michael
authors.initials: M
authors.lastname: Glogauer
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Bromage
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Kaartinen
authors.forename: Malcolm L
authors.initials: ML
authors.lastname: Snead
mesh_terms: D000565:Ameloblasts / Q000378:metabolism / Q000473:pathology; D000566:Amelogenesis / Q000235:genetics*; D053523:Amelogenin / Q000096:biosynthesis; D000818:Animals; D003743:Dental Enamel / Q000002:abnormalities*; D003744:Dental Enamel Hypoplasia / Q000235:genetics*; D003746:Dental Enamel Proteins / Q000096:biosynthesis; D004848:Epithelium / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D015398:Signal Transduction / Q000235:genetics; D014074:Tooth Calcification / Q000235:genetics; D020830:rac1 GTP-Binding Protein / Q000235:genetics* / Q000502:physiology*
chemical_list: C490890:Ambn protein, mouse; D053523:Amelogenin; D003746:Dental Enamel Proteins; D020830:rac1 GTP-Binding Protein