title: GTPases RhoA and Rac1 are important for amelogenin and DSPP expression during differentiation of ameloblasts and odontoblasts.
abstract: Morphogenesis and cytodifferentiation are distinct processes in tooth development. Cell proliferation predominates in morphogenesis; differentiation involves changes in form and gene expression. The cytoskeleton is essential for both processes, being regulated by Rho GTPases. The aim of this study was to verify the expression, distribution, and role of Rho GTPases in ameloblasts and odontoblasts during tooth development in correlation with actin and tubulin arrangements and amelogenin and dentin sialophosphoprotein (DSPP) expression. RhoA, Rac1, and Cdc42 were strongly expressed during morphogenesis; during cytodifferentiation, RhoA was present in ameloblasts and odontoblasts, Rac1 and its effector Pak3 were observed in ameloblasts; and Cdc42 was present in all cells of the tooth germ and mesenchyme. The expression of RhoA mRNA and its effectors RockI and RockII, Rac1 and Pak3, as analyzed by real-time polymerase chain reaction, increased after ameloblast and odontoblast differentiation, according to the mRNA expression of amelogenin and DSPP. The inhibition of all Rho GTPases by Clostridium difficile toxin A completely abolished amelogenin and DSPP expression in tooth germs cultured in anterior eye chamber, whereas the specific inhibition of the Rocks showed only a partial effect. Thus, both GTPases are important during tooth morphogenesis. During cytodifferentiation, Rho proteins are essential for the complete differentiation of ameloblasts and odontoblasts by regulating the expression of amelogenin and DSPP. RhoA and its effector RockI contribute to this role. A specific function for Rac1 in ameloblasts remains to be elucidated; its punctate distribution indicates its possible role in exocytosis/endocytosis.
authors.affiliation: Department of Cell and Developmental Biology, University of São Paulo, São Paulo, SP, Brazil. micbiz@uol.com.br
authors.forename: Michelle Tillmann
authors.initials: MT
authors.lastname: Biz
authors.forename: Mara Rúbia
authors.initials: MR
authors.lastname: Marques
authors.forename: Virgínia Oliveira
authors.initials: VO
authors.lastname: Crema
authors.forename: Anselmo Sigari
authors.initials: AS
authors.lastname: Moriscot
authors.forename: Marinilce Fagundes
authors.initials: MF
authors.lastname: dos Santos
mesh_terms: D000565:Ameloblasts / Q000166:cytology* / Q000201:enzymology; D053523:Amelogenin / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D015971:Gene Expression Regulation, Enzymologic; D009804:Odontoblasts / Q000166:cytology* / Q000201:enzymology; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012795:Sialoglycoproteins / Q000235:genetics / Q000378:metabolism*; D014070:Tooth / Q000166:cytology / Q000201:enzymology / Q000254:growth & development; D014083:Tooth Germ / Q000166:cytology / Q000201:enzymology / Q000254:growth & development; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000235:genetics / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D000099311:Dentin Sialophosphoprotein
chemical_list: D053523:Amelogenin; D016326:Extracellular Matrix Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D012795:Sialoglycoproteins; D020830:rac1 GTP-Binding Protein; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D000099311:Dentin Sialophosphoprotein