title: Tooth morphogenesis and ameloblast differentiation are regulated by micro-RNAs.
abstract: Teeth form as appendages of the ectoderm and their morphogenesis is regulated by tissue interactions mediated by networks of conserved signal pathways. Micro-RNA (miRNA) pathway has emerged as important regulator of various aspects of embryonic development, but its function in odontogenesis has not been elucidated. We show that the expression of RNAi pathway effectors is dynamic during tooth morphogenesis and differentiation of dental cells. Based on microarray profiling we selected 8 miRNAs expressed during morphogenesis and 7 miRNAs in the incisor cervical loop containing the stem cell niche. These miRNAs were mainly expressed in the dental epithelium. Conditional deletion of Dicer-1 in the epithelium (Dcr(K14)(-)(/)(-)) resulted in rather mild but significant aberrations in tooth shape and enamel formation. The cusp patterns of the Dcr(K14)(-)(/)(-) molar crowns resembled the patterns of both ancestral muroid rodents and mouse mutants with modulated signal pathways. In the Dcr(K14)(-)(/)(-) incisors, longitudinal grooves formed on the labial surface and these were shown to result from ectopic budding of the progenitor epithelium in the cervical loop. In addition, ameloblast differentiation was impaired and resulted in deficient enamel formation in molars and incisors. To help the identification of candidate target genes of the selected tooth enriched miRNAs, we constructed a new ectodermal organ oriented database, miRTooth. The predicted targets of the selected miRNAs included several components of the main morphogenetic signal pathways regulating tooth development. Based on our findings we suggest that miRNAs modulate tooth morphogenesis largely by fine tuning conserved signaling networks and that miRNAs may have played important roles during tooth evolution.
authors.affiliation: Institute of Biotechnology, Developmental Biology Program, PO Box 56, University of Helsinki, FIN-00014, Helsinki, Finland. Frederic.Michon@helsinki.fi
authors.forename: Frederic
authors.initials: F
authors.lastname: Michon
authors.forename: Mark
authors.initials: M
authors.lastname: Tummers
authors.forename: Marika
authors.initials: M
authors.lastname: Kyyrönen
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Frilander
authors.forename: Irma
authors.initials: I
authors.lastname: Thesleff
mesh_terms: D000565:Ameloblasts / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D004622:Embryo, Mammalian / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007180:Incisor / Q000196:embryology / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008822:Mice, Transgenic; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008963:Molar / Q000196:embryology / Q000378:metabolism / Q000648:ultrastructure; D009024:Morphogenesis / Q000235:genetics / Q000502:physiology*; D009805:Odontogenesis / Q000235:genetics; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D014070:Tooth / Q000166:cytology / Q000196:embryology* / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; D012333:RNA, Messenger