title: Circadian rhythms and gene expression during mouse molar tooth development.
abstract: OBJECTIVE
  Incremental markings in dental enamel suggest that the circadian clock may influence the molecular underpinnings orchestrating enamel formation. The aim of this study was to investigate whether the genes and microRNAs (miRNAs) oscillate in a circadian pattern during tooth and enamel development.
  
  
  METHODS
  Comparative gene and miRNA expression profiling of the first mandibular molar tooth germ isolated at different time-points during the light and night period was performed using microarrays and validated using real-time RT-PCR. Bioinformatic analysis was carried out using Ingenuity Pathway Analysis (IPA), and TargetScan software was used in order to identify computationally predicted miRNA-mRNA target relationships.
  
  
  RESULTS
  In total, 439 genes and 32 miRNAs exhibited significantly different (p < 0.05) levels of expression in the light phase compared with the night phase tooth germs. Genes involved in enamel formation, i.e. Amelx, Ambn, Amtn, and Odam, oscillated in a circadian pattern. Furthermore, the circadian clock genes, in particular Clock and Bmal1, oscillated in mouse molar tooth germ during 24-h intervals. The expression of Clock and Bmal1 was inversely correlated with the expression of miR-182 and miR-141, respectively.
  
  
  CONCLUSIONS
  MiRNAs, including miR-182 and miR-141, are involved in the control of peripheral circadian rhythms in the developing tooth by regulating the expression of genes coding for circadian transcription factors such as CLOCK and BMAL1. Regulation of circadian rhythms may be important for enamel phenotype, and the morphology of dental enamel may vary between individuals due to differences in circadian profiles.
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Minou
authors.initials: M
authors.lastname: Nirvani
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Cuong
authors.initials: C
authors.lastname: Khuu
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.|b Department of Medical Biochemistry , Oslo University Hospital , Oslo , Norway.|c Department of Ophthalmology , Drammen Hospital, Vestre Viken Hospital Trust , Drammen , Norway.|d Faculty of Health Sciences , University College of South East Norway , Kongsberg, Norway.
authors.forename: Tor Paaske
authors.initials: TP
authors.lastname: Utheim
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Henriette Stavik
authors.initials: HS
authors.lastname: Hollingen
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Simon Furre
authors.initials: SF
authors.lastname: Amundsen
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Lars Peter
authors.initials: LP
authors.lastname: Sand
authors.affiliation: a Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.
authors.forename: Amer
authors.initials: A
authors.lastname: Sehic
mesh_terms: D000566:Amelogenesis; D000818:Animals; D002940:Circadian Rhythm; D003743:Dental Enamel / Q000254:growth & development; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D035683:MicroRNAs; D008963:Molar / Q000737:chemistry / Q000254:growth & development*; D009805:Odontogenesis / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D014074:Tooth Calcification / Q000235:genetics*; D014083:Tooth Germ / Q000254:growth & development*
chemical_list: D035683:MicroRNAs; D012333:RNA, Messenger
keywords: Clock genes; dental enamel; microRNAs; microarrays; odontogenesis