title: Diurnal expression of the thrombopoietin gene is regulated by CLOCK.
abstract: BACKGROUND
  Most physiologic processes exhibit diurnal fluctuations controlled by the circadian regulation of sleep-wake behavior and feeding cycles. In addition, many cell types express endogenous circadian rhythms that affect cell-specific processes. Independent reports support the hypothesis that thrombopoietin (TPO) is under circadian control.
  
  
  OBJECTIVE
  The current study tested the hypothesis that CLOCK, a circadian transcription factor, may regulate Thpo, the gene encoding TPO.
  
  
  METHODS
  Circadian gene expression patterns were analyzed in mice and in human cell lines, Small interfering RNA was used to knock down CLOCK expression in cell lines, and gene expression was also examined in Clock(Δ19/Δ19) mutant mice.
  
  
  RESULTS
  It was found that there was a diurnal rhythm in the expression of Thpoin vivo in mice, and that this was associated with concomitant rhythms of protein abundance. Thpo was rhythmically expressed in human cell lines, consistent with the gene being directly or indirectly regulated by the circadian clock. Silencing of CLOCK in the Huh7 human hepatoma cell line led to a significant reduction in the rhythmicity of Thpo expression. The expression of Mpl in murine marrow also displayed diurnal rhythmicity in vivo. In Clock(Δ19/Δ19) mutant mice, Thpo and Mpl expression was disrupted and there was an increase in the number of mature megakaryocytes, but no change in the ploidy distribution within the megakaryocyte population.
  
  
  CONCLUSIONS
  These findings establish that Clock regulates Thpo and Mpl expression in vivo, and demonstrate an important link between the body's circadian timing mechanisms and megakaryopoiesis.
authors.affiliation: University/BHF Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Tracey
authors.forename: X
authors.initials: X
authors.lastname: Pan
authors.forename: J H
authors.initials: JH
authors.lastname: Catterson
authors.forename: A J
authors.initials: AJ
authors.lastname: Harmar
authors.forename: M M
authors.initials: MM
authors.lastname: Hussain
authors.forename: P S
authors.initials: PS
authors.lastname: Hartley
mesh_terms: D000818:Animals; D056926:CLOCK Proteins / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm / Q000235:genetics; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D010976:Platelet Count; D011003:Ploidies; D034622:RNA Interference; D053628:Receptors, Thrombopoietin / Q000235:genetics / Q000378:metabolism; D034061:Thrombopoiesis / Q000235:genetics; D013926:Thrombopoietin / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection
chemical_list: C481270:Mpl protein, mouse; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin; D056926:CLOCK Proteins; C538943:CLOCK protein, human; C538944:Clock protein, mouse