title: Functional central rhythmicity and light entrainment, but not liver and muscle rhythmicity, are Clock independent.
abstract: The circadian rhythmicity of hormone secretion, body temperature, and sleep/wakefulness results from an endogenous rhythm of neural activity generated by clock genes in the suprachiasmatic nucleus (SCN). One of these genes, Clock, has been considered essential for the generation of cellular rhythmicity centrally and in the periphery; however, melatonin-proficient Clock(Delta19) + MEL mutant mice retain melatonin rhythmicity, suggesting that their central rhythmicity is intact. Here we show that melatonin production in these mutants was rhythmic in constant darkness and could be entrained by brief single daily light pulses. Under normal light-dark conditions, per2 and prokineticin2 (PK2) mRNA expression was rhythmic in the SCN of Clock(Delta19) + MEL mice. Expression of Bmal1 and npas2 was not altered, whereas per1 expression was arrhythmic. In contrast to the SCN, per1 and per2 expression, as well as Bmal1 expression in liver and skeletal muscle, together with plasma corticosterone, was arrhythmic in Clock(Delta19) + MEL mutant mice in normal light-dark conditions. npas2 mRNA was also arrhythmic in liver but rhythmic in muscle. The Clock(Delta19) mutation does not abolish central rhythmicity and light entrainment, suggesting that a functional Clock homolog, possibly npas2, exists in the SCN. Nevertheless, the SCN of Clock(Delta19) + MEL mutant mice cannot maintain liver and muscle rhythmicity through rhythmic outputs, including melatonin secretion, in the absence of functional Clock expression in the tissues. Therefore, liver and muscle, but not SCN, have an absolute requirement for CLOCK, with as yet unknown Clock-independent factors able to generate the latter.
authors.affiliation: Research Centre for Reproductive Health, Discipline of Obstetrics and Gynaecology, Medical School, University of Adelaide, Frome Rd., Adelaide, South Australia 5000, Australia. david.kennaway@adelaide.edu.au
authors.forename: David J
authors.initials: DJ
authors.lastname: Kennaway
authors.forename: Julie A
authors.initials: JA
authors.lastname: Owens
authors.forename: Athena
authors.initials: A
authors.lastname: Voultsios
authors.forename: Tamara J
authors.initials: TJ
authors.lastname: Varcoe
mesh_terms: D056930:ARNTL Transcription Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000502:physiology*; D003345:Corticosterone / Q000097:blood; D003624:Darkness; D005260:Female; D005768:Gastrointestinal Hormones / Q000235:genetics; D008099:Liver / Q000502:physiology*; D008297:Male; D008550:Melatonin / Q000097:blood; D051379:Mice; D008807:Mice, Inbred BALB C; D008808:Mice, Inbred CBA; D008817:Mice, Mutant Strains; D018482:Muscle, Skeletal / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics; D009479:Neuropeptides / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D056950:Period Circadian Proteins; D017440:Photoperiod; D010870:Pineal Gland / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics
chemical_list: D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D003345:Corticosterone; D005768:Gastrointestinal Hormones; D008550:Melatonin; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; C538961:Bmal1 protein, mouse; C491259:Npas2 protein, mouse; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; C486586:Prok2 protein, mouse; C538944:Clock protein, mouse