title: The role of Clock in the plasticity of circadian entrainment.
abstract: The mammalian circadian clock lying in suprachiasmatic nucleus (SCN) is synchronized to about 24 h by the environmental light-dark cycle (LD). The circadian clock exhibits limits of entrainment above and below 24 h, beyond which it will not entrain. Little is known about the mechanisms regulating the limits of entrainment. In this study, we show that wild-type mice entrain to only an LD 24 h cycle, whereas Clock mutant mice can entrain to an LD 24, 28, and 32 h except for LD 20 h and LD 36 h cycle. Under an LD 28 h cycle, Clock mutant mice showed a clear rhythm in Per2 mRNA expression in the SCN and behavior. Light response was also increased. This is the first report to show that the Clock mutation makes it possible to adapt the circadian oscillator to a long period cycle and indicates that the clock gene may have an important role for the limits of entrainment of the SCN to LD cycle.
authors.affiliation: Department of Pharmacology, School of Science and Engineering, Waseda University, Bldg 61, Room 515, Ohkubo 3-4-1, Shinjuku-ku, Tokyo 169-8555, Japan.
authors.forename: Ryuta
authors.initials: R
authors.lastname: Udo
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Hamada
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Horikawa
authors.forename: Eiko
authors.initials: E
authors.lastname: Iwahana
authors.forename: Kazuko
authors.initials: K
authors.lastname: Miyakawa
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Otsuka
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Shibata
mesh_terms: D000818:Animals; D001831:Body Temperature; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D003624:Darkness; D015870:Gene Expression; D005838:Genotype; D008027:Light; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D009043:Motor Activity / Q000235:genetics / Q000502:physiology; D009154:Mutation; D009687:Nuclear Proteins / Q000096:biosynthesis; D056950:Period Circadian Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D056926:CLOCK Proteins; C538944:Clock protein, mouse