title: Ontogenesis of photoperiodic entrainment of the molecular core clockwork in the rat suprachiasmatic nucleus.
abstract: The molecular mechanism underlying a generation of circadian rhythmicity within the suprachiasmatic nucleus (SCN) is based on interactive negative and positive feedback loops that drive the rhythmic transcription of clock genes and translation of their protein products. In adults, the molecular mechanism is affected by seasonal changes in day length, i.e., photoperiod. The photoperiod modulates phase, waveform, and amplitude of the rhythmic clock genes expression as well as the phase relationship between their profiles. To ascertain when and how the photoperiod affects the circadian core clock mechanism during ontogenesis, the rhythmic expression of clock genes, namely of Per1, Per2, Cry1 and Bmal1 was determined in 3-, 10- and 20-day-old rat pups maintained under either a long photoperiod with 16 h of light and 8 h of darkness per day (LD 16:8) or under a short, LD 8:16 photoperiod. The daily profiles in the level of clock genes mRNA were studied in constant darkness. The photoperiod affected the profile of Per1 and Per2 mRNA in 20- and 10- but not yet in 3-day-old pups. Expression of Cry1 was affected only in 20-day-old pups, whereas expression of Bmal1 was not yet affected even in 20-day-old rats. The results demonstrate no effect of the photoperiod on 3-day-old pups, only partial entrainment of the molecular core clockwork in 10-day-old pups and a more mature, though not yet fully complete, entrainment in 20-day-old pups as compared with adult animals. The developmental interval when the photoperiod begins to entrain the core clock mechanism completely might thus occur around the time of weaning.
authors.affiliation: Department of Neurohumoral Regulations, Institute of Physiology, Academy of Sciences of the Czech Republic, Vídenská 1083, 142 20 Prague 4, Czech Republic.
authors.forename: Z
authors.initials: Z
authors.lastname: Kováciková
authors.forename: M
authors.initials: M
authors.lastname: Sládek
authors.forename: K
authors.initials: K
authors.lastname: Laurinová
authors.forename: Z
authors.initials: Z
authors.lastname: Bendová
authors.forename: H
authors.initials: H
authors.lastname: Illnerová
authors.forename: A
authors.initials: A
authors.lastname: Sumová
mesh_terms: D056930:ARNTL Transcription Factors; D000375:Aging / Q000235:genetics*; D000704:Analysis of Variance; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D001683:Biological Clocks / Q000235:genetics*; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000235:genetics*; D056931:Cryptochromes; D005260:Female; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D008027:Light; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins; D017440:Photoperiod; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000528:radiation effects; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D056931:Cryptochromes; D005420:Flavoproteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; C538961:Bmal1 protein, mouse; C538964:Cry1 protein, mouse; C538965:Cry1 protein, rat; C539023:Per1 protein, mouse; C539024:Per1 protein, rat; C513312:Per2 protein, mouse; C513311:Per2 protein, rat; C538944:Clock protein, mouse; C538945:Clock protein, rat