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Results for “Biological Clocks”

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PubMed2003

The molecular workings of the Neurospora biological clock.

In Neurosporacrassa the FRQ/WC feedback loop has been shown to be central to the function of the circadian clock. Similar to other eukaryotic systems it is based on a transcription-translation PAS heterodimer type feedback. FRQ levels cycle with a period identical to that of the Neurospora circadian cycle and its expression is rapidly induced by light. A complex of White Collar 1 (WC-1) and White Collar 2 (WC-2) (the WCC) is required for the transcriptional activation of frq. The oscillation in frq message is transcriptionally regulated via a single necessary and sufficient cis-acting element in the frq promoter, the Clock-Box (CB) bound by WCC. Light-induction of frq transcription is mediated by WCC binding to two cis-acting elements (LREs) in the frq promoter. WC-1, with flavin adenine dinucleotide (FAD) as a cofactor, is the blue-light photoreceptor. The original description of a frq-null strain, frq9, (Loros et al 1986) included a description of oscillations in asexual conidial banding that occasionally appeared following 3 to 7 days of arrhythmic development now referred to as FLO for FRQ-less oscillator. Unlike the intact clock, FLO period is sensitive to media composition. We have identified a circadianly regulated gene whose mutation interferes with FLO even under temperature entrainment conditions. This same mutation affects the circadian clock in a frq+ background causing a shorter period length as well as temperature response defects. This gene may be an entry point to study the connection between the biological clock and other basic cellular mechanisms.

Circadian Rhythm↗
PubMed1989

Periodic feeding of SCN-lesioned pregnant rats entrains the fetal biological clock.

Destruction of the maternal suprachiasmatic nuclei (SCN) early in gestation disrupts maternal communication of time-of-day information to the rat fetus. In the present study, we demonstrated that periodic feeding (food cue) to SCN-lesioned pregnant rats entrains the fetal biological clock. The phase of the drinking behavior rhythm was examined in pups reared in constant darkness, beginning at weaning. In several control (uncued) litters, pup phases at weaning were scattered. In other control litters where within-litter coordination of phase was observed, the average litter phase was unpredictable. In contrast, drinking rhythms of pups whose dams had received food cue during gestation were synchronized within- and between-litters, suggesting that prenatal food cue entrained the fetuses. The effect of food cue occurs prenatally, as similar results were obtained when offspring of SCN-lesioned, cued dams were fostered to lesioned, uncued dams on the day of birth. The present results, along with data from this and other laboratories, suggest that redundant mechanisms communicate time-of-day information to the fetus.

Animals↗
PubMed2006

Biologic clocks and the gut.

The gastrointestinal tract displays biologic rhythms in basal gastric acid output, epithelial cell proliferation, gastrointestinal motility, and appetite regulation. Furthermore, the development of gastrointestinal complications after administration of aspirin and after chemo- and radiotherapy for metastatic colon cancer depends on the time of administration. Biologic rhythms are driven by so-called clock genes. Thus, it is conceivable that subsets of genes in the gastrointestinal tract are under clock gene control as well. The purpose of this article is to discuss basic concepts in the studies of biologic rhythms, to review examples of biologic rhythms in the gastrointestinal tract, and to discuss examples of gastrointestinal diseases in which alterations in biologic rhythms may play a pathogenetic role.

Animals↗