Eolution: Tantalizing timeless
Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR 97403, USA. Science
(Impact Factor: 33.61).
07/2007; 316(5833):1851-2. DOI: 10.1126/science.1145053
The circadian clock regulating daily activities is distinct from the photoperiodic timer that regulates seasonal activities
Available from: Hideharu Numata
- "Several authors have pointed out the functional involvement of individual circadian clock genes in insect photoperiodic diapause [15-17]. However, these results could be due to the pleiotropic effects of these individual clock genes on diapause itself and may not involve the circadian clock as an integrated physiological function [18-20]. Thus, involvement of the circadian clock into photoperiodism has yet to be verified at the molecular level. "
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ABSTRACT: Most organisms have evolved a circadian clock in order to anticipate daily environmental changes and many of these organisms are also capable of sophisticated measurement of daylength (photoperiodism) that is used to regulate seasonal events such as diapause, migration and polymorphism. It has been generally accepted that the same elements are involved in both circadian (daily) and seasonal (annual) rhythms because both rely upon daily light-dark cycles. However, as reasonable as this sounds, there remains no conclusive evidence of such a molecular machinery in insects. We have approached this issue by using RNA interference (RNAi) in Riptortus pedestris.
The cuticle deposition rhythm exhibited the major properties of circadian rhythms, indicating that the rhythm is regulated by a circadian clock. RNAi directed against the circadian clock genes of period and cycle, which are negative and positive regulators in the circadian clock, respectively, disrupted the cuticle deposition rhythm and distinct cuticle layers were produced by these RNAi. Simultaneously, period RNAi caused the insect to avert diapause under a diapause-inducing photoperiod whereas cycle RNAi induced diapause under a diapause-averting photoperiod. The expression patterns of juvenile hormone-regulated genes and the application of juvenile hormone analogue suggested that neither ovarian development itself nor a downstream cascade of juvenile hormone secretion, were disturbed by period and cycle RNAi.
This study revealed that the circadian clock genes are crucial not only for daily rhythms but also for photoperiodic diapause. RNAi directed against period and cycle had opposite effects not only in the circadian cuticle deposition rhythm but also in the photoperiodic diapause. These RNAi also had opposite effects on juvenile hormone-regulated gene expression. It is still possible that the circadian clock genes pleiotropically affect ovarian development but, based on these results, we suggest that the circadian clock operated by the circadian clock genes, period and cycle, governs seasonal timing as well as the daily rhythms.
Available from: Vladimír Kostál
- "In contrast, the physiological mechanisms of the photoperiodic calendar remain little understood (Tauber and Kyriacou, 2001; Saunders, 2002; Saunders et al., 2004; Danks, 2005; Bradshaw and Holzapfel, 2007; Kyriacou et al., 2007; Goto et al., 2010). In 1936, Erwin Bü nning first proposed that photoperiodic sensitivity is based on circadian functions. "
Available from: Sheeba Vasu
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ABSTRACT: Molecular genetic analysis of the fruit fly Drosophila melanogaster has revolutionized our understanding of the transcription/translation loop mechanisms underlying the circadian molecular oscillator. More recently, Drosophila has been used to understand how different neuronal groups within the circadian pacemaker circuit interact to regulate the overall behavior of the fly in response to daily cyclic environmental cues as well as seasonal changes. Our present understanding of circadian timekeeping at the molecular and circuit level is discussed with a critical evaluation of the strengths and weaknesses of present models. Two models for circadian neural circuits are compared: one that posits that two anatomically distinct oscillators control the synchronization to the two major daily morning and evening transitions, versus a distributed network model that posits that many cell-autonomous oscillators are coordinated in a complex fashion and respond via plastic mechanisms to changes in environmental cues.
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