Photoperiod regulates multiple gene expression in the suprachiasmatic nuclei and pars tuberalis of the Siberian hamster (Phodopus sungorus)

Jun 28, 2005The European journal of neuroscience

Day length affects gene activity in the brain's daily rhythm and hormone control areas of Siberian hamsters

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Abstract

Photoperiod significantly modulates the rhythmic expression of clock genes in the suprachiasmatic nucleus (SCN) of Siberian hamsters.

In the SCN, genes such as Per1, Per2, Cry1, and Rev-erbalpha show rhythmic expression that is influenced by the length of the photoperiod.
Long photoperiods lead to earlier peak mRNA expression of clock genes compared to short photoperiods, indicating a photoperiod-dependent timing mechanism.
Melatonin secretion onset and offset in the pituitary is associated with the expression of Cry1 and Per1 genes, respectively, specifically under long photoperiod conditions.
In short photoperiods, Cry1 expression tracks melatonin onset, but Per1 does not exhibit rhythmic expression, suggesting different regulatory mechanisms in the pituitary.

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Photoperiod regulates the seasonal physiology of many mammals living in temperate latitudes. Photoperiodic information is decoded by the master circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and then transduced via pineal melatonin secretion. This neurochemical signal is interpreted by tissues expressing melatonin receptors (e.g. the pituitary pars tuberalis, PT) to drive physiological changes. In this study we analysed the photoperiodic regulation of the circadian clockwork in the SCN and PT of the Siberian hamster. Female hamsters were exposed to either long or short photoperiod for 8 weeks and sampled at 2-h intervals across the 24-h cycle. In the SCN, rhythmic expression of the clock genes Per1, Per2, Cry1, Rev-erbalpha, and the clock-controlled genes arginine vasopressin (AVP) and d-element binding protein (DBP) was modulated by photoperiod. All of these E-box-containing genes tracked dawn, with earlier peak mRNA expression in long, compared to short, photoperiod. This response occurred irrespective of the presence of additional regulatory cis-elements, suggesting photoperiodic regulation of SCN gene expression through a common E-box-related mechanism. In long photoperiod, expression of Cry1 and Per1 in the PT tracked the onset and offset of melatonin secretion, respectively. However, whereas Cry1 tracked melatonin onset in short period, Per1 expression was not detectably rhythmic. We therefore propose that, in the SCN, photoperiodic regulation of clock gene expression primarily occurs via E-boxes, whereas melatonin-driven signal transduction drives the phasing of a subset of clock genes in the PT, independently of the E-box.

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Photoperiod regulates multiple gene expression in the suprachiasmatic nuclei and pars tuberalis of the Siberian hamster (Phodopus sungorus)

Abstract

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