Circadian profile and photic regulation of clock genes in the suprachiasmatic nucleus of a diurnal mammal arvicanthis ansorgei

Feb 1, 2003Neuroscience

Daily patterns and light effects on internal clock genes in the brain’s time-keeping center of a daytime-active mammal

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Abstract

All clock genes studied in the day-active rodent Arvicanthis ansorgei exhibited circadian expression patterns.

Per1 and Per2 mRNA levels increased during the subjective day and decreased during the subjective night.
Bmal1 showed a circadian expression pattern that was out of phase with Per1.
Cry2 expression increased during the late subjective day and decreased during the late subjective night.
Light exposure at night induced an increase in Per1 and Per2 expression while decreasing Cry2 levels.
Bmal1 expression was not affected by light pulses during the circadian times examined.
The findings suggest similarities in the molecular mechanisms of circadian rhythmicity and photic synchronization between diurnal and nocturnal mammals.

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The molecular mechanisms of the mammalian circadian clock located in the suprachiasmatic nucleus have been essentially studied in nocturnal species. Currently, it is not clear if the clockwork and the synchronizing mechanisms are similar between diurnal and nocturnal species. Here we investigated in a day-active rodent Arvicanthis ansorgei, some of the molecular mechanisms that participate in the generation of circadian rhythmicity and processing of photic signals. In situ hybridization was used to characterize circadian profiles of expression of Per1, Per2, Cry2 and Bmal1 in the suprachiasmatic nucleus of A. ansorgei housed in constant dim red light. All the clock genes studied showed a circadian expression. Per1 and Per2 mRNA increased during the subjective day and decreased during the subjective night. Also, Bmal1 exhibited a circadian expression, but in anti-phase to that of Per1. The expression of Cry2 displayed a circadian pattern, increasing during the late subjective day and decreasing during the late subjective night. We also obtained the phase responses to light for wheel-running rhythm and clock gene expression. At a behavioral level, light was able to induce phase shifts only during the subjective night, like in other diurnal and nocturnal species. At a molecular level, light pulse exposure during the night led to an up-regulation of Per1 and Per2 concomitant with a down-regulation of Cry2 in the suprachiasmatic nucleus of A. ansorgei. In contrast, Bmal1 expression was not affected by light pulses at the circadian times investigated. This study demonstrates that light exposure during the subjective night has opposite effects on the expression of the clock genes Per1 and Per2 compared with that of Cry2. These differential effects can participate in photic resetting of the circadian clock. Our data also indicate that the molecular mechanisms underlying circadian rhythmicity and photic synchronization share clear similarities between diurnal and nocturnal mammals.

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Circadian profile and photic regulation of clock genes in the suprachiasmatic nucleus of a diurnal mammal arvicanthis ansorgei

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