Abstract
Vertebrates have a central clock and also several peripheral clocks. Light responses might result from the integration of light signals by these clocks. The dermal melanophores of Xenopus laevis have a photoreceptor molecule denominated melanopsin (OPN4x). The mechanisms of the circadian clock involve positive and negative feedback. We hypothesize that these dermal melanophores also present peripheral clock characteristics. Using quantitative PCR, we analyzed the pattern of temporal expression of Opn4x and the clock genes Per1, Per2, Bmal1, and Clock in these cells subjected to a 14-h light:10-h dark (14L:10D) regime or constant darkness (DD). Also, in view of the physiological role of melatonin in the dermal melanophores of X. laevis, we determined whether melatonin modulates the expression of these clock genes. These genes show a time-dependent expression pattern when these cells are exposed to 14L:10D, which differs from the pattern observed under DD. Cells kept in DD for 5 days exhibited overall increased mRNA expression for Opn4x and Clock, and a lower expression for Per1, Per2, and Bmal1. When the cells were kept in DD for 5 days and treated with melatonin for 1 h, 24 h before extraction, the mRNA levels tended to decrease for Opn4x and Clock, did not change for Bmal1, and increased for Per1 and Per2 at different Zeitgeber times (ZT). Although these data are limited to one-day data collection, and therefore preliminary, we suggest that the dermal melanophores of X. laevis might have some characteristics of a peripheral clock, and that melatonin modulates, to a certain extent, melanopsin and clock gene expression.
Highlights
IntroductionThere are three structures in the core of the circadian system that regulate and control several forms of rhythmic expression in vertebrates, namely the retinas, the pineal complex (pineal body and the eye/parietal organ) and the suprachiasmatic nucleus (SCN) [1]
There are three structures in the core of the circadian system that regulate and control several forms of rhythmic expression in vertebrates, namely the retinas, the pineal complex and the suprachiasmatic nucleus (SCN) [1]
SCN and peripheral clocks work through a transcriptional circuit of clock genes, which generate the rhythmic patterns of protein expression during metabolism, and participate in several other functions [3,4,5]
Summary
There are three structures in the core of the circadian system that regulate and control several forms of rhythmic expression in vertebrates, namely the retinas, the pineal complex (pineal body and the eye/parietal organ) and the suprachiasmatic nucleus (SCN) [1]. The circadian system includes hierarchically organized peripheral oscillators located outside the main oscillator itself [1]. These peripheral oscillators can be coupled or not, even though they are linked to the SCN. Their expression is connected and depends on the temporal structure of the organism, even though they are self-sustained and independently capable of generating oscillation for the cell or tissue where they are located [2]. The molecular mechanism of the circadian clock has been confirmed in other organisms such as mice and humans [7]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have