Illuminating the Role of Opsin Proteins in Circadian Rhythm Regulation
Date
2022-08
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Abstract
Circadian rhythms allow organisms from bacteria to humans to entrain with the environmental light: dark cycle and regulate their physiological, metabolic, and behavioral activities. The rhythms are regulated by the oscillations of four core circadian genes: Period, Cryptochrome, BMAL1 and CLOCK. These rhythms synchronize to the light: dark cycle of the environment. Detecting light is necessary not only for vision but also for the proper synchronization of circadian rhythms. Opsins are proteins that detect light and are primarily expressed in the retina for visual light detection. Studies have demonstrated that opsins synchronize the circadian rhythms of an organism; however if opsins show rhythmic expression is still being studied. Furthermore, opsins are expressed in the skin where their function is poorly understood. Some of the current treatments for circadian rhythm disorders are light exposure based. Better understanding of the regulation of light-detecting proteins will aid in the development of more effective treatment. I focus on how mRNAs and proteins for opsins in the skin are regulated over 24 hours. Specifically, I studied opsin regulation in pigmented cells of the skin known as melanocytes (mammals) and melanophores (non-mammalian vertebrates). These cells exhibit dynamic pigmentation responses to environmental light and dark. Using Xenopus laevis as a model organism, I analyzed the expression of 22 opsin genes previously identified in this species in the skin by RT-PCR. Highly expressed in melanophores were: opn5 (a neuropsin), and the two melanopsin homologues opn4 and opn4b, as well as the four core clock genes. In-situ hybridization studies showed opn5 mRNA to be expressed in a punctate manner similar to the distribution of the melanosomes (organelles containing melanin pigment), suggesting a particular intracellular distribution of the mRNA. Protein distribution of the opsins, determined by immunohistochemistry, shows a similar pattern, suggesting specific localized expression of Opn5. Preliminary data suggest that while opn4b mRNA is regulated in a circadian manner, protein expression remains relatively constant. Whereas both the mRNA and protein of Opn5 show changes over time. My results indicate that at least two opsins are expressed in a cyclic manner in the pigmented skin cells.
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Keywords
circadian rhythms, opsin
Citation
Debnath, N. (2022). Illuminating the role of opsin proteins in circadian rhythm regulation (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.