Abstract
Melanopsin has been implicated in the mammalian photoentrainment by blue light. This photopigment, which maximally absorbs light at wavelengths between 470 and 480 nm depending on the species, is found in the retina of all classes of vertebrates so far studied. In mammals, melanopsin activation triggers a signaling pathway which resets the circadian clock in the suprachiasmatic nucleus (SCN). Unlike mammals, Drosophila melanogaster and Danio rerio do not rely only on their eyes to perceive light, in fact their whole body may be capable of detecting light and entraining their circadian clock. Melanopsin, teleost multiple tissue (tmt) opsin and others such as neuropsin and va-opsin, are found in the peripheral tissues of Danio rerio, however, there are limited data concerning the photopigment/s or the signaling pathway/s directly involved in light detection. Here, we demonstrate that melanopsin is a strong candidate to mediate synchronization of zebrafish cells. The deduced amino acid sequence of melanopsin, although being a vertebrate opsin, is more similar to invertebrate than vertebrate photopigments, and melanopsin photostimulation triggers the phosphoinositide pathway through activation of a Gq/11-type G protein. We stimulated cultured ZEM-2S cells with blue light at wavelengths consistent with melanopsin maximal absorption, and evaluated the time course expression of per1b, cry1b, per2 and cry1a. Using quantitative PCR, we showed that blue light is capable of slightly modulating per1b and cry1b genes, and drastically increasing per2 and cry1a expression. Pharmacological assays indicated that per2 and cry1a responses to blue light are evoked through the activation of the phosphoinositide pathway, which crosstalks with nitric oxide (NO) and mitogen activated protein MAP kinase (MAPK) to activate the clock genes. Our results suggest that melanopsin may be important in mediating the photoresponse in Danio rerio ZEM-2S cells, and provide new insights about the modulation of clock genes in peripheral clocks.
Highlights
Melanopsin was discovered in 1998 by Provencio and coworkers [1] in Xenopus leavis melanophores
Rhabdomeric photoreceptor signaling was mainly studied in Drosophila melanogaster [15] and it involves the activation of Gq/11 protein, phospholipase C (PLC) and subsequent opening of transient receptor potential channels (TRPCs), resulting in membrane depolarization
This experimental set-up has been established taking in account that (1) all the reactions to regenerate the chromophore have to happen within the same cell type; three among the five zebrafish melanopsins are bistable [7], that is the regeneration of 11-cis from all-trans chromophore occurs in situ, in response to a different wavelength, a typical mechanism of rhabdomeric opsins; (2) all 5 melanopsins of D. rerio transfected into Neuro-2A cells exhibit a better response to light if the assay is supplemented with the aldehyde [7]; (3) serum concentration in ZEM-2S cells was reduced to 2% during the assays
Summary
Melanopsin was discovered in 1998 by Provencio and coworkers [1] in Xenopus leavis melanophores. This opsin arose as a strong candidate to mediate the synchronization process of the biological clock to light because it was found in the skin and in the retina of this animal. Different groups have demonstrated that melanopsin activates PLC with a subsequent production of inositol-3-phosphate (IP3), a raise in intracellular calcium, and protein kinase C (PKC) activation in both native [20,21,22,23] and heterologous [19], [24] systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
