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notes from XB-ART-57377
encephalopsin (opn3), a brain-expressed opsin described originally in mouse and human , is conserved as a single copy in the X. laevis genome. The predicted protein (gene 108,713,805; chromosome L1; 3 exons) is a truncated form with only 183 aa, while the X. tropicalis gene contains 7 exons and encodes a 424 aa peptide, suggesting a possible error in X. laevis during genome sequencing and/or annotation. Indeed, using cDNA from stage 43/44 X. laevis embryos, and primers raised against X. tropicalis, we amplified 1010 base pairs (bp) of opn3 that spread across 5 exons, encoding a putative peptide of 336 aa with 80% identity with the tropicalis peptide. opn3 is expressed in the PC as determined by RT-PCR (Fig. 4A). Unfortunately, we were unable to identify specific cells expressing opn3 in the PC by ISH because the sense and the antisense probes generated a high background. Three paralogous genes related phylogenetically to mammalian opn3, named teleost multiple tissue opsin genes (tmtops; tmtopsb and tmtops2; a.k.a. tmta, tmtc, and tmt respectively) were found in the X. laevis genome. The tmtops genes remain duplicated (Fig. 2A), and are not expressed in the PC as determined by RT-PCR (Fig. 4A)."
Source: Bertolesi etal 2020. The regulation of skin pigmentation in response to environmental light by pineal Type II opsins and skin melanophore melatonin receptors. Journal of Photochemistry and Photobiology B: BiologyVolume 212, November 2020, 112024