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What is RHO? What is Rhodopsin?
RHO is the gene that codes for the protein rhodopsin. Rhodopsin enables light sensation at the retina in the eye (1). Rhodopsin is found in the rod cells of the retina, and converts photons into signals that are able to be interpreted by neurons.
Gene and protein sequences
Gene and protein sequences
The RHO mature mRNA sequence is coded for by 1047 nucleotides.
The Rhodopsin protein monomer is composed of 348 amino acids.
Use the buttons below to explore the RHO mRNA transcript and the Rhodopsin protein amino acid sequence.
Gene location
Gene location
The RHO gene has the chromosomal location 3q22.1.
Figure 1: G banding pattern for human chromosome 3, used to determine the location of the RHO gene. The red box highlights the location of region 2, band 2, sub-band 1 on the q arm of chromosome 3, representing the relative location of RHO.
Gene expression in human tissues
Gene expression in human tissues
Figure 2: A bar graph representation of the tissue-specific rhodopsin RNA expression of 95 human samples, with 27 tissues examined. The level of expression is presented on the y-axis, and the tissue sample type is presented on the x-axis. The data and graphical presentation are sourced from NIH.
NIH rhodopsin: https://www.ncbi.nlm.nih.gov/gene/6010
RHO is expressed primarily in human brain tissue. This suggests that rhodopsin is related to neural functionality, specifically related to the retina as a photoreceptor (2).
RHO is also expressed in skin and fat. This reveals that opsins are present in tissues extensively exposed to light, such as skin (3).
RHO gene expression is also shown in the testis. Research has shown that spermatozoa possess a temperature sensing mechanism that utilises G protein coupled receptors that can also act as visual photosensors (4), including rhodopsin.
Reading frames for RHO
Reading frames for RHO
Figure 3: The reading frames for the RHO gene, as determined through the Expasy translate tool using the cDNA sequence of RHO. Reading frames are highlighted in red, with the longest reading frame likely to confer to the functional protein of interest (rhodopsin).
Reading frame analysis conducted by Expasy translate tool: https://web.expasy.org/translate/
Reading frame: the reading frame is highlighted in figure 3, with a large region of the sequence uninterrupted by stop codons or introns being identified. This reading frame of interest is the 5' --> 3' +3 reading frame.
Figure 4: open reading frame 18 (ORF18), determined to be the true open reading frame for the RHO gene through the use of ORF finder. This was confirmed through the use of a BLAST search, which showed a 100% identity match of ORF18 with homo sapien rhodopsin.
Open reading frame finder: https://www.ncbi.nlm.nih.gov/orffinder/
ORF finder, as demonstrated in figure 4, was used to confirm the true open reading frame of the RHO gene -> ORF18. BLAST supported this statement, confirming an 100% similarity report for the amino acid sequence produced by ORF18 to homo sapien rhodopsin. ORF18 being in the +3 frame, matches the Expasy data.
References:
1. Zhou XE, Melcher K, Xu HE. Structure and activation of rhodopsin. Acta Pharmacologica Sinica. 2012;33(3):291–9. doi:10.1038/aps.2011.171
2. Shichida Y, Matsuyama T. Evolution of opsins and phototransduction. Philosophical Transactions of the Royal Society B: Biological Sciences. 2009;364(1531):2881–95. doi:10.1098/rstb.2009.0051
3. Suh S, Choi EH, Atanaskova Mesinkovska N. The expression of opsins in the human skin and its implications for photobiomodulation: A systematic review. Photodermatology, Photoimmunology & Photomedicine. 2020;36(5):329–38. doi:10.1111/phpp.12578
4. Pérez-Cerezales S, Boryshpolets S, Afanzar O, Brandis A, Nevo R, Kiss V, et al. Involvement of opsins in mammalian sperm thermotaxis. Scientific Reports. 2015;5(1). doi:10.1038/srep16146
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