UCSCGeneAnnotation:hg18-358

Canonical gene details RHO uc003emt.1
Description: rhodopsin
RefSeq Summary (NM_000539): Retinitis pigmentosa is an inherited progressive disease which is a major cause of blindness in western communities. It can be inherited as an autosomal dominant, autosomal recessive, or X-linked recessive disorder. In the autosomal dominant form,which comprises about 25% of total cases, approximately 30% of families have mutations in the gene encoding the rod photoreceptor-specific protein rhodopsin. This is the transmembrane protein which, when photoexcited, initiates the visual transduction cascade. Defects in this gene are also one of the causes of congenital stationary night blindness.
(description snapshot 09:14, 4 September 2008 (PDT))
Alternate Gene Symbols: NM_000539, NP_000530, OPN2, OPSD_HUMAN, P08100, Q16414, Q2M249

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created: tom 09:14, 4 September 2008 (PDT) uc003emt.1

This gene encodes rhodopsin, the much-studied 7-transmembrane protein responsible for vertebrate dim light (grayscale) vision in retinal rod cells. Its 11-cis-retinal cofactor detects incoming photons but with wavelength sensitivity shifted from its inherent ultraviolet adsorption to a peak around 500 nm by a dozen tuning residues, not all in direct physical proximity. Evolution of RHO spectral tuning has been the subject of a Sept 2008 review.

There is profound potential for nomenclatural confusion because 'rhodopsin' is also used for highly non-orthologous (melanopsin-class opsins) genes in fruit fly and other protostomes. Worse, the entire subdivision of GPCR (heterotrimeric G protein coupled receptors) is often called rhodopsin although many members have no connection whatsoever to photoreception. Consequently key word searches are all but useless at GenBank and PubMed for retrieving rod-specific opsin information.

Deuterostome imaging opsins such as RHO arose during the Cambrian subsequent to the divergences of echinoderms, urochordates and cephalochordates but prior to lamprey ancestor. However ciliary opsins themselves (which include RHO) arose in pre-Bilatera and persisted to the present day in non-imaging roles in both protostomes and deuterostomes.

A common misconception is that rod vision arose first, with color vision a later elaboration. This is factually backwards as seen from lamprey which has a full complement of color vision opsins. There is universal agreement that the gene tree for imaging opsins is best described by serial tandem expansions of LWS (long wave sensitive), with RHO the last to emerge. Vertebrate imaging opsins themselves arose from ciliary opsin genes found today in pineal photoreceptors.

Even though the era of ciliary opsin gene expansion matches perfectly, the overall opsin gene tree topology conflicts with theories of one or two rounds of whole genome polyploidization prior to lamprey divergence. If 1R or 2R occured, it was irrelevent to opsin gene family expansion (notably emergence of RHO) because the history is entirely of tandem duplications followed by local inversions and later translocations to other chromosomes.

RHO was named in the 1870s by Kuehne but it took over a century to determine the first structure of bovine rhodopsin, a great advamce in the overall understanding of GPCR signaling proteins. Hundreds of other human genes can be modeled accurately via this structure, though not to the level of detail needed for pharmacological work.

RHO orthologs have been sequenced for a great many species. However for many purposes it is preferable to use a phylogenetically dispersed representative sub-sample. A curated collection of RHO (and all other opsins) is available in the comparative genomics section of genomeWiki.