title: gammaN-crystallin and the evolution of the betagamma-crystallin superfamily in vertebrates.
abstract: The beta and gamma crystallins are evolutionarily related families of proteins that make up a large part of the refractive structure of the vertebrate eye lens. Each family has a distinctive gene structure that reflects a history of successive gene duplications. A survey of gamma-crystallins expressed in mammal, reptile, bird and fish species (particularly in the zebrafish, Danio rerio) has led to the discovery of gammaN-crystallin, an evolutionary bridge between the beta and gamma families. In all species examined, gammaN-crystallins have a hybrid gene structure, half beta and half gamma, and thus appear to be the 'missing link' between the beta and gamma crystallin lineages. Overall, there are four major classes of gamma-crystallin: the terrestrial group (including mammalian gammaA-F); the aquatic group (the fish gammaM-crystallins); the gammaS group; and the novel gammaN group. Like the evolutionarily ancient beta-crystallins (but unlike the terrestrial gammaA-F and aquatic gammaM groups), both the gammaS and gammaN crystallins form distinct clades with members in fish, reptiles, birds and mammals. In rodents, gammaN is expressed in nuclear fibers of the lens and, perhaps hinting at an ancestral role for the gamma-crystallins, also in the retina. Although well conserved throughout vertebrate evolution, gammaN in primates has apparently undergone major changes and possible loss of functional expression.
authors.affiliation: National Eye Institute, National Institutes of Health, Bethesda, MD 20892-0703, USA. graeme@helix.nih.gov
authors.forename: Graeme
authors.initials: G
authors.lastname: Wistow
authors.forename: Keith
authors.initials: K
authors.lastname: Wyatt
authors.forename: Larry
authors.initials: L
authors.lastname: David
authors.forename: Chun
authors.initials: C
authors.lastname: Gao
authors.forename: Orval
authors.initials: O
authors.lastname: Bateman
authors.forename: Steven
authors.initials: S
authors.lastname: Bernstein
authors.forename: Stanislav
authors.initials: S
authors.lastname: Tomarev
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Segovia
authors.forename: Christine
authors.initials: C
authors.lastname: Slingsby
authors.forename: Thomas
authors.initials: T
authors.lastname: Vihtelic
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D003459:Crystallins / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D005123:Eye / Q000033:anatomy & histology / Q000378:metabolism; D020440:Gene Duplication; D005786:Gene Expression Regulation; D007908:Lens, Crystalline / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014018:Tissue Distribution; D015027:Zebrafish
chemical_list: D003459:Crystallins; D020033:Protein Isoforms; D011994:Recombinant Proteins