부산대학교 도서관

Theβ andγ 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 ofγ-crystallins expressed in mammal, reptile, bird and fish species (particularly in the zebrafish,Danio rerio) has led to the discovery ofγN-crystallin, an evolutionary bridge between theβ andγ families. In all species examined,γN-crystallins have a hybrid gene structure, halfβ and halfγ, and thus appear to be the‘missing link’ between theβ andγ crystallin lineages. Overall, there are four major classes ofγ-crystallin: the terrestrial group (including mammalianγA–F); the aquatic group (the fishγM-crystallins); theγS group; and the novelγN group. Like the evolutionarily ancientβ-crystallins (but unlike the terrestrialγA–F and aquaticγM groups), both theγS andγN crystallins form distinct clades with members in fish, reptiles, birds and mammals. In rodents,γN is expressed in nuclear fibers of the lens and, perhaps hinting at an ancestral role for theγ-crystallins, also in the retina. Although well conserved throughout vertebrate evolution,γN in primates has apparently undergone major changes and possible loss of functional expression. [ABSTRACT FROM AUTHOR]