Fig. 13

Molecular co-option in the evolution of lens crystallin proteins. The α, β, and γ crystallins are ubiquitous among vertebrates, though the embryonic γ crystallin has been lost in birds. Other crystallins are shown for the specific taxa in which they have been found, and this may not reflect their overall distribution among animals (A). Each of these crystallins is similar to another protein with a different function (B), suggesting that it was co-opted from an existing protein in a new role in refracting light in the eye. In fact, many crystallin proteins are expressed in tissues besides eye lenses where they carry out additional functions unrelated to vision (see Piatigorsky 2007). From True and Carroll (2002), reproduced by permission from the Annual Review of Cell and Developmental Biology, Volume 18 ©2002 by Annual Reviews www.annualreviews.org