Gene sharing, lens crystallins and speculations on an eye/ear evolutionary relationship

The crystallins comprise 80–90% of the water-soluble proteinsof the transparent, cellular, refractive eye lens and are responsiblefor its optical properties. Comparative studies have establishedthat the crystallins are surprisingly diverse and often differamong species in a taxon-specific fashion. In general, the crystallinsare derived from or identical to metabolic enzymes or stress(small heat shock) proteins that are expressed to a lesser extentin other tissues where they have non-refractive roles. We callthe phenomenon of having the small heat shock protein or enzymeand lens crystallin encoded in the identical gene "gene sharing";examples include small heat shock protein/