Review: A case for corneal crystallins

It is established that the diverse, multifunctional crystallins are respons ible for the optical properties of the cellular, transparent lens of the co mplex eyes of vertebrates and invertebrates. Lens crystallins often differ among species and may be enzymes or stress proteins. I present here the ide a that abundant water-soluble enzymes and other proteins may also be used f or cellular transparency in the epithelial cells and, possibly, stromal ker atocytes of the cornea. Aldehyde dehydrogenases and transketolase are among the putative "corneal crystallins" in mammals, and gelsolin may be a corne al crystallin in the zebrafish. In invertebrates, the glutathione S-transfe rase-related S-crystallins of the lens appear to be used also as corneal cr ystallins in the squid, and an aldehyde dehydrogenase-related protein is th e crystallin in the lens and, possibly, cornea of the scallop. The use of a bundant, taxonspecific water-soluble proteins as crystallins for cellular t ransparency in the cornea would provide a new conceptual link between this tissue and the lens.