Lens crystallin changes associated with amphibian metamorphosis: Involvement of a β-crystallin polypeptide

Lens crystallins isolated from the tadpole and frog lenses were compared with regard to the developmental changes of crystallin compositions. The major changes during the process of metamorphosis were (1) the total contents of α- and γ-crystallins decrease from more than 70 % to less than 60 % and (2) one of the major β-crystallin polypeptides increases from less than 1 % to about 6 % and (3) an amphibian-specific ρ{variant}-crystallin also increases from about 6 % to more than 10 % of total soluble proteins of the lens. We have characterized the metamorphosis-dependent β-crystallin polypeptide by peptide mapping and sequence determination of the protease-digested fragments. This polypeptide showed very high sequence homology to that of the major βBp-crystallin chain reported for the mammalian lenses. The changes of the relative abundance of various crystallins and the gradually-elevated levels of the expression of this βBp-like crystallin in the developing lens during metamorphosis may also have some bearing on the maintenance of lens stability in the adult frog lenses.