Expression of crystallin genes in embryonic and regenerating newt lenses.

The spatio-temporal expression of three crystallin genes (alphaA, betaB1 and gamma) in the developing and regenerating lenses of newt was compared by in situ hybridization in lens differentiation in normal development with during regeneration. In normal development, all crystallin transcripts were first detected at the same stage in the posterior region of the lens vesicle (McDevitt's lens development stage V) and continued during lens fiber differentiation of the posterior cells into the primary lens fiber cell differentiation (McDevitt's lens development stage VII-VIII). At later stages, the expression of the three genes was restricted to the secondary lens fibers and gradually became undetectable in primary lens fibers (McDevitt's lens development stage X). The signal for gamma-crystallin was never detected in lens epithelium at any stage, whereas signals for alphaA- and betaB1-crystallin were detected in the lens epithelium at the stage when the primary lens fiber mass was formed. During lens regeneration, signals for the three crystallins were first detected at the same stage at the ventral margin of a regenerating lens vesicle (Sato's lens regeneration stage IV). The expression patterns of three crystallin genes were similar to those in normal development (Sato's lens regeneration stage V-X). The expression pattern of the crystallin genes in normal lens development fundamentally resembles that during lens regeneration, suggesting the absence of unique expression programs of crystallin genes for lens regeneration not found in ontogeny.