Cloning of the αA-crystallin genes of a blind cave form and the epigean form of Astyanax fasciatus: A comparative analysis of structure, expression and evolutionary conservation

In the present study we have analyzed the integrity and expression of the αA-crystallin gene, that codes for a major structural component of the lens, in a blind cave form of the teleostean fish, Astyanax fasciatus. This is the first αA-crystallin gene cloned from a teleostean fish. Sequence comparison of this cave-form gene with its epigean conspecific and with homologs of distantly related taxa has illustrated conservation of regulatory and coding regions. Although no crystallin proteins are produced in the lens of the cave form, and the mRNA of this gene could not be detected by in situ hybridization of different developmental stages, the promoter region of cave-fish αA-crystallin is functionally intact. The deduced amino-acid sequence of the αA-crystallin gene of the cave form differs from that of its epigean conspecific at only one position (139). This is within an important, small heat-shock protein-related region, HCR2. A comparison of the 5'-flanking regions of the A. fasciatus αA-crystallin gene with the chicken homolog revealed the high conservation of lens-specific regulatory sequences and further demonstrates the evolutionary conservation of this gene.