POSNER, M.*; LOW, S.; RUNKLE, S.; KANTOROW, M.; HORWITZ, J.: Chaperone function of the small heat shock protein alpha crystallin in the zebrafish, Danio rerio

Alpha crystallin is a small heat shock protein expressed primarily in the ocular lens of all vertebrate taxa. In the mammalian lens this protein plays a role in preventing cataracts by binding to denatured proteins before they can aggregate and scatter light. We are investigating this molecular chaperone function in the zebrafish to determine the physiological role of alpha crystallin in ancestral ectothermic vertebrates. We previously reported the sequence and expression pattern for zebrafish alpha B-crystallin, which has more limited expression than its mammalian orthologue. Here we report the sequence and expression pattern of zebrafish alpha A-crystallin, and the chaperone function of alpha B-crystallin. Semi-quantitative RT-PCR analysis showed high alpha A-crystallin expression in the zebrafish lens, and low expression in the spleen and liver. Extralenticular expression in mammals is limited to the spleen. Chaperone assays indicated that zebrafish alpha B-crystallin is less effective in preventing the heat-induced aggregation of a target protein compared to its mammalian orthologue at 37�C. Additional experiments will assess chaperone activity over a range of temperatures to determine potential thermal variation in zebrafish alpha crystallin function. Differences in expression pattern and chaperone function suggest that alpha crystallin plays a different physiological function in the zebrafish than it does in mammals. This difference may be a result of the cooler body temperature and shorter lifespan of the zebrafish. This research is a first step towards investigating the changing role of alpha crystallin during vertebrate evolution.