Two zebrafish (Danio rerio) antizymes with different expression and activities

Cellular polyamines are regulated by a unique feedback mechanism involving ornithine decarboxylase (ODC) antizyme. The synthesis of mammalian antizyme requires a programmed translational frameshift event induced by polyamines . Antizyme represses ODC, a key enzyme for polyamine synthesis, through acc elerating enzyme degradation by the 26 S proteasome. Antizyme also inhibits the cellular uptake of polyamines. In the present study we isolated two di stinct zebrafish (Danio rerio) antizyme cDNA clones (AZS and AZL) from an e mbryonic library. Their sequences revealed that both clones required transl ational frameshifting for expression. Taking account of + 1 frame shifting, AZS and AZL products were 214 and 218 residues long respectively and share d 51.8 %, amino acid identity. In rabbit reticulocyte lysates, both mRNA sp ecies were translated through spermidine-induced frameshifting. The presenc e of the two antizyme mRNA species in embryos, adult fish and a cultured ce ll line was confirmed by Northern blot analysis. The ratio of AZS mRNA to A ZL mRNA in the adult fish was 1.8-fold fisher than in the embryos. Whole-mo unt hybridization in situ demonstrated that both mRNA species are expressed in every tissue in embryo, but predominantly in the central nervous system and the eyes. Bacterial expression products of both cDNA species inhibited ODC activity, but only the AZS product accelerated ODC degradation in vitr o. These results show that both zebrafish antizymes are induced by polyamin es but their mRNA species are expressed differently during development. The difference in activities on ODC degradation suggests their functional dive rgence.