Characterization of zebrafish caspase-3 and induction of apoptosis through ceramide generation in fish fathead minnow tailbud cells and zebrafish embryo

Caspase-3 was cloned from zebrafish embryos and its properties were characterized to identify the biological implications of caspase in embryogenesis and apoptosis in zebrafish, which is a model organism in vertebrate developmental biology and genetics. The predicted amino acid sequence, totalling 282 amino acid residues, consisted of the prodomain and large and small subunits. Phylogenetic analysis showed that the cloned zebrafish caspase was a member of the caspase-3 subfamily with approx. 60% identity with caspase-3 from Xenopus, chicken and mammals. In addition, recombinant zebrafish caspase hydrolysed acetyl-Asp-Glu-Val-Asp-4-methyl-coumaryl-7-amide, and exhibited similar substrate specificity to the mammalian caspase-3 subfamily. Therefore this caspase was designated zebrafish caspase-3. Overexpression of zebrafish caspase-3 induced apoptosis and increased ceramide levels in fish fathead minnow tailbud cells and zebrafish embryos. Both ceramide generation and apoptosis induction were inhibited by treatment with a caspase inhibitor, benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone. Moreover, zebrafish caspase-3 mRNA was present in early embryos up to the 1000-cell stage as a maternal factor, and was then expressed throughout the body after the gastrula stage by zygotic expression. These findings indicate that the isolated caspase-3 plays an important role in the induction of ceramide generation as well as apoptosis in fish cells and the zebrafish embryo, and suggest that caspase-3 functions as a modulator of the pro-apoptotic signal in development.