BIM and other BCL-2 family proteins exhibit cross-species conservation of function between zebrafish and mammals.

Here we investigate the function of zebrafish Bcl-2 family proteins and demonstrate important conservation of function across zebrafish and mammalian systems. We have isolated a zebrafish ortholog of mammalian BIM and show that it is the most toxic of the zebrafish BH3-only genes examined, sharing this characteristic with the mammalian BIM gene. The zebrafish bad gene shows a complete lack of embryonic lethality, but like mammalian BAD, its pro-apoptotic activity is regulated through phosphorylation of critical serines. We also found that the pattern of mitochondrial dysfunction observed by zebrafish BH3 domain peptides in a mammalian cytochrome c release assay recapitulates the pattern of embryonic lethality induced by the respective mRNA injections in vivo. In contrast to zebrafish Bim, Bid exhibited only weak binding to zebrafish Bcl-2 and moderate-to-weak overall lethality in zebrafish embryos and isolated mitochondria. Given that zebrafish Bcl-2 binds strongly to mammalian BID and BIM peptides and proteins, the protein identified as the zebrafish Bid ortholog has different properties than mammalian BID. Overall, our results demonstrate the high degree of functional conservation between zebrafish and mammalian Bcl-2 family proteins, thus validating the zebrafish as a model system to further dissect the molecular mechanisms that regulate apoptosis in future forward genetic and chemical modifier screens.