The evolutionary conservation of the core components necessary for the extrinsic apoptotic signaling pathway, in Medaka fish.
BACKGROUND
Death receptors on the cell surface and the interacting cytosolic molecules, adaptors and initiator caspases, are essential as core components of the extrinsic apoptotic signaling pathway. While the apoptotic machinery governing the extrinsic signaling pathway is well characterized in mammals, it is not fully understood in fish.


RESULTS
We identified and characterized orthologs of mammalian Fas, FADD and caspase-8 that correspond to the death receptor, adaptor and initiator caspase, from the Medaka fish (Oryzias latipes). Medaka Fas, caspase-8 and FADD exhibited protein structures similar to that of their mammalian counterparts, containing a death domain (DD), a death effector domain (DED) or both. Functional analyses indicated that these molecules possess killing activity in mammalian cell lines upon overexpression or following activation by apoptotic stimuli, suggesting similar pro-apoptotic functions in the extrinsic pathway as those in mammals. Genomic sequence analysis revealed that the Medaka fas (tnfrsf6), fadd and caspase-8 (casp8) genes are organized in a similar genomic structure as the mammalian genes. Database search and phylogenetic analysis revealed that the fas gene, but not the fadd and casp8 genes, appear to be present only in vertebrates.


CONCLUSIONS
Our results indicate that the core components necessary for the extrinsic apoptotic pathway are evolutionarily conserved in function and structure across vertebrate species. Based on these results, we presume the mechanism of apoptosis induction via death receptors was evolutionarily established during the appearance of vertebrates.
Sakamaki
Kazuhiro
K
Department of Animal Development and Physiology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan. ksakamak@lif.kyoto-u.ac.jp
Nozaki
Masami
M
Kominami
Katsuya
K
Satou
Yutaka
Y
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D053181:Caspase 8 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D018076:DNA, Complementary; D030541:Databases, Genetic; D004622:Embryo, Mammalian; D004625:Embryo, Nonmammalian; D019143:Evolution, Molecular; D005091:Exons; D020224:Expressed Sequence Tags; D053222:Fas Ligand Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D053200:Fas-Associated Death Domain Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D016678:Genome; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D016366:Open Reading Frames; D009990:Oryzias / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D053218:Receptors, Death Domain / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
D018076:DNA, Complementary; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D053218:Receptors, Death Domain; D053181:Caspase 8