title: Functional conservation of the apoptotic machinery from coral to man: the diverse and complex Bcl-2 and caspase repertoires of Acropora millepora.
abstract: BACKGROUND
  Apoptotic cell death is a defining and ubiquitous characteristic of metazoans, but its evolutionary origins are unclear. Although Caenorhabditis and Drosophila played key roles in establishing the molecular bases of apoptosis, it is now clear that cell death pathways of these animals do not reflect ancestral characteristics. Conversely, recent work suggests that the apoptotic networks of cnidarians may be complex and vertebrate-like, hence characterization of the apoptotic complement of representatives of the basal cnidarian class Anthozoa will help us to understand the evolution of the vertebrate apoptotic network.
  
  
  RESULTS
  We describe the Bcl-2 and caspase protein repertoires of the coral Acropora millepora, making use of the comprehensive transcriptomic data available for this species. Molecular phylogenetics indicates that some Acropora proteins are orthologs of specific mammalian pro-apoptotic Bcl-2 family members, but the relationships of other Bcl-2 and caspases are unclear. The pro- or anti-apoptotic activities of coral Bcl-2 proteins were investigated by expression in mammalian cells, and the results imply functional conservation of the effector/anti-apoptotic machinery despite limited sequence conservation in the anti-apoptotic Bcl-2 proteins. A novel caspase type ("Caspase-X"), containing both inactive and active caspase domains, was identified in Acropora and appears to be restricted to corals. When expressed in mammalian cells, full-length caspase-X caused loss of viability, and a truncated version containing only the active domain was more effective in inducing cell death, suggesting that the inactive domain might modulate activity in the full-length protein. Structure prediction suggests that the active and inactive caspase domains in caspase-X are likely to interact, resulting in a structure resembling that of the active domain in procaspase-8 and the inactive caspase domain in the mammalian c-FLIP anti-apoptotic factor.
  
  
  CONCLUSIONS
  The data presented here confirm that many of the basic mechanisms involved in both the intrinsic and extrinsic apoptotic pathways were in place in the common ancestor of cnidarians and bilaterians. With the identification of most or all of the repertoires of coral Bcl-2 and caspases, our results not only provide new perspectives on the evolution of apoptotic pathways, but also a framework for future experimental studies towards a complete understanding of coral bleaching mechanisms, in which apoptotic cell death might be involved.
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. aurelie.moya@jcu.edu.au.
authors.forename: Aurelie
authors.initials: A
authors.lastname: Moya
authors.affiliation: Department of Animal Development and Physiology, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8501, Japan. sakamaki.kazuhiro.7u@kyoto-u.ac.jp.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sakamaki
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. bmason2@stanford.edu.|Comparative Genomics Centre and Department of Molecular and Cell Biology, James Cook University, Townsville, Queensland, 4811, Australia. bmason2@stanford.edu.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Mason
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. lottehuisman@googlemail.com.|Section of Computational Science, Universiteit van Amsterdam, Science Park 904, 1098, XH, Amsterdam, The Netherlands. lottehuisman@googlemail.com.
authors.forename: Lotte
authors.initials: L
authors.lastname: Huisman
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. sylvain.foret@anu.edu.au.|Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Bldg. 46, Canberra, ACT, 0200, Australia. sylvain.foret@anu.edu.au.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Forêt
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. yvonne.weiss@my.jcu.edu.au.|Comparative Genomics Centre and Department of Molecular and Cell Biology, James Cook University, Townsville, Queensland, 4811, Australia. yvonne.weiss@my.jcu.edu.au.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Weiss
authors.affiliation: Comparative Genomics Centre and Department of Molecular and Cell Biology, James Cook University, Townsville, Queensland, 4811, Australia. tara.bull@my.jcu.edu.au.
authors.forename: Tara E
authors.initials: TE
authors.lastname: Bull
authors.affiliation: Biotechnology Research Institute for Drug Discovery, Department of Life Science and Biotechnology, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo, 135-0064, Japan. k-tomii@aist.go.jp.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tomii
authors.affiliation: Biotechnology Research Institute for Drug Discovery, Department of Life Science and Biotechnology, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo, 135-0064, Japan. kenichiro.imai@aist.go.jp.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Imai
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Bldg. 46, Canberra, ACT, 0200, Australia. david.hayward@anu.edu.au.
authors.forename: David C
authors.initials: DC
authors.lastname: Hayward
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. eldon.ball@anu.edu.au.|Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Bldg. 46, Canberra, ACT, 0200, Australia. eldon.ball@anu.edu.au.
authors.forename: Eldon E
authors.initials: EE
authors.lastname: Ball
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. david.miller@jcu.edu.au.|Comparative Genomics Centre and Department of Molecular and Cell Biology, James Cook University, Townsville, Queensland, 4811, Australia. david.miller@jcu.edu.au.
authors.forename: David J
authors.initials: DJ
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D037421:Anthozoa / Q000235:genetics; D017209:Apoptosis / Q000235:genetics*; D053181:Caspase 8 / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics; D004330:Drosophila / Q000235:genetics; D019143:Evolution, Molecular; D010802:Phylogeny; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D053181:Caspase 8