title: Regulation of apoptotic mediators reveals dynamic responses to thermal stress in the reef building coral Acropora millepora.
abstract: BACKGROUND
  Mass coral bleaching is increasing in scale and frequency across the world's coral reefs and is being driven primarily by increased levels of thermal stress arising from global warming. In order to understand the impacts of projected climate change upon corals reefs, it is important to elucidate the underlying cellular mechanisms that operate during coral bleaching and subsequent mortality. In this respect, increased apoptotic cell death activity is an important cellular process that is associated with the breakdown of the mutualistic symbiosis between the cnidarian host and their dinoflagellate symbionts.
  
  
  RESULTS
  The PRESENT study reports the impacts of different stressors (colchicine and heat stress) on three phases of apoptosis: (i) the potential initiation by differential expression of Bcl-2 members, (ii) the execution of apoptotic events by activation of caspase 3-like proteases and (iii) and finally, the cell disposal indicated by DNA fragmentation in the reef building coral Acropora millepora. In corals incubated with colchicine, an increase in caspase 3-like activity and DNA fragmentation was associated with a relative down-regulation of Bcl-2, suggesting that the initiation of apoptosis may be mediated by the suppression of an anti-apoptotic mechanism. In contrast, in the early steps of heat stress, the induction of caspase-dependent apoptosis was related to a relative up-regulation of Bcl-2 consecutively followed by a delayed decrease in apoptosis activity.
  
  
  CONCLUSIONS
  In the light of these results, we propose a model of heat stress in coral hosts whereby increasing temperatures engage activation of caspase 3-dependent apoptosis in cells designated for termination, but also the onset of a delayed protective response involving overexpression of Bcl-2 in surviving cells. This mitigating response to thermal stress could conceivably be an important regulatory mechanism for cell survival in corals exposed to sudden environmental changes.
authors.affiliation: Coral Reef Ecosystem Laboratory, Global Change Institute, ARC Centre for Excellence in Coral Reef Studies, The University of Queensland, St Lucia, Queensland, Australia. m.pernice@uq.edu.au
authors.forename: Mathieu
authors.initials: M
authors.lastname: Pernice
authors.forename: Simon R
authors.initials: SR
authors.lastname: Dunn
authors.forename: Thomas
authors.initials: T
authors.lastname: Miard
authors.forename: Sylvie
authors.initials: S
authors.lastname: Dufour
authors.forename: Sophie
authors.initials: S
authors.lastname: Dove
authors.forename: Ove
authors.initials: O
authors.lastname: Hoegh-Guldberg
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D037421:Anthozoa / Q000502:physiology*; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D057894:Coral Reefs; D053938:DNA Fragmentation; D004141:Dinoflagellida; D057232:Global Warming; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D013559:Symbiosis
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D053148:Caspase 3