Journal
PROTEOMICS
Volume 11, Issue 17, Pages 3540-3555Publisher
WILEY
DOI: 10.1002/pmic.201000552
Keywords
Bleaching; Cell biology; Cnidarian; Lipid droplets; Symbiodinium; Symbiont
Funding
- National Science Council of Taiwan [NSC 98-2311-B-291-001-MY3, NSC 98-2311-291-002-MY3]
- National Museum of Marine Biology and Aquarium [99200311, 99200313]
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Gastrodermal lipid bodies (LBs) are organelles involved in the regulation of the mutualistic endosymbiosis between reef-building corals and their dinoflagellate endosymbionts (genus Symbiodinium). As their molecular composition remains poorly defined, we herein describe the first gastrodermal LB proteome and examine in situ morphology of LBs in order to provide insight into their structure and function. After tissue separation of the tentacles of the stony coral Euphyllia glabrescens, buoyant LBs of the gastroderm encompassing a variety of sizes (0.5-4 mu m in diameter) were isolated after two cycles of subcellular fractionation via stepwise sucrose gradient ultracentrifugation and detergent washing. The purity of the isolated LBs was demonstrated by their high degree of lipid enrichment and as well as the absence of contaminating proteins of the host cell and Symbiodinium. LB-associated proteins were then purified, subjected to SDS-PAGE, and identified by MS using an LC-nano-ESI-MS/MS. A total of 42 proteins were identified within eight functional groups, including metabolism, intracellular trafficking, the stress response/molecular modification and development. Ultrastructural analyses of LBs in situ showed that they exhibit defined morphological characteristics, including a high-electron density resulting from a distinct lipid composition from that of the lipid droplets of mammalian cells. Coral LBs were also characterized by the presence of numerous electron-transparent inclusions of unknown origin and composition. Both proteomic and ultrastructural observations seem to suggest that both Symbiodinium and host organelles, such as the ER, are involved in LB biogenesis.
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