Department of Zoology, Oregon State University, Corvallis, OR 97331-2914, USA.
J Exp Biol. 2013 Aug 1;216(Pt 15):2813-20. doi: 10.1242/jeb.087858. Epub 2013 Apr 25.
Coral bleaching occurs when there is a breakdown of the symbiosis between cnidarian hosts and resident Symbiodinium spp. Multiple mechanisms for the bleaching process have been identified, including apoptosis and autophagy, and most previous work has focused on the Symbiodinium cell as the initiator of the bleaching cascade. In this work we show that it is possible for host cells to initiate apoptosis that can contribute to death of the Symbiodinium cell. First we found that colchicine, which results in apoptosis in other animals, causes cell death in the model anemone Aiptasia sp. but not in cultured Symbiodinium CCMP-830 cells or in cells freshly isolated from host Aiptasia (at least within the time frame of our study). In contrast, when symbiotic Aiptasia were incubated in colchicine, cell death in the resident Symbiodinium cells was observed, suggesting a host effect on symbiont mortality. Using live-cell confocal imaging of macerated symbiotic host cell isolates, we identified a pattern where the initiation of host cell death was followed by mortality of the resident Symbiodinium cells. This same pattern was observed in symbiotic host cells that were subjected to temperature stress. This research suggests that mortality of symbionts during temperature-induced bleaching can be initiated in part by host cell apoptosis.
珊瑚白化是由于刺胞动物宿主和驻留的 Symbiodinium spp. 之间的共生关系破裂而发生的。已经确定了白化过程的多种机制，包括细胞凋亡和自噬，并且大多数先前的工作都集中在 Symbiodinium 细胞作为白化级联的启动子。在这项工作中，我们表明宿主细胞有可能启动凋亡，从而导致 Symbiodinium 细胞死亡。首先，我们发现秋水仙碱会导致其他动物的细胞凋亡，从而导致模型海葵 Aiptasia sp. 的细胞死亡，但不会导致培养的 Symbiodinium CCMP-830 细胞或从宿主 Aiptasia 中新鲜分离的细胞死亡（至少在我们的研究时间范围内）。相比之下，当共生的 Aiptasia 被置于秋水仙碱中时，观察到驻留的 Symbiodinium 细胞死亡，表明宿主对共生体死亡率有影响。使用活细胞共聚焦显微镜对粉碎的共生宿主细胞分离物进行成像，我们确定了一种模式，其中宿主细胞死亡的开始伴随着驻留的 Symbiodinium 细胞的死亡。在受到温度胁迫的共生宿主细胞中也观察到了同样的模式。这项研究表明，在温度诱导的白化过程中，共生体的死亡率部分可以由宿主细胞凋亡引发。
