Data from: Are Niemann-Pick type C proteins key players in cnidarian-dinoflagellate endosymbioses?

The symbiotic interaction between cnidarians, such as corals and sea anemones, and the unicellular algae Symbiodinium is regulated by yet poorly understood cellular mechanisms, despite the ecological importance of coral reefs. These mechanisms, including host-symbiont recognition and metabolic exchange, control symbiosis stability under normal conditions, but also lead to symbiosis breakdown (bleaching) during stress. This study describes the repertoire of the sterol-trafficking proteins Niemann-Pick type C (NPC1 and NPC2) in the symbiotic sea anemone Anemonia viridis. We found one NPC1 gene instead of two in vertebrates. While only one NPC2 gene is present in most metazoans, this gene has been duplicated in cnidarians and we detected four NPC2 genes in A. viridis. However, only one gene (AvNPC2-d) was upregulated in symbiotic sea anemones and displayed higher expression in the gastrodermis (symbiont-containing tissue) than in the epidermis. We performed immunolabeling experiments on tentacle cross sections and demonstrated that the AvNPC2-d protein was closely associated with symbiosomes. In addition, AvNPC1 and AvNPC2-d gene expression was strongly downregulated during stress, especially at the onset of symbiosis breakdown. These data suggest that AvNPC2-d is involved in both the stability and dysfunction of cnidarian-dinoflagellate symbioses.

尽管珊瑚礁具有重要的生态价值，但珊瑚、海葵等刺胞动物（cnidarians）与单细胞藻类虫黄藻（Symbiodinium）之间的共生互作，其背后的细胞调控机制仍未被充分阐明。这类机制涵盖宿主-共生体识别与代谢交换等过程，不仅能在正常生理条件下维持共生体系的稳定性，还会在胁迫环境下触发共生崩溃（即珊瑚白化）。本研究针对共生海葵紫点海葵（Anemonia viridis）体内的固醇转运蛋白尼曼-匹克C型（Niemann-Pick type C，NPC1与NPC2）的编码基因谱进行了系统描述：研究发现该物种仅存在1个NPC1基因，而脊椎动物中则有2个该类基因；尽管多数后生动物（metazoans）仅携带1个NPC2基因，但刺胞动物中该基因发生了复制事件，我们在紫点海葵中检测到4个NPC2同源基因。不过，仅有1个基因（AvNPC2-d）在共生海葵中呈现上调表达，且其在胃皮层（包含共生体的组织）中的表达量显著高于表皮。我们对触手横切片开展了免疫标记实验，证实AvNPC2-d蛋白与共生体囊泡（symbiosomes）紧密结合。此外，在胁迫条件下，尤其是共生崩溃初期，AvNPC1与AvNPC2-d的基因表达均显著下调。上述数据表明，AvNPC2-d参与了刺胞动物-甲藻（dinoflagellate）共生关系的维持与功能失调过程。