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 te...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）之间的共生相互作用，其调控的细胞机制仍未得到充分阐释。这类机制涵盖宿主-共生体识别与代谢交换，不仅在正常生理条件下维持共生体系的稳定性，同时在胁迫环境下会引发共生破裂（即白化现象）。本研究对共生海葵（Anemonia viridis）体内的固醇转运蛋白尼曼-匹克C型（Niemann-Pick type C，NPC1与NPC2）的基因谱进行了系统描述。我们发现该物种仅存在1个NPC1基因，而脊椎动物（vertebrates）通常拥有2个该类基因。尽管大多数后生动物（metazoans）仅含有1个NPC2基因，但刺胞动物体内的该基因发生了复制事件，我们在A. viridis中检测到了4个NPC2基因。不过，仅1个基因（AvNPC2-d）在共生海葵中呈现上调表达，且在胃层（即含有共生体的组织）中的表达水平显著高于表皮层。我们针对……开展了免疫标记实验