PDF(Pubmed)
Abstract：
Insect respiration has long been thought to be solely dependent on an elaborate tracheal system without assistance from the circulatory system or immune cells1,2. Here we describe that Drosophila crystal cells-myeloid-like immune cells called haemocytes-control respiration by oxygenating Prophenoloxidase 2 (PPO2) proteins. Crystal cells direct the movement of haemocytes between the trachea of the larval body wall and the circulation to collect oxygen. Aided by copper and a neutral pH, oxygen is trapped in the crystalline structures of PPO2 in crystal cells. Conversely, PPO2 crystals can be dissolved when carbonic anhydrase lowers the intracellular pH and then reassembled into crystals in cellulo by adhering to the trachea. Physiologically, larvae lacking crystal cells or PPO2, or those expressing a copper-binding mutant of PPO2, display hypoxic responses under normoxic conditions and are susceptible to hypoxia. These hypoxic phenotypes can be rescued by hyperoxia, expression of arthropod haemocyanin or prevention of larval burrowing activity to expose their respiratory organs. Thus, we propose that insect immune cells collaborate with the tracheal system to reserve and transport oxygen through the phase transition of PPO2 crystals, facilitating internal oxygen homeostasis in a process that is comparable to vertebrate respiration.
摘要：
长期以来，人们一直认为昆虫呼吸仅依赖于复杂的气管系统，而没有循环系统或免疫细胞的帮助。在这里，我们描述了果蝇晶体细胞-髓样免疫细胞称为血细胞-通过氧化酚氧化酶原2（PPO2）蛋白控制呼吸。晶体细胞引导血细胞在幼虫体壁的气管和循环之间的运动以收集氧气。在铜和中性pH的帮助下，氧被捕获在晶体细胞中PPO2的晶体结构中。相反，当碳酸酐酶降低细胞内pH时，PPO2晶体可以溶解，然后通过粘附在气管上而在细胞中重新组装成晶体。生理学上,缺乏晶体细胞或PPO2的幼虫，或表达PPO2的铜结合突变体的幼虫，在常氧条件下表现出低氧反应，并且容易缺氧。这些低氧表型可以通过高氧来拯救，节肢动物血蓝蛋白的表达或防止幼虫挖洞活动以暴露其呼吸器官。因此，我们建议昆虫免疫细胞与气管系统合作，通过PPO2晶体的相变来储备和运输氧气，在与脊椎动物呼吸相当的过程中促进内部氧稳态。
