Ahmed Shabbir, Stanley David, Kim Yonggyun
Department of Plant Medicals, College of Natural Sciences, Andong National University, Andong, South Korea.
Biological Control of Insects Research Laboratory, United States Department of Agriculture-Agricultural Research Service, Columbia, MO, United States.
Front Physiol. 2018 Sep 4;9:1231. doi: 10.3389/fphys.2018.01231. eCollection 2018.
Eicosanoids, oxygenated metabolites of C20 polyunsaturated fatty acids (PUFAs), mediate fundamental physiological processes, including immune reactions and reproduction, in insects. Prostaglandins (PGs) make up one group of eicosanoids, of which PGE is a relatively well-known mediator in various insect taxa. While PG biosynthesis has been reported, the specific biosynthetic pathway for PGE is not known in insects. Here, we posed the hypothesis that mediates biosynthesis of physiologically active PGE through its cognate protein. To test this hypothesis, we interrogated a transcriptome of the lepidopteran insect, , to identify a candidate PGE synthase () and analyzed its sequence and expression. Its predicted amino acid sequence contains a consensus thioredoxin homology sequence (Cys-x-x-Cys) responsible for catalytic activity along with an N-terminal membrane-associated hydrophobic domain and C-terminal cytosolic domain. It also shares sequence homology (36.5%) and shares almost overlapping three dimensional structures with a membrane-bound human PGES2 (mPGES2). was expressed in all developmental stages with high peaks during the late larval instar and adult stages. Immune challenge significantly up-regulated its expression levels in hemocytes and fat body. Injecting double-stranded RNA (dsRNA) specific to significantly impaired two cellular immune responses, hemocyte-spreading behavior and nodule formation following bacterial challenge. Humoral immunity was also significantly suppressed, registered as reduced phenoloxidase activity and antimicrobial peptide expression levels. The suppressed immune responses were reversed following PGE, but not arachidonic acid (AA), treatments. RNAi treatments also reduced the egg-laying behavior of females. Control females mated with the RNAi-treated males led to substantially reduced egg-laying behavior, which was also reversed following PGE injections into females. These results strongly bolster our hypothesis that acts in the biosynthesis of PGE, a crucial biochemical signal mediating immune and reproductive physiology of .
类二十烷酸是C20多不饱和脂肪酸（PUFAs）的氧化代谢产物，在昆虫中介导包括免疫反应和繁殖在内的基本生理过程。前列腺素（PGs）是类二十烷酸的一类，其中PGE在各种昆虫分类群中是一种相对知名的介质。虽然已经报道了PG的生物合成，但昆虫中PGE的具体生物合成途径尚不清楚。在这里，我们提出假设，即 通过其同源蛋白介导生理活性PGE的生物合成。为了验证这一假设，我们对鳞翅目昆虫 的转录组进行了研究，以鉴定候选PGE合酶（ ）并分析其序列和表达。其预测的氨基酸序列包含一个负责催化活性的共有硫氧还蛋白同源序列（Cys-x-x-Cys），以及一个N端膜相关疏水结构域和C端胞质结构域。它还与膜结合的人PGES2（mPGES2）具有序列同源性（36.5%），并且具有几乎重叠的三维结构。 在所有发育阶段均有表达，在幼虫晚期和成虫阶段达到高峰。免疫刺激显著上调了其在血细胞和脂肪体中的表达水平。注射特异于 的双链RNA（dsRNA）显著损害了两种细胞免疫反应，即细菌攻击后的血细胞铺展行为和结节形成。体液免疫也受到显著抑制，表现为酚氧化酶活性和抗菌肽表达水平降低。PGE处理后，受抑制的免疫反应得到逆转，但花生四烯酸（AA）处理后未逆转。RNAi处理还降低了雌性的产卵行为。与经RNAi处理的雄性交配的对照雌性产卵行为大幅减少，向雌性注射PGE后这种行为也得到逆转。这些结果有力地支持了我们的假设，即 在PGE的生物合成中起作用，PGE是介导 免疫和生殖生理的关键生化信号。
