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Abstract：
Insects rely on an innate immune system to recognize and eliminate pathogens. Key components of this system are highly conserved across all invertebrates. To detect pathogens, insects use Pattern recognition receptors (PRRs) that bind to signature motifs on the surface of pathogens called Pathogen Associated Molecular Patterns (PAMPs). In general, insects use peptidoglycan recognition proteins (PGRPs) in the Immune Deficiency (IMD) pathway to detect Gram-negative bacteria, and other PGRPs and Gram-negative binding proteins (GNBPs) in the Toll pathway to detect Gram-positive bacteria and fungi, although there is crosstalk and cooperation between these and other pathways. Once pathogens are recognized, these pathways activate the production of potent antimicrobial peptides (AMPs). Most PRRs in insects have been reported from genome sequencing initiatives but few have been characterized functionally. The initial studies on insect PRRs were done using established dipteran model organisms such as Drosophila melanogaster, but there are differences in the numbers and functional role of PRRs in different insects. Here we describe the genomic repertoire of PGRPs in Rhodnius prolixus, a hemimetabolous hemipteran vector of the parasite Trypanosoma cruzi that causes Chagas disease in humans. Using a de novo transcriptome from the fat body of immune activated insects, we found 5 genes encoding PGRPs. Phylogenetic analysis groups R. prolixus PGRPs with D. melanogaster PGRP-LA, which is involved in the IMD pathway in the respiratory tract. A single R. prolixus PGRP gene encodes isoforms that contain an intracellular region or motif (cryptic RIP Homotypic Interaction Motif-cRHIM) that is involved in the IMD signaling pathway in D. melanogaster. We characterized and silenced this gene using RNAi and show that the PGRPs that contain cRHIMs are involved in the recognition of Gram-negative bacteria, and activation of the IMD pathway in the fat body of R. prolixus, similar to the PGRP-LC of D. melanogaster. This is the first functional characterization of a PGRP containing a cRHIM motif that serves to activate the IMD pathway in a hemimetabolous insect.
摘要：
昆虫依靠先天免疫系统来识别和消除病原体。该系统的关键组件在所有无脊椎动物中都高度保守。为了检测病原体，昆虫使用模式识别受体（PRR），该受体与病原体表面的特征基序结合，称为病原体相关分子模式（PAMP）。总的来说,昆虫在免疫缺陷（IMD）途径中使用肽聚糖识别蛋白（PGRP）来检测革兰氏阴性菌，和其他PGRPs和革兰氏阴性结合蛋白（GNBPs）在Toll途径中检测革兰氏阳性细菌和真菌，尽管这些途径和其他途径之间存在串扰和合作。一旦病原体被识别出来,这些途径激活了强效抗菌肽(AMP)的产生。已经从基因组测序计划中报道了昆虫中的大多数PRR，但很少有功能特征。对昆虫PRR的初步研究是使用已建立的双翅目模型生物进行的，例如果蝇，但PRR在不同昆虫中的数量和功能作用存在差异。在这里，我们描述了Rhodniusprolixus中PGRP的基因组库，一种寄生虫克氏锥虫的半代谢型半翅目载体，引起人类锥虫病。使用来自免疫激活昆虫的脂肪体的从头转录组，我们发现了5个编码PGRPs的基因。系统发育分析组R.prolixusPGRP与D.melanogasterPGRP-LA，参与呼吸道IMD通路。单个R.prolixusPGRP基因编码同种型，该同种型包含细胞内区域或基序（隐蔽的RIP同型相互作用基序-cRHIM），该基序参与黑腹D.melanogaster的IMD信号传导途径。我们使用RNAi对该基因进行了表征和沉默，并显示含有cRHIMs的PGRPs参与了革兰氏阴性细菌的识别，并激活了原毛囊脂肪体内的IMD通路，类似于D.melanogaster的PGRP-LC。这是含有cRHIM基序的PGRP的第一个功能表征，该基序用于激活半代谢昆虫中的IMD途径。
