Supplementary Material for: Tissue-Specific Regulation of Drosophila NF-κB Pathway Activation by Peptidoglycan Recognition Protein SC

In Drosophila, peptidoglycan (PGN) is detected by PGN recognition proteins (PGRPs) that act as pattern recognition receptors. Some PGRPs such as PGRP-LB or PGRP-SCs are able to cleave PGN, therefore reducing the amount of immune elicitors and dampening immune deficiency (IMD) pathway activation. The precise role of PGRP-SC is less well defined because the PGRP-SC genes (PGRP-SC1a, PGRP-SC1b and PGRP-SC2) lie very close on the chromosome and have been studied using a deletion encompassing the three genes. By generating PGRP-SC-specific mutants, we reevaluated the roles of PGRP-LB, PGRP-SC1 and PGRP-SC2, respectively, during immune responses. We showed that these genes are expressed in different gut domains and that they follow distinct transcriptional regulation. Loss-of-function mutant analysis indicates that PGRP-LB is playing a major role in IMD pathway activation and bacterial load regulation in the gut, although PGRP-SCs are expressed at high levels in this organ. We also demonstrated that PGRP-SC2 is the main negative regulator of IMD pathway activation in the fat body. Accordingly, we showed that mutants for either PGRP-LB or PGRP-SC2 displayed a distinct susceptibility to bacteria depending on the infection route. Lastly, we demonstrated that PGRP-SC1 and PGRP-SC2 are required in vivo for full Toll pathway activation by Gram-positive bacteria.在果蝇（Drosophila）中，肽聚糖（peptidoglycan, PGN）可被作为模式识别受体的肽聚糖识别蛋白（PGN recognition proteins, PGRPs）识别。部分PGRP家族成员，如PGRP-LB与PGRP-SCs，可裂解肽聚糖，从而减少免疫激发子的总量，并抑制免疫缺陷（immune deficiency, IMD）通路的激活。由于PGRP-SC家族基因（PGRP-SC1a、PGRP-SC1b与PGRP-SC2）在染色体上位置紧邻，且既往研究均采用覆盖这三个基因的缺失突变体进行分析，因此PGRP-SC的确切功能尚未被充分阐明。本研究通过构建PGRP-SC基因特异性突变体，重新评估了PGRP-LB、PGRP-SC1与PGRP-SC2在免疫应答过程中的各自功能。研究结果显示，这些基因在肠道的不同区域特异性表达，并受各异的转录调控机制调控。功能缺失突变分析表明，尽管PGRP-SCs在肠道中高表达，但PGRP-LB在肠道IMD通路激活与细菌载量调控中发挥核心作用。本研究同时证实，PGRP-SC2是脂肪体中IMD通路激活的主要负调控因子。据此，我们发现PGRP-LB或PGRP-SC2的突变体对细菌的易感性因感染途径不同而呈现显著差异。最后，本研究证明，PGRP-SC1与PGRP-SC2在体内参与革兰氏阳性菌（Gram-positive bacteria）介导的完整Toll通路（Toll pathway）激活过程。