Understanding Crassostrea virginica tolerance of Perkinsus marinus through global gene expression analysis

Disease tolerance, a host's ability to limit damage from a given parasite burden, is quantified by the relationship between pathogen load and host survival or reproduction. Dermo disease, caused by the protozoan parasite Perkinsus marinus, negatively impacts survival in both wild and cultured eastern oyster (Crassostrea virginica) populations. Resistance to P. marinus has been the focus of previous studies, but tolerance also has important consequences for disease management in cultured and wild populations. In this study we measured dermo tolerance and evaluated global expression patterns of two sensitive and two tolerant eastern oyster families experimentally challenged with distinct doses of P. marinus (0, 106, 107, and 108 parasite spores per gram wet weight, n=3-5 per family per dose). Weighted Gene Correlation Network Analysis (WGCNA) identified several modules correlated with increasing parasite dose/infection intensity, as well as phenotype. Modules positively correlated with dose included transcripts and enriched GO terms indicating increased hemocyte activation and cell cycle activity. Additionally, these modules included G-protein coupled receptor, toll-like receptor, and tumor necrosis factor pathways, which are important for immune effector molecule and apoptosis activation. Increased metabolic activity was also positively correlated with treatment. The module negatively correlated with infection intensity was enriched with GO terms associated with normal cellular activity and growth, indicating a trade-off with increased immune response. The module positively correlated with the tolerant phenotype was enriched for transcripts associated with "programmed cell death" and contained a large number of tripartite motif-containing proteins. Differential expression analysis was also performed on the 108 dosed group using the most sensitive family as the comparison reference. Results were consistent with the network analysis, but signals for "programmed cell death" and serine protease inhibitors were stronger in one tolerant family than the other, suggesting that there are multiple avenues for disease tolerance. These results provide new insight for defining dermo response traits and have important implications for applying selective breeding for disease management.

疾病耐受性，即宿主限制特定寄生虫负担所造成的损害的能力，可通过病原体负荷与宿主存活或繁殖之间的关联进行量化。由原生动物寄生虫Perkinsus marinus引起的皮炎疾病，对野生和养殖的东部牡蛎（Crassostrea virginica）种群中的存活产生负面影响。对P. marinus的抵抗力一直是先前研究关注的焦点，但耐受性对于养殖和野生种群中的疾病管理也具有重要意义。在本研究中，我们测量了皮炎耐受性，并评估了两种敏感性和两种耐受性东部牡蛎家族在全球表达模式上，经不同剂量P. marinus（每克湿重0、10^6、10^7和10^8个寄生虫孢子，每家族每剂量n=3-5）实验挑战下的表现。加权基因相关网络分析（WGCNA）鉴定出与增加的寄生虫剂量/感染强度以及表型相关联的多个模块。与剂量呈正相关的模块包括表明增加血细胞活化和细胞周期活动的转录本以及富集的GO术语。此外，这些模块还包含G蛋白偶联受体、Toll样受体和肿瘤坏死因子途径，这些途径对于免疫效应分子和细胞凋亡激活至关重要。代谢活动的增加也与治疗呈正相关。与感染强度负相关的模块富含与正常细胞活动和生长相关的GO术语，表明与增强的免疫反应存在权衡。与耐受性表型正相关的模块富含与“程序性细胞死亡”相关的转录本，并含有大量包含三重螺旋结构域的蛋白质。此外，还针对108剂量组进行了差异表达分析，以最敏感的家庭作为比较参考。结果与网络分析一致，但在一种耐受性家庭中，“程序性细胞死亡”和丝氨酸蛋白酶抑制剂的信号比另一种耐受性家庭更强，这表明存在多种耐受疾病途径。这些结果为定义皮炎反应性状提供了新的见解，并对应用选择性育种进行疾病管理具有重要意义。