Parasites employ proteases to evade host immune systems, feed and replicate and are often the target of anti-parasite strategies to disrupt these interactions. Myxozoans are obligate cnidarian parasites, alternating between invertebrate and fish hosts. Their genes are highly divergent from other metazoans, and available genomic and transcriptomic datasets are limited. Some myxozoans are important aquaculture pathogens such as Sphaerospora molnari replicating in the blood of farmed carp before reaching the gills for sporogenesis and transmission. Proliferative stages cause a massive systemic lymphocyte response and the disruption of the gill epithelia by spore-forming stages leads to respiratory problems and mortalities. In the absence of a S. molnari genome, we utilized a de novo approach to assemble the first transcriptome of proliferative myxozoan stages to identify S. molnari proteases that are upregulated during the first stages of infection when the parasite multiplies massively, rather than in late spore-forming plasmodia. Furthermore, a subset of orthologs was used to characterize 3D structures and putative druggable targets. An assembled and host filtered transcriptome containing 9436 proteins, mapping to 29,560 contigs was mined for protease virulence factors and revealed that cysteine proteases were most common (38%), at a higher percentage than other myxozoans or cnidarians (25–30%). Two cathepsin Ls that were found upregulated in spore-forming stages with a presenilin like aspartic protease and a dipeptidyl peptidase. We also identified downregulated proteases in the spore-forming development when compared with proliferative stages including an astacin metallopeptidase and lipases (qPCR). In total, 235 transcripts were identified as putative proteases using a MEROPS database. In silico analysis of highly transcribed cathepsins revealed potential drug targets within this data set that should be prioritised for development. In silico surveys for proteins are essential in drug discovery and understanding host-parasite interactions in non-model systems. The present study of S. molnari’s protease arsenal reveals previously unknown proteases potentially used for host exploitation and immune evasion. The pioneering dataset serves as a model for myxozoan virulence research, which is of particular importance as myxozoan diseases have recently been shown to emerge and expand geographically, due to climate change.

中文翻译：

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molpha sphaerospora molnari（Cnidaria，Myxosporea）血液阶段的转录组提供蛋白水解的阿森纳作为对抗普通鲤鱼sphaerosporosis的潜在治疗靶标。

寄生虫利用蛋白酶逃避宿主免疫系统，进食和复制，通常是破坏这些相互作用的抗寄生虫策略的目标。黏附动物是专性的刺胞寄生虫，在无脊椎动物和鱼类宿主之间交替。他们的基因与其他后生动物高度不同，可用的基因组和转录组数据集也很有限。一些粘虫类动物是重要的水产养殖病原体，例如，在到达carp进行孢子发生和传播之前，在养殖的鲤鱼血液中复制的莫氏乳杆菌（Sphaerospora molnari）。增殖阶段引起大量的全身淋巴细胞反应，而孢子形成阶段对the上皮的破坏导致呼吸系统疾病和死亡。在没有葡萄球菌的基因组的情况下，我们利用从头方法组装了增生的黏附子虫阶段的第一个转录组，以鉴定在寄生虫大量繁殖而不是在孢子形成后期的疟原虫感染的感染的第一阶段上调的链球菌。此外，直系同源物的一个子集用于表征3D结构和推定的可靶向药物。提取了一个包含9436个蛋白的组装并宿主过滤的转录组，定位到29,560个重叠群，以发现蛋白酶毒力因子，结果表明半胱氨酸蛋白酶是最常见的（38％），其百分比高于其他粘虫类或刺胞动物（25-30％）。发现两个组织蛋白酶Ls在孢子形成阶段被早老素如天冬氨酸蛋白酶和二肽基肽酶上调。与增生阶段，包括阿斯达辛金属肽酶和脂肪酶（qPCR）相比，我们还发现了孢子形成过程中蛋白酶的下调。使用MEROPS数据库，总共鉴定出235种转录物为推定的蛋白酶。对高度转录的组织蛋白酶的计算机分析表明，该数据集中潜在的药物靶标应优先开发。在计算机上对蛋白质进行的调查对于发现药物和了解非模型系统中宿主与寄生虫的相互作用至关重要。莫氏葡萄球菌蛋白酶库的当前研究表明，以前未知的蛋白酶可能用于宿主开发和免疫逃逸。开拓性的数据集可作为粘液动物毒力研究的模型，