Department of Comparative Biomedicine and Food Science, University of Padova, Viale Dell'Università, 16 35020, Legnaro, PD, Italy.
Division of Comparative Biomedical Sciences, OIE Reference Centre for Viral Encephalopathy and Retinopathy, Istituto Zooprofilattico Sperimentale Delle Venezie (IZSVe), Padua, Italy.
Fish Shellfish Immunol. 2021 Jul;114:282-292. doi: 10.1016/j.fsi.2021.04.021. Epub 2021 May 7.
The gilthead sea bream (Sparus aurata) is a marine fish of great importance for Mediterranean aquaculture. This species has long been considered resistant to Nervous Necrosis Virus (NNV), an RNA virus that causes massive mortalities in several farmed fish animals. However, the recent appearance of RGNNV/SJNNV reassortant strains started to pose a serious threat to sea bream hatcheries, as it is able to infect larvae and juveniles of this species. While host response to NNV has been extensively studied in adult fish, little attention has been devoted to early life history stages, which are generally the most sensitive ones. Here we report for the first time a time-course RNA-seq analysis on 21-day old fish gilthead sea bream larvae experimentally infected with a RGNNV/SJNNV strain. NNV-infected and mock-infected samples were collected at four time points (6 h, 12 h, 24 h, and 48 h post infection). Four biological replicates, each consisting of five pooled larvae, were analysed for each time point and group. A large set of genes were found to be significantly regulated, especially at early time points (6 h and 12 h), with several heat shock protein encoding transcripts being up-regulated (e.g. hspa5, dnaj4, hspa9, hsc70), while many immune genes were down-regulated (e.g. myd88 and irf5 at T06, pik3r1, stat3, jak1, il12b and il6st at T12). A gene set enrichment analysis (GSEA) identified several altered pathways/processes. For instance, the formation of peroxisomes, which are important anti-viral components as well as essential for nervous system homeostasis, and the autophagy pathway were down-regulated at 6 h and 24 h post infection (hpi). Finally, two custom "reactomes" (i.e. significant gene sets observed in other studies) were defined and used. The first reactome integrated the transcriptomic response to NNV in different fish species, while the second one included all genes found to be stimulated either by interferon (IFN) or by IFN and Chikungunya virus in zebrafish. Genes in both reactomes showed predominant up-regulation at 6hpi and 12hpi and a general down-regulation at 24hpi. Such evidence suggest a certain degree of similarity between the response of sea bream and that of other fish species to NNV, while the observed down-regulation of IFN- and viral-stimulated pathways argues for a possible interference of NNV against the host response.
金头鲷（Sparus aurata）是一种对地中海水产养殖非常重要的海鱼。该物种长期以来被认为对神经坏死病毒（NNV）具有抗性，NNV 是一种 RNA 病毒，可导致多种养殖鱼类大量死亡。然而，最近出现的 RGNNV/SJNNV 重组株开始对金头鲷孵化场构成严重威胁，因为它能够感染该物种的幼虫和幼鱼。虽然宿主对 NNV 的反应已在成年鱼类中得到广泛研究，但对早期生活史阶段的关注较少，而这些阶段通常是最敏感的。在这里，我们首次报道了对 21 天大的金头鲷幼鱼进行的一项时间序列 RNA-seq 分析，这些幼鱼在实验中感染了 RGNNV/SJNNV 株。在感染 NNV 和模拟感染的样本中，在四个时间点（感染后 6 小时、12 小时、24 小时和 48 小时）收集了样本。每个时间点和组分析了四个生物学重复，每个重复由五个幼虫混合组成。结果发现大量基因显著调控，尤其是在早期时间点（6 小时和 12 小时），许多热休克蛋白编码转录本上调（例如 hspa5、dnaj4、hspa9、hsc70），而许多免疫基因下调（例如，T06 时的 myd88 和 irf5，T12 时的 pik3r1、stat3、jak1、il12b 和 il6st）。基因集富集分析（GSEA）确定了几个改变的途径/过程。例如，过氧化物酶体的形成，过氧化物酶体是重要的抗病毒成分，也是神经系统内稳态所必需的，以及自噬途径在感染后 6 小时和 24 小时（hpi）时下调。最后，定义并使用了两个自定义“反应组”（即其他研究中观察到的显著基因集）。第一个反应组整合了不同鱼类物种对 NNV 的转录组反应，而第二个反应组包括在斑马鱼中被干扰素（IFN）或 IFN 和基孔肯雅病毒刺激的所有基因。两个反应组中的基因在 6hpi 和 12hpi 时主要上调，在 24hpi 时普遍下调。这些证据表明，金头鲷对 NNV 的反应与其他鱼类物种之间存在一定程度的相似性，而 IFN 和病毒刺激途径的下调表明 NNV 可能对宿主反应产生干扰。
