Faculty of Veterinary Medicine, Sea Lice Research Centre, Norwegian University of Life Sciences, 1433, Aas, Norway.
Department of Epidemiology, Norwegian Veterinary Institute, Pb. 750 Sentrum, 0106, Oslo, Norway.
Parasit Vectors. 2020 Jul 10;13(1):344. doi: 10.1186/s13071-020-04211-1.
Hydrogen peroxide (HO) is one of the delousing agents used to control sea lice infestations in salmonid aquaculture. However, some Lepeophtheirus salmonis populations have developed resistance towards HO. An increased gene expression and activity of catalase, an enzyme that breaks down HO, have been detected in resistant lice, being therefore introduced as a resistance marker in the salmon industry. In the present study the aim was to validate the use of catalase expression as a marker and to identify new candidate genes as additional markers to catalase, related to HO resistance in L. salmonis.
A sensitive and an HO resistant laboratory strain (P0 generation, not exposed to HO for several years) were batch crossed to generate a cohort with a wide range of HO sensitivities (F2 generation). F2 adult females were then exposed to HO to separate sensitive and resistant individuals. Those F2 lice, the P0 lice and field-collected resistant lice (exposed to HO in the field) were used in an RNA sequencing study.
Catalase was upregulated in resistant lice exposed to HO compared to sensitive lice. This was, however, not the case for unexposed resistant P0 lice. Several other genes were found differentially expressed between sensitive and resistant lice, but most of them seemed to be related to HO exposure. However, five genes were consistently up- or downregulated in the resistant lice independent of exposure history. The upregulated genes were: one gene in the DNA polymerase family, one gene encoding a Nesprin-like protein and an unannotated gene encoding a small protein. The downregulated genes encoded endoplasmic reticulum resident protein 29 and an aquaporin (Glp1_v2).
Catalase expression seems to be induced by HO exposure, since it was not upregulated in unexposed resistant lice. This may pose a challenge for its use as a resistance marker. The five new genes associated with resistance are put forward as complementary candidate genes. The most promising was Glp1_v2, an aquaglyceroporin that may serve as a passing channel for HO. Lower channel number can reduce the influx or distribution of HO in the salmon louse, being directly involved in the resistance mechanism.
过氧化氢（HO）是一种用于控制鲑鱼养殖中虱子感染的除虱剂。然而，一些鲑虱种群对 HO 产生了抗药性。在耐药虱子中，已检测到过氧化氢酶（一种分解 HO 的酶）的基因表达和活性增加，因此被引入鲑鱼产业作为一种耐药标志物。本研究旨在验证过氧化氢酶表达作为标志物的使用，并鉴定新的候选基因作为过氧化氢酶的附加标志物，与 L. salmonis 中的 HO 耐药性相关。
敏感和耐药的实验室品系（P0 代，多年未接触 HO）进行批量杂交，产生具有广泛 HO 敏感性的品系（F2 代）。然后，将 F2 代成年雌虱暴露于 HO 中，以分离敏感和耐药个体。将这些 F2 虱、P0 虱和野外采集的耐药虱（在野外接触 HO）用于 RNA 测序研究。
暴露于 HO 的耐药虱中过氧化氢酶上调，而敏感虱则不然。然而，未暴露于 HO 的耐药 P0 虱则并非如此。在敏感和耐药虱之间还发现了几个其他基因的差异表达，但它们大多数似乎与 HO 暴露有关。然而，有五个基因在耐药虱中无论暴露史如何都一致上调或下调。上调的基因包括：一个 DNA 聚合酶家族的基因、一个编码 Nesprin 样蛋白的基因和一个未注释的编码小蛋白的基因。下调的基因编码内质网驻留蛋白 29 和一个水通道蛋白（Glp1_v2）。
过氧化氢酶的表达似乎是由 HO 暴露诱导的，因为未暴露于 HO 的耐药虱中没有上调。这可能对其作为耐药标志物的使用提出挑战。与耐药性相关的五个新基因被提出作为互补的候选基因。最有前途的是 Glp1_v2，它是一种 aquaglyceroporin，可能作为 HO 的通道。通道数量的减少可以减少 HO 在鲑虱中的流入或分布，直接参与耐药机制。
