Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian, Scotland, United Kingdom.
Int J Parasitol. 2011 Aug 1;41(9):935-42. doi: 10.1016/j.ijpara.2011.03.015. Epub 2011 May 31.
Anthelmintic resistance in parasitic nematodes of small ruminants is widespread and, in some parts of the world, threatens the sustainability of sheep production. The genetic changes underlying resistance to anthelmintics, particularly ivermectin (IVM), remain to be determined. The majority of studies to date have investigated target site mutations; relatively little attention has been paid to the role of changes in gene expression. In this study, we investigated the expression of putative drug transporter molecules, P-glycoproteins (Pgps), in Teladorsagia circumcincta, the predominant parasitic nematode species of sheep in the UK and the major anthelmintic resistant species. Utilising a degenerate PCR approach, 11 partial Pgp sequences were identified. Constitutive differences in gene expression between an IVM-susceptible (MTci2) and a multidrug-resistant (MTci5) isolate were determined for 10 of the Pgps using the ΔΔCt TaqMan® real-time PCR method. Gene expression differences were particularly marked in one of these genes, namely Tci-pgp-9. In the MTci5 isolate, statistically significant increases in Tci-pgp-9 expression, at the mRNA level, were observed across all life-cycle stages and most notably in eggs (55-fold increase). Comparison of the partial Tci-pgp-9 nucleotide sequences from MTci2 and MTci5 also identified high levels of polymorphism. This work has shown that constitutively increased expression in Tci-pgp-9, coupled with increased sequence polymorphism, could play a role in allowing multidrug-resistant T. circumcincta to survive IVM exposure. The genetic changes underpinning these gene expression changes remain to be elucidated and need to be investigated in other isolates. These changes could form the basis of an IVM resistance marker to monitor the spread of resistance and to evaluate management practices aimed at delaying its spread.
绵羊寄生性线虫的驱虫剂耐药性普遍存在，在世界某些地区，这威胁到绵羊生产的可持续性。驱虫剂耐药性的遗传变化，特别是伊维菌素（IVM），仍有待确定。迄今为止，大多数研究都调查了靶位突变；相对较少关注基因表达的变化。在这项研究中，我们研究了主要绵羊寄生性线虫物种泰乐菌素线虫中假定的药物转运蛋白分子 P-糖蛋白（Pgps）的表达，这是英国绵羊的主要寄生虫和主要驱虫剂耐药物种。利用退化的 PCR 方法，鉴定了 11 个部分 Pgp 序列。使用 ΔΔCt TaqMan®实时 PCR 方法，针对 10 个 Pgps 确定了对伊维菌素敏感（MTci2）和多药耐药（MTci5）分离株之间的基因表达的组成差异。在这些基因中，特别是一个基因 Tci-pgp-9 的基因表达差异非常明显。在 MTci5 分离株中，在所有生命周期阶段和最明显的卵期（55 倍增加）观察到 Tci-pgp-9 表达的统计学显著增加。对 MTci2 和 MTci5 的部分 Tci-pgp-9 核苷酸序列的比较也表明了高水平的多态性。这项工作表明，Tci-pgp-9 的组成性表达增加，加上序列多态性增加，可能在允许多药耐药泰乐菌素线虫耐受 IVM 暴露方面发挥作用。这些基因表达变化的遗传变化仍有待阐明，需要在其他分离株中进行调查。这些变化可以作为 IVM 抗性标记的基础，以监测抗性的传播，并评估旨在延迟其传播的管理实践。
