Vector Group, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
PLoS One. 2011;6(12):e29237. doi: 10.1371/journal.pone.0029237. Epub 2011 Dec 19.
Enzymes of the glutathione S-transferase (GST) family play critical roles in detoxification of xenobiotics across many taxa. While GSTs are ubiquitous both in animals and plants, the GST epsilon class (GSTE) is insect-specific and has been associated with resistance to chemical insecticides. While both Aedes aegypti and Anopheles gambiae GSTE clusters consist of eight members, only four putative orthologs are identifiable between the species, suggesting independent expansions of the class in each lineage. We used a primer walking approach, sequencing almost the entire cluster from three Anopheles species (An. stephensi, An. funestus (both Cellia subgenus) and An. plumbeus (Anopheles subgenus)) and compared the sequences to putative orthologs in An. gambiae (Cellia) in an attempt to trace the evolution of the cluster within the subfamily Anophelinae. Furthermore, we measured transcript levels from the identified GSTE loci by real time reverse transcription PCR to determine if all genes were similarly transcribed at different life stages. Among the species investigated, gene order and orientation were similar with three exceptions: (i) GSTE1 was absent in An. plumbeus; (ii) GSTE2 is duplicated in An. plumbeus and (iii) an additional transcriptionally active pseudogene (ψAsGSTE2) was found in An. stephensi. Further statistical analysis and protein modelling gave evidence for positive selection on codons of the catalytic site in GSTE5 albeit its origin seems to predate the introduction of chemical insecticides. Gene expression profiles revealed differences in expression pattern among genes at different life stages. With the exception of GSTE1, ψAsGSTE2 and GSTE2b, all Anopheles species studied share orthologs and hence we assume that GSTE expansion generally predates radiation into subgenera, though the presence of GSTE1 may also suggest a recent duplication event in the Old World Cellia subgenus, instead of a secondary loss. The modifications of the catalytic site within GSTE5 may represent adaptations to new habitats.
谷胱甘肽 S-转移酶 (GST) 家族的酶在许多生物类群的外来化合物解毒中起着关键作用。虽然 GST 在动物和植物中无处不在，但 GST ε 类（GSTE）是昆虫特异性的，与对化学杀虫剂的抗性有关。虽然埃及伊蚊和冈比亚按蚊 GSTE 簇都由 8 个成员组成，但在这两个物种之间只能识别出 4 个假定的直系同源物，表明 GSTE 类在每个谱系中都有独立的扩张。我们使用引物行走方法，从三种按蚊物种（斯氏按蚊、致倦库蚊（均为细胞亚属）和致倦库蚊（按蚊亚属））中几乎对整个簇进行测序，并将序列与冈比亚按蚊（细胞亚属）中的假定直系同源物进行比较，试图在按蚊亚科内追踪该簇的进化。此外，我们通过实时逆转录 PCR 测量鉴定的 GSTE 基因座的转录本水平，以确定所有基因在不同的生命阶段是否以相似的方式转录。在所研究的物种中，基因顺序和方向相似，但有三个例外：（i）GSTE1 在致倦库蚊中缺失；（ii）GSTE2 在致倦库蚊中重复；（iii）在斯氏按蚊中发现了一个额外的转录活性假基因（ψAsGSTE2）。进一步的统计分析和蛋白质建模表明，尽管 GSTE5 的催化位点的密码子似乎起源于化学杀虫剂引入之前，但 GSTE5 的催化位点的密码子受到正选择。基因表达谱揭示了不同生命阶段基因表达模式的差异。除 GSTE1、ψAsGSTE2 和 GSTE2b 外，研究的所有按蚊物种都具有直系同源物，因此我们假设 GSTE 扩张通常发生在辐射进入亚属之前，尽管 GSTE1 的存在也可能表明旧世界细胞亚属最近发生了复制事件，而不是二次丢失。GSTE5 中催化位点的修饰可能代表了对新栖息地的适应。
