Department of Biology, University of Utah, Salt Lake City, Utah, United States of America.
PLoS One. 2012;7(8):e41510. doi: 10.1371/journal.pone.0041510. Epub 2012 Aug 22.
Detoxification enzymes play a key role in plant-herbivore interactions, contributing to the on-going evolution of ecosystem functional diversity. Mammalian detoxification systems have been well studied by the medical and pharmacological industries to understand human drug metabolism; however, little is known of the mechanisms employed by wild herbivores to metabolize toxic plant secondary compounds. Using a wild rodent herbivore, the desert woodrat (Neotoma lepida), we investigated genomic structural variation, sequence variability, and expression patterns in a multigene subfamily involved in xenobiotic metabolism, cytochrome P450 2B (CYP2B). We hypothesized that differences in CYP2B expression and sequence diversity could explain differential abilities of woodrat populations to consume native plant toxins. Woodrats from two distinct populations were fed diets supplemented with either juniper (Juniperus osteosperma) or creosote bush (Larrea tridentata), plants consumed by woodrats in their respective desert habitats. We used Southern blot and quantitative PCR to determine that the genomic copy number of CYP2B in both populations was equivalent, and similar in number to known rodent copy number. We compared CYP2B expression patterns and sequence diversity using cloned hepatic CYP2B cDNA. The resulting sequences were very diverse, and clustered into four major clades by amino acid similarity. Sequences from the experimental treatments were distributed non-randomly across a CYP2B tree, indicating unique expression patterns from woodrats on different diets and from different habitats. Furthermore, within each major CYP2B clade, sequences shared a unique combination of amino acid residues at 13 sites throughout the protein known to be important for CYP2B enzyme function, implying differences in the function of each major CYP2B variant. This work is the most comprehensive investigation of the genetic diversity of a detoxification enzyme subfamily in a wild mammalian herbivore, and contributes an initial genetic framework to our understanding of how a wild herbivore responds to critical changes in its diet.
解毒酶在植物-草食动物相互作用中起着关键作用，有助于生态系统功能多样性的持续进化。医学和药理学行业已经对哺乳动物的解毒系统进行了深入研究，以了解人类的药物代谢；然而，对于野生草食动物如何代谢有毒植物次生化合物的机制知之甚少。我们使用一种野生啮齿动物——沙漠木鼠（Neotoma lepida），研究了参与外来化合物代谢的多基因亚家族细胞色素 P450 2B（CYP2B）的基因组结构变异、序列变异性和表达模式。我们假设 CYP2B 表达和序列多样性的差异可以解释木鼠种群消耗本地植物毒素的不同能力。来自两个不同种群的木鼠分别喂食补充有杜松（Juniperus osteosperma）或三齿拉瑞阿（Larrea tridentata）的饮食，这两种植物都是木鼠在各自沙漠栖息地食用的。我们使用 Southern blot 和定量 PCR 来确定两个种群的 CYP2B 基因组拷贝数是相等的，并且与已知的啮齿动物拷贝数相似。我们使用克隆的肝脏 CYP2B cDNA 比较 CYP2B 的表达模式和序列多样性。所得序列非常多样化，并根据氨基酸相似性聚类为四个主要的聚类。来自实验处理的序列在 CYP2B 树上呈非随机分布，表明来自不同饮食和不同栖息地的木鼠具有独特的表达模式。此外，在每个主要 CYP2B 聚类中，序列在整个蛋白质中共享 13 个位点的独特氨基酸残基组合，这些位点已知对 CYP2B 酶功能很重要，这意味着每个主要 CYP2B 变体的功能不同。这项工作是对野生哺乳动物草食动物解毒酶亚家族遗传多样性的最全面研究，为我们理解野生草食动物如何应对其饮食的关键变化提供了初步的遗传框架。
