Variation in gene expression within clones of the earthworm <i>Dendrobaena octaedra</i>

Gene expression is highly plastic, which can help organisms to both acclimate and adapt to changing environments. Possible variation in gene expression among individuals with the same genotype (among clones) is not widely considered, even though it could impact the results of studies that focus on gene expression phenotypes, for example studies using clonal lines. We examined the extent of within and between clone variation in gene expression in the earthworm Dendrobaena octaedra, which reproduces through apomictic parthenogenesis. Five microsatellite markers were developed and used to confirm that offspring are genetic clones of their parent. After that, expression of 12 genes was measured from five individuals each from six clonal lines after exposure to copper contaminated soil. Variation in gene expression was higher over all genotypes than within genotypes, as initially assumed. A subset of the genes was also examined in the offspring of exposed individuals in two of the clonal lines. In this case, variation in gene expression within genotypes was as high as that observed over all genotypes. One gene in particular (chymotrypsin inhibitor) also showed significant differences in the expression levels among genetically identical individuals. Gene expression can vary considerably, and the extent of variation may depend on the genotypes and genes studied. Ensuring a large sample, with many different genotypes, is critical in studies comparing gene expression phenotypes. Researchers should be especially cautious inferring gene expression phenotypes when using only a single clonal or inbred line, since the results might be specific to only certain genotypes.基因表达具有高度可塑性，可帮助生物体适应多变环境。即便同一基因型个体（即克隆个体）间的基因表达差异可能对以基因表达表型为研究对象的实验（例如使用克隆系开展的研究）结果产生影响，此类差异却尚未得到广泛关注。我们以通过无融合孤雌生殖（apomictic parthenogenesis）繁殖的八毛蚓（Dendrobaena octaedra）为研究对象，探究其克隆内与克隆间的基因表达变异程度。我们开发了5个微卫星标记（microsatellite markers）以确认子代即为亲本的遗传克隆。随后，我们将6个克隆系的各5个个体暴露于铜污染土壤后，检测了12个基因的表达水平。研究结果显示，如最初假设那般，所有基因型间的基因表达变异程度高于克隆内变异。我们还在其中2个克隆系的暴露个体子代中检测了部分基因的表达情况，此时克隆内的基因表达变异程度与所有基因型间的变异程度相当。其中尤以胰凝乳蛋白酶抑制剂（chymotrypsin inhibitor）基因最为突出，其在遗传背景完全一致的个体间的表达水平存在显著差异。基因表达可发生显著波动，其变异程度或取决于所研究的基因型与基因类型。在比较基因表达表型的研究中，纳入涵盖多种基因型的大样本量至关重要。研究者在仅使用单个克隆系或近交系开展研究并推断基因表达表型时需格外谨慎，因为所得结果或仅适用于特定基因型。