Lucas Eric R, Romiguier Jonathan, Keller Laurent
Department of Ecology and Evolution, Biophore, University of Lausanne, Lausanne, Switzerland.
Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK.
Mol Ecol. 2017 Oct;26(19):5058-5073. doi: 10.1111/mec.14256. Epub 2017 Aug 24.
Phenotypic plasticity, where a single genome can give rise to different phenotypes, underlies many remarkable features of the natural world and occurs in a wide range of organisms. Understanding the transcriptional differences that underlie plastic phenotypes remains a major unsolved problem in biology. In many ants, females can develop into either queens or workers, two phenotypes with different morphology, behaviour and longevity. In comparison with workers, queens are larger, more fecund and longer lived. Here, we study gene expression differences between queens and workers in the ant Lasius niger. The analysis of age- and tissue-specific RNA sequencing showed that patterns of caste-biased gene expression vary considerably between ages and tissues. Expression was more tightly linked to age than caste despite the important morphological and behavioural differences between queens and workers. Our data allowed us to identify genes that are consistently biased across biological contexts. Caste-biased genes showed faster rates of molecular evolution, lower levels of DNA methylation and greater variability in expression than unbiased genes. Our results indicate that a substantial proportion of caste-biased expression is ephemeral and that taking account of age and tissue is critical to understanding the transcriptomic basis of plastic phenotypes. By contrast, the biological context of expression bias did not broadly affect methylation or the rate of evolution. The faster rate of evolution and greater variability of expression of caste-biased genes indicate that caste-biased genes evolve from loosely regulated genes that can be co-opted for caste-specific tasks because of the lax control over their expression.
表型可塑性是指单个基因组能够产生不同的表型，它是自然界许多显著特征的基础，并且在广泛的生物体中都有发生。理解构成可塑性表型基础的转录差异仍然是生物学中一个主要的未解难题。在许多蚂蚁中，雌性可以发育成蚁后或工蚁，这两种表型具有不同的形态、行为和寿命。与工蚁相比，蚁后体型更大、繁殖力更强且寿命更长。在此，我们研究了黑褐蚁蚁后和工蚁之间的基因表达差异。对年龄和组织特异性RNA测序的分析表明，不同年龄和组织之间， caste偏向性基因表达模式差异很大。尽管蚁后和工蚁之间存在重要的形态和行为差异，但基因表达与年龄的关联比与caste的关联更为紧密。我们的数据使我们能够识别在不同生物学背景下始终存在偏向性的基因。与无偏向性的基因相比， caste偏向性基因显示出更快的分子进化速率、更低的DNA甲基化水平和更大的表达变异性。我们的结果表明，相当一部分caste偏向性表达是短暂的，并且考虑年龄和组织对于理解可塑性表型的转录组基础至关重要。相比之下，表达偏向性的生物学背景并没有广泛影响甲基化或进化速率。 caste偏向性基因更快的进化速率和更大的表达变异性表明， caste偏向性基因是从调控松散的基因进化而来的，由于对其表达的控制较为宽松，这些基因可以被用于特定caste的任务。
