Loire Etienne, Tusso Sergio, Caminade Pierre, Severac Dany, Boursot Pierre, Ganem Guila, Smadja Carole M
Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de l'Evolution UMR 5554, Institut pour la Recherche et le Développement (IRD), EPHE, Université de Montpellier, Montpellier, France.
Montpellier GenomiX (MGX), Institut de Génomique Fonctionnelle, Montpellier Cedex 5, France.
Mol Ecol. 2017 Oct;26(19):5189-5202. doi: 10.1111/mec.14212. Epub 2017 Jul 16.
Expression divergence, rather than sequence divergence, has been shown to be important in speciation, particularly in the early stages of divergence of traits involved in reproductive isolation. In the two European subspecies of house mice, Mus musculus musculus and Mus musculus domesticus, earlier studies have demonstrated olfactory-based assortative mate preference in populations close to their hybrid zone. It has been suggested that this behaviour evolved following the recent secondary contact between the two taxa (~3,000 years ago) in response to selection against hybridization. To test for a role of changes in gene expression in the observed behavioural shift, we conducted a RNA sequencing experiment on mouse vomeronasal organs. Key candidate genes for pheromone-based subspecies recognition, the vomeronasal receptors, are expressed in these organs. Overall patterns of gene expression varied significantly between samples from the two subspecies, with a large number of differentially expressed genes between the two taxa. In contrast, only ~200 genes were found repeatedly differentially expressed between populations within M. m. musculus that did or did not display assortative mate preferences (close to or more distant from the hybrid zone, respectively), with an overrepresentation of genes belonging to vomeronasal receptor family 2. These receptors are known to play a key role in recognition of chemical cues that handle information about genetic identity. Interestingly, four of five of these differentially expressed receptors belong to the same phylogenetic cluster, suggesting specialization of a group of closely related receptors in the recognition of odorant signals that may allow subspecies recognition and assortative mating.
在物种形成过程中，尤其是在生殖隔离相关性状分化的早期阶段，表达差异而非序列差异已被证明具有重要意义。在小家鼠的两个欧洲亚种，即小家鼠指名亚种（Mus musculus musculus）和小家鼠家鼠亚种（Mus musculus domesticus）中，早期研究已证明在靠近其杂交区的种群中存在基于嗅觉的选型交配偏好。有人提出，这种行为是在这两个分类群最近的二次接触（约3000年前）之后，为应对杂交选择而进化出来的。为了测试基因表达变化在观察到的行为转变中所起的作用，我们对小鼠犁鼻器进行了RNA测序实验。基于信息素的亚种识别的关键候选基因，即犁鼻器受体，在这些器官中表达。两个亚种样本之间的基因表达总体模式差异显著，两个分类群之间有大量差异表达基因。相比之下，在小家鼠指名亚种中，表现出或未表现出选型交配偏好的种群（分别靠近或远离杂交区）之间，仅发现约200个基因反复差异表达，其中属于犁鼻器受体家族2的基因占比过高。已知这些受体在识别处理有关遗传身份信息的化学信号中起关键作用。有趣的是，这五个差异表达的受体中有四个属于同一系统发育簇，这表明一组密切相关的受体在识别气味信号方面具有特异性，这可能有助于亚种识别和选型交配。
