Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
Department of Ecology & Evolution, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
Nat Ecol Evol. 2022 Sep;6(9):1343-1353. doi: 10.1038/s41559-022-01830-y. Epub 2022 Jul 21.
Despite numerous examples of chemoreceptor gene family expansions and contractions, how these relate to modifications in the sensory neuron populations in which they are expressed remains unclear. Drosophila melanogaster's odorant receptor (Or) family is ideal for addressing this question because most Ors are expressed in distinct olfactory sensory neuron (OSN) types. Between-species changes in Or copy number may therefore indicate increases or reductions in the number of OSN populations. Here we investigated the Or67a subfamily, which exhibits copy number variation in D. melanogaster and its closest relatives: D. simulans, D. sechellia and D. mauritiana. These species' common ancestor had three Or67a paralogues that had already diverged adaptively. Following speciation, two Or67a paralogues were lost independently in D. melanogaster and D. sechellia, with ongoing positive selection shaping the intact genes. Unexpectedly, the functionally diverged Or67a paralogues in D. simulans are co-expressed in a single neuron population, which projects to a glomerulus homologous to that innervated by Or67a neurons in D. melanogaster. Thus, while sensory pathway neuroanatomy is conserved, independent selection on co-expressed receptors has contributed to species-specific peripheral coding. This work reveals a type of adaptive change largely overlooked for olfactory evolution, raising the possibility that similar processes influence other cases of insect Or co-expression.
尽管有许多化学感受器基因家族扩增和收缩的例子，但它们与表达它们的感觉神经元群体的变化有何关系尚不清楚。黑腹果蝇的气味受体（Or）家族是解决这个问题的理想选择，因为大多数 Ors 都表达在不同的嗅觉感觉神经元（OSN）类型中。因此，物种间 Or 拷贝数的变化可能表明 OSN 群体数量的增加或减少。在这里，我们研究了 Or67a 亚家族，它在黑腹果蝇及其最亲近的亲属：D. simulans、D. sechellia 和 D. mauritiana 中表现出拷贝数的变化。这些物种的共同祖先有三个已经适应地分化的 Or67a 旁系同源物。在物种形成之后，两个 Or67a 旁系同源物在黑腹果蝇和 D. sechellia 中独立丢失，而完整的基因则受到持续的正选择的影响。出乎意料的是，D. simulans 中功能分化的 Or67a 旁系同源物在单个神经元群体中共表达，该神经元投射到与黑腹果蝇 Or67a 神经元支配的肾小球同源的位置。因此，尽管感觉通路神经解剖学是保守的，但共表达受体的独立选择导致了种间特有的外围编码。这项工作揭示了一种在嗅觉进化中很大程度上被忽视的适应性变化，这增加了类似的过程可能影响其他昆虫 Or 共表达的可能性。
