Developmental constraints shape the evolution of the nematode mid-developmental transition
Developmental constraints shape the evolution of the nematode mid-developmental transition
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DOI：
10.1038/s41559-017-0113
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发表时间：
2017-05-01
影响因子：
16.8
通讯作者：
Yanai, Itai
中科院分区：
文献类型：
--
作者：
Zalts, Harel;Yanai, Itai
进化理论认为，遗传变异是均匀和渐进的性质，但形态和基因表达的研究表明，不同的生命阶段表现出不同程度的跨物种保护。特别是，在中期胚胎发生的阶段是高度保守的跨物种的相同的门，这表明这个阶段是受发展的限制，无论是通过增加纯化选择或由一个强大的突变偏置。然而，另一种解释认为，同样的“沙漏”变异模式可能是由于在发育的早期和晚期增加了正向选择。为了区分这些情况下，我们研究了线虫线虫的种群中的基因表达变异，使用的实验设计，消除了积极的选择的影响。通过测量20个菌株在整个发育过程中所有基因的基因表达，我们发现，在整个发育过程中，变异是高度不均匀的，在胚胎发育中期有显著的耗竭。特别是，同源结构域转录因子家族，其表达通常与中期胚胎发生一致，在高度限制下进化。我们的数据进一步表明，在形态发生过程中负责胚层整合的基因是最受限制的一类基因。总之，这些结果提供了强有力的证据，发展的制约因素的机制下的沙漏模型的动物进化。了解发育限制的模式和机制提供了一个框架，以了解进化过程如何与胚胎发生相互作用，并导致地球上动物生命的多样性。
Evolutionary theory assumes that genetic variation is uniform and gradual in nature, yet morphological and gene expression studies have revealed that different life-stages exhibit distinct levels of cross-species conservation. In particular, a stage in mid-embryogenesis is highly conserved across species of the same phylum, suggesting that this stage is subject to developmental constraints, either by increased purifying selection or by a strong mutational bias. An alternate explanation, however, holds that the same 'hourglass' pattern of variation may result from increased positive selection at the earlier and later stages of development. To distinguish between these scenarios, we examined gene expression variation in a population of the nematode Caenorhabditis elegans using an experimental design that eliminated the influence of positive selection. By measuring gene expression for all genes throughout development in 20 strains, we found that variations were highly uneven throughout development, with a significant depletion during mid-embryogenesis. In particular, the family of homeodomain transcription factors, whose expression generally coincides with mid-embryogenesis, evolved under high constraint. Our data further show that genes responsible for the integration of germ layers during morphogenesis are the most constrained class of genes. Together, these results provide strong evidence for developmental constraints as the mechanism underlying the hourglass model of animal evolution. Understanding the pattern and mechanism of developmental constraints provides a framework to understand how evolutionary processes have interacted with embryogenesis and led to the diversity of animal life on Earth.