In search of the vertebrate phylotypic stage: A molecular examination of the developmental hourglass model and von Baer's third law
In search of the vertebrate phylotypic stage: A molecular examination of the developmental hourglass model and von Baer's third law
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DOI：
10.1002/jez.b.21033
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发表时间：
2005-03-15
影响因子：
2.2
通讯作者：
Graur, D
中科院分区：
文献类型：
--
作者：
Hazkani-Covo, E;Wool, D;Graur, D
1828年，卡尔·冯·贝尔提出了一套关于胚胎发育的四条进化“定律”。根据冯·贝尔第三定律，不同物种的年轻胚胎相对未分化，彼此相似，但随着发育的进行，该物种的不同特征开始出现，不同物种的胚胎逐渐分化。丹尼斯·杜布勒和鲁道夫·拉夫在20世纪90年代独立提出了这一定律的扩展，称为“沙漏模型”。根据沙漏模型，个体发育的特点是不同的分类群在起点上彼此明显不同，然后是分类间变异性降低的阶段(系统学阶段)，并以分类群之间类似von-Baer的逐渐分化结束。将沙漏模型“翻译”成分子术语可能会表明，沙漏锥形部分所描述的阶段中表达的同源基因应该比在系统发育阶段之前或之后的扩张部分中表达的同源基因更相似。我们使用了在26个胚胎阶段表达的1585个小鼠基因和它们的人类同源基因来验证这一假设。通过计算小鼠和人类相应的同源蛋白之间的配对距离，估计了不同胚胎阶段的进化差异。使用了两个独立的数据集。一个数据集包含仅在单个发育阶段表达的基因；第二个数据集由不同发育阶段表达的基因组成。在第二个数据集中，根据基因表达的最早阶段对基因进行了分类。我们对两个数据集进行了二次多项式的拟合。这两个多项式如沙漏模型所预期的那样显示了极小值。分子结果表明，尽管力度很小，但确实存在一个系统学阶段(或时期)。它的时间位置，有时在第一体节阶段和后神经孔的形成之间，与形态上定义的系统型阶段大致一致。沙漏模型后期部分，即冯·贝尔第三定律的分子证据比早期部分更强。(C)2005年Wiley-Liss，Inc.
In 1828, Karl von Baer proposed a set of four evolutionary "laws" pertaining to embryological development. According to von Baer's third law, young embryos from different species are relatively undifferentiated and resemble one another but as development proceeds, distinguishing features of the species begin to appear and embryos of different species progressively diverge from one another. An expansion of this law, called "the hourglass model," has been proposed independently by Denis Duboule and Rudolf Raff in the 1990s. According to the hourglass model, ontogeny is characterized by a starting point at which different taxa differ markedly from one another, followed by a stage of reduced intertaxonomic variability (the phylotypic stage), and ending in a von-Baer-like progressive divergence among the taxa. A possible "translation" of the hourglass model into molecular terminology would suggest that orthologs expressed in stages described by the tapered part of the hourglass should resemble one another more than orthologs expressed in the expansive parts that precede or succeed the phylotypic stage. We tested this hypothesis using 1,585 mouse genes expressed during 26 embryonic stages, and their human orthologs. Evolutionary divergence was estimated at different embryonic stages by calculating pairwise distances between corresponding orthologous proteins from mouse and human. Two independent datasets were used. One dataset contained genes that are expressed solely in a single developmental stage; the second was made of genes expressed at different developmental stages. In the second dataset the genes were classified according to their earliest stage of expression. We fitted second order polynomials to the two datasets. The two polynomials displayed minima as expected from the hourglass model. The molecular results suggest, albeit weakly, that a phylotypic stage (or period) indeed exists. Its temporal location, sometimes between the first-somites stage and the formation of the posterior neuropore, was in approximate agreement with the morphologically defined phylotypic stage. The molecular evidence for the later parts of the hourglass model, i.e., for von Baer's third law, was stronger than that for the earlier parts. (c) 2005 Wiley-Liss, Inc.