Expression of somite segmentation genes in amphioxus: a clock without a wavefront?
Expression of somite segmentation genes in amphioxus: a clock without a wavefront?
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DOI：
10.1007/s00427-008-0257-5
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发表时间：
2008-12-01
影响因子：
2.4
通讯作者：
Holland, Linda Z.
中科院分区：
文献类型：
--
作者：
Beaster-Jones, Laura;Kaltenbach, Stacy L.;Holland, Linda Z.
文昌鱼的体节延伸至身体的全长。最前面的体节在原肠胚和神经胚阶段从原肠的背外侧沟开始。剩下的从尾芽上一次一个地掐掉。这些后体节似乎是同源的脊椎动物，即使后者夹断带的前端preomitic中胚层，而不是直接从尾芽。为了深入了解脊索动物中胚层分节的进化，我们确定了10个基因在文昌鱼初生体节中的表达。5个（Uncx4.1、NeuroD/atonal相关、IrxA、Pcdh delta 2-17/18和Hey 1）在原肠胚阶段的背外侧中胚层和尾芽中以条纹形式表达，而3个（Paraxis、Lcx和Axin）在原肠胚和神经胚阶段的后中内胚层和后期的尾芽中表达。两个基因（Pbx和OligA）的表达表明在前体节的作用，可能是无关的初始分割。与以前的数据一起，我们的研究结果表明，除了Engrailed只在前体节中分段表达外，控制前体节和后体节形成的遗传机制可能基本相同。因此，涉及Notch-Delta、Wnt/β-连环蛋白和Fgf信号传导的中胚层分割的基本途径已经在文昌鱼和脊椎动物的共同祖先中就位，尽管从表现出Notch、Wnt和Fgf靶基因表达波的前体中胚层条带中出芽的体节可能是脊椎动物的新奇。鉴于文昌鱼和脊椎动物体节之间的分段基因表达的保守性，我们提出，时钟机制可能已经建立在基底脊索动物，而波前进化后期的脊椎动物谱系。
In the basal chordate amphioxus (Branchiostoma), somites extend the full length of the body. The anteriormost somites segment during the gastrula and neurula stages from dorsolateral grooves of the archenteron. The remaining ones pinch off, one at a time, from the tail bud. These posterior somites appear to be homologous to those of vertebrates, even though the latter pinch off from the anterior end of bands of presomitic mesoderm rather than directly from the tail bud. To gain insights into the evolution of mesodermal segmentation in chordates, we determined the expression of ten genes in nascent amphioxus somites. Five (Uncx4.1, NeuroD/atonal-related, IrxA, Pcdh delta 2-17/18, and Hey1) are expressed in stripes in the dorsolateral mesoderm at the gastrula stage and in the tail bud while three (Paraxis, Lcx, and Axin) are expressed in the posterior mesendoderm at the gastrula and neurula stages and in the tail bud at later stages. Expression of two genes (Pbx and OligA) suggests roles in the anterior somites that may be unrelated to initial segmentation. Together with previous data, our results indicate that, with the exception that Engrailed is only segmentally expressed in the anterior somites, the genetic mechanisms controlling formation of both the anterior and posterior somites are probably largely identical. Thus, the fundamental pathways for mesodermal segmentation involving Notch-Delta, Wnt/beta-catenin, and Fgf signaling were already in place in the common ancestor of amphioxus and vertebrates although budding of somites from bands of presomitic mesoderm exhibiting waves of expression of Notch, Wnt, and Fgf target genes was likely a vertebrate novelty. Given the conservation of segmentation gene expression between amphioxus and vertebrate somites, we propose that the clock mechanism may have been established in the basal chordate, while the wavefront evolved later in the vertebrate lineage.