How was the notochord born?
How was the notochord born?
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DOI：
10.1111/j.1525-142x.2011.00522.x
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发表时间：
2012-01-01
影响因子：
2.9
通讯作者：
Takahashi, Hiroki
中科院分区：
文献类型：
--
作者：
Satoh, Nori;Tagawa, Kuni;Takahashi, Hiroki
五亿五千多万年前，脊索动物与非脊索动物的后口动物有着共同的祖先，它们进化出了一种新的幼虫--蝌蚪幼虫。“脊索是幼虫尾巴的支撑器官，也是脊索动物最突出的特征;事实上，脊索动物门就是以这个器官命名的。本文就脊索动物进化过程中脊索形成的分子机制进行综述，重点介绍T-box基因家族成员Brachyury。将单细胞领鞭藻的解码基因组与海绵和刺胞动物的基因组进行比较，表明T-box基因家族出现在多细胞动物进化的同时。原肠胚形成是一种形态发生运动，对于形成两层或三层胚层的胚胎至关重要。Brachyury在胚孔（bp）区域瞬时表达，在那里它赋予细胞进行内陷的能力。这一过程涉及到所有后生动物原肠的形成。这是Brachyury的“主要”功能。在脊索动物的进化过程中，Brachyury在bp的背中线区域获得了额外的表达结构域。在这个新的表达域中，Brachyury发挥了它的“次要”功能，招募另一组靶基因形成背轴器官脊索。Wnt/β-连环蛋白、BMP/Nodal和FGF信号通路参与Brachyury的转录激活。我们讨论的背腹（D-V）反转理论和aboral-dorsalization假说的背景下，Brachyury的次级功能的分子机制。虽然这篇综述的范围需要一定程度的过度简化的Brachyury功能，这是有益的，以促进脊索的形成，在后生动物进化史上的一个中心进化发育生物学问题的研究，指出首先由亚历山大Kowalevsky。
More than 550 million years ago, chordates originated from a common ancestor shared with nonchordate deuterostomes by developing a novel type of larva, the "tadpole larva." The notochord is the supporting organ of the larval tail and the most prominent feature of chordates; indeed, phylum Chordata is named after this organ. In this review, we discuss the molecular mechanisms involved in the formation of the notochord over the course of chordate evolution with a special emphasis on a member of T-box gene family, Brachyury. Comparison of the decoded genome of a unicellular choanoflagellate with the genomes of sponge and cnidarians suggests that T-box gene family arose at the time of the evolution of multicellular animals. Gastrulation is a morphogenetic movement that is essential for the formation of two-or three-germ-layered embryos. Brachyury is transiently expressed in the blastopore (bp) region, where it confers on cells the ability to undergo invagination. This process is in-volved in the formation of the archenteron in all metazoans. This is a "primary" function of Brachyury. During the evolution of chordates, Brachyury gained an additional expression domain at the dorsal midline region of the bp. In this new expression domain, Brachyury served its "secondary" function, recruiting another set of target genes to form a dorsal axial organ, notochord. The Wnt/beta-catenin, BMP/Nodal, and FGF-signaling pathways are involved in the transcriptional activation of Brachyury. We discuss the molecular mechanisms of Brachyury secondary function in the context of the dorsalventral (D-V) inversion theory and the aboral-dorsalization hypothesis. Although the scope of this review requires some degree of oversimplification of Brachyury function, it is beneficial to facilitate studies on the notochord formation, a central evolutionary developmental biology problem in the history of metazoan evolution, pointed out first by Alexander Kowalevsky.