Dorsoventral patterning in hemichordates: insights into early chordate evolution.
Dorsoventral patterning in hemichordates: insights into early chordate evolution.
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DOI：
10.1371/journal.pbio.0040291
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发表时间：
2006-09
期刊：
影响因子：
9.8
通讯作者：
Gerhart J
中科院分区：
文献类型：
--
作者：
Lowe CJ;Terasaki M;Wu M;Freeman RM Jr;Runft L;Kwan K;Haigo S;Aronowicz J;Lander E;Gruber C;Smith M;Kirschner M;Gerhart J
我们比较了半足动物和脊索动物的背腹发育，以推断它们共同祖先的组织结构，从而确定在谱系分裂后脊索动物体轴的进化变化。在半足胚中，编码骨形态发生蛋白（Bmp） 2/4和5/8的基因，以及Bmp活性调节因子的几个基因，在外胚层中线的一条细条纹中表达，历史上称为“背”。在相反的中线，编码Chordin和抗背化形态发生蛋白（anti dorsalizing morphogenetic protein, Admp）的基因表达。因此，我们发现了一条bp - chordin发育轴在半足动物解剖背腹轴的前面和下面，增加了来自果蝇和脊索动物的证据，表明这条轴可能至少与最早的双侧动物一样古老。许多编码转录因子和信号配体的基因在半硬核胚胎的三个胚层中分别在不同的背腹区表达，如Bmp侧的pox neuro、pituitary homeobox、distalless和tbx2/3，以及choro - admp侧的netrin、mnx、mox和single-minded。当我们将胚胎暴露在过量的Bmp蛋白中，或者当我们通过小干扰RNA注射耗尽内源性Bmp时，这些表达域会扩张或收缩，反映它们被Bmp激活或抑制，胚胎发育为背化或腹化极限形式。背腹侧模式独立于前/后模式，如果蝇，而不是脊索动物。与脊索动物和果蝇不同，半足虫的神经基因表达不受Bmp高水平的抑制，这与它们发育为弥漫性而非集中式神经系统一致。我们认为，半足虫和脊索动物的共同祖先并没有使用其Bmp-Chordin轴来分离表皮和神经外胚层，而是在胚层的许多其他背腹侧方面形成模式，包括弥漫性神经系统中的神经细胞命运。因此，脊索动物系通过神经-表皮分离，由先前存在的Bmp-Chordin轴介导，增加了中心化。最后，由于半足动物的嘴在非bmp的一侧发育，就像节肢动物一样，但与脊索动物相反，嘴和Bmp-Chordin轴可能在脊索动物线上重新排列，一个相对于另一个。Bmp和脊索蛋白在半脊索动物背腹轴发育中的作用的实验和解剖学证据为脊索动物谱系的进化提供了见解。
We have compared the dorsoventral development of hemichordates and chordates to deduce the organization of their common ancestor, and hence to identify the evolutionary modifications of the chordate body axis after the lineages split. In the hemichordate embryo, genes encoding bone morphogenetic proteins (Bmp) 2/4 and 5/8, as well as several genes for modulators of Bmp activity, are expressed in a thin stripe of ectoderm on one midline, historically called “dorsal.” On the opposite midline, the genes encoding Chordin and Anti-dorsalizing morphogenetic protein (Admp) are expressed. Thus, we find a Bmp-Chordin developmental axis preceding and underlying the anatomical dorsoventral axis of hemichordates, adding to the evidence from Drosophila and chordates that this axis may be at least as ancient as the first bilateral animals. Numerous genes encoding transcription factors and signaling ligands are expressed in the three germ layers of hemichordate embryos in distinct dorsoventral domains, such as pox neuro, pituitary homeobox, distalless, and tbx2/3 on the Bmp side and netrin, mnx, mox, and single-minded on the Chordin-Admp side. When we expose the embryo to excess Bmp protein, or when we deplete endogenous Bmp by small interfering RNA injections, these expression domains expand or contract, reflecting their activation or repression by Bmp, and the embryos develop as dorsalized or ventralized limit forms. Dorsoventral patterning is independent of anterior/posterior patterning, as in Drosophila but not chordates. Unlike both chordates and Drosophila, neural gene expression in hemichordates is not repressed by high Bmp levels, consistent with their development of a diffuse rather than centralized nervous system. We suggest that the common ancestor of hemichordates and chordates did not use its Bmp-Chordin axis to segregate epidermal and neural ectoderm but to pattern many other dorsoventral aspects of the germ layers, including neural cell fates within a diffuse nervous system. Accordingly, centralization was added in the chordate line by neural-epidermal segregation, mediated by the pre-existing Bmp-Chordin axis. Finally, since hemichordates develop the mouth on the non-Bmp side, like arthropods but opposite to chordates, the mouth and Bmp-Chordin axis may have rearranged in the chordate line, one relative to the other. Experimental and anatomical evidence for the role of Bmp and Chordin in the development of the dorsal-ventral axis of hemichordates provides insights into the evolution of the chordate lineage.
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