Tsukushi cooperates with VG1 to induce primitive streak and Hensen's node formation in the chick embryo
Tsukushi cooperates with VG1 to induce primitive streak and Hensen's node formation in the chick embryo
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DOI：
10.1242/dev.02579
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发表时间：
2006-10
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影响因子：
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通讯作者：
K. Ohta;S. Kuriyama;T. Okafuji;R. Gejima;S. Ohnuma;Hideaki Tanaka
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文献类型：
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作者：
K. Ohta;S. Kuriyama;T. Okafuji;R. Gejima;S. Ohnuma;Hideaki Tanaka
在鸡胚中轴的形成过程中，VG1、WNT和BMP这三类信号分子起着重要的作用。虽然VG1和WNT信号在诱导胚胎中线的原条和Hensen结中具有关键功能，但它们的作用由BMP拮抗剂补充，所述BMP拮抗剂保护预期的轴向组织免受从外周分泌的BMP的抑制性影响。我们以前曾报道，一个分泌因子，鸡Tsukushi（TSK），表达在原条和亨森氏结，在那里它作为BMP拮抗剂。在这里，我们描述了一个新的关键功能，TSK在促进形成的原条和亨森结的积极调节VG1活性。我们提供的证据表明，TSK直接结合VG1在体外，TSK和VG1功能相互作用的轴的形成，如所示的生物测定在鸡和非洲爪蟾胚胎。此外，我们表明，TSK RNA的选择性剪接导致两种异构体（TSKA，最初指定为TSK，和TSKB）的形成，其C-末端区域不同。生物化学和生物学测定表明，TSKB是一种比TSKA弱得多的BMP拮抗剂，尽管这两种亚型都能有效地与VG1相互作用。值得注意的是，虽然TSKA和TSKB都在整个早期延伸的原条中表达，但它们的表达模式在原肠胚形成期间有所不同。TSKA表达集中在亨森氏结，一个众所周知的抗BMP信号的来源，而TSKB积累在中间原条（MPS），一个已知的区域作为一个节点诱导中心，其中VG1表达也具体定位。功能丧失实验表明，TSKB，而不是TSKA，功能需要在MPS诱导亨森结。两者合计，这些结果表明，TSK异构体发挥了至关重要的作用，在鸡轴的形成，通过局部调节原肠形成过程中的VG1和BMP的活动。
Three classes of signaling molecule, VG1, WNT and BMP, play crucial roles in axis formation in the chick embryo. Although VG1 and WNT signals have a pivotal function in inducing the primitive streak and Hensen's node in the embryo midline, their action is complemented by that of BMP antagonists that protect the prospective axial tissue from the inhibitory influence of BMPs secreted from the periphery. We have previously reported that a secreted factor, chick Tsukushi (TSK), is expressed in the primitive streak and Hensen's node, where it works as a BMP antagonist. Here, we describe a new crucial function for TSK in promoting formation of the primitive streak and Hensen's node by positively regulating VG1 activity. We provide evidence that TSK directly binds VG1 in vitro, and that TSK and VG1 functionally interact in axis formation, as shown by biological assays performed in chick and Xenopus embryos. Furthermore, we show that alternative splicing of TSK RNA leads to the formation of two isoforms (TSKA, originally designated as TSK, and TSKB) that differ in their C-terminal region. Biochemical and biological assays indicate that TSKB is a much weaker BMP antagonist than TSKA, although both isoforms efficiently interact with VG1. Remarkably, although both TSKA and TSKB are expressed throughout the early extending primitive streak, their expression patterns diverge during gastrulation. TSKA expression concentrates in Hensen's node, a well-known source of anti-BMP signals, whereas TSKB accumulates in the middle primitive streak (MPS), a region known to work as a node-inducing center where VG1 expression is also specifically localized. Loss-of-function experiments demonstrate that TSKB, but not TSKA, function is required in the MPS for induction of Hensen's node. Taken together, these results indicate that TSK isoforms play a crucial role in chick axis formation by locally modulating VG1 and BMP activities during gastrulation.