Kuriyama Sei, Lupo Giuseppe, Ohta Kunimasa, Ohnuma Shin-Ichi, Harris William A, Tanaka Hideaki
Division of Developmental Neurobiology, Graduate School of Medical Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
Development. 2006 Jan;133(1):75-88. doi: 10.1242/dev.02178. Epub 2005 Nov 30.
In Xenopus, ectodermal patterning depends on a mediolateral gradient of BMP signaling, higher in the epidermis and lower in the neuroectoderm. Neural crest cells are specified at the border between the neural plate and the epidermis, at intermediate levels of BMP signaling. We recently described a novel secreted protein, Tsukushi (TSK), which works as a BMP antagonist during chick gastrulation. Here, we report on the Xenopus TSK gene (X-TSK), and show that it is involved in neural crest specification. X-TSK expression accumulates after gastrulation at the anterior-lateral edges of the neural plate, including the presumptive neural crest region. In gain-of-function experiments, X-TSK can strongly enhance neural crest specification by the dorsolateral mesoderm or X-Wnt8 in ectodermal explants, while the electroporation of X-TSK mRNA in the lateral ectoderm of embryos after gastrulation can induce the expression of neural crest markers in vivo. By contrast, depletion of X-TSK in explants or embryos impairs neural crest specification. Similarly to its chick homolog, X-TSK works as a BMP antagonist by direct binding to BMP4. However, X-TSK can also indirectly regulate BMP4 mRNA expression at the neural plate border via modulation of the Delta-Notch signaling pathway. We show that X-TSK directly binds to the extracellular region of X-delta-1, and modulates Delta-dependent Notch activity. We propose that X-TSK plays a key role in neural crest formation by directly regulating BMP and Delta activities at the boundary between the neural and the non-neural ectoderm.
在非洲爪蟾中，外胚层模式形成依赖于骨形态发生蛋白（BMP）信号的中外侧梯度，在表皮中较高，而在神经外胚层中较低。神经嵴细胞在神经板和表皮之间的边界处，即BMP信号的中间水平被特化。我们最近描述了一种新的分泌蛋白，肌腱蛋白（TSK），它在鸡原肠胚形成过程中作为BMP拮抗剂发挥作用。在此，我们报道非洲爪蟾TSK基因（X-TSK），并表明它参与神经嵴的特化。X-TSK的表达在原肠胚形成后在神经板的前外侧边缘积累，包括假定的神经嵴区域。在功能获得实验中，X-TSK可以强烈增强外胚层外植体中背外侧中胚层或X-Wnt8诱导的神经嵴特化，而在原肠胚形成后对胚胎外侧外胚层进行X-TSK mRNA电穿孔可在体内诱导神经嵴标志物的表达。相比之下，在外植体或胚胎中耗尽X-TSK会损害神经嵴的特化。与其鸡同源物类似，X-TSK通过直接结合BMP4作为BMP拮抗剂发挥作用。然而，X-TSK还可以通过调节Delta-Notch信号通路间接调节神经板边界处的BMP4 mRNA表达。我们表明X-TSK直接结合X-delta-1的细胞外区域，并调节Delta依赖的Notch活性。我们提出，X-TSK通过直接调节神经和非神经外胚层边界处的BMP和Delta活性，在神经嵴形成中起关键作用。
