Barsi Julius C, Li Enhu, Davidson Eric H
Division of Biology and Biological Engineering, Caltech, Pasadena, CA 91125, USA.
Division of Biology and Biological Engineering, Caltech, Pasadena, CA 91125, USA Warp Drive Bio, LLC, 400 Technology Square, Cambridge, MA 02139, USA.
Development. 2015 Mar 1;142(5):953-61. doi: 10.1242/dev.117986. Epub 2015 Feb 5.
The trapezoidal ciliated band (CB) of the postgastrular sea urchin embryo surrounds the oral ectoderm, separating it from adjacent embryonic territories. Once differentiated, the CB is composed of densely arranged cells bearing long cilia that endow the larva with locomotion and feeding capability. The spatial pattern from which the CB will arise is first evidenced during pregastrular stages by expression of the pioneer gene onecut. Immediately after gastrulation, the CB consists of four separate regulatory state domains, each of which expresses a unique set of transcription factors: (1) the oral apical CB, located within the apical neurogenic field; (2) the animal lateral CB, which bilaterally separates the oral from aboral ectoderm; (3) the vegetal lateral CB, which bilaterally serves as signaling centers; and (4) the vegetal oral CB, which delineates the boundary with the underlying endoderm. Remarkably, almost all of the regulatory genes specifically expressed within these domains are downregulated by interference with SoxB1 expression, implying their common activation by this factor. Here, we show how the boundaries of the CB subdomains are established, and thus ascertain the design principle by which the geometry of this unique and complex regulatory state pattern is genomically controlled. Each of these boundaries, on either side of the CB, is defined by spatially confined transcriptional repressors, the products of regulatory genes operating across the border of each subdomain. In total this requires deployment of about ten different repressors, which we identify in this work, thus exemplifying the complexity of information required for spatial regulatory organization during embryogenesis.
原肠胚后期海胆胚胎的梯形纤毛带（CB）围绕口外胚层，将其与相邻的胚胎区域分隔开来。一旦分化，CB由紧密排列的细胞组成，这些细胞带有长纤毛，赋予幼虫运动和摄食能力。CB出现的空间模式在原肠胚前期阶段首先通过先驱基因onecut的表达得以证明。原肠胚形成后立即，CB由四个独立的调控状态域组成，每个域表达一组独特的转录因子：（1）口顶端CB，位于顶端神经发生区域内；（2）动物侧CB，双侧将口外胚层与反口外胚层分开；（3）植物侧CB，双侧作为信号中心；（4）植物口CB，划定与下方内胚层的边界。值得注意的是，几乎所有在这些域中特异性表达的调控基因都因干扰SoxB1表达而下调，这意味着它们由该因子共同激活。在这里，我们展示了CB亚域边界是如何建立的，从而确定了这种独特而复杂的调控状态模式的几何形状在基因组上受到控制的设计原则。CB两侧的每个边界都由空间受限的转录抑制因子定义，这些抑制因子是在每个亚域边界起作用的调控基因的产物。总共需要部署大约十种不同的抑制因子，我们在这项工作中识别出了它们，从而例证了胚胎发生过程中空间调控组织所需信息的复杂性。
