Dynamic regulatory mechanisms of robust pattern formation in the neural tube

摘要 我们研究的长期目标是理解允许发育系统 健壮地构建出具有正确图案、形状和大小的胚胎。发展系统面临着一系列 来自不同来源的变异，包括环境、遗传和随机变异，表现为多个 从分子到细胞再到器官的水平。面对这些挑战，生物体被设计成 通过进化来缓冲这些变异的表型，以便顽强地实现发育 沃丁顿将这一过程称为运河化。因为我们对分子和细胞细节的了解 图案化系统已经扩展，现在有机会了解系统级的机制 这导致了健壮的图案形成。在这里，我们将重点关注模式的健壮性，通过缩放和 大小控制。缩放是一个非凡的过程，在这个过程中，图案的大小可以调整到可用的 组织的大小。自从汉斯·德里施在人类历史上发现了 1885年发现，当一个两细胞阶段的海胆胚胎的卵裂球被分离时，结果并不是 两个部分胚胎，而是两个完整的胚胎，在这些胚胎中，它们的所有模式都被缩小了一半。相似的结果 后来在各种生物体中都发现了，但产生大小所需的外科操作- 减少的动物通常是困难的，并导致很大的变异性，从而限制了定量研究。 最近，我们开发了一种新的方法来产生不同大小的斑马鱼卵，这种方法不仅健壮，而且 可重现的。这样的胚胎有质量上正常但有比例的图案，并能产生可存活的成体。 在分子水平上，我们发现大多数基因表达模式(例如，形态原及其靶点)与 它们形成的组织；然而，一小部分基因，那些感知组织大小来调节比例的基因 (例如，通过与形态生物质相互作用)，不要。因此，这些大小改变的胚胎代表了一种强大的 识别和确定图案缩放机制的唯一方法。最终，组织的大小是 通过平衡发育过程中的增殖和分化速度来确定。我们有 发现神经管中增殖和分化的平衡处于负反馈控制下 通过机械加压/纸巾包装。在这里，我们将使用定量成像、分子和 机械扰动和计算机建模，以确定系统级机制，从而允许：1) 形态图案化以适应可用空间，以及2)增殖和分化率 平衡以使组织生长以适合可用空间。这些问题将在 斑马鱼神经管，但我们预计由此产生的机制将得到广泛应用。这样一个完整的 了解这一点对于诊断和治疗神经管缺陷等出生缺陷以及 工程组织的合理设计。

Abstract The long-term goal of our research is to understand the principles that permit developmental systems to robustly construct embryos of the correct pattern, shape, and size. Developmental systems face a gamut of variations from different sources including environmental, genetic, and stochastic, which manifest at multiple levels from molecules to cells to organs. In the face of these challenges, organisms have been designed through evolution to buffer the phenotype against these variations in order to robustly achieve a developmental norm, a process Waddington termed canalization. As our knowledge of the molecular and cellular details of patterning systems has expanded, there is now the opportunity to understand the systems level mechanisms that give rise to robust pattern formation. Here we focus on pattern robustness through the lens of scaling and size control. Scaling is a remarkable process in which the size of a pattern can be adjusted to the available size of the tissue. Scaling has fascinated and baffled embryologists since the time of Hans Driesch who in 1885 found that when the blastomeres of a two-cell stage sea urchin embryo are separated, the result is not two partial embryos but rather two complete embryos in which all their pattern is scaled by half. Similar results have since been found in a variety of organisms, but the surgical manipulations required to generate size- reduced animals are generally difficult and result in a lot of variability, thus limiting quantitative investigation. Recently, we have developed a new method for generating zebrafish eggs of different size that is robust and reproducible. Such embryos have qualitatively normal but scaled patterning and can give rise to viable adults. At a molecular level we find that most gene expression patterns (e.g. morphogens and their targets) scale with the tissues they pattern; however, a small subset of genes, the ones that sense tissue size to regulate scaling (e.g. by interacting with morphogens), do not. Thus, these size altered embryos represent a powerful and unique method to identify and determine the mechanisms of pattern scaling. Ultimately, tissue size is determined by balancing the rates of proliferation and differentiation over the course of development. We have found that the balance of proliferation and differentiation in the neural tube is under negative feedback control by mechanical pressure/tissue packing. Here we will use a combination of quantitative imaging, molecular and mechanical perturbations, and computer modeling to determine the systems-level mechanisms that allow: 1) morphogen patterning to scale to fit the available space, and 2) proliferation and differentiation rates to be balanced to cause a tissue to grow to fit the available space. These questions will be addressed in the zebrafish neural tube, but we expect the resulting mechanisms to be widely applicable. Such an integrated understanding is important for diagnosing and treating birth defects such as neural tube defects and in the rational design of engineered tissues.