Dynamic regulatory mechanisms of robust pattern formation in the neural tube

 描述(由申请人提供)：我们研究的长期目标是了解允许发育系统强有力地构建正确模式、形状和大小的胚胎的原理。发育系统面临着来自不同来源的一系列变化，包括环境、遗传和随机，这些变化表现在从分子到细胞再到器官的多个水平上。面对这些挑战，生物体被设计通过进化来缓冲这些变异的表型，以便有力地实现发育规范，这一过程被沃丁顿称为管道化。随着我们对图案化系统的分子和细胞细节的了解不断扩大，现在有机会了解导致强健图案形成的系统级机制。在这里，我们关注神经管的背腹模式，其中被认为是信号分子Sonic Hedgehog的平滑和稳定的梯度作为形态原，作为浓度的函数精确地指定神经前体细胞在指定位置的不同结构域。使用我的实验室开发的一种名为在斑马鱼身上进行Toto成像的新方法，我们发现实际上，随着细胞做出命运决定，形态来源和反应都是嘈杂的和动态变化的。我们发现，这种嘈杂和动态的形态生成物导致了命运限制的祖细胞以混合和重叠的模式指定。然后，指定单元格的定向排序会纠正这些位置错误，从而产生明确定义的域。值得注意的是，强制指定异位位置的运动神经元前体细胞会导致这些细胞移动到运动神经元前体细胞(PMN)区域，并取代原本的PMN细胞，从而产生一个正常模式的、可存活的胚胎，形成一个非常不同的发育轨迹。在这里，我们试图阐明这种健壮性背后的机制。利用定量时移成像、精确的遗传扰动、生物物理测量和建模相结合的方法，我们将：1)破译大量随时间增加的Shh信号是如何被处理的，从而产生一小组离散的细胞命运；2)确定斑马鱼神经管模式中细胞分选的机制。我们的工作应该有助于解释分子和细胞机制如何在多个步骤相互作用，以确保精确的图案形成。这种完整的理解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非常重要。

 DESCRIPTION (provided by applicant): 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 dorsal-ventral patterning of the neural tube where it is thought that a smooth and steady gradient of the signaling molecule Sonic Hedgehog acts as a morphogen to precisely specify different domains of neural progenitors at defined positions as a function of concentration. Using a novel approach developed in my lab called in Toto imaging in zebrafish, we have discovered that in reality both the morphogen source and response are noisy and dynamically changing as cells make fate decisions. We have found that this noisy and dynamic morphogen results in specification of fate-restricted progenitors in a mixed and overlapping pattern. Directional sorting of specified cells then corrects these positional errors resulting in sharply defined domains. Remarkably, forced specification of motor neuron progenitors at ectopic locations causes these cells to move to the motor neuron progenitor (pMN) domain and replace the would be pMN cells resulting in a normally patterned and viable embryo formed from a very different developmental trajectory. Here we seek to elucidate the mechanisms underlying this robustness. Using a combination of quantitative time-lapse imaging, precise genetic perturbations, biophysical measurements, and modeling, we will: 1) Decode how a large diversity of temporally increasing Shh signals are processed to give rise to a small set of discrete cell fates; 2) Determine the mechanism of cell sorting in zebrafish neural tube patterning. Together our work should help explain how molecular and cellular mechanisms interact at multiple steps to ensure precise pattern formation. 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.