The emergence of complex structural organisation in skeletal muscle

在发育过程中，一个生物体从一个受精细胞到一个有多个器官的成年人。这些器官的形状精确，内部细胞结构紧密，以确保有效的功能。例如，肺产生大规模的分支网络，使氧气能够快速输送到血液中。在骨骼肌中，肌细胞形成细长的且通常为多核的纤维，其能够产生显著的力。在发育过程中如何形成复杂的器官形状一直是生物学中一个长期存在的问题，甚至可以追溯到达西·汤普森之前。然而，理解潜在的过程长期以来一直被证明是具有挑战性的，部分原因是难以以适当的空间和时间分辨率对细胞过程进行成像。近年来，我们取得了三项重大进展，有助于我们应对这一挑战。首先，生物物理模型已被证明是非常强大的描述生物材料的材料特性的结构变化。发育中的组织可以经历转变，例如在流体样（即快速细胞重排）和固体样（即刚性内部结构）之间。其次，成像技术的进步意味着我们可以以亚细胞分辨率记录活胚胎中细胞形态发生的动态。第三，我们在使用机器学习和更传统的方法分割和量化复杂生物成像数据的能力方面取得了重大进展。由于细胞结构变化的速度，包括细胞融合，肌纤维形成的分析尤其具有挑战性。通过将这些进展与斑马鱼胚胎强大的遗传学和光学可及性相结合，我们的目标是剖析骨骼肌的内部结构组织是如何出现的。通过以下目的，我们探索发育中的骨骼肌是否经历了其性质的材料变化以及细胞过程如何驱动细胞和组织成形：1）首次解剖脊椎动物内部器官中每个细胞到达其最终位置和形态时的动力学。2)3）使用合适的突变体来扰乱细胞环境，以测试我们的细胞和组织成形模型。在目标1中，我们将开发成像和图像分析技术，使我们能够访问整个初始骨骼肌发育过程中的细胞行为。我们将跟踪每个选定的未来肌肉节段中每个细胞的位置和形态，因为它们从圆形细胞到高度细长和结构紧密的肌肉。定量数据是我们分析组织结构顺序的关键输入，以测试材料性质是否存在转变的标志。在目标2中，我们剖析了驱动细胞和组织形状变化的一些亚细胞机制。我们专注于微管，因为它们在与肌肉形成相关的一系列细胞过程中的重要性。我们将利用晶格光片显微镜-它可以在高空间分辨率下非常快速地成像-来记录骨骼肌形成过程中微管及其相关运动蛋白的动态。我们将结合联合收割机这与合适的药物和光可调扰动解剖微管在指导肌肉morphogenesis.In目的3的作用，我们利用一系列的突变体，以进一步探索驱动组织组织的机制。我们专注于扰乱肌肉细胞的命运规范和抑制肌肉融合。这些扰动使我们能够了解生化和生物力学输入在驱动骨骼肌形成中的作用。人体质量的40%左右是骨骼肌。利用斑马鱼的发展。我们将解剖基本的机制，确保这个组织是精确的结构。

During development, an organism goes from a single fertilised cell through to an adult with multiple organs. These organs are precisely shaped and the internal cellular structure tightly defined to ensure efficient function. For example, the lungs generate a large-scale branching network to enable rapid oxygen transport into the bloodstream. In the skeletal muscle, muscle cells form elongated, and typically multinucleated, fibres that enable the generation of significant force. How complex organ shape emerges during development has been a long standing question in biology, going back to before even D'Arcy Thompson. Yet, understanding the underlying processes has long proven challenging, partially due to the difficulty of imaging the cellular processes at appropriate spatial and temporal resolution. Recent years have seen three major advances that are helping us to tackle this challenge. First, biophysical models have proven to be very powerful in describing the structural changes in the material properties of biological materials. Developing tissues can undergo transitions, such as between fluid-like (i.e. rapid cell rearrangements) and solid-like (i.e. rigid internal structure). Second, imaging advances mean we can record with subcellular resolution the dynamics of cell morphogenesis in living embryos. Third, there have been major steps forward in our ability to segment and quantify complex biological imaging data using machine learning and more traditional approaches. Analysis of muscle fibre formation is especially challenging due to the speed with which the cell structure changes, including cell fusion. By combining these advances with the powerful genetics and optical accessibility of the zebrafish embryo, here we aim to dissect how the internal structural organisation of skeletal muscle emerges. Through the following Aims, we explore if the developing skeletal muscle undergoes a material change in its properties and how cellular processes drive cell and tissue shaping:1) Provide the first dissection of the dynamics for every cell within an internal vertebrate organ as they reach their final position and morphology. 2) Uncover the mechanisms happening within the cells that drive cell and nucleus reshaping and positioning.3) Use suitable mutants to perturb the cellular environment to test our models of cell and tissue shaping.In Aim 1, we will develop imaging and image analysis techniques to allow us to access the cellular behaviour throughout initial skeletal muscle development. We will track the position and morphology of every cell within each selected future muscle segment as they go from round cells through to the highly elongated and tightly structured muscle. The quantitative data is a key input into our analysis of the tissue structural order, to test if there are hallmarks of transitions in the material properties.In Aim 2, we dissect some of the subcellular mechanisms driving the changes in cell and tissue shape. We focus on microtubules due to their importance in a range of cellular processes associated with muscle formation. We will utilise lattice light-sheet microscopy - which enables very fast imaging at high spatial resolution - to record the dynamics of microtubules and their associated motor proteins during skeletal muscle formation. We will combine this with suitable drug and light-tuneable perturbations to dissect the role of microtubules in guiding muscle morphogenesis.In Aim 3, we utilise a range of mutants to further explore the mechanisms driving tissue organisation. We focus on perturbing muscle cell fate specification and inhibiting muscle fusion. These perturbations allow us to access the role of both biochemical and biomechanical inputs in driving skeletal muscle formation.Around 40% of human body mass is skeletal muscle. Using zebrafish development. we will dissect the fundamental mechanisms ensuring this tissue is precisely structured.