Size Matters: A systems approach to understanding cell size control in a developing multicellular tissue

尺寸很重要：一种了解发育中多细胞组织中细胞尺寸控制的系统方法

• 批准号: BB/S003584/1
• 负责人: James Murray
• 金额: $ 53.72万
• 依托单位: CARDIFF UNIVERSITY
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FS003584%2F1
• 关键词: Size; Matters; systems; approach; understanding

Cells are the building blocks of tissues, but how 3D structures are built from cells is a fundamental unsolved problem in biology. It is even more complex when we consider a growing tissue, in which the physical properties of the building blocks (cells) change constantly as they grow and divide. We study the growing shoot tip or shoot meristem of the model plant Arabidopsis. This structure is required to produce new leaves and flowers as the plant grows. The early stages of organ development require efficient tissue growth and an increase in cell size is normally observed at this time. Over several years, we have developed techniques allowing us to image the meristem over extended periods in the confocal microscope. We can follow individual cells over time and determine their growth and division. In order to divide, a cell goes through a defined series of processes known as the cell cycle. Using fluorescent reporters we have developed, we can for the first time simultaneously determine the position of all cells in the cell cycle during imaging time courses of growing plant tissues. Our recently published study showed that the size cells reach when they divide is on average consistent for a given tissue and set of environmental conditions, but is highly plastic when these change. For example we found that cells were smaller, and tissue growth slower, when plants were grown under environmental conditions that restrict photosynthesis. Variation in cell size arises through unequal division and has to be removed. This is done by establishing a balance between growth and division on a cell by cell basis. The plasticity of the system leads us to consider that cell size at division is not determined by a direct "cellular ruler" but is instead determined as a consequence (or "emergent property") of the contributing processes of growth and division. This mechanism appears to be conserved from unicellular organisms which can also achieve a larger cell size and higher absolute growth rate under plentiful conditions. Regulation of cell size in these simple cells is achieved by balancing cell growth and division via the protein synthetic capacity of the cell. We have developed a model that can predict accurately the size of plant cells based on the rate of growth and the accumulation of activity of two regulatory proteins required for cell division (called CDKs) as the cell grows. We tested this extensively using different mutants and growth conditions and identified the key processes that lead to cell size control. These processes appear to be the production and thresholding of CDK activity. In this proposal we will identify the "sizer" molecules involved in these processes that establish the link between growth and division of cells and analyse their function using our state-of-the-art imaging and analysis techniques. We have a number of candidate sizers, with known roles in CDK regulation, but we will also carry out experiments to identify new candidates in an unbiased manner using a genome-wide approach based on identifying the rate at which proteins are being synthesized under different conditions. We will use a combination of experiments and mathematics to develop a model that will allow us to understand how these sizer molecules are regulated and what effect this has on cell size control.

细胞是组织的构建块，但如何从细胞构建3D结构是生物学中一个未解决的基本问题。当我们考虑一个生长的组织时，它甚至更加复杂，其中构建块（细胞）的物理特性随着它们的生长和分裂而不断变化。以模式植物拟南芥为材料，研究了茎尖或茎分生组织的生长过程。随着植物的生长，这种结构需要产生新的叶子和花朵。器官发育的早期阶段需要有效的组织生长，此时通常会观察到细胞大小的增加。几年来，我们已经开发出技术，使我们能够在共聚焦显微镜下长时间成像分生组织。我们可以随着时间的推移跟踪单个细胞，并确定它们的生长和分裂。为了分裂，细胞经历一系列被称为细胞周期的过程。使用我们已经开发的荧光报告，我们可以第一次同时确定所有细胞在细胞周期中的位置，在生长的植物组织的成像时间过程中。我们最近发表的研究表明，细胞分裂时达到的大小对于给定的组织和一组环境条件来说是平均一致的，但当这些条件发生变化时，它具有高度的可塑性。例如，我们发现，当植物生长在限制光合作用的环境条件下时，细胞较小，组织生长较慢。细胞大小的变化是由于不均等分裂而产生的，必须去除。这是通过在细胞基础上建立生长和分裂之间的平衡来实现的。系统的可塑性使我们认为，细胞分裂时的大小不是由直接的“细胞标尺”决定的，而是由生长和分裂过程的结果（或“涌现特性”）决定的。这种机制似乎是保守的单细胞生物体，也可以实现更大的细胞大小和更高的绝对生长速率在丰富的条件下。这些简单细胞中细胞大小的调节是通过细胞的蛋白质合成能力平衡细胞生长和分裂来实现的。我们已经开发出一种模型，可以准确地预测植物细胞的大小的基础上的生长速度和细胞分裂所需的两个调节蛋白（称为CDKs）的活性的积累，随着细胞的生长。我们使用不同的突变体和生长条件进行了广泛的测试，并确定了导致细胞大小控制的关键过程。这些过程似乎是CDK活性的产生和阈值化。在这项提案中，我们将确定参与这些过程的“sizer”分子，这些分子建立了细胞生长和分裂之间的联系，并使用我们最先进的成像和分析技术分析它们的功能。我们有许多候选分子筛，它们在CDK调节中具有已知的作用，但我们还将进行实验，使用基于识别不同条件下蛋白质合成速率的全基因组方法，以公正的方式识别新的候选分子。我们将使用实验和数学相结合的方法来开发一个模型，使我们能够了解这些分子是如何调节的，以及这对细胞大小控制有什么影响。

项目成果

Segmentation of Meristem Cells by an Automated Optimization Algorithm

通过自动优化算法分割分生组织细胞

• DOI: 10.3390/app10238523
• 发表时间: 2020
• 期刊: Applied Sciences
• 作者: Rojas O