Contributions of cell behaviours to dorsal closure in Drosophila abdomen

尽管最近取得了进展，但组织发育过程中细胞行为的调节和协调仍然知之甚少。我试图通过使用基于主体的计算模型来研究果蝇成年腹部表皮形态发生过程中不同细胞行为对背侧闭合的影响程度，从而解决这个问题。组织和器官的形成是形态发生过程的结果，它依赖于多种细胞行为的调节和协调。在这个项目中，我将重点研究果蝇成体腹部表皮的发育，在这个过程中，幼虫上皮细胞（LECs）被成体组织母细胞[1]取代。活体四维显微镜（对活果蝇的研究）为我们提供了收集数据的手段。多尺度数学模型使我们能够展示我们对组织内细胞动力学的理解，并使我们能够做出与数据相比较的预测。然而，由于它们涉及的假设，目前可用的模型只能提供有限的见解。其中一个例子是，大多数模型将细胞表示为具有直边的多边形。然而，在形态发生过程中，细胞可以形成弯曲的片状足状突起，用来推动自己向前。为了研究这些突起在多大程度上影响细胞迁移，这对成年表皮[1]的正常闭合是必不可少的，我的目标是扩展现有的模型，包括通过板足的迁移。我还打算将细胞死亡调节的不同方式之间的区别纳入我的模型中。先前的一项研究发现，抑制组织母细胞增殖导致LEC死亡延迟，这表明存在一种协调这些过程的机制。然而，这项研究并没有得出这个机制所依赖的结论。数学建模使我们有机会研究调节细胞死亡的不同事件（即接触、机械信号和化学信号）与[2]中确定的机制之间的关系。在机械信号方面，数据显示局部组织力学影响细胞分层（细胞从上皮中移除的一种方式）的可能性，这通常会导致细胞死亡。先前的研究表明，大多数上皮细胞直到组织母细胞巢（最初，组织母细胞聚集在一起形成“巢”）开始扩大后才会死亡。在此背景下，我将研究由组织母细胞巢扩张引起的机械力导致上皮细胞分层和死亡的假设。我将使用基于细胞的计算框架Chaste[4]，因为这将使我能够模拟单个细胞的行为。从一个简单的模型开始，我将设计图像分析和推理算法来量化实验观察到的行为。然后可以将其与模型结果进行比较，突出显示应该进行调整的地方。我将继续这个模型修改和实验验证的循环，直到我的模型代表了组织中细胞动力学的全部范围。果蝇的遗传工具可以用于实验操作该系统，从而允许测试不同的假设。通过操纵单个模型参数，我可以比较这些结果，这将突出表明应该如何更新假设。模型和实验数据之间的相互作用将是至关重要的。我的模型所描述的复杂的组织重塑是高等生物中类似现象的代表。因此，由于生物之间的高度遗传相似性，我开发的工具将与人类健康研究相关-特别是伤口愈合[5]和肿瘤生长[6]，因为这些过程也依赖于细胞死亡和迁移行为的变化。

Despite recent progress, the regulation and coordination of cell behaviours during tissue development remain poorly understood. I seek to address this issue by using agent-based computational models to investigate the extent to which different cell behaviours contribute to dorsal closure during morphogenesis of the Drosophila adult abdominal epidermis. Shaping of tissues and organs arises as a result of morphogenetic processes, which rely on the regulation and coordination of a multitude of cell behaviours. In this project, I will be focusing on the development of the Drosophila (fruit fly) adult abdominal epidermis, during which larval epithelial cells (LECs) are replaced by adult histoblast cells [1].In vivo 4D microscopy (the study of live Drosophila) provides us with the means to collect data. Multi-scale mathematical models allow us to demonstrate our understanding of cell dynamics within a tissue and enable us to make predictions that can be compared to the data. However, due to assumptions that they involve, currently available models only provide limited insights. One example of this is that most models represent cells as polygons, which have straight edges. However, during morphogenesis, it has been shown that cells can form curved, lamellipodia-like protrusions that they use to propel themselves forwards. To investigate the extent to which these protrusions affect cell migration, which has been shown to be essential for the normal closure of the adult epidermis [1], I aim to extend existing models, by including migration via lamellipodia. I also aim to incorporate a distinction between the different ways in which cell death is regulated into my models. A previous study found that inhibiting histoblast proliferation led to a delay in LEC death, suggesting that there exists a mechanism which coordinates these processes [2]. However, the study did not conclude what this mechanism relies on. Mathematical modelling gives us the opportunity to investigate the relationship between the different events which regulate cell death, namely contact, mechanical signals and chemical signals, and the mechanism identified in [2].In terms of mechanical signals, data has shown that local tissue mechanics impact the likelihood that a cell will delaminate (a way that cells are removed from the epithelia), which usually then leads to cell death [3]. Previous research has shown that most LECs do not die until after the histoblast nests (initially, histoblasts are clustered together in 'nests') start to expand [1]. Given this background, I am to investigate the hypothesis that mechanical forces arising from histoblast nest expansion causes delamination and then death of LECs.I will be using the cell-based computational framework Chaste [4] as this will enable me to model individual cell behaviour. Starting with a simple model, I will design image analysis and inference algorithms to quantify behaviours observed experimentally. This can then be compared to the model outcomes, highlighting where adjustments should be made. I will continue with this cycle of model alterations and experimental validation until my model represents the full range of cell dynamics in a tissue. Genetic tools in Drosophila can be used to experimentally manipulate the system, which allows varying hypotheses to be tested. By manipulating individual model parameters, I can compare these results, which will highlight how the hypothesis should be updated. This interplay between model and experimental data will be vital.The complex reshaping of tissue that my models will describe is representative of similar phenomena in higher organisms. Therefore, due to the high genetic similarity between organisms, the tools I develop will be relevant to the study of human health - particularly wound healing [5] and tumour growth [6], as these processes also rely on both cell death and changes in migratory behaviour.