Growing with an 'advantage': Dissecting the links between embryonic cell competition and tumourigenesis

肿瘤启动的一个关键机制涉及早期恶性细胞获得选择性优势，从而击败并消除邻近的非转化细胞。这种“超级竞争”行为通常与致癌基因MYCN的活性增加有关，MYCN也与神经母细胞瘤有关，神经母细胞瘤是婴儿中最常见的颅外实体瘤。神经母细胞瘤肿瘤发生在胚胎发育期间，通常在躯干水平，在多能细胞群-神经嵴（NC）-产生肾上腺和交感神经节。我们最近建立了一个易于处理的系统，促进MYCN驱动的神经母细胞瘤起始的颞叶解剖。这涉及人胚胎干细胞（hESC）向躯干NC及其衍生物的逐步分化（Frith et al. 2018; Frith et al. 2019）。为了模拟MYCN活性亢进，我们设计了hESC，使其以多西环素（Dox）诱导的方式与荧光报告基因同时过表达MYCN。我们的初步数据显示，Dox诱导的MYCN活性升高促进肿瘤发生的标志，如分化受损和增殖增加。这个博士项目旨在了解MYCN如何促进躯干NC细胞中的肿瘤起始，并测试这一假设，即通过选择超级竞争细胞发生。我们将首先研究MYCN过表达细胞与其正常同基因对应物之间的竞争性细胞相互作用模式。为此，我们将在NC分化的不同时间点使用延时成像监测嵌合培养物中荧光标记的野生型和MYCN过表达细胞的相互作用（Price et al. 2021）。然后，我们将使用转录组分析，候选信号通路的药理学抑制和电生理学的组合来定义超级竞争细胞的选择和消除其邻居的机制。最后，我们将上述实验的结果整合在一个已建立的细胞竞争计算框架内，以获得神经母细胞瘤起始及其克隆进化的定量预测模型。

A key mechanism underlying tumour initiation involves the acquisition of a selective advantage by early malignant cells, which outcompete and eliminate neighbouring non-transformed cells. This 'super-competitive' behaviour is often linked to increased activity of the oncogene MYCN, which is also associated with neuroblastoma, the most common extra-cranial solid tumour in infants. Neuroblastoma tumours arise during embryonic development, typically at the trunk level, within a multipotent cell population - the neural crest (NC) - that gives rise to the adrenal gland and sympathetic ganglia. We recently established a tractable system that facilitates the temporal dissection of MYCN-driven neuroblastoma initiation. This involves the stepwise differentiation of human embryonic stem cells (hESCs) toward trunk NC and its derivatives (Frith et al. 2018; Frith et al. 2019). To mimic MYCN hyperactivity, we engineered hESCs to overexpress MYCN simultaneously with the fluorescent reporter in a Doxycycline (Dox)-inducible manner. Our preliminary data shows that Dox-inducible elevation of MYCN activity promotes hallmarks of tumourigenesis such as impaired differentiation and increased proliferation.This PhD project aims to understand how MYCN promotes tumour initiation in trunk NC cells and test the hypothesis that this occurs via the selection of super-competitive cells. We will first examine the mode of competitive cell interactions between MYCN-overexpressing cells and their normal isogenic counterparts. To this end we will monitor interactions of fluorescently-labelled wild-type and MYCN-overexpressing cells in mosaic cultures using time-lapse imaging at different time points of NC differentiation (Price et al. 2021). We will then define the mechanisms underlying the selection of super-competitive cells and elimination of their neighbours using a combination of transcriptome analysis, pharmacological inhibition of candidate signalling pathways and electrophysiology. Finally, we will integrate findings from the above experiments within an established computational framework for cell competition to obtain a quantitative, predictive model for neuroblastoma initiation and its clonal evolution.