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

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.