Pathways governing the competitive behaviour of pluripotent cells

AE1: Signal transduction pathways regulating stem cell fitness/behaviour in the early mouse embryo AE2: ES cell biology

Ensuring that mutations are not propagated within stem cell populations is key to proper development and homeostasis. This is especially relevant when it comes to pluripotent cells, that not only can give rise to all lineages, including the germ line, but that are also of great importance to regenerative medicine. We have found that cell competition is a novel mechanism that ensures the fitness of the mammalian pluripotent stem cell pool. We found that during the onset of differentiation, cell competition measures the relative fitness of pluripotent cells and eliminates those cells that are less-fit than their neighbours. This implies that cell fitness is not only a cell-intrinsic property, but is also measured relative to a cells' neighbours. We do not know how cells perform this relative fitness sensing and this will be the thrust of this proposal. In preliminary work to this proposal we have identified that specifically when wild-type and defective pluripotent cells are confronted with each other at the onset of differentiation, the defective cells decrease mTOR signalling and this decrease is sufficient to explain their elimination. Furthermore, we have shown that restoring mTOR signalling in loser cells is sufficient to rescue their elimination. These results indicate that the mTOR pathway is key read-out of the competitive behaviour of cells. Here we will do four things. First, we will study the pathways regulated by mTOR during differentiation to understand how mTOR mediates defective cell elimination. We will also study the signals upstream of mTOR to gain insight into the mechanisms by which cells communicate their relative fitness levels. Third, we will screen for novel pathways that regulate cell competition. Finally, we will study what happens when cell competition fails to gain insight into the fate of cells not eliminated by this mechanism.

Our studies will uncover the mechanisms that ensure the fitness of pluripotent stem cells. The large promise that pluripotent stem cells hold for regenerative medicine, where stem cell are induced to differentiate towards specialised cells that are then transplanted into patients, has carried with it a large degree of interest both from the academic and medical communities. Furthermore, with the advances in reprogramming there is an enormous scope for applying in vitro differentiation of patient-derived induced pluripotent stem (iPS) cells to study diseases. However, increased knowledge about how specific cell types are induced in an irreversible way as well as how to differentiate cells down specific lineages is vital to control that the correct cell types are generated before these stem cell therapy becomes meaningful clinically. Therefore, the results obtained in this study will be of direct relevance to translational research. Given that understanding how cellular fitness is regulated is a key question in cancer, our work will also be of interest to researchers working in this field.

The primary beneficiaries and users of this research are members of the academic sector - research workers, teachers and students. Other beneficiaries are the general public and commercial sector. In particular, the data obtained in this project will benefit the companies developing stem cell-based assays for drug screening (e.g. AstraZeneca) as well as companies developing media for pluripotent stem cell maintenance and differentiation (e.g. STEMCELL Technologies, Millipore), and pharmaceutical and biotech companies developing hESC-based cell replacement therapies for treatment of degenerative diseases (e.g. Advanced Cell Technologies, Viacyte).

A further beneficiary of our work will be the lay public. Given the medical relevance and ethical implications of understanding developmental processes, and its impact on stem cell biology, our work will provide factual input to and therefore benefit the public discussion about the advantages and risks of stem cell therapy.

The results of this research will be conveyed to other researchers through the publication of findings in peer-reviewed journals, by reporting unpublished work at conferences and through personal communication with other scientists. Though the results will primarily be disseminated through scientific journals, we will liaise with dedicated Media Teams at Imperial College and the University of Sheffield to issue a press release when appropriate. We take seriously the responsibility of scientists to engage with the lay public, to raise awareness among them of the results of publicly funded research, to openly debate ethical issues relating to our research so that public opinion may be formed in an informed manner and to take the excitement of our research to the children of today, who will be the scientists of tomorrow. For these reasons we engage through the University but also as individuals in activities aimed at the public dissemination of science.

This project will also train early-career researchers in emerging methodologies, contributing to their career development, as well as producing individuals capable of carrying out future research in the biomedical sciences. At a time when industry is moving in the direction of interdisciplinary research, such individuals will be highly sought-after not only in academia but also in the commercial sector.