MacArthur BB/L000512/1 Dissecting the molecular basis of cell-cell variability in mouse embryonic stem cell populations using system approaches

Stem cells are present during all phases of development, from the embryo to the adult, and are responsible for orchestrating tissue growth and repair. Embryonic stem cells (ESCs), which are derived from the very early embryo, have the ability to produce all of the body's tissues, a property that is known as pluripotency. By contrast, adult stem cells are only multipotent: they are able to produce a limited number of tissues similar to their tissue of origin. Due to their remarkable regenerative capacity, stem cells (of all different types) have become a point of focus for regenerative medicine strategies, which aim to clinically replace or restore tissue damaged due to disease or trauma. However, the molecular bases of stem cell multi- and pluripotency are still incompletely understood, hindering their clinical use. In the body, stem cells are either found in small numbers (as is the case for ESCs during early development) or are extremely rare (as is the case for stem cells found in adult tissues) and can, therefore, be difficult to examine. Typically this problem is overcome by examining the average behaviour of (perhaps small) populations of cells. However, a number of recent studies have used advanced single cell gene expression profiling to examine stem cell populations in more detail. These reports have uncovered a surprising degree of cell-to-cell variability within apparently functionally homogeneous stem cell populations, indicating that population-based experiments may, in fact, be masking significant cell-cell variability. This is important because cell-cell variability may profoundly affect the long-term regenerative potential of the population as a whole in ways that are hard to decipher using population-based experiments. So, before new regenerative medicine strategies can be safely used in the clinic it is therefore necessary to fully understand cell-cell variability in stem cell populations. This project aims to make use of the latest high-throughput single cell profiling technologies (which are able to profile hundreds of individual cells per experiment) in combination with computational and mathematical analysis to dissect the origin and functional consequences of cell-cell variability in mouse ESC populations as a model system. Mouse ESC populations have been chosen since they are easily obtained, experimentally reproducible, well studied and ethically uncontroversial. However, we anticipate that understanding of mouse ESC biology will inform our understanding of human pluripotent stem cells and, ultimately, provide wide-ranging clinical benefits.