Investigating the mechanisms for building the embryonic body plan: harnessing a paradigm for cell differentiation

The fundamental job of embryo development is to build the adult body, made of hundreds of different kinds of cell, starting with a few identical cells, at the right place and time. If we were to know precisely how this happens, we could control this process in a dish to generate cells that could be transplanted to repair damage in degenerative disease and injury. In animals with a backbone, all the cell types except those in the head form from a set of unspecialised cells (neuromesodermal progenitors) at the tail end of the embryo, progressively laying down the spinal cord, muscles and skeleton in sequence from neck to tail. During this period, cells have to decide between alternative types and typically have a greater potential than their eventual fate (a property called 'plasticity') and only later irreversibly commit to a given cell identity. We have found that neuromesodermal progenitors mature over time as they produce the neck, then the ribcage, lower vertebrae and optional tail. We propose that this maturation process is important for the different cell types formed along the head-to-tail axis. We have found conditions to culture these cells, and will test molecules in culture that our previous work has suggested is important for making these progenitors mature. We will check if the cell types formed from progenitors at different stages of maturity have different functions. We will also find out how cells commit to given cell types by studying plasticity in individual cells, and, in parallel cells, the different genes that are active in cells that can change identity and those that do not. We will test whether loss or gain of any of these differentially-active genes changes cells' ability to commit to their fates.

The mechanisms by which the embryo lays down its body plan, and in particular, constructs the tissues along its AP axis, are fundamental to our understanding of biology. They are also crucial to understanding of in vitro differentiation of pluripotent cells. During AP axis development, populations of progenitors are found in the posterior end of the embryo, These include neuromesodermal progenitors (NMPs), stem cell-like progenitors that produce both more NMPs as well as the spinal cord and musculoskeleton in a head-to-tail sequence. However, their gene expression normally changes over time. Despite successfully producing functional NMPs from pluripotent mouse and human cells, these are a heterogeneous mixture of early and mid-stage progenitors. We plan to explore the significance of temporal change in NMPs, first by defining in vitro conditions that promote NMPs of early, middle and late identities, then by inducing differentiation from each progenitor type and defining the in vitro phenotype of cells. Functional cell types will be explored by grafting to cultured embryos. This addresses an important question in regenerative medicine: how similar do cell types need to be to functionally integrate in a tissue? A second fundamental question in developmental biology that is also crucial for developing in vitro differentiation protocols is: how do cells commit to given cellular identities? We will investigate this issue by first defining at single cell level the plasticity of cell types in the epiblast and region containing NMPs. Using transcriptomic comparisons between cells at specific regions where plasticity is known we will identify candidate factors governing plasticity versus commitment. One such factor is Oct4, which also changes prospective late axial identity towards an early/mid-stage, and using DamID-seq technology we will investigate differential targets in NMPs versus subregions of the epiblast.

1. Research staff employed on this project will receive both highly specialist and generic/transferable skills training.
The skills set in this lab are not available anywhere else in the UK, and in very few labs worldwide. Training will therefore produce researchers with unique skills and qualities. In terms of career progression and diversification, the University of Edinburgh is recognised by the UK Research Councils as a Centre of Excellence for generic and transferable skills training.

2. Students
I consider enthusing students about the research I do, and about stem cell and developmental biology research, one of my most important roles as a lecturer and researcher. Students will benefit by understanding why research is interesting, by entering research themselves, but at least by being aware of issues related to this research

3. Members of the public interested in stem cells
Through my webpage and a diverse range of outreach events organised by a dedicated team of outreach personnel in the Scottish Centre for Regenerative Medicine, the public will gain awareness of the scope of this research: what it does and does not do.

4. Patients:

People suffering from a range of health problems for which neuromesodermal stem cells may be of therapeutic benefit, e.g. spinal cord injury, muscular dystrophy will benefit in the long term by a knowledge of whether it is feasible to generate cell types of therapeutic value.