Mechanical and Other Directional Signals Controlling Vertebrate Planar Cell Polarity

In the past twenty-five years there has been dramatic progress in our ability to take embryonic cells and guide them biochemically to become a range of different specific cell types. This knowledge promises to allow us to use such cells to repair or replace damaged or diseased cells in the body. Medical advances in this area are known as "regenerative medicine" and the types of cells used as the starting material are called "stem cells" and our expertise with these has been built on a foundation of basic developmental biology. The next frontier is to go beyond control of cell type and begin to understand the assembly of complex tissues and structures - "morphogenesis" - since it is the architecture of tissues that is critical for their function. To achieve this understanding it is necessary to break down morphogenesis into its constituent processes. One such process is convergent extension (CE) in which tissue narrows and lengthens by self-organised directional rearrangement of its cells. This process requires the function of a set of molecules referred to as the Wnt-PCP pathway. Wnt is a soluble molecule that can diffuse through tissue and it has been thought that it provides a long-range directional cue for the direction of rearrangements in CE. However, there are hints that Wnt may not be the cue, or not the only cue: work in Drosophila fly embryos and some in Xenopus, including our own, has suggested that mechanical force can align the orientation of CE and PCP molecules within cells. This project will test (1) whether mechanical force, either self-organised or externally applied, aligns CE in tissues, (2) whether tissue boundaries of different types can themselves provide the orientation cues for CE and (3) whether Wnt itself can re-orientate CE with or without mechanical force. Together these experiments will give us a good idea about how CE is normally orientated and therefore how we might control its orientation ultimately to enable the sculpting of tissue architectures for the purposes of regenerative medicine.

Convergent extension (CE) is a major morphogenetic process in development in which tissue elongates and narrows by cell rearrangement. It is important in body axis elongation, neural tube closure, cochlear elongation and likely many other contexts in which cell rearrangements are only beginning to be appreciated as important. It depends on the Wnt-Planar Cell Polarity (Wnt-PCP) core system. We will exploit a Xenopus mesoderm cell aggregate system that self-organises its CE from a disc to a rod. It provides unsurpassed ability to manipulate the mechanics, geometry and molecules of CE PCP. Work so far suggests a model in which physical boundaries align self-reinforcing mechanical tension and intercalation. To test this model we will first map tension and cell alignment during self-organised CE and determine the effect of externally applied tension on CE alignment. We will then determine the importance of tissue boundaries, specifically boundaries where there is stiffness difference, adhesion difference and layer separation, all of which are straightforwardly adjusted in the Xenopus system. Finally, we shall assess the CE-orientating effects of Wnt11 and Wnt5a directly in relation to mechanical tension and test propagation of CE movements through tissue via Wnt gradients and mechanical coupling in cell aggregates and in tissues in vivo.

Who will benefit from this research?
This is basic research and does not pretend to being translatable in the very short term. However, it is also critical strategically for translational purposes because it will provide a part of the crucial foundation for the morphogenetic aspects of regenerative medicine that are currently in a very primitive state.
Beneficiaries will include:
(i) Tissue engineers in diverse areas engaged in using biomaterials to constrain or enhance tissue shape.
(iii) Biotechnology companies interested in developing histologically faithful tissues and organoids for the purposes of drug testing

How will they benefit from this research?

Health will be improved if regenerative therapies are successfully developed and this research will provide the basic foundations for such therapies to be applied to real structures rather than just amorphous clumps of cells or poorly self-assembled organoids.

Wealth will be improved by building knowledge in this area and its ultimate application as above within the UK biotechnology and tissue engineering sectors, but also by developing training and expertise at the interface of biology and engineering that can be applied in related enterprises. This kind of research will further establish the UK as one of the top places in the world for regenerative medicine, and so attract companies and talent.

Culture will benefit because the understanding of biological form is fundamental to the understanding of nature in general, freeing the public from mystical or superstitious ideas about the "miracle" of evolution while sustaining and appreciation of the beauty of biological processes and structures.

Health and wealth impacts will be long term. The nearest parallel is the early use of growth factors in tissue specification from embryonic cells in the early 1990s that is now being applied in clinical trials with embryonic stem cells, i.e. 20-25 years.

Staff working on the project will develop research and professional skills that they could apply in all employment sectors since in addition to lab work, they will be trained in oral and written presentational skills and computer skills with wide and general relevance.

What will be done to ensure that they benefit from this research?

This investigator is very active in publishing and presenting the group's work through active ongoing contact with regenerative medicine/tissue engineering groups and companies within King's College London Dental Institute and King's Health Partnerships, and to the UK and worldwide health sectors.

The proposed research project will be managed to engage users and beneficiaries and increase the likelihood of impacts with public engagement via talks given to schools, presentations on the media, including radio and the World Wide Web.