Understanding how PAR proteins cooperate to establish cell polarity (New Investigator)

To generate an organism from an initially symmetric one-cell embryo, cells divide and lose their initial symmetry, acquiring structural and functional differences through a process termed cell polarisation. A crucial step in the polarisation of animal cells is the distribution of conserved polarity effectors to discrete domains on the cell surface. From their asymmetric position these key proteins control important events that build an organism, including the generation of the plethora of cell types needed, the organization of tissues into organs and the establishment of embryonic axes that lay the bases for the architectural plan of an animal. Therefore, when the position and function of these polarity effectors is impaired a wide range of diseases can arise including cancer.

What ensures the correct localisation and function of these polarity proteins? We recently identified a new way of regulation for these polarity effectors. We found that, like in a manufacturing factory, there is a division of labour for the polarity proteins that will specify a cell domain. They group themselves into distinct protein-complexes, which become specialised in a given function. For the proteins we studied we found that there are at least two distinct protein-complexes, one specialised in the asymmetric distribution of the polarity proteins and the other focused on their activation. A very tight functional coordination between these protein-complexes is required to generate an asymmetric and active domain of polarity proteins that will polarise cells, allowing the development of an organism. We do not know how this important cooperation is achieved; therefore we propose innovative cell biology techniques to identify the players involved and their modes of action.

By understanding how cells are polarised we will give insight into key aspects of human embryo development and we will pinpoint events that can go wrong and cause disease. Thus it is important that we identify the mechanisms that control correct cell polarisation; understanding this will, in the long-term, provide new avenues in the design of drugs that can correct errors in these mechanisms of control.

To generate a complex, highly structured organism from a symmetric one-cell embryo, cells undergo genetically-encoded programs where as they divide they acquire structural and functional differences through a process termed cell polarisation. A crucial step in the polarisation of animal cells is the localisation of conserved polarity effectors, among them the PAR proteins, to discrete membrane domains on the cell surface. When these processes are impaired, developmental disorders can arise including cancer.

We recently discovered an important layer of regulation for PAR proteins (Rodriguez et al DevCell 2017). PARs generally define two membrane domains within polarising cells, i.e. antero-posterior for the asymmetrically dividing C.elegans zygote (one-cell embryo) or apico-basal for epithelial cells. We have found that the set of PARs that define the anterior zygote actually work as two distinct protein complexes that cooperate to polarise the zygote. These PAR complexes have different functions; one focuses on sensing cues to become asymmetrically localised and the other on activating the main signaling component, aPKC kinase. Coupling of these complexes is strictly necessary to generate an asymmetric and active domain of aPKC, which will signal the zygotes' asymmetric division, leading to the soma and germline lineage. We found that aPKC activity is required to functionally couple these complexes and the goal of this project will be to understand how aPKC achieves this important task. We will identify aPKC substrates and the mechanisms that regulate this dynamic cooperation between PAR protein complexes.

By elucidating the fundamental principles that govern the asymmetric organization and function of polarity effectors we will understand a process that sits at the heart of many important developmental biology events. We expect our research to provide new avenues for drug design strategies in different developmental disorders.

Our research will reveal the fundamental principles of how PAR proteins, key regulators of cell polarity, coordinate their tasks to generate specialised domains within cells. This polarisation of cells is critical to many aspects of embryo development, including asymmetric cell division, tissue formation, neuronal development, cell migration and embryos axis establishment. Given that cell polarity sits at the heart of a wide range of cell biological processes, which are all important for the development of humans, we expect our findings to be of broad popular interest.

The most immediate impact will be in the SCIENTIFIC COMMUNITIES described under academic beneficiaries (cell and developmental biology, cell polarity, cell division, cell fate, cytoskeleton dynamics, stem cell biology, signaling and developmental disorders), mainly through collaborations, participation at conferences and publication in high impact open access journals. We will ensure wide dissemination of the data, reagents and methods generated to the UK and international research community.

In the long term because cell polarity is crucial to most developmental processes, we expect that by understanding the fundamental mechanisms that regulate polarity we will find aspects that can go wrong in developmental disorders. This will allow the development of novel therapeutic strategies, impacting on the PHARMACEUTICAL AND PUBLIC HEALTH SECTOR. Currently inhibitors of aPKC (the PAR signaling component focus of our studies) are being tested as drugs against cancer and nervous system disorders. Indeed, in our previous publication we have characterised an aPKC inhibitor developed by Cancer Research Technology Limited. Our future mass spectrometry analyses and genetic screens (AIMs1&2 from research proposal) will identify aPKC substrates and regulators that in a similar way can be putative therapeutic targets for cancer or other developmental disorders. I will meet annually with the Business Development at Newcastle University to examine the possibilities for application and commercialization of our research. Commercially exploitable intellectual property (IP) will be assessed prior to publication.

The cutting edge research techniques developed during this project in mass spectrometry and live cell super-resolution imaging, will directly benefit Newcastle proteomics facility and the Bio-imaging unit. In particular, our work will help validate and commercialise the iSIM super-resolution imaging technology benefiting the developer, a local LIFE SCIENCE TECHNOLOGY company (VisiTech International, Sunderland). In addition, our methods and tools will be immediately shared with members of the University and our collaborators.

The RA working on the project will benefit from innovative technical skills and research experience. This work will also benefit other members of the Cell Division Biology Group, including PhD and master students, through exposure to new techniques and research areas. Thus, this grant will contribute towards UK SCIENCE through developing expertise and training skilled researchers that will be highly employable in public and private research sectors, increasing capacity in growing research areas.

During the course of this project we will take opportunities to engage with the GENERAL PUBLIC. I have a demonstrated interest in presenting my work to the public, having been involved in outreach activities with schools, science festivals and patients. During this project the RA and I will participate in the organization and delivery of "Soap Box Science" events in central Newcastle, and "Meet the Scientist" days focusing on C.elegans research and cell division at the International Centre for Life museum. All of these will be invaluable opportunities to attract public attention towards our research interests, which will be supported by press releases from our work (university website, local and national press) and the use of social media.