Coordinating the remodelling of cell polarity to form a functional organ.

Lead Research Organisation: University College London
Department Name: Lab for Molecular Cell Bio MRC-UCL

Abstract

The cells that make up our tissues adopt complex shapes. In most cases, each cell is able to do part of this process autonomously by defining an intrinsic polarity axis, so they know which end is up and which end is down. For epithelial cells, which line most of our organs, one end must point to the inside and one to the outside. This is true for all organs, and in epithelia is important because it underpins their function in absorbing nutrients (intestine), oxygen (lung) or filtering out salts and toxins (kidney or liver). Loss of polarity affects tissue health and the ability of epithelial cells to adhere to one another, which in turn can lead to cancer cells escaping a tissue to invade another through the process of metastasis. The aim of this programme is to figure out the mechanisms that induce polarised organisation of individual cells, and to determine how these cells work together to form complex multicellular structures in 3D. These structures can consist of cells that arrange themselves into layers found one on top of another, as in the skin or oesophagus, for example. How such tissue organisation is created is not well understood and will be studied with this research grant. Recent work in our laboratory has identified factors that are required for epithelial polarity, some of which have been previously linked to human pathologies. Our results also indicate that mechanical forces might play an essential role in coordinating polarity between cells, as they assemble into a tissue. In summary, we aim to elucidate how cells work together to induce polarised organisation of a complex animal tissue in health and disease.

Technical Summary

The objective of this new research grant is to elucidate how polarised tissue organisation arises from the collective action of individual cells. While a small set of conserved cell-intrinsic polarity regulators has been identified through genetic studies across a range of systems, we do not yet have a good understanding of the general logic by which these proteins break cellular symmetry to polarise an entire cell. Nor do we understand how this information is combined with extrinsic cues, both soluble and mechanical, to coordinate the formation of a complex 3D multicellular tissue during development. The developing fly eye is one of the best systems to study this in a living animal. Building upon unexpected findings in our laboratory that alternative mechanisms control polarity in different retinal epithelial cell types, we will reveal i) the different pathways by which polarity is induced in individual cells, and ii) how interactions between cells coordinate this polarity across a tissue in space and time. We expect that the principles we uncover will be of general importance, since cell polarity is critical for epithelia to function as selective barriers that mediate exchange between the outside and inside of an organism. By focusing on a genetically tractable, physiological animal model system of organogenesis, this proposal aims to elucidate how polarity machineries working within cells and communication between cell types come together to induce the functional polarised organisation of complex animal tissues, in health and disease.

Planned Impact

Our proposal aims to address fundamental questions concerning the biology of epithelial cells and organs, and will be of broad interest to the biomedical community.

- Fundamental biology and biomedical community: Epithelial cells are the building blocks of most of our organs, and their polarity is essential for their function as selective barriers. To function they have to coordinate their polarity, so tissue organisation is polarised. Complex multicellular patterning in 3D, as seen in most organs, has not been extensively studied. Therefore, our work has great potential to open new avenues of research and to have significant impact in biology and medicine by discovering new processes and mechanisms. Elucidating how cells work together to generate a complex tissue architecture during organogenesis will further our understanding of how defects in this process might impact on pathogenesis and will help us to better understand the mechanisms of organ development, repair and regeneration. We anticipate our work to reveal mechanisms that will be broadly relevant for epithelial and neuroepithelial tissue development in animals. Loss of cell polarity is a hallmark of cancer. Mutations in Rap1 are found in many epithelial cancers (e.g. breast, pancreas), and loss of Afadin/Cno is associated with poor prognostics of breast cancer. By elucidating how these factors induce polarised cell organisation, our work will help further our understanding of how their deregulation might contribute to pathogenesis. In addition, our work on machine learning to improve segmentation of large electron microscopy data sets should have a significant impact on the way researchers process these data by making data segmentation less labor intensive. In summary, we fully expect our work to impact on academic scientists outside of our immediate community. These include medical scientists interested in the transfer of basic research to the clinic. Additionally, we hope that our work will be of interest to the general public.

- Industrial partnership: We are collaborating with two global players in microscopy, Zeiss and 3i. These collaborations aim to address the technological challenges around imaging epithelial cells at ultra-high spatial and temporal resolution in a living animal, during organ development. With this new research grant, we will combine lattice light sheet and scanning array tomography electron microscopy to examine retinal cells as they work together to generate the eye. This part of our work will require protocol development and optimisation (e.g. correlative lattice/3D EM reconstruction). These will be shared with the community and will open paths to novel approaches to studying animal tissues across scales.

- Public engagement: We will continue to take advantage of UCL Open Days and MRC led events to present our work to the general public and school pupils. We will continue to contribute to the annual school visit at the LMCB, to familiarise young students with the higher education sector and to encourage them to consider a career in life sciences and medicine.
 
Description Enabling imaging of cells and tissues across scales
Amount £333,750 (GBP)
Funding ID 218278/Z/19/Z 
Organisation Wellcome Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2019 
End 08/2024
 
Title Enabling live Super Resolution imaging of cells 
Description Algorithms enabling diffraction limit imaging of live cellular structures with of focus on studying epithelial cells. 
Type Of Material Technology assay or reagent 
Year Produced 2018 
Provided To Others? No  
Impact No impact yet- needs to be published first and made available to the community. 
 
Description Auxetic retina 
Organisation Institute of Biomedicine of Seville
Country Spain 
Sector Public 
PI Contribution Luis Ma Escudero, Seville University, Spain
Collaborator Contribution One PhD student in the Escudero lab is using our data in the fly retina to develop a new mathematical model of tissue curvature.
Impact No publication yet, but the works progressing well. The mathematical model is working. We are now testing some of its predictions using genetics in the fly retina.
Start Year 2022
 
Description Collaboration Neural Crest cells. Prof Roberto Mayor 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Expanding on our discovery that cortical neuron polarisation requires nuclear export of a polarity factor, LKB1, this collaboration allowed us to show this new polarity pathway also regulate polarity in neural crest cells.
Collaborator Contribution Expert in Neural Crest cell biology.
Impact RanBP1 plays an essential role in directed migration of neural crest cells during development. Barriga EH, Alasaadi DN, Mencarelli C, Mayor R, Pichaud F. Dev Biol. 2022 Dec;492:79-86. doi: 10.1016/j.ydbio.2022.09.010. Epub 2022 Oct 4. PMID: 36206829
Start Year 2019
 
Description Vertex model - Tissue curvature 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Dr Angelika Manhart (Mathematics department) is working with us towards developing a new vertex model of tissue curvature in organogenesis.
Collaborator Contribution Training my Wellcome PhD student and supervising her work on the vertex model.
Impact Vertex model is almost ready. Preparing the publication.
Start Year 2022
 
Description Open day for a local school 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact approximately 25 pupil each year. Access to our fly facility including microscopes.

Overall feedbacks are very positive.
Year(s) Of Engagement Activity 2007,2009,2011,2013,2015,2016,2017,2018,2019
 
Description Tweeter feed - Cell polarity@pichaud lab 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Tweeter feed to promote our work on epithelial cell polarity.
Year(s) Of Engagement Activity 2016
URL https://twitter.com/PichaudLab