Parallel notch activation mechanisms provide robustness to developmental patterning in Drosophila

Lead Research Organisation: University of Manchester
Department Name: Life Sciences

Abstract

Multicellular organisms like humans and fruit flies, develop from the proliferation of a single cell. An important problem in biology is to understand how it is that the millions of cells present in the adult body arise. These cells have to perform many different functions in diverse tissues and therefore they become differently specialised, for example into heart cells or brain cells. It is an important challenge in biology to understand, not only how this specialisation occurs, but also how each specialised cell arises in the correct place at the correct time of development. This is not only important from the point of view of adding to our fundamental biological knowledge, but it has important implications for our understanding of diseases like cancer, heart disease and dementia. This is because the signals that control the development of the organism are often signals that go wrong when we are suffering such medical problems. If we can understand how these signals function normally in development then this will provide essential insight into how to correct defects in these signals when they go wrong. For example sometimes cancer is caused when a signal is switched on permanently by a mutation, rather being regulated on and off. If we can find a way to block such signals without harming its normal functions, then it might be possible to cure particular cancers. It is obviously difficult both practically and ethically, to find out the answers to these problems by experimenting on humans. However, because all living organisms today have evolved from a common ancestor, it is possible to understand problems related to human biology and medicine, by studying other organisms. The fruit fly is one powerful model system that is often used to understand problems of signalling and development. The major signals that control fruit fly development are conserved with humans, including many of the signals that are associated with human diseases such as cancer. It is a wonderful model organism because it is so easy to manipulate by making mutations in its genes. This means we can study signals in intact tissue rather than trying to deduce their function by studying isolated cells in a dish. The latter approach is also very useful but can give misleading answers unless it can be combined with the investigation of signalling in real tissues. Studying fruit flies has resulted in the identification of many signals that are misregulated in human cancers. Our aim is to investigate a critical signal that is mediated by a protein called Notch. This protein is used many times in development and in many different tissues. One of the most well known uses is during the development of the brain. The function of Notch is to ensure that correctly specialised cells arise in the proper places in the body. My research recently found out that our understanding of how this receptor works is incomplete. This is very important to know because this protein is used many times in development and it is misregulated in many types of cancer. We have now discovered that there is a way for Notch to signal that was not known before. This programme aims to understand this new signal by identifying its required components and finding out what they do during development of the fruit fly brain, and other tissues. The work has an enormous potential to help find ways to cure diseases like cancer. It may also help find ways to solve problems associated with aging and help us to lead healthier lives for longer. This is because Notch regulates stem cells and these contribute to keeping our tissues and organs healthy over our lifespan. It also functions in the brain cells to help us remember events for a long time. A decline in the ability to form memories is a problem often associated with age-related conditions such as dementia. Understanding how Notch works may help lead to solutions to these challenging problems in the future.

Technical Summary

A critical and conserved developmental signal is mediated by the Notch receptor which is utilised in numerous key decisions and patterning processes. The Notch signal refines, to a single cell resolution, more broad patterns laid down by long-range signals. DSL-domain ligands activate Notch by causing proteolytic release of the Notch intracellular domain. The latter translocates to the nucleus to regulate gene expression. However, recent work from my group, using the Drosophila model organism, shows a proportion of Notch signalling depends on a DSL ligand-independent signal, that regulates the trafficking of Notch to the lysosome membrane. We propose that parallel pathways of Notch activation contribute to developmental robustness during cell fate patterning. To characterise the novel pathway further, we need to identify the remaining components and their functions. We will determine the full contribution of the alternative Notch pathway to development by identifying any redundancy, or parallel pathways by which Notch traffics to the lysosome. We will understand the impact of endocytic sorting on Notch signalling, by investigating how the pathway can be switched between positive and negative outcomes, and the relationship between the endocytosis-induced and the DSL ligand-induced signals. Our hypothesis is that these are distinct routes to activation rather than being part of the same linear pathway. However we will rigorously test this hypothesis by comparing the structure/function requirements of Notch in the two pathways, and the requirements for the pathway components. The outcomes from the above will enable us to generate more realistic models of the Notch signalling network during pattern formation, exploiting an existing collaboration to generate predictive computer simulations. This more comprehensive understanding will inevitably be informative for the ability to manipulate Notch signal activity for therapeutic purposes.

Publications


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Baron M (2012) Endocytic routes to Notch activation. in Seminars in cell & developmental biology
Whiteman P (2013) Molecular basis for Jagged-1/Serrate ligand recognition by the Notch receptor. in The Journal of biological chemistry
Yamada K (2011) Roles of Drosophila deltex in Notch receptor endocytic trafficking and activation. in Genes to cells : devoted to molecular & cellular mechanisms
 
Description Developmental signaling is remarkably robust to environmental variation, including temperature. For example, in ectothermic animals such as Drosophila, Notch signaling is maintained within functional limits across a wide temperature range. We combine experimental and computational approaches to show that temperature compensation of Notch signaling is achieved by an unexpected variety of endocytic-dependent routes to Notch activation which, when superimposed on ligand-induced activation, act as a robustness module. Thermal compensation arises through an altered balance of fluxes within competing trafficking routes, coupled with temperature-dependent ubiquitination of Notch. This flexible ensemble of trafficking routes supports Notch signaling at low temperature but can be switched to restrain Notch signaling at high temperature and thus compensates for the inherent temperature sensitivity of ligand-induced activation. The outcome is to extend the physiological range over which normal development can occur. Similar mechanisms may provide thermal robustness for other developmental signals.
Exploitation Route The work provides the basis for understanding the impact of numerous Notch regulators in the framework of a regulatory endocytic network and a basis for understanding the complex genotype phenotype relationship of the Notch genetic locus with implications for the study of cancer associated mutations
Sectors Education,Pharmaceuticals and Medical Biotechnology
URL http://www.sciencedirect.com/science/article/pii/S0092867414004802
 
Description My lab has devised primary school teaching package illustrating the use of Drosophila in research and demonstrating aspects of the national curriculum associated with heredity and evolution
First Year Of Impact 2015
Sector Education
Impact Types Societal
 
Description Molecular basis for jagged-1/serrate ligand recognition by the notch receptor. 
Organisation University of Oxford
Department Department of Plant Sciences
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Research collaboration established with Department of Biochemistry, University of Oxford bringing together physical studies on the structure and function of Notch with our functional analysis and genetic dissection of Notch activities.
Start Year 2010
 
Description Role of Notch trafficking regulation in early Drosophila embryo patterning 
Organisation Osaka University
Country Japan 
Sector Academic/University 
PI Contribution Co-supervision of a post doc appointed in collaborators laboratory including 2 visits to Osaka per year
Collaborator Contribution Hosting jointly supervised post doc and providing research infrastructure for the project
Impact Post doc has been identified and appointed. First research visit has been completed
Start Year 2014
 
Description mathematical modelling of Notch signal regulation 
Organisation University of Sheffield
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution We provided experiemental data to create and validate the mathematical model
Collaborator Contribution Partner supervised and provided intellectual inout into the creation and use of the modelling by a PhD student who worked on the project in Manchester
Impact Resulted in Cell paper Multidisciplinary Biological sciences and mathematics
Start Year 2012
 
Description Science outreach 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The brain box.. science fair in Town Hall Manchester, part of European City of Science celebrations
Year(s) Of Engagement Activity 2016
 
Description school visit.. 
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 visited school parents evening where `i am a governor and advertised and promoted Manchester Science week out reach activities

Increased participation of parents/pupils teachers in visiting inscience week events
science week promoted in school assemble
Year(s) Of Engagement Activity 2014,2015,2016
 
Description science spectacular outreach activity 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Demonstrations of uses of Fruit flies in research with hands on practical experiments

Enagagement with public in the role of the fly in research including as an alternative to animal models
Year(s) Of Engagement Activity 2014