Complement as a novel regulator of Wnt signalling during craniofacial development

Lead Research Organisation: University College London
Department Name: Cell and Developmental Biology

Abstract

According to the World Health Organization, birth defects affect one in every 33 infants, resulting in approximately 3.2 million disabilities every year (http://www.who.int/mediacentre/factsheets/fs370/en/). Deformations of the head and face, termed craniofacial defects, make up one third of this total. Such anomalies typically result from faulty formation of the bones and cartilage in this region. It is important, therefore, that we understand how these structures are normally formed if we want to devise effective ways to treat or prevent such defects from occurring.
To do that, we have turned our attention to a group of embryonic cells called the neural crest. The neural crest is a population of cells found early in the life of an embryo. Shortly after their formation, these cells move through the embryo and establish the tissues that will eventually become mature structures such as ribs, muscles, nerves and many of the components of the face and neck. In order to build these structures in the correct sizes and shapes, the movements and behaviour of the neural crest cells must be precisely controlled. When this control fails malformations of these structures often results. Our aim is to understand the way in which this control operates.
Some clues have come from the field of genetics. Indeed, a number of craniofacial anomalies are known to have a genetic origin, but in only a few cases have the mutated genes been identified. One such gene is responsible for producing a chemical signal called Wnt, which is critical for the formation of neural crest cells. For embryos to develop properly it is essential that Wnt signaling occurs at the correct times and places, yet exactly how this is achieved in the embryo remains a mystery.
Our preliminary work has revealed an unexpected way in which this might happen. It seems that a group of proteins normally involved in immunity may play a critical role. The complement cascade, as they are collectively known, is responsible for killing foreign pathogens and monitoring self versus non-self recognition in the immune system. We have found that if we block the cascade's function in young embryos neural crest formation and migration are defective. Our data indicate that this is due to a deficiency in Wnt signalling. Furthemore, a recent publication shows that complement deficiencies lead to dramatic craniofacial defects (Rooryck et al (2011) Nat Genet 43, 197).
These findings suggest that the complement cascade is important for normal craniofacial development and may shed light on causes of craniofacial defects that remain poorly understood. Consequently, this work may have a profound impact on health policy. For example, the results from our research may suggest that pregnant women should avoid certain treatments for autoimmune disorders that target the complement cascade, as these could have devastating consequences for the child, equivalent to the use of thalidomide in the past.

Technical Summary

The importance of Wnt signalling in embryonic development has been well documented. In adult life, Wnt signalling continues to be critically important for processes such as governing cell fate decisions and maintaining the stem cell niche. During these processes, as in neural crest induction, levels of Wnt activity must be precisely controlled in time and space. Yet many of the molecular details underlying this regulation remain poorly understood.
Our preliminary data suggest that the complement cascade, normally associated with the immune response, may be an important regulator of Wnt signalling during neural crest induction and may, therefore, play an important role in craniofacial development. As the complement cascade contains more than 35 proteins we will focus our attention on the terminal effector of the pathway, complement component C9. In this project we will propose the novel hypothesis that C9 controls Wnt signalling during neural crest and craniofacial development.
The aim of this project is to identify the molecular mechanism by which C9 controls Wnt signalling in general, and how this is important for neural crest and craniofacial development. The major contributions to be expected from this project are:
i) The discovery of a novel regulator of Wnt activity, a signalling pathway essential for normal development and critical in disease.
ii) The characterization of a completely new and unexpected role for C9 in neural crest and craniofacial formation.
iii) The description of the mechanism by which C9 regulates Wnt signalling.j
iv) The identification of novel C9 partners involved in neural crest formation that could also be partners of C9 in the immune system.

Our findings could have important implications for human health, as it may suggest the avoidance of complement inhibitors to treat immune diseases during pregnancy

Planned Impact

Impact summary
We propose to test the novel idea that complement factors could play a role in early development by controlling Wnt signalling. This knowledge will have a large impact on the science directly related to this topic. It will impact on developmental biologists and clinicians interested in understanding neural crest and craniofacial development. In addition it will impact cell and cancer biologists working on Wnt signalling. However it could have a more immediate and dramatic effect on the general public as described below:

1. Birth defects: The rate of birth defects in England is 1.1% (UK Health Research), and many of these defects are related to neural crest derivatives. Understanding how neural crest develops during embryogenesis will help to develop diagnostic and therapeutic tools for birth defects associated to a failure in neural crest formation. It is important to mention that several trials have been performed to test complement inhibitors in their efficacy to treat immune disease; however pregnant woman have been excluded from these trials. Our prediction, based on our hypothesis, is that administration of complement inhibitors during the first period of gestation could have devastation consequence for the embryo, from subtle craniofacial abnormalities to more series defects, and even death. In addition, a reduction in complement level has been associated to unexplained spontaneous abortions. Thus, this project could have a high impact in public health policies, by developing a tighter regulation in the use of complement inhibitors. The result of this project will be immediately used to screen for craniofacial abnormalities in complement deficient patients.

2. Immunology: In this project we propose to analyze the role that complement has on early embryonic development. Complement has an important function in the protection against external agents such as microbes, but its uncontrolled activation can also have devastating consequences on several autoimmune diseases. Several research centres and biotechnology industries are currently designing inhibitors of the complement to control specific immune diseases. These inhibitors have being designed in the understanding that complement suppression will not have side effects, others that immune-depression. If our work shows that complement is required for normal early development, many of these complement inhibitors should not be used by pregnant women. The results of our project could have a deep impact on human health.

For all these cases in which we anticipate an impact of our project on the community we will ensure that proper people would have the opportunity to benefit from our research by making use of the programs that University College London has (translational research programs and extensive programme of public engagement).

Publications

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Barriga EH (2015) Embryonic cell-cell adhesion: a key player in collective neural crest migration. in Current topics in developmental biology

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Barriga EH (2015) Animal models for studying neural crest development: is the mouse different? in Development (Cambridge, England)

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Kotini M (2015) Connexins in migration during development and cancer. in Developmental biology

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Mayor R (2016) The front and rear of collective cell migration. in Nature reviews. Molecular cell biology

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Roycroft A (2016) Molecular basis of contact inhibition of locomotion. in Cellular and molecular life sciences : CMLS

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Roycroft A (2015) Forcing contact inhibition of locomotion. in Trends in cell biology

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Scarpa E (2016) Collective cell migration in development. in The Journal of cell biology

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Shellard A (2016) Chemotaxis during neural crest migration. in Seminars in cell & developmental biology