Defining the role of SEMA3E and PLXND1 in the GnRH neuron system that regulates sexual reproduction in mammals

Lead Research Organisation: University College London
Department Name: Institute of Ophthalmology

Abstract

During foetal development, gonadotropin releasing hormone (GnRH) neurons are born in the nose and must migrate to the hypothalamus, a brain structure in which these neurons make contact with blood vessels to secrete the hormone they produce into the general circulation. Mistakes made during the establishment of the GnRH neuron system impair hormone secretion and therefore delay puberty and sexual reproduction, for example in the condition Kallmann Syndrome. Accordingly, understanding how the GnRH neuron system forms provides important inside into the origin of genetic disorders such as Kallmann Syndrome and help identify novel targets for mutation screening in patients seeking genetic diagnosis and treatment. For example, the early diagnosis of genetic defects that cause GnRH neuron deficiency allows timely treatment with hormone therapy to ameliorate or prevent the onset of symptoms. However, only some of the genetic causes have been identified so far. Recently, we discovered that a signalling molecule called VEGF-A promotes the survival of GnRH neurons when they migrate through the nose to reach the brain. We also discovered that a different signalling molecule called SEMA3A is essential to establish the neural 'highway' on which migrating GnRH neurons travel to reach the brain. Our findings underpinned subsequent studies of others, who identified genetic mutations that impair SEMA3A function in patients with Kallmann Syndrome. We now seek funding to study a related semaphorin known as SEMA3E and its receptor PLXND1 in the GnRH neuron system, because our pilot experiments suggest that the interaction of these two molecules is essential at later stages of GnRH neuron development. This research will significantly enhance our understanding of the GnRH neuron system and advance the development of novel tests for patients seeking genetic diagnosis for reproductive disorders.

Technical Summary

Gonadotropin releasing hormone (GnRH) neurons are neuroendocrine cells that arise in the nasal placodes during embryogenesis, but migrate to the hypothalamus, where they regulate puberty and sexual reproduction by secreting GnRH into the circulation. Studying the generation, migration, survival and neurite projection of GnRH neurons provides an excellent model system to elucidate the molecular and cellular mechanisms of neural development and the formation of neuroendocrine systems that regulate physiological functions in mammals. We have recently identified two different signalling pathways that are essential for the normal migration versus survival of a significant proportion of GnRH neurons during their migration through the nose. Moreover, we found that the joint loss of both pathways caused a catastrophic failure of assembling the GnRH neuron system. Our new pilot data show that PLXND1, a molecule known best for its role as SEMA3E receptor in blood vessel patterning and axon guidance, is similarly important for normal GnRH neuron development. We now wish to extend these findings to define the precise roles of PLXND1 and its ligand SEMA3E in the GnRH neuron system and assess the impact of losing this signalling pathway on GnRH cell behaviour, gonad development and fertility. We will use a combination of expression, genetic, functional and biochemical assays to identify and distinguish possible roles for SEMA3E and PLXND1 in GnRH neuron generation, migration, survival and axon projection. The proposed programme of work will advance significantly our understanding of the mechanisms that establish the GnRH neuron system and provide fundamental information on a signalling pathway affected in Kallmann Syndrome.

Planned Impact

Academia: This project will significantly enhance our knowledge of the developmental processes that establish functional brain wiring patterns and will be specifically important for national and international researchers in the areas of neurodevelopment, molecular genetics, endocrinology and sexual reproduction. In the medium term, this research will also benefit translational researchers aiming to design new clinical tests for inherited forms of infertility. Beyond their interest to the academic community, the results will impact on several other identifiable beneficiaries, as listed below.

Commercial private sector and clinical services: Because this work will identify novel functions for semaphorin signalling pathways, the results are likely to be of interest to the commercial sector involved in developing diagnostic tests for patients with neurological or reproductive disorders, as they may be able to capitalise on this new knowledge. Accordingly, this project is likely to contribute new knowledge that will lead to more translational research in the medium term. In the long term, the academic knowledge generated will benefit clinical medicine to impact positively on public health in the UK and abroad, both generally by expanding our knowledge base and specifically by advancing the generation of novel diagnostic tests to improve health and well-being.

General public: An immediate impact of this project is its opportunity to raise awareness and understanding of science and research through public dissemination of novel findings and explaining their significance. Knowledge of the developmental processes that promote neurodevelopment and normal sexual reproduction is key to understanding how we function as adult human beings. Learning about the normal mechanisms that control these processes will also improve the public's understanding of the origins of reproductive disorders, an area of high clinical need and social importance. These topics will be incorporated in outreach activities to engage with the public about this work, for example by providing work experience and giving lectures to secondary school students.

UK and International Research Base: By endowing researchers with both project specific and transferable skills, this project will lead to highly skilled workers that will benefit the UK's economic competitiveness. The project will also lead to new international collaborations and therefore enhance knowledge transfer and increase the international profile of our Universities.

Publications

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Description We found a genetic fault that prevents a molecule called SEMA3E from working correctly in two brothers with Kallmann Syndrome, an inherited condition that prevents people from undergoing puberty. SEMA3E was found to protect neurons that regulate sexual reproduction by producing gonadotropin releasing hormone (GnRH), which is needed to stimulate puberty. Our research showed that these GnRH-producing neurons could not survive their migration from their birthplace to their site of function without SEMA3E to protect them. This work was published in the Journal of Clinical Investigation. Importantly, our work followed prior clinical work up with laboratory studies to go far beyond simply identifying candidate genes linked to the disease. Thus, by recreating previously identified mutations and testing them in neuronal cells in tissue culture and by examining mice born without the genes that were mutated in both brothers, we provided concrete evidence to show how these mutations actually cause the condition. Our study therefore provides proof-of-principle for a powerful method to identify disease mechanism relevant to Kallmann Syndrome. This advance was recognised with an award to the first author of the study by a relevant learnt society, and we have since been contacted by endocrinologists working with patients suffering from delayed puberty or Kallmann Syndrome to help define the underlying genetic causes and their mechanisms of action. We have since continued our research to identify additional genes that contribute to both Kallmann Syndrome/hypogonadic hyogonadism and delayed puberty, with an additional manuscript published on a gene that is mutated in a family with inherited delayed puberty and two other manuscripts in preparation.
Exploitation Route Kallmann Syndrome can be treated with hormone injections if identified early enough in the teenager, but it is difficult to diagnose - only about 40% of cases can currently be genetically diagnosed. Accordingly, doctors often will not know whether a teenage child is going to start puberty late or not at all. We have not only found a new gene to screen for, but also demonstrated a method that can be used to reliably identify many more genes in the future. This approach is now being applied more widely by us and others to identify the underlying genetic defects in patients with fertility disorders but without a molecular diagnosis. We have also identified a genetic cause of delayed puberty that will spontaneously resolve. This type of work will help to genetically distinguish patients with genetically determined, but self-limited delayed puberty, who do not require treatment, from patients with Kallmann Syndrome/hypogonadic hyogonadism, who require treatment.
Sectors Education,Healthcare

 
Description A manuscript published in 2015 with a press release was featured on several public websites for lay audience, as it describes a new gene and mechanism that gives rise to infertility. A follow-on collaborative publication in prepared to describe the genetic basis of familial delayed puberty.
First Year Of Impact 2015
Sector Education
Impact Types Societal

 
Description Collaboration with ICH 
Organisation University College London
Department Institute of Child Health
Country United Kingdom 
Sector Academic/University 
PI Contribution Define the impact of mutations observed in patients with Kallmann Syndrome on nervous system development through cell and animal models
Collaborator Contribution Collect DNA from patients with Kallmann Syndrome and their families for exome sequencing to identify candidate genes for further investigation through cell and animal models
Impact A paper was published. The postdoc has presented this work at conferences, the PI has presented the work in research seminars at other organisations. The work has received awards. The work was publicised through news digests for lay audiences.
Start Year 2013
 
Description Collaboration with Marseille 
Organisation Aix-Marseille University
Country France 
Sector Academic/University 
PI Contribution We have established a collaboration with Prof F Mann Marseille, France, on the role of SEMA3E in GnRH neuron development. My team has developed the ideas and contributed the bulk of the materials and data and prepared a joint manuscript which was published.
Collaborator Contribution Our collaborators have provided samples and ideas. They have commented on the manuscript.
Impact A paper was published. The postdoc has presented this work at conferences, the PI has presented the work in research seminars at other organisations. The work has received awards. The work was publicised through news digests for lay audiences.
Start Year 2013
 
Description Collaboration with Milan 
Organisation University of Milan
Country Italy 
Sector Academic/University 
PI Contribution Provision of tissue samples to generate research data
Collaborator Contribution 2 months work by MSc student in my lab to process tissue samples and generate data, funded by a COST action for endocrinology.
Impact Manuscript in preparation Award of MSc degree to student who included research data in their thesis
Start Year 2013
 
Description Collaboration with QMUL 
Organisation Queen Mary University of London
Department Barts and The London School of Medicine and Dentistry
Country United Kingdom 
Sector Academic/University 
PI Contribution We provide mouse models to study disease mechanisms for patients with delayed puberty.
Collaborator Contribution Our collaborators identify candidate genes that may cause nervous system defects in patients with delayed puberty.
Impact Manuscript in preparation
Start Year 2016
 
Description press releases and blogs on Kallmann Syndrome causes 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact press releases and communication with lay audiences interested new scientific advances relevant to human health
Year(s) Of Engagement Activity 2015