The cellular basis of FMRP function

Lead Research Organisation: University of Edinburgh
Department Name: Biomedical Sciences

Abstract

Fragile X syndrome is the most common form of mental retardation that can be inherited from ones? parents. It is caused by the absence of a single protein called the fragile X mental retardation protein or FMRP. As the same implies, the gene that makes FMRP is located on the X chromosome. Men have one copy of the X chromosome whereas women have two copies, each containing a copy of the FMRP gene. Interestingly, the two X-chromosomes in females do not express their genes equally; during early foetal development each cell makes a decision to inactivate one X-chromosome (in a process known as X-inactivation) apparently at random. In the case of females with FXS, if a cell inactivates the chromosome containing the normal gene, the cell will not make FMRP. Similarly, if the cell inactivates the X-chromosome containing the mutant FMR1 gene, the cell will make normal levels of FMRP. Because X-inactivation is random, the severity of neurological defects in females varies depending on the relative number of mutant and normal cells. In mice, we can exploit the fact that females have normal and abnormal cells to learn about how FMRP regulates brain development and whether or not the disease is treatable to certain types of drug treatments. For example the presence of cells with normal levels of FMRP may secrete some factors that rescue the cells that do not express FMRP. Women would only show symptoms if the proportion of normal cells is too low to effectively rescue the mutant cells. In this case identification of the factors by which rescue occurs would provide excellent prospective drug therapies for male and female FXS sufferers. Alternatively, the presence of normal cells may not be able to rescue the mutant cells because the mutant cells do not have the ability to respond to factors made by the normal cells. In this case, alternative forms of treatments that either directly alter the genetics of the mutant cells or that can bypass the normal role of FMRP would have to be pursued. All of the experiments will focus on neurons of the cerebral cortex and hippocampus, brain regions that mediate cognition and memory in mammals. These experiments will therefore guide future research into treatments of FXS. Furthermore, they will be the first experiments to directly examine the development of FXS in females.

Technical Summary

Fragile X syndrome (FXS) is the most common genetically inherited form of mental retardation. FXS results from the silencing of the fragile X mental retardation 1 gene (FMR1) and loss of the protein it encodes, FMRP. Humans and mice lacking FMRP show abnormalities in dendritic branching, spine density and morphology, and synaptic plasticity. Preliminary evidence from our laboratory has also revealed a defect in the differentiation of the primary somatosensory cortex of mice lacking FMRP. These developmental morphological and physiological changes are likely to underlie the cognitive deficits associated with FXS.

As its name implies, FXS is an X chromosome-linked disorder. Although females have two X-chromosomes, the process of X-chromosome inactivation results in one of these being silenced. The result is that females heterozygous for the mutant FMR1 allele are mosaics, with some cells expressing normal levels of FMRP (FMR1+), while others lack FMRP (FMR1-). By examining Fmr1- and Fmr1+ cells in Fmr1+/- mosaic female mice we will determine whether the mutant phenotypes that result from deletion of the Fmr1 gene result from cell autonomous or cell non-autonomous processes. This distinction will give important insight into the cellular processes regulated by FMRP and will have implications for treatments for the disease as has been shown for other X-linked dieases (Guy et al., 2007). Furthermore, this is will be the first study to fully characterize the developmental aetiology of mutant phenotypes in female mice lacking FMRP.

We will take advantage of the stereotypical progression of sensory map formation in primary somatosensory cortex to study early developmental processes. Since much work on the roles of FMRP have used hippocampus, we will also focus on the well-characterised CA3 to CA1 connection to examine juvenile neuronal development and plasticity. In both cases all analysis will be conducted at the level of individual neurons.
Specific Aim 1: To determine whether the Fmr1- and Fmr1+ cells contribute equally to the differentiation of the primary somatosensory cortex in Fmr1+/- female mice.
Specific Aim 2: To determine whether Fmr1- cells have defects in dendrite and spine development in cortical and hippocampal neurons of Fmr1+/- female mice.
Specific Aim 3: To determine whether synaptic plasticity in the hippocampus is altered in Fmr1- cells in Fmr1+/- female animals.

These studies will give valuable insight into the normal function of FMRP in developing neurons and will provide valuable information that will guide future research aimed at finding theapeutic agents to treat FXS.

Publications

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Barnes SA (2015) Convergence of Hippocampal Pathophysiology in Syngap+/- and Fmr1-/y Mice. in The Journal of neuroscience : the official journal of the Society for Neuroscience

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Crocker-Buque A (2015) Experience-Dependent, Layer-Specific Development of Divergent Thalamocortical Connectivity. in Cerebral cortex (New York, N.Y. : 1991)

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Kind PC (2013) The development and activity-dependent expression of aggrecan in the cat visual cortex. in Cerebral cortex (New York, N.Y. : 1991)

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McMahon AC (2012) SynGAP isoforms exert opposing effects on synaptic strength. in Nature communications

 
Description Autistica Fellowship
Amount £90,000 (GBP)
Organisation Autistica 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2012 
End 01/2016
 
Description MRC Project Grant
Amount £828,859 (GBP)
Funding ID MR/K014137/1 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 01/2013 
End 01/2016
 
Description MRC Project Grant
Amount £1,352,057 (GBP)
Funding ID MR/P006213/1 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 09/2016 
End 08/2020
 
Description Research Centre Grant
Amount रू 670,000,000 (INR)
Organisation Ministry of Science and Technology India 
Department Department of Biotechnology, India
Sector Public
Country India
Start 06/2014 
End 05/2019
 
Description Shirley Foundation Research Award
Amount £1,000,000 (GBP)
Organisation Shirley Foundation 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2012 
End 01/2015
 
Description Simons Initiative for the Developing Brain
Amount £20,000,000 (GBP)
Organisation Simons Foundation 
Department Simons Foundation Autism Research Initiative
Sector Charity/Non Profit
Country United States
Start 04/2017 
End 03/2022
 
Description Sir Henry Wellcome Postdoctoral Fellowship to Lynsey Meikle
Amount £250,000 (GBP)
Funding ID 089047/Z/09/Z 
Organisation Wellcome Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2009 
End 07/2013
 
Description Examining the alteration in synaptic structure in FXS 
Organisation University of Bordeaux
Department UMR 5297 (Institute for Interdisciplinary Neuroscience)
Country France 
Sector Academic/University 
PI Contribution My Postdoctoral Fellow visited Bordeaux to apply super-resolution microscopy to understand the cellular deficits associated with FXS.
Collaborator Contribution They are the experts in this form of microscopy.
Impact We have, for the first time, seen alterations in the morphological feature of dendritic spine neck width in FXS.
Start Year 2012
 
Description Pharmaceutical Strategies for FXS 
Organisation Seaside Therapeutics
Country United States 
Sector Private 
PI Contribution Part of a research team examining the ability of arbaclofen (STX-209) to reverse the cellular alterations in a mouse model of FXS.
Collaborator Contribution They also provided data and intellectual input to the project
Impact The data was published in a high profile paper in Science Translational Medicine.
Start Year 2011
 
Description Understanding the role of FMRP and TSC2 in Cortical Development 
Organisation Massachusetts Institute of Technology
Department Picower Centre MIT
Country United States 
Sector Academic/University 
PI Contribution The TSC project is part of an Lynsey Meikle's Sir Henry Wellcome fellowship. In term of the FXS project, the majority of the research as conducted in our laboratory under this grant. Our collaborators lab is testing whether the smaller than predicted increase in protein synthesis in Fmr1 ko mice results from an increase in protein degradation which will contribute one figure to a nine figure paper which we plan to submit soon.
Collaborator Contribution Lynsey Meikle spent a year at a laboratory at MIT learning in vivo record of visually-evoked potentials. She is now in the process of setting up this technology in Edinburgh. We also are collaborating with this lab and we expect that the data generated will be included in a manuscript on the role of FMRP in early synaptogenesis to be submitted for publication in the next few months.
Impact As noted above, we hope to have two joint manuscripts , on eon TSC and one on FMRP submitted in the coming months.
Start Year 2009
 
Description Annual Sandoz Lecture 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact I presented a poster at a public day.

The aim is to give the public a glimpse into the Psychiatric and Neurological research that takes place at the University of Edinburgh.
Year(s) Of Engagement Activity 2009
 
Description Attended a conference on "Ethics in Autism" 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Working scientist in the field of autism. Participated in informal discussion concerning therapeutic strategies and the ethical implications in treating autism.

Ongoing process and difficult to assess, but I continue to be invited to these events.
Year(s) Of Engagement Activity 2010
 
Description Edinburgh Neuroscience Christmas Lecture - 2017 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact This was the special invited Edinburgh Neuroscience Christmas Lecture for the public. The lecture was entitled "Understanding Disorders of the Developing Brain in the 21st Century". The event was sold out with around 200 individuals attending.The talk provided an update on the state of research within the field of autism.
Year(s) Of Engagement Activity 2017
URL https://www.edinburghneuroscience.ed.ac.uk/events/christmas-lecture-2017
 
Description Facility tour for the board members of Fragile X Society (UK) 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Primary Audience Participants in your research and patient groups
Results and Impact This has been an ongoing process of interaction between our newly formed Patrick Wild Centre for Research into Autism, Fragile X Syndrome and Intellectual Disabilities.

We are planning on conducting Phase 2b clinical trials with Novartis in the new year. These tours of our laboratories have been instrumental in building a relationship with the Fragile X Society, most of whom are parent of people with FXS.
Year(s) Of Engagement Activity 2009
 
Description Kili4-X thank you event 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact It was an evening to say thank you to a group of donors to Fragile X research at the University of Edinburgh. They sponsored a climb of Mount Kilimanjaro.

We are in the process of setting up a Centre for Childhood Cognitive Impairment that focuses on FXS and Autism. These activities are designed to raise its profile.
Year(s) Of Engagement Activity 2009
 
Description Kili4X conference open keynote talks from eminent Neuroscientists 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Primary Audience Participants in your research and patient groups
Results and Impact We held an international conference on Fragile X and related learning disabilities in August 2010. At the conference dinner and on the last day of the conference, parents of individuals with FXS and members of the Fragile X SOciety were invited to take part. Several pre-eminent researchers in the field from the University of Edinburgh, Rockefeller University and M.I.T, USA gave open lectures.

The feedback from the parents and the FX Society was very positive, which has strengthened the relationship of the FXS community and the Patrick Wild Centre.
Year(s) Of Engagement Activity 2010
 
Description Media inteviews 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact I have conducted interviews on radio (Five Live) and TV (STV), as well as for numerous newspapers including the Guardian, the Independent and the Times. Some of the interviews resulted from the Neuron paper (Harlow et al., 2010), but most were as a result of the opening of the Patrick Wild Centre, of which I am a Co-director, in November, 2010.

This is difficult to determine, but I hope it as increased the awareness of FXS and other forms of developmental neurological conditions as well as educating the public.
Year(s) Of Engagement Activity 2010
 
Description Visit from Meeting of the Minds 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Third sector organisations
Results and Impact Meeting of Minds is a parent led support group which gives parents and care givers of children with autism the opportunity to connect with key professionals in a relaxed and friendly environment. They support families in helping their children with additional/complex needs. They also provide the opportunity for parents to meet and support each other. The executive committee of the charity were invited to visit The Patrick Wild Centre in on 13th November 2017. They met with academics working in the field of autism and were given a tour of the research facilities.
Year(s) Of Engagement Activity 2017
URL https://www.facebook.com/Meeting-of-Minds-1609824922672530/