Sex Chromosomes in Development and Disease

Lead Research Organisation: MRC National Inst for Medical Research

Abstract

Infertility is a common problem, affecting at least 15% of couples in the UK. It is thought that many cases of infertility are caused by errors in a stage of the development of sex cells (gametes) called meiosis. This is the stage during which chromosomes inherited from the mother and father physically pair and exchange genetic information. My lab has found that when chromosomes fail to pair, they are silenced, such that genes on those unpaired chromosomes cannot be expressed. The result is that gametes will be starved of important gene products, thereby causing cell death and ultimately infertility. We use mouse models to unravel the molecular players involved in this silencing pathway, and we are trying to rescue infertility in infertile mouse models by genetically ablating the silencing process. Other research in our lab aims to determine the role of the X chromosome in male infertility. We have found that a very large proportion of genes on the mouse X chromosome are expressed only in the male, during gamete development, and some of these are also present on the human X chromosome. We are using genetic approaches to prevent expression of each of these genes in male mice and we are looking for the effect that this will have on male gamete development. We are also investigating whether these genes are mutated in men with unexplained infertility. Over all, our research will provide much needed insight into the cause of infertility in humans.

Technical Summary

The over all research interest of my lab is human infertility. A critical stage in the development of germ cells is meiosis, when maternal and paternal chromosomes pair and exchange genetic material, and errors in either of these steps gives rise to germ cell arrest. We have discovered that unpaired meiotic chromosomes are silenced at the level of transcription by a mechanism called Meiotic Silencing of Unsynapsed Chromatin (MSUC). Our work aims to determine whether this mechanism is responsible for the infertility associated with common chromosome pairing abnormalities, including Turner syndrome (XO) and Double Y syndrome (XYY). In collaboration with other labs outside the NIMR (Allan Bradley, Sanger Centre, Eric Brown, University Pennsylvania), we generate mouse models of these and other chromosome abnormalities to study the molecular players involved in the MSUC pathway (which include the tumour suppressor BRCA1), and we are genetically manipulating MSUC to try and rescue infertility in these models. Much of our research involves studying genes expression at the chromosomal level by RNA fluorescence in-situ hybridisation (FISH), together with fluorescence microscopy. Other research in our lab aims to investigate what role the X chromosome plays in normal male fertility. Previous research has suggested that the mouse X chromosome is depleted of spermatogenesis genes; however we have discovered that approximately 18% of all X chromosomal genes show testis-specific expression, and these are likely to be involved specifically in the maturation of mature sperm; spermatozoa. We plan to look for orthologues of these genes on the human X chromosome, and we will then study whether any of these genes are mutated in cases of unexplained human male infertility. Unexpectedly, a large number of the X-linked male testis-expressed genes that we identified on the X chromosome also turn out to be cancer testis antigens (CTAs). These are genes that are normally expressed only in the testis but that are inappropriately activated in cancers. We aim to ablate the expression of these genes by RNA-interference in mice, in order to elucidate their precise roles in germ cell development, and this will provide valuable information when understanding tumour progression.

Publications

10 25 50
 
Description Member of NIMR Graduate Education and Advisory Committee
Geographic Reach National 
Policy Influence Type Membership of a guidance committee
Impact My role in the panel has been to aid in improving the PhD programme within NIMR.
 
Description Member of NIMR Internal Communications Committee
Geographic Reach National 
Policy Influence Type Membership of a guidance committee
Impact I have been extensively involved in improving the dissemination of research achievements within NIMR to both other labs both within and outside the institute.
 
Description Member of the Hinxton Steering Committee on Stem Cells, Ethics and Law
Geographic Reach National 
Policy Influence Type Membership of a guidance committee
Impact The Hinxton Group is an international consortium of scientists and bioethicists that met in 2008 in order to explore the ethical and policy challenges of transnational scientific collaboration raised by variations in national regulations governing embryo research and stem cell science. The guidelines resulting from this meeting were published in Science (vol 313, p921-2)
 
Description Clinician Fellowship
Amount £30,000 (GBP)
Organisation Academy of Medical Sciences (AMS) 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2011 
End 08/2013
 
Title Induced pluripotent stem cell technology 
Description My postdoc Mahesh Sangrithi and I set up the system for reprogramming fully differentiated cells from adult mice into pluripotent stem cells originally described by Yamanaka and colleagues. 
Type Of Material Technology assay or reagent 
Year Produced 2009 
Provided To Others? Yes  
Impact This technology will allow all other researchers within NIMR to use iPS cell technology and will allow us to pursue our studies of in vitro gametogenesis 
 
Title RNA FISH 
Description RNA FISH is an invaluable and powerful mechanism for studying gene expression in vivo. 
Type Of Material Data analysis technique 
Year Produced 2008 
Provided To Others? Yes  
Impact The establishment of this technique has been invaluable to our studies; we have used it in several important papers, including two in Nature Genetics (15580272 and 18454149) two in Current Biology (15589157 and 19716301) and one in Developmental Cell (16580996). We have also written a book chapter on this subject, and have disseminated reagents and advice to numerous groups inside and outside NIMR. 
 
Title Setting up of opossum colony 
Description I was the first to import and establish a colony of marsupials (opossums) at NIMR. These animals are a superb model organism for studying diverse processes such as neurogenesis, X chromosome inactivation, limb development, carcinogenesis, etc. 
Type Of Material Model of mechanisms or symptoms - mammalian in vivo 
Year Produced 2009 
Provided To Others? Yes  
Impact We maintain the only colony of opossums within Europe and are able to provide these to collaborators both within and outside NIMR. We have already used these animals in a key publication studying the evolution of X chromosome inactivation (19716301) 
 
Description Allan Bradley collaboration 
Organisation The Wellcome Trust Sanger Institute
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution We carried out extensive analysis on XYY mice showing that failure to inactivate the Y chromosome causes meiotic infertility
Collaborator Contribution Provided engineered BACs
Impact Publication in press: Evidence that Meiotic Sex Chromosome Inactivation Is Essential for Male Fertility (2010) Current Biology
Start Year 2007
 
Description Attila Toth collaboration 
Organisation University of Dresden
Country Germany 
Sector Academic/University 
PI Contribution Provision of ATR knockout material
Collaborator Contribution Analysis of phosphorylation of HORMAD, a protein implicated in meiotic checkpoint control.
Impact Study to be submitted to PLoS Genetics
Start Year 2010
 
Description Greg Elgar collaboration 
Organisation Medical Research Council (MRC)
Department MRC National Institute for Medical Research (NIMR)
Country United Kingdom 
Sector Public 
PI Contribution Provision of metatherian genome sequence
Collaborator Contribution Bioinformatic analysis tracing the evolution of an RNA involved in X chromosome inactivation
Impact Study ongoing
Start Year 2011
 
Description John McCarrey collaboration 
Organisation University of Texas at San Antonio
Department Department of Biology
Country United States 
Sector Academic/University 
PI Contribution We characterised X chromosome inactivation in the female marsupial using RNA FISH and epigenetic analyses; the results showed that key features of the X inactivation process appeared very early in evolution.
Collaborator Contribution They provided initial marsupial material for our studies of X chromosome inactivation prior to us setting up our own colony at NIMR
Impact 19716301
Start Year 2008
 
Description Michael Mitchell collaboration 
Organisation National Institute of Health and Medical Research (INSERM)
Department INSERM 910 (Structure and Activity of Normal and Pathologic Biomolecules)
Country France 
Sector Public 
PI Contribution We carried out extensive analysis on XYY mice showing that failure to inactivate the Y chromosome causes meiotic infertility
Collaborator Contribution The collaborator provided various BAC probes and performed BAC engineering
Impact Publication in press: Evidence that Meiotic Sex Chromosome Inactivation Is Essential for Male Fertility (2010) Current Biology
Start Year 2007
 
Description Mike Gilchrist collaboration 
Organisation Medical Research Council (MRC)
Department MRC National Institute for Medical Research (NIMR)
Country United Kingdom 
Sector Public 
PI Contribution Provision of RNA Seq data
Collaborator Contribution Analysis of RNA Seq data to identify genes implicated in infertility in Klinefelter syndrome
Impact Ongoing work
Start Year 2012
 
Description Paul Serhal collaboration 
Organisation University College London
Department Division of Medicine
Country United Kingdom 
Sector Academic/University 
PI Contribution Analysis of copy number variation in X multicopy genes in men with idiopathic infertility
Collaborator Contribution Provision of testis samples / DNA from infertile men
Impact Study just initiated
Start Year 2012
 
Description Scott Keeney collaboration 
Organisation Memorial Sloan Kettering Cancer Center
Country United States 
Sector Academic/University 
PI Contribution Provision of ATR knockout material
Collaborator Contribution Analysis of DNA double-strand break formation in ATR knockout mice
Impact Study ongoing
Start Year 2012
 
Description Victor Tybulewicz collaboration 
Organisation Medical Research Council (MRC)
Department MRC National Institute for Medical Research (NIMR)
Country United Kingdom 
Sector Public 
PI Contribution Analysis of the mechanisms underlying germ cell loss in aneuploid female mice
Collaborator Contribution Provision of aneuploid Down syndrome mouse model
Impact Paper in submission with Nature Cell Biology
Start Year 2009
 
Description Biological Services Seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Primary Audience Participants in your research and patient groups
Results and Impact I was asked to give a general talk on X chromosome inactivation pitched at a lay level.

I received very positive feedback from the audience and felt that the talk would help those looking after my animal colonies to have a greater insight into how and why the research is carried out
Year(s) Of Engagement Activity 2009
 
Description NIMR Teacher's Day 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Primary Audience Schools
Results and Impact The talk was on the biology of reproductive decline in older women and the increased incidence of aneuploidy in offspring from this age group. It required a recap on meiosis, the specialised cell division that gives rise to eggs and sperm, a topic that is taught in school. The talk was attended by around 80 teachers. There was a great deal of interest from a number of those attending.

Teacher's Day is an annual forum in which scientists provide local teachers with updates on latest developments in research

The talk initiated a number of contacts from teachers asking me for further information on the discussed topic.
Year(s) Of Engagement Activity 2011
 
Description School Open Day - NIMR 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Primary Audience Schools
Results and Impact I was part of a panel of scientists whose role was to answer questions on topical areas in biology, as well as in my area of research (germ cell development).

I and the rest of the panel managed to clarify many of the common misconceptions that young people had on aspects of stem cell and reproductive biology.
Year(s) Of Engagement Activity 2006