Group leader: 

Ian Chambers

Position: 

Professor of Pluripotent Stem Cell Biology; Theme leader Pluripotency and iPS

Contact: 

ichambers [at] ed [dot] ac [dot] uk

Aims
We study pluripotent Embryonic Stem (ES) cells. Our goal is to define the mechanisms by which key regulatory molecules direct ES cell self-renewal and differentiation, with our principal focus on self-renewal. To achieve this it is important to (i) identify the molecules that direct self-renewal, (ii) determine the biological function of these molecules and (iii) define how these molecules interact at an atomic level to fulfil their function.

Background
Embryonic stem (ES) cells possess the paradoxical capabilities for both self-renewal and differentiation into derivative cells of all three primary germ layers. Indeed it is the simultaneous possession of these two properties that defines ES cells and makes them useful.

We cloned the pluripotent cell specific transcription factor Nanog using a genetic screen for enhanced self-renewal.  As Nanog allows ES cells to self-renew under conditions in which they would normally differentiate, we named it after Tir nan Og, the mythological Celtic land of the ever-young.

We have found that undifferentiated ES cells are not all the same. Indeed undifferentiated ES cells fluctuate between status of high Nanog expression, associated with a high probability of self-renewal, and low Nanog, associated with a pre-disposition towards differentiation. Therefore loss of Nanog can be dissociated from commitment to differentiation. Rather than being essential for ES cell self-renewal, Nanog acts like a dimmer switch to modulate ES cell self-renewal efficiency (see Figure above).

Although Nanog -/- ES cells maintain somatic pluripotency, in the absence of Nanog primordial germ cell development fails between E11.5 and E12.5, around the time of epigenetic reprogramming. In collaboration with Phil Avner's lab at the Institut Pasteur, Paris, we have found that the most dramatic epigenetic function that occurs in mammalian development, the activation of the silent X-chromosome, is dictated through binding of Nanog, Oct4 and Sox2 to the gene encoding the cis acting mediator of X-inactivation, Xist.

To understand how Nanog works, it is essential to determine how it interacts with its partner proteins, including itself. We have shown that Nanog exists in equilibrium between monomeric and dimeric forms (K_d of 3 µM). The dimerisation region is a sequence in which every fifth amino acid is tryptophan, and is essential for Nanog to confer cytokine independent self-renewal.

To identify partner proteins important in mediating Nanog function, we have collaborated with Raymond Poot's lab at Erasmus Medical Center, Rotterdam, to develop an affinity purification protocol coupled to mass spectrometric identification of proteins. We have used this approach re-iteratively to identify an extended network of interacting proteins centred on Oct4.

Approaches and progress
We are currently investigating the differences between ES cells that do or do not express Nanog and are particularly interested in the mechanisms by which cells switch between the two states. In addition, we are investigating the molecular relationship between ES cells and the developmentally more advanced pluripotent cells of the post implantation embryo and their in vitro derivatives, epiblast stem cells (EpiSCs).

Do you want to join our group?
We always welcome speculative approaches from people with a genuine interest in the fundamental controls of pluripotent stem cell function. Please address informal enquiries to ichambers [at] ed [dot] ac [dot] uk.

Selected publications

Research papers

• Festuccia N and Chambers I. 2011. Quantification of pluripotency factor levels in embryonic stem cells by flow cytometry. Curr. Protoc. Stem Cell Biol. 19:1B.9.1-1B.9.13.
• Navarro P, Oldfield A, Legoupi J, Festuccia N, Dubois A, Attia M, Schoorlemmer J, Rougeulle C, Chambers I and Avner P. Molecular coupling of Tsix regulation and pluripotency. Nature 468:457–460. doi:10.1038/nature09496.
• Van den Berg DL, Snoek T, Mullin NP, Yates A, Bezstarosti K, Demmers J, Chambers I, Poot RA. 2010. An Oct4-centered protein interaction network in embryonic stem cells. Cell Stem Cell 6: 369-381.
• Silva J, Nichols J, Theunissen TW, Guo G, Van Oosten AL, Barrandon O, Wray J, Yamanaka S, Chambers I, Smith A. 2009. Nanog is the gateway to the pluripotent ground state. Cell 138:722-737.
• Navarro P, Chambers I, Karwacki-Neisius V, Chureau C, Morey C, Rougelle C, Avner P. 2008. Direct molecular coupling of Xist regulation and pluripotency. Science 321:1693-1695. Press release.
• Mullin NP, Yates A, Rowe A, Nijmeijer B, Barlow PN, Walkinshaw MD, Chambers I. 2008. The pluripotency rheostat Nanog functions as a dimer. Biochem J 411:227-231.
• Chambers I, Silva J, Colby D, Nichols J, Robertson M, Nijmeijer B, Vrana J, Jones K, Grotewold L, Smith A. 2007. Nanog safeguards pluripotency and mediates germ cell development. Nature 450:1230-1234.
• Chambers I, Colby D, Robertson M, Nichols J, Lee S, Tweedie S and Smith AG. 2003. Functional expression cloning of Nanog, a pluripotency sustaining factor in mouse embryonic stem cells. Cell 113:643-655.

Reviews

• Chambers I and Tomlinson S. 2009. The transcriptional foundation of pluripotency. Development 136:2311-2322.
• Chambers I and Smith A. 2004. Self-renewal of teratocarcinoma and embryonic stem cells. Oncogene 23(43):7150-7160.

Book chapters

• Mullin N and Chambers I. 2011. The function of Nanog in pluripotency. In 'Nuclear Reprogramming and Stem Cells' editors Ainscough J, Yamanaka S and Tada T. Humana Press, USA. In press.

Funding
Medical Research Council
The Wellcome Trust
Human Frontier Science Program (HFSP)
EuroSyStem
Scottish Funding Council