EDUCATION: 1989 Ph.D in Genetics and Development Columbia University, New York , 1980 B.Sc. Biology University of Patras Greece. POSITIONS: 2011-present Professor in Developmental Biology, Faculty of Medicine; 1995-2011 Group Leader MRC CSC Institute, Imperial College London; 1992-1994 Lecturer St. Mary’s Medical School, London. EXTERNAL APPOINTMENTS: 2006-2007 Director Alexander Fleming Institute, Athens Greece (Visiting); 2013 Visiting Professor, Columbia University, New York (Sabbatical)
The objective of my group is to identify specific genes and pathways that underlie major developmental events in mammalian embryonic patterning and neural development. Our studies focus on the Transforming Growth Factor (TGF) beta family and its two signalling branches Nodal and BMP which are transduced by Smad2/3 and Smad1/5/8 effectors respectively. Several members of the family have morphogen activity and exhibit different cellular responses depending on the intracellular levels of activated effector Smads.
It is unclear how cells assess intracellular levels of proteins, in this case activated Smad effectors, and how these select different target genes to activate depending on their concentration. We refer to this question as the “dose-dependent” cellular responses or the “dose-dependent” functions.
Specifically we study high Nodal signalling levels because these are required for the development of anterior structures, while lower levels are required for more posterior ones. Anterior tissues include the head and brain, craniofacial structures and the foregut along with its derivative organs, liver, pancreas and lung.
We address the dose-dependent responses/functions using as experimental systems: (a) Embryonic Stem Cells, in which we manipulate genes with CRISPR technology and then assay their differentiation capability towards anterior cell fates in vitro; and (b) Mice, in which we combine gene mutations in candidate factors and assay their effects on brain development in vivo.
This research places us at the forefront of developmental neurobiology, molecular cell biology and signalling, and it has relevance to regenerative medicine. We discovered a ubiquitin ligase that we named Arkadia (RNF111), which is responsible for establishing high Nodal signalling and thus it is essential for the development of all anterior tissues including head/brain in the embryo (Arkadia null mice are headless) Episkopou et al Nature 2001 & Niederlander et al Nature 2001. We also know in part the molecular mechanism of Arkadia’s function within the Nodal-Smad2/3 pathway (Mavrakis et al PLoS Biol 2007; Nagano et al JBC 2007 & Levy et al MCB 2007)and this is the key that would lead us in realising our objective to determine “how cells establish a high Nodal threshold”.
I am delighted to present the preprint of my paper with results that answer the above questions. Published in BioRxiv:
Arkadia degrades SNON to activate level-specific NODAL responses
However, we are still working on BMP-SMAD branch of the TGFbeta signalling pathway:
Furthermore, we study high BMP-Smad1/5/8 signalling (the other TGFbeta branch) because we discovered that it plays a role in motor neuron axon connectivity with specific muscles. It remains unknown how the billion of neurons in our nervous system make the precise connections required to function properly. However, our discovery implicates the BMP pathway in this process, specifically in this case for establishing the connections of motor neurons with muscles. For this research we have discovered another ubiquitin ligase RNF165 (Ark2), a close homologue of Arkadia, and have shown that it enhances BMP-Smad1/5/8 signalling within motor neurons. Loss of Ark2 causes loss of motor neuron innervation to a subset of muscles in the limb (Kelly et al PLoS Biol 2013). We use mainly mice and ESC to address this dose dependent function of BMP-Smads in motor neurons. Although we are studying only a small subset of neural connections, with the advantage that this is a tractable system, we expect that this will reveal general mechanisms and/or principles that apply throughout the nervous system.
SAMPLE OF EXPERIMENTATION
Motor neuron axons innervating the forelimb.
We also developed a technique to follow and quantitate BMP-Smad1/5/8 signaling in cells and tissues, Thymiakou and Episkopou, J. Vis. Exp. (49), 2011) (see video: http://www.jove.com/video/2631)
Dr Jonathon Carthy
Tia MacIntyre (student)
Christina Hiemeyer (student)
Europe: George Spyroulias School of Pharmacology Univ. of Patras, Greece (Structural biology NMR,); Ann Zwijsen VIB institute Leuven, Belgium
UK: Jackie De Belleroche, Tristan Rodriguez Imperial College London; Jesus Gil, MRC LMS; James Briscoe and Robin Lovell-Badge, The Francis Crick Institute, London.
et al., 2014, Coordination of progenitor specification and growth in mouse and chick spinal cord, Science, Vol:345, ISSN:0036-8075, Pages:1-11
et al., 2013, Interplay between Homeobox proteins and Polycomb repressive complexes in p16(INK4a) regulation, EMBO Journal, Vol:32, ISSN:0261-4189, Pages:982-995
et al., 2013, Rnf165/Ark2C enhances BMP-smad signaling to mediate motor axon extension, PLOS Biology, Vol:11, ISSN:1544-9173
et al., 2013, TGF-beta/Smad2/3 signaling directly regulates several miRNAs in mouse ES cells and early embryos, PLOS One, Vol:8, ISSN:1932-6203
et al., 2011, Enhancement of TGF-beta Signaling Responses by the E3 Ubiquitin Ligase Arkadia Provides Tumor Suppression in Colorectal Cancer, Cancer Research, Vol:71, ISSN:0008-5472, Pages:6438-6449
Thymiakou E, Episkopou V, 2011, Detection of Signaling Effector-Complexes Downstream of BMP4 Using in situ PLA, a Proximity Ligation Assay, Jove-journal of Visualized Experiments, ISSN:1940-087X
et al., 2009, Graded Smad2/3 activation is converted directly into levels of target gene expression in embryonic stem cells, PLOS One, Vol:4, ISSN:1932-6203, Pages:1-20
et al., 2007, Arkadia enhances nodal/TGF-beta signaling by coupling phospho-Smad2/3 activity and turnover, PLOS Biology, Vol:5, ISSN:1545-7885, Pages:586-603
et al., 2005, Neuronal migration and ventral subtype identity in the telencephalon depend on SOX1, PLOS Biology, Vol:3, ISSN:1544-9173, Pages:1111-1122
Episkopou V, 2005, SOX2 functions in adult neural stem cells, Trends in Neurosciences, Vol:28, ISSN:0166-2236, Pages:219-221
et al., 2003, SOX1-deficient mice suffer from epilepsy associated with abnormal ventral forebrain development and olfactory cortex hyperexcitability, Neuroscience, Vol:119, ISSN:0306-4522, Pages:421-432
et al., 2001, Induction of the mammalian node requires Arkadia function in the extraembryonic lineages, Nature, Vol:410, ISSN:0028-0836, Pages:825-830
et al., 2001, Arkadia enhances nodal-related signalling to induce mesendoderm, Nature, Vol:410, ISSN:0028-0836, Pages:830-834