Group leader: 

Josh Brickman

Contact: 

josh [dot] brickman [at] ed [dot] ac [dot] uk

Aims
Mesendoderm is an embryonic tissue that both patterns the anterior-posterior neural axis and gives rise to organs such as the liver and pancreas. Our goal is to understand the mechanism by which sequence specific DNA binding proteins guide early embryo and embryonic stem cell differentiation into mesendoderm. We are particular interested in the developmentally important and relatively non-specific homeodomain transcription factors and the mechanism by which they can induce highly specific responses in both mesendoderm patterning and induction. We seek to understand the mechanism by which these proteins influence the output of specific signalling events to guide key cell fate decisions both in vivo and in vitro.

Background
During gastrulation a series of cell movements and inductive interactions generate the foundation of the vertebrate body plan and define the three germ layers: endoderm, mesoderm and ectoderm. One of the earliest events in gastrulation is the formation of an embryonic signaling centre known as the organizer (mesendoderm). As the induction of mesendoderm is one of the earliest events in gastrulation, elucidation of the transcriptional regulatory cascades involved in specification of mesendoderm can also be modeled in vitro, using ES cell differentiation. Descendents of progenitor cells in the mesendoderm give rise to a number of endodermal organs and the characterization of these cell types is therefore of considerable interest for regenerative medicine.

We have focused on the role of two classes of homeodomain proteins and their interaction with the core signaling pathways implicated in mesendoderm induction: canonical Wnt signaling and Nodal class TGF's. The homeodomain transcription factors include Hex and members of the Class V POU domain proteins (e.g. Oct4, an important regulator of ES cell self renewal and pluripotency). Hex is an early marker of anterior identity and is expressed in some of the earliest forming anterior mesendoderm, while Oct4 is down regulated as mesendoderm is induced. We have evidence that both these proteins regulate germ layer specification through interactions with Nodal class TGF's and canonical Wnts.

Our work on the Class V POU domain proteins has also lead to the discovery of a conserved role for these proteins in suppressing embryonic differentiation in vertebrate gastrulation. We believe that this ancient function for these proteins in suppressing embryonic progenitor cell commitment is the reason that Oct4 is such an important regulator of ES cell self-renewal.

Approaches and progress
We use a combination of ES cells, mouse and Xenopus embryos to examine the role of these transcription factors in early cell fate determination and commitment within the mesendoderm. We combine the study of purified populations of differentiating ES cells with biochemistry and Developmental Biology. We have a number of reporter lines that give a fluorescent read out of mesendoderm induction in vitro and are using these lines alongside high throughput screening technologies to identify key regulators of mesendoderm induction, commitment, and patterning. These technologies include gene trapping, transcriptional profiling and the construction of quantum dot encoded libraries coupled to microspheres.

A schematic illustration of insertional mutagenesis with one of our gene trap vectors. The vector integrates into intronic DNA and splices reporters/selection cassettes onto endogenous exons.

Selected publications

• Canham MA, Sharov AA, Ko MSH, Brickman JM. 2010. Functional heterogeneity of embryonic stem cells revealed through translational amplification of an early endodermal transcript. PLoS Biology. doi:10.1371/journal.pbio.1000379. Press Release.
• Morrison GM, Oikonomopoulou I, Migueles RP, Soneji S, Livigni A, Enver T, Brickman JM. 2008. Anterior definitive endoderm from ESCs reveals a role for FGF signaling. Cell Stem Cell 3(4):402-415.
• Buscarlet M, Perin A, Laing A, Brickman JM, Stifani S. 2008. Inhibition of cortical neuron differentiation by Groucho/TLE1 requires interaction with WRPW, but not Eh1, repressor peptides. Journal of Biological Chemistry 283:24881-24888.
• Tsakiridis A, Tzouanacou E, Larralde O, Watts TM, Wilson V, Forrester L, Brickman JM. 2007. Technology Report: A novel triple fusion reporter system for use in gene trap mutagenesis. Genesis 45:353-60.
• Zamparini AL, Watts T, Gardner CE, Tomlinson SR, Johnston GI, Brickman JM. 2006. Hex acts with beta-catenin to Regulate Anterior-Posterior Patterning via a Groucho-related co-repressor andNodal. Development 133(18):3709-3722. Press release; Going backstage.
• Morrison G and Brickman JM. 2006. Conserved Roles for Oct4 Homologues in Maintaining Multipotency during Early Vertebrate Development. Development 133(17):2011-2022. Press release; Going backstage.
• Carvalho LR, Woods KS, Mendonca BB, Marcal N, Zamparini AL, Stifani S, Brickman JM, Arnhold IJ, Dattani MT. 2003. A homozygous mutation in HESX1 is associated with evolving hypopituitarism due to impaired repressor-corepressor interaction. J Clin Invest 112(8):1192-1201.
• Roberts C, Sutherland HF, Farmer H, Kimber W, Halford S, Carey A, Brickman JA, Wynshaw-Boris A, Scambler PJ. 2002. Targeted mutagenesis of the Hira gene results in gastrulation defects and patterning abnormalities of mesoendodermal derivatives prior to early embryonic lethality. Mol Cell Biol 22(7):2318-2328.
• Brickman JM and Burdon TG. 2002. Pluripotency and tumorigenicity. Nature Genetics 32(4):557 -558.
• Brickman JM, Jones CM, Clements M, Smith JC, Beddington RSP. 2000. Hex is a transcriptional repressor that contributes to anterior identity and suppresses Spemann organiser function. Development 127(11):2303-2315.

Funding
Biotechnology and Biological Sciences Research Council (BBSRC)
The Wellcome Trust
Juvenile Diabetes Research Fund (JDRF)