Molecular Embryology
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The origin and developmental potential of Embryonic Stem Cells

James A. Thomson, et al (1998)

Embryonic Stem Cell Lines Derived from Human Blastocysts

Science (6), 282:1145-1147

Current iPS-based projects

Signalling in hESCs and hiPSCs

In hESCs (human embryonic stem cells) and hiPSCs (human induced pluripotent stem cells) the TGFß signaling pathway is crucial for maintaining self renewal and pluripotency (Babaie et al. 2007, Greber et al, 2007; Greber et al., 2008). Infact the TGFß/ACTIVIN/NODAL axis of the pathway needs to be activated via phosphorylation of SMAD2,3 and the BMP axis repressed via the non-phosphorylation of SMAD1,5,8 inorder to sustain self renewal and prevent differentiation- see figure below taken from Greber et al. 2007.

We have shown that the growth factor, FGF2 regulates the expression of key members of the TGFß pathway with ACTIVIN-A, TGFß1, GREM1, and BMP4 being the most likely candidates encoding the above activities (Greber et al. 2007). The genes GREM1, CER1 and GDF3 are expressed in undifferentiated hESCs and hiPSCs, and they encode proteins known to act as antagonist of BMP4 activity. Stimulation of hESCs or iPSCs with BMP2 or BMP4 induces differentiation to the trophoblast lineage.

(A) Phase contrast images of ESCs and fetal foreskin fibroblast-derived iPSCs showing similarities in cell morphologies. (B) The transcriptomes are 90% identical based on whole genome microarray-based gene expression analysis. (C) Transcription of self-renewal and pluripotency associated genes are activated upon cellular reprogramming. Prigione et al. 2010

The use of embryonic stem cells in cell replacement therapy remains problematic for a number of reasons, including ethical as well as host rejection of allogeneic cells. As a means of overcoming these problems, we are deriving iPSCs from healthy and diseased individuals (Type 1 diabetes, Alzheimer’s Nijmegen Breakage Syndrome and Steatosis) from dermal fibroblasts, mesenchymal stromal cells, chorionic villi and amniotic fluid cells employing retroviral-mediated transduction of OCT4, SOX2, KLF4 and C-MYC.

These iPS cells express telomerase activity, pluripotency-associated cell surface antigens and genes specific to human ES cells. Furthermore, they maintain the developmental potential to differentiate into advanced derivates of all three primary germ layers both in vivo and in vitro

Our research on aging is based firmly on the concept that the same signaling mechanisms that regulate the plasticity of stem cells are altered during aging and in age-related diseases. We also attempt to reverse the aging phenotype of somatic cells by cellular reprogramming to by-pass senescence. This approach enables the study of genome stability, mitochondria biogenesis and stem cell fate. Accordingly, an understanding of molecular and signaling mechanisms underlying the aging process is likely to lead to novel approaches to preventing and treating age-related diseases.

Systems biology of stem cell fate and cellular reprogramming

The maintenance of pluripotency and self-renewal of human ES and iPS cells are intrinsically complex processes driven by the co-ordinated dynamic expression of a plethora of genes, their encoded proteins and associated signalling pathways in response to external signaling cues such as FGF2. Our systems biology approach combines high throughput approaches (OCT4 ChIP-chip, ChIP-seq, RNAi, protein interaction networks, metabolomics and cytokine stimulations of hESCs) and advanced computational techniques to dissect the molecular mechanisms of stem cell fate and cellular reprogramming.

Network Reconstruction, analysis and network-based modeling of the human ES and iPS self-renewal Gene Regulatotry Network are carried out within the framework of the EU project “Experimental Network for Functional Integration” (ENFIN/FP6) Enabling Systems Biology.

An OCT4 gene regulatory network is illustrated below:

STRING network (v.8.0) based on only OCT4 /OTF3C (red) using high confidence, and network depth 2. Green line indicates links based on textmining, violet based on experiments.

(http://string.embl.de/)

Additionally, we have created the user-friendly database ESCDb integrating available genomics related datasets in both human and mouse ES and EC cells. In the current era of systems biology driven research, we envisage that our integrated embryonic stem cell database will prove beneficial to the booming field of ES, iPS and cancer research.

last updated: 25 January, 2010