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Understanding Mammalian Cellular Diversity


Comprehending how mammalian cells with apparently identical genetic background acquire their extraordinarily specific, stable and yet extremely diverse phenotypes poses one of the most daunting challenges of modern biomedical research. Until the molecular principles that govern branching and maintenance of the basic cellular lineages in the embryo and in the mature organism become clear, it will not be possible to fully address persistent questions in developmental biology, regenerative medicine, cancer biology, and the pathophysiology of degenerative diseases.
 
Embryonic stem (ES) and ES-like cells (induced pluripotent stem cells, iPS) afford ideal model systems for unraveling the complex molecular networks that give rise to cellular identity. They are relatively easy to generate and maintain in culture and are amenable to manipulation with the growing repertoire of molecular research tools now in the hands of cell biologists. More importantly, they have the property of pluripotency, meaning that they can differentiate to many cell types in the body, even to germ cells. Several groups believe that a small core set of regulatory factors, including Pou5f1 (encoding the Oct4 protein), Sox2 and Nanog, maintain ES cells in the pluripotent state by acting on a limited number of target genes. This fundamental concept has generated enormous excitement in the biomedical community, leading to successful reprogramming of somatic cells to an ES-like state. Yet, recent discoveries in our laboratory suggest that the complement of factors needed to direct ES cell pluripotency is considerably larger than originally thought.
 
We plan to generate a comprehensive list of pluripotency factors that would serve as foundation for identifying alternative networks of key factors involved in the maintenance of pluripotency. This quest will include candidate proteins we have already identified (e.g., Ronin) as well as others known to be associated with stem cell self-renewal and differentiation function. The most obvious question raised by the discovery of novel pluripotency factors is whether they could be used, either alone or in combination to reprogram somatic cells to an ES cell-like state (iPS cells). Such studies are under way in our lab, and early indications are that such manipulation is not only feasible, but will add significantly to the body of knowledge on stem cell regulation. Most exciting, perhaps, is the possibility that some of these factors are not specific for a particular cellular state but rather open up the epigenome to other factors that can effectively change the epigenetic landscape towards a different cell type. Thus, cellular reprogramming may not be limited to iPS cells but may also allow differentiation from one somatic cell type to another assuming that the appropriate core set of regulation genes is found. In this way, our laboratory hopes to make important new advances towards a greater understanding of pluripotency and its use in medical and nonmedical settings.

Projects



  • Where do embryonic stem cells come from?  
  • Which mechanisms are involved in maintaining embryonic stem cell identity?  
  • How are caspases regulating pluripotency and differentiation of embryonic stem cells?  
  • Which non-canonical transcription factors are regulating emryonic stem cell identity and how?  
  • Which role does Ronin play in maintaining embyronic stem cell pluripotency?  
  • How do the findings in embryonic stem cells translate to other stem cell systems?  

Collaborations

  • Young Lab, Whitehead Research Institute for Biomedical Reserach, MIT, Boston, MA  
  • Jaenisch Lab, Whitehead Research Institute for Biomedical Reserach, MIT, Boston, MA  
  • Surani Lab, Gudon Institute, Cambridge, UK  
  • Barton Lab, University of Texas, M.D. Anderson Cancer Center, Houston, TX  
  • Behringer Lab, Univeristy of Texas, M.D. Anderson Cancer Center, Houston, TX  
  • Kyba Lab, University of Minnesota, Twin Cities, MN  

Featured Literature
Thomson - Science - 1998 - Click for abstract
   
Embryonic stem cell lines derived from human blastocysts. 
Thomson JA, Itskovitz-Eldor J, Shapiro SS, Waknitz MA, Swiergiel JJ, Marshall VS, Jones JM. 
Science. 1998 Nov 6;282(5391):1145-7. Erratum in: Science 1998 Dec 4;282(5395):1827. 
PMID: 9804556
Abstract
Human blastocyst-derived, pluripotent cell lines are described that have normal karyotypes, express high levels of telomerase activity, and express cell surface markers that characterize primate embryonic stem cells but do not characterize other early lineages. After undifferentiated proliferation in vitro for 4 to 5 months, these cells still maintained the developmental potential to form trophoblast and derivatives of all three embryonic germ layers, including gut epithelium (endoderm); cartilage, bone, smooth muscle, and striated muscle (mesoderm); and neural epithelium, embryonic ganglia, and stratified squamous epithelium (ectoderm). These cell lines should be useful in human developmental biology, drug discovery, and transplantation medicine.
Comment in
Publishing controversial research. [Science. 1998]
A versatile cell line raises scientific hopes, legal questions. [Science. 1998]
New potential for human embryonic stem cells. [Science. 1998]

​Manuscript

Takahashi - Cell - 2006 - Click for abstract
   
Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. 
Takahashi K, Yamanaka S. 
Cell. 2006 Aug 25;126(4):663-76. Epub 2006 Aug 10. 
PMID: 16904174
Abstract
Differentiated cells can be reprogrammed to an embryonic-like state by transfer of nuclear contents into oocytes or by fusion with embryonic stem (ES) cells. Little is known about factors that induce this reprogramming. Here, we demonstrate induction of pluripotent stem cells from mouse embryonic or adult fibroblasts by introducing four factors, Oct3/4, Sox2, c-Myc, and Klf4, under ES cell culture conditions. Unexpectedly, Nanog was dispensable. These cells, which we designated iPS (induced pluripotent stem) cells, exhibit the morphology and growth properties of ES cells and express ES cell marker genes. Subcutaneous transplantation of iPS cells into nude mice resulted in tumors containing a variety of tissues from all three germ layers. Following injection into blastocysts, iPS cells contributed to mouse embryonic development. These data demonstrate that pluripotent stem cells can be directly generated from fibroblast cultures by the addition of only a few defined factors.
Comment in
Achieving pluripotency. [Nat Rev Mol Cell Biol. 2010]
A transcriptional logic for nuclear reprogramming. [Cell. 2006]

​Manuscript

Dejosez - Annual Review of Biochemistry- 2012 - Click for abstract
   
Pluripotency and nuclear reprogramming. 
Dejosez M, Zwaka TP. 
Annu Rev Biochem. 2012;81:737-65. doi: 10.1146/annurev-biochem-052709-104948. Epub 2012 Mar 20. Review. 
PMID: 22443931
Abstract
Pluripotency is a "blank" cellular state characteristic of specific cells within the early embryo (e.g., epiblast cells) and of certain cells propagated in vitro (e.g., embryonic stem cells, ESCs). The terms pluripotent cell and stem cell are often used interchangeably to describe cells capable of differentiating into multiple cell types. In this review, we discuss the prevailing molecular and functional definitions of pluripotency and the working parameters employed to describe this state, both in the context of cells residing within the early embryo and cells propagated in vitro.

​Manuscript


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