You are here

Pluripotent Stem Cells

Comment

Discuss

mESC Showdown: 2i vs. Serum - “The Transcriptional and Epigenomic Foundations of Ground State Pluripotency”

Embryonic stem cells (ESCs) maintained in serum are often morphologically heterogeneous and also express pluripotency associated transcription factors in a heterogeneous manner (Toyooka et al) perhaps suggesting that the pluripotent state in unstable. However, the derivation and maintenance of mESCs in serum-free conditions through the use of two small molecule kinase (Mek and GSK3) inhibitors (“2i” - PD0325901 and CHIR99021) which shield pluripotent cells from differentiation triggers (Ying et al) and eliminates mosaic transcription factor expression (Wray et al), has enabled derivation of germline-competent ESCs from all mouse strains tested and for the first time from rats (Hanna et al, and Nichols et al). 2i conditions are suggested to mimic the environment in the mature mouse inner cell mass (ICM) thereby allowing ESCs to enter a “naïve” ground state (Guo et al). Now, researchers from the laboratories of From the labs of Austin Smith and Hendrik G. Stunnenberg have applied genome wide transcriptional and epigenomic analysis to serum-maintained ESCs and 2i-maintained “naïve” ESCs and have uncovered some interesting  differences between ESCs in the two growth conditions (Marks et al).

Helpful “Stroke” by iPSCs - “Human-iPSCs form Functional Neurons and Improve Recovery After Grafting in Stroke-Damaged Brain”

 

Ischemic stroke is the rapid loss of brain function due to disturbance in the blood supply to the brain leading to a loss of function in the affected area.   Studies in rodents have shown that embryonic stem cell (ESC) -derived neural stem cells (NSCs) (Daddi et al, Hicks et aland Ramos-Cabrer et al) and human foetal NSCs (Darsalia et al 2007, Darsalia et al 2011 and Kelly et al)can differentiate into neurons leading to some improvement in impaired function in stroke following transplantation into the affected area, however this has not been attempted with cells derived from human induced pluripotent stem cells (hiPSCs).   Now, in a report in Stem Cells, researchers from the group of Zaal Kokaia at the Lund Stem Cell Center, Sweden have transplanted long-term self-renewing neuroepithelial-like stem cells, generated from adult human fibroblast-derived iPSCs (hiPS-It-NES), into the stroke-damaged mouse and rat striatum or cortex and show evidence that this is a safe and efficient approach to promote recovery after stroke and can be used to supply the injured brain with new neurons for replacement (Oki, Tatarishvili, Wood,Koch et al).

Same Network Different Outcomes - Distinct Lineage Specification Roles for NANOG, OCT4, and SOX2 in hESCs

 

NANOG, OCT4 and SOX2 are often given the grand title of master regulators of pluripotency, being tightly associated with human embryonic stem cell (hESC) identity and acting as some of the key reprogramming factors used in common protocols for the production of induced pluripotent stem cells (iPSCs).   Studies in mouse ESCs (mESCs) have shown that the loss of each of these genes generally leads to differentiation towards specific lineages; however in hESCs the findings have been more confusing, suggesting that an all-encompassing mechanistic overview of NANOG, OCT4 and SOX2 function in humans is required.   This has now been completed by the researchers from the group of Natalia Ivanova at the Yale Stem Cell Center, Yale University, USA, and by using specific knockdowns (KD) and overexpressions (OE) they identify general and cell-line specific requirements for NANOG, OCT4, and SOX2 in hESCs which suggests that, rather than being pan-repressors, each factor represses a specific cell fate (Wang et al).

Using iPSC Technology for Clinically Relevant Progenitors

 

Two recent articles in Cell Stem Cell have highlighted a growing trend in induced pluripotent stem cell (iPSC) biology; direct reprogramming of somatic cells to tissue stem cells such as the direct reprogramming of fibroblasts into induced neural stem cells (iNSCs).   Building on work from Sheng Ding and Marius Wernig, who first reprogrammed neural progenitors from fibroblasts (Kim et al and Lujan et al), the reports discussed herein from Frank Edenhofer and Hans R. Schöler now show the efficient derivation of iNSCs with extensive proliferative potential, a facet lacking from earlier reports, alongside neural morphology, expression profile, self-renewing capacity, epigenetic status and differentiation potential, as well as in vitro and in vivo functionality.

Prolonged Maturation Culture Favors a Reduction in the Tumorigenicity and the Dopaminergic Function of hESC-Derived Neural Cells in a Primate Model of Parkinson’s Disease

 

Other than purity and optimal functionality, one of the main concerns with the transplantation of embryonic stem cell (ESC)- or induced pluripotent stem cell (iPSC)-derived cells is their potential tumourigenicity in vivo. To address this, researchers from the group of Jun Takahashi from Kyoto University, Japan studied the effect of transplantation of neural progenitor cells (NPCs) derived from human ESCs (hESCs) into mouse brain and then into the brain of primate models of Parkinson’s disease. Interestingly, their findings conclude that prolonged in vitro culture of NPCs significantly reduces the risk of tumourigenesis, and that dopaminergic (DA) neurons derived from transplanted cells can lead to behavioural improvements (Doi and Morizane et al).

Tumor Tropism of Intravenously Injected Human iPSC-derived NSCs and their Gene Therapy Application in a Metastatic Breast Cancer Model

 

Neural stem cell (NSC)-based cancer therapeutics show great potential as while they display an inherent tropism for sites of brain injury they also effectively target sites of tumourigenesis through as yet unappreciated mechanisms (Aboody et al 2000 and Aboody et al 2008). For this reason NSCs could be utilised in gene therapy strategies against various types of tumours. To avoid an immune-response from the patient it is also desirable for NSCs to be matched to each patient, a strategy which may be completed through the use of induced pluripotent stem cells (iPSCs) and their subsequent differentiation to NSCs. These ideas prompted the study by researchers from the laboratory of Shu Wang at the University of Singapore in which they demonstrate that tumor-tropic iPSC-derived NSCs can be used to attenuate tumor growth in both immunodeficient and immunocompetent mice (Yang and Lam et al)

DOT-ty about Reprogramming - Chromatin-modifying enzymes as modulators of reprogramming

From Nature 
By Stuart P. Atkinson

Cellular reprogramming through the forced expression of specific transcription factors in somatic cells to produce induced pluripotent stem cells (iPSCs) has been long understood to involve a genome wide change in the chromatin environment from a largely repressive environment, non-conducive to wide-spread gene expression to a largely permissive environment that permits the expression of genes required for pluripotency and any potential lineage choice during differentiation. However, the chromatin modifying factors that are important to the reprogramming process are largely unknown, even though several proteins are known to regulate chromatin marks associated with the distinct epigenetic states of cells before and after reprogramming (Hawkins et al and Mikkelsen et al). Now, using short hairpin RNAs (shRNAs) to target genes important to DNA and histone methylation pathways, researchers from the laboratory of George Q. Daley have identified the histone H3 lysine 79 methyltransferase DOT1L as an important chromatin modifying factor in the reprogramming process (Onder et al).

CD49f enhances multipotency and maintains stemness through the direct regulation of OCT4 and SOX2

From Stem Cells 
By Stuart P. Atkinson

Heterogeneity of stem cells and their progeny has been rightly identified as being a major problem in taking stem cell therapies toward the clinic. Many important studies have attempted to address this problem with the ultimate aim of devising strategies to segregate interesting or potentially useful cell types. A example of this was a recent report on the StemCellsPortal, which described a study in which researchers have started to identify cohorts of cell surface markers for mouse stem cells and embryo’s which may ultimately allow high purity cell sorting (Rugg-Gunn, Cox and Lanner et al). Towards this goal in human stem cells, researchers from the group of Kyung-Sun Kang, while working of cultivation techniques for human mesenchymal stem cells (hMSC) which allow better proliferation and higher osteogenic and adipogenic capabilities, discovered the cell surface marker CD49f to be an important mediator of stemness through PI3K/AKT/p53 activity and went on to show a further role for CD49f in pluripotency of human ESCs (hESCs) through direct regulation of OCT4 and SOX2 (Yu and Yang et al).

Too Hot for FGF? – Thermal Stability of FGF Protein is a Determinant Factor in Regulating Self-Renewal, Differentiation and Reprogramming in Human Pluripotent Stem Cells

From Stem Cells
By Stuart P. Atkinson

Amongst the factors that are know to maintain pluripotent cell types, factors in the FGF pathway are perhaps the most important, as they have been implicated in cell survival, proliferation, pluripotency, and lineage determination during differentiation (Eisellova et al, Lanner and Rossant, Levenstein et al, Vallier et al and Xu et al). FGF2 is most commonly used to maintain self-renewal and pluripotency of human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) (Akopian et al). However, there are several unknowns, such as the mechanisms behind FGF2 function and why high concentrations of FGF2 are required, questions which have been addressed in a study from the laboratory of James A. Thomson at the University of Wisconsin, USA (Chen and Gulbranson et al (2012)).

BMP-ing Up Endoderm Efficiency – Activin and BMP4 Synergistically Promote Formation of Definitive Endoderm in hESCs

From Stem Cells
By Stuart P. Atkinson

Protocols for the production of hepatocytes and insulin-secreting pancreatic beta cells from human embryonic stem cells (hESCs) for treatment of disease and injury, begins with the production of definitive endoderm (DE), but while factors such as Activin A, which activates SMAD2/3, FGF, WNT and BMP (Arnold and Robertson, and Tam and Loebel) are thought to be important for DE differentiation, further differentiation of these cells into pancreatic progenitors, for example, is not efficient. This suggested to the group of N. Ray Dunn at A*STAR, Singapore, that if initial DE differentiation protocols could be made more efficient, this could allow for subsequent high efficiency differentiation of DE-derivatives (Teo and Ali et al).

Pages

Subscribe to RSS - Pluripotent Stem Cells