Reprogramming

Here human embryonic stem cell lines are derived by somatic cell nuclear transfer from cells of a newborn and from skin cells of an adult, a female with type 1 diabetes; the stem cells produced are pluripotent and can be differentiated into insulin-producing beta cells.

Generation of human induced pluripotent stem cells from patient fibroblasts containing ring chromosomes with large deletions reveals that reprogrammed cells lose the abnormal chromosome and duplicate the wild-type homologue through compensatory uniparental disomy, suggesting that cellular reprogramming may hold potential for ‘chromosome therapy’.

Short-term treatment with cytokines reprograms acinar cells into beta cells and restores durable normoglycemia in diabetic mice.

Two studies show direct conversion of mouse embryonic fibroblasts to oligodendrocyte progenitor cells capable of generating myelinating oligodendrocytes.

Two studies show direct conversion of mouse embryonic fibroblasts to oligodendrocyte progenitor cells capable of generating myelinating oligodendrocytes.

Differentiation of pluripotent cells into renal lineages has had limited success so far. Melissa Little and colleagues have used defined medium conditions that induce posterior primitive streak and intermediate mesoderm using growth factors used during normal embryogenesis. This results in the synchronous induction of both components of the kidney, the ureteric bud and metanephric mesenchyme, which form a self-organizing nephron structure in vitro.

Pei and colleagues show that introduction of the pluripotency reprogramming factors in sequence (Oct4–Klf4, c-Myc and finally Sox-2), rather than introducing them all together, increases reprogramming efficiency. This sequential delivery activates the epithelial-to-mesenchymal transition (EMT) before the mesenchymal-to-epithelial transition (MET), which was previously reported to occur during reprogramming. The authors also show that addition of EMT modulators influences reprogramming in a similar manner.

Differentiation of pluripotent cells into renal lineages has so far demonstrated limited success. Juan Carlos Ispizua Belmonte and colleagues have used defined medium conditions to obtain committed renal progenitor cells that are able to integrate into a ureteric bud in a three-dimensional culture system.

The mesendoderm is located in the embryonic primitive streak's anterior region, which is specified by the transcription factor FOXH1. Here, the authors show that human fibroblasts transit through a mesendoderm-like state during reprogramming into pluripotent cells, and that expression of FOXH1 enhances reprogramming efficiency.

The forkhead box transcription factor Foxo1 is required for the maintenance of pluripotency in human embryonic stem cells. Here Koga et al.show that expression of another forkhead box transcription factor, Foxd1, promotes and indicates successful reprogramming of mouse embryonic fibroblasts.

Piero Carninci and colleagues report the discovery of a large class of noncoding RNAs, non-annotated stem cell transcripts (NASTs), which are implicated in the regulation of stem cell properties. The authors identify 8,873 mouse and 3,042 human NASTs and functionally validate 4 as having an important role in the maintenance of pluripotency.

Guo-Liang Xu, Duanqing Pei and colleagues show that during induced pluripotent cell reprogramming Tet1 regulates 5-hydroxymethylcytosine levels at loci critical for mesenchymal-to-epithelial transition in a vitamin C–dependent fashion. They also show that Tet1 either enhances or inhibits somatic cell reprogramming, depending on the absence or presence of vitamin C, respectively.

Cardiomyocytes generated from induced pluripotent cells hold great promise for understanding and treating heart disease. William Pu and his colleagues apply new technologies for studying such cardiomyocytes from patients with Barth syndrome to explore how the mitochondrial defects characteristic of this syndrome lead to heart dysfunction.

In two new studies, Helen Blau and Bradley Olwin and their colleagues show that muscle stem cells in aged mice have an intrinsic defect in their stem cell capacity, contributing to age-related sarcopenia. They also provide mechanistic insight to explain this phenomenon and show that biochemical and biophysical manipulations can overcome the defect, suggesting a possible future route of therapy.

In two new studies, Helen Blau and Bradley Olwin and their colleagues show that muscle stem cells in aged mice have an intrinsic defect in their stem cell capacity, contributing to age-related sarcopenia. They also provide mechanistic insight to explain this phenomenon and show that biochemical and biophysical manipulations can overcome the defect, suggesting a possible future route of therapy.

This paper describes a method based on sib-selection to isolate rare human pluripotent stem cell clones with a precise engineered mutation.

Treatment with DMSO improves the differentiation of multiple human pluripotent stem cell lines into cells of all three germ layers.

Differences in substrate adhesion strength are exploited in a label-free approach to separate human pluripotent stem cells from other cell types. This approach can separate fully and partially reprogrammed human induced pluripotent stem cells.

The authors of this Protocol describe how to generate endothelial cells and pericytes and how to functionally evaluate the cells' ability to generate primary vascular plexus and incorporate it into the zebrafish vasculature.

Human endogenous retrovirus subfamily H (HERVH) is a class of transposable elements expressed preferentially in human embryonic stem cells (hESCs). A new study now shows that the long terminal repeats of HERVH function as enhancers and that HERVH is a nuclear long noncoding RNA required to maintain hESC identity.

Individual microRNAs (miRNAs) can target many mRNAs that form networks of presumably cooperating genes. A new study now tests this idea by screening miRNAs and their targets in the context of dedifferentiation, or reprogramming, of mouse fibroblasts to induced pluripotent stem cells. These data establish two networks of miRNA-mRNA interactions that act together to suppress early stages of reprogramming.

Naive pluripotent embryonic stem cells (ESCs) and embryonic germ cells (EGCs) have distinct developmental origins. Genome-wide expression and global DNA-methylation analyses now reveal that ESCs and ESGs are highly similar at the transcriptome level and, contrary to previous assumptions, are both characterized by DNA hypomethylation. Also, global methylation levels in both ESCs and EGCs are directly responsive to culture conditions.

The unique ability of human pluripotent stem cells to self-renew and to differentiate into cells of the three germ layers makes them an invaluable tool for the future of regenerative medicine and tumorigenic research. It was assumed that human induced pluripotent stem cells (HiPSCs) would behave like their embryonic counterparts in respect to their tumorigenicity, but a rapidly accumulating body of evidence suggests that there are important differences.

The use of multipotent stem cells to achieve regeneration in cardiovascular disease has been the subject of continuous evaluation over the past decade. Dr Behfar and colleagues review experience obtained from trials of 'first-generation' cell-based therapy, and discuss the advances that have enabled the development of 'next-generation' stem-cell-based therapies targeting cardiovascular disease.

Replacing the β-cell mass in individuals with diabetes mellitus could restore normal metabolic control, and might become a therapy choice for these patients. This Review summarizes the options for regenerative therapy in pancreatic disease with focus on diabetes mellitus.

The derivation of disease-relevant cell types from pluripotent stem cells holds much promise for disease therapy. The recent progress in directed differentiation and the challenges ahead are discussed in this Review.

Our understanding of the molecular steps that occur during reprogramming somatic cells to induced pluripotent stem cells has recently been improved through analyses of cell populations and single cells. Here the authors consider the phases of reprogramming, models for describing the process and the roles of reprogramming factors.

Pluripotent stem cell lines differ in their capacity to differentiate into desired cell typesin vitro. Genetic and epigenetic variations contribute to functional variability between cell lines and heterogeneity within single clones. Characterizing such variations is important for the use of pluripotent stem cells in disease modelling and developmental processes and for their applications in regenerative medicine.

During cell reprogramming and direct cell fate conversion, changes in somatic and pluripotent cell fates do not require the passage through a hierarchy of distinct cell fates that are proposed to occur during normal development and are consistent with the original Waddington model. Instead, a 'flat epigenetic disc' model might explain cell fate transitions during these processes.

Worldwide increases in life expectancy have been paralleled by a greater prevalence of chronic and age-associated disorders, particularly of the cardiovascular, neural and metabolic systems. Patient-specific induced pluripotent stem (iPS) cells are finding applications in disease modelling, drug testing and drug discovery, thus enabling researchers to undertake studies for treating diseases 'in a dish'.

Six scientists in the field of stem cell research comment on our basic understanding of stem cells and other pluripotent cells, on their potential therapeutic use and on key challenges that remain.

As the prevalence of chronic kidney disease increases, new strategies to reverse or prevent tissue damage are under investigation. Here, Rabelink and Little describe progenitor cell populations that may have a key role in tissue repair and regeneration in the kidney. They also discuss the potential to harness the innate regenerative capacity of the kidney in the context of ongoing studies of mesenchymal stromal cell therapy.