A real-time pluripotency reporter for human stem cells

A real-time pluripotency reporter for the long-term and real-time monitoring of pluripotency changes in induced pluripotent stem cells

To master the technology of reprogramming mouse somatic cells to induced pluripotent stem cells (iPSCs), which will lay a good foundation for setting up a technology platform on reprogramming human cancer cells into iPSCs. Mouse iPSCs (i.e., Oct4-GFP miPSCs) was successfully generated from mouse embryonic fibroblasts (MEFs) harboring Oct4-EGFP transgene by introducing four factors, Oct4, Sox2, c-Myc and Klf4, under mESC (Murine embryonic stem cells) culture conditions. Oct4-GFP miPSCs were similar to mESCs in morphology, proliferation, mESC-specific surface antigens and gene expression. Additionally, Oct4-GFP miPSCs could be cultured in suspension to form embryoid bodies (EBs) and differentiate into cell types of the three germ layers in vitro. Moreover, Oct4-GFP miPSCs could develop to teratoma and chimera in vivo. Unlike cell cycle distribution of MEFs, Oct4-GFP miPSCs are similar to mESCs in the cell cycle structure which consists of higher S phase and lower G1 phase. More importantly, our data demonstrated that MEFs harboring Oct4-EGFP transgene did not express GFP, until they were reprogrammed to the pluripotent stage (iPSCs), while the GFP expression was progressively lost when these pluripotent Oct4-GFP miPSCs exposed to EB-mediated differentiation conditions, suggesting the pluripotency of Oct4-GFP miPSCs can be real-time monitored over long periods of time via GFP assay. Altogether, our findings demonstrate that Oct4-GFP miPSC line is successfully established, which will lay a solid foundation for setting up a technology platform on reprogramming cancer cells into iPSCs. Furthermore, this pluripotency reporter system permits the long-term real-time monitoring of pluripotency changes in a live single-cell, and its progeny.

Construction of a Dual-Fluorescence Reporter System to Monitor the Dynamic Progression of Pluripotent Cell Differentiation

Oct4 is a crucial germ line-specific transcription factor expressed in different pluripotent cells and downregulated in the process of differentiation. There are two conserved enhancers, called the distal enhancer (DE) and proximal enhancer (PE), in the 5' upstream regulatory sequences (URSs) of the mouse Oct4 gene, which were demonstrated to control Oct4 expression independently in embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs). We analyzed the URSs of the pig Oct4 and identified two similar enhancers that were highly consistent with the mouse DE and PE. A dual-fluorescence reporter was later constructed by combining a DE-free-Oct4-promoter-driven EGFP reporter cassette with a PE-free-Oct4-promoter-driven mCherry reporter cassette. Then, it was tested in a mouse ESC-like cell line (F9) and a mouse EpiSC-like cell line (P19) before it is formally used for pig. As a result, a higher red fluorescence was observed in F9 cells, while green fluorescence was primarily detected in P19 cells. This fluorescence expression pattern in the two cell lines was consistent with that in the early naïve pluripotent state and late primed pluripotent state during differentiation of mouse ESCs. Hence, this reporter system will be a convenient tool for screening out ESC-like naïve pluripotent stem cells from other metastable state cells in a heterogenous population.

Use of UTF1 genetic control elements as iPSC reporter

The reprogramming of adult somatic cells into an embryonic stem cell (ESC) state by various means has opened a new chapter in basic and applied life science. While this technology will create great opportunities for regenerative medicine, the more immediate impact is likely to be found in human disease modeling and drug testing/development. An important aspect in the latter contexts is the ability to reliably monitor the pluripotent stem cell state, in particular with respect to human cell reprogramming using patient-specific somatic cells and high-throughput screens. Undifferentiated transcription factor 1 (UTF1) belongs to the core transcriptional network characterizing pluripotency. UTF1 is involved in ESC-specific chromatin organization, and its expression pattern during cell reprogramming and subsequent differentiation appears to be tightly connected with the pluripotent stem cell state. Here, we capitalized on these features and generated a reliable reporter system that was used to monitor induced pluripotent stem cell (iPSC) formation and subsequent differentiation. Our reporter cassette comprises less than 2.3 kb and remains functional during many cell passages after genomic integration. The fact that the human UTF1 genetic control elements work in a mouse background and the demonstrated functionality of the reporter in an epigenetic state further qualifies this system as a versatile new tool for iPSC research.

Sigma-2 receptor as potential indicator of stem cell differentiation

PURPOSE

The sigma-2 (σ(2)) receptor is a potential biomarker of proliferative status of solid tumors. Specific synthetic probes using N-substituted-9-azabicyclo [3.3.1]nonan-3α-yl carbamate analogs have been designed and implemented for experimental cancer diagnosis and therapy.

PROCEDURES

We employed the fluorescently labeled σ(2) receptor probe, SW120, to evaluate σ(2) receptor expression in human stem cells (SC), including: bone marrow stromal, neural progenitor, amniotic fluid, hematopoetic, and embryonic stem cells. We concurrently evaluated the intensity of SW120 and 5-ethynyl-2'-deoxyuridine (EdU) relative to passage number and multi-potency.

RESULTS

We substantiated significantly higher σ(2) receptor density among proliferating SC relative to lineage-restricted cell types. Additionally, cellular internalization of the σ(2) receptor in SC was consistent with receptor-mediated endocytosis and confocal microscopy indicated SW120 specific co-localization with a fluorescent marker of lysosomes in all SC imaged.

CONCLUSION

These results suggest that σ(2) receptors may serve to monitor stem cell differentiation in future experimental studies.

Increase developmental plasticity of human keratinocytes with gene suppression

Recent evidence indicates that p53 suppression increased the efficiency of induced pluripotent stem cell (iPSC) generation. This occurred even with the enforced expression of as few as two canonical transcription factors, Oct4 and Sox2. In this study, primary human keratinocytes were successfully induced into a stage of plasticity by transient inactivation of p53, without enforced expression of any of the transcription factors previously used in iPSC generation. These cells were later redifferentiated into neural lineages. The gene suppression plastic cells were morphologically indistinguishable from human ES cells. Gene suppression plastic cells were alkaline phosphatase-positive, had normal karyotypes, and expressed p53. Together with the accumulating evidence of similarities and overlapping mechanisms between iPSC generation and cancer formation, this finding sheds light on the emerging picture of p53 sitting at the crossroads between two intricate cellular potentials: stem cell vs. cancer cell generation. This finding further supports the crucial role played by p53 in cellular reprogramming and suggests an alternative method to switch the lineage identity of human cells. This reported method offers the potential for directed lineage switching with the goal of generating autologous cell populations for novel clinical applications for neurodegenerative diseases.

A biological global positioning system: considerations for tracking stem cell behaviors in the whole body

Many recent research studies have proposed stem cell therapy as a treatment for cancer, spinal cord injuries, brain damage, cardiovascular disease, and other conditions. Some of these experimental therapies have been tested in small animals and, in rare cases, in humans. Medical researchers anticipate extensive clinical applications of stem cell therapy in the future. The lack of basic knowledge concerning basic stem cell biology-survival, migration, differentiation, integration in a real time manner when transplanted into damaged CNS remains an absolute bottleneck for attempt to design stem cell therapies for CNS diseases. A major challenge to the development of clinical applied stem cell therapy in medical practice remains the lack of efficient stem cell tracking methods. As a result, the fate of the vast majority of stem cells transplanted in the human central nervous system (CNS), particularly in the detrimental effects, remains unknown. The paucity of knowledge concerning basic stem cell biology--survival, migration, differentiation, integration in real-time when transplanted into damaged CNS remains a bottleneck in the attempt to design stem cell therapies for CNS diseases. Even though excellent histological techniques remain as the gold standard, no good in vivo techniques are currently available to assess the transplanted graft for migration, differentiation, or survival. To address these issues, herein we propose strategies to investigate the lineage fate determination of derived human embryonic stem cells (hESC) transplanted in vivo into the CNS. Here, we describe a comprehensive biological Global Positioning System (bGPS) to track transplanted stem cells. But, first, we review, four currently used standard methods for tracking stem cells in vivo: magnetic resonance imaging (MRI), bioluminescence imaging (BLI), positron emission tomography (PET) imaging and fluorescence imaging (FLI) with quantum dots. We summarize these modalities and propose criteria that can be employed to rank the practical usefulness for specific applications. Based on the results of this review, we argue that additional qualities are still needed to advance these modalities toward clinical applications. We then discuss an ideal procedure for labeling and tracking stem cells in vivo, finally, we present a novel imaging system based on our experiments.