Advancing Stem Cell Technologies and Applications: A Special Collection from the PluriCore Network in the German Stem Cell Network (GSCN).

Current Protocols in Stem Cell Biology is publishing a special collection of eight articles from members of the PluriCore Network in the German Stem Cell Network. © 2020 Wiley Periodicals LLC.

The German stem cell network GSCN - a nationwide network with many tasks.

The German Stem Cell Network (GSCN) aims at creating synergies between all areas of basic and applied stem cell research and to provide an interface between science, education, politics and society as a whole. The central task of the GSCN is to pool the expertise in stem cell research in Germany and develop synergies between basic research, regenerative medicine and pharmacology. The initiative promotes innovative research activities on a national and international level. In addition, targeted information and events are offered to encourage the public discourse on stem cell research. The objectives of the network are.

Author Correction: Isolation and cultivation of naive-like human pluripotent stem cells based on HERVH expression.

In the published version of this paper, the authors omitted a funding source. L.D.H. acknowledges support from the European Research Council (Advanced Grant ERC-2014-ADG 669207). The original article has not been corrected.

Isolation and cultivation of naive-like human pluripotent stem cells based on HERVH expression.

The ability to derive and stably maintain ground-state human pluripotent stem cells (hPSCs) that resemble the cells seen in vivo in the inner cell mass has the potential to be an invaluable tool for researchers developing stem cell-based therapies. To date, derivation of human naive-like pluripotent stem cell lines has been limited to a small number of lineages, and their long-term culturing remains problematic. We describe a protocol for genetic and phenotypic tagging, selecting and maintaining naive-like hPSCs. We tag hPSCs by GFP, expressed by the long terminal repeat (LTR7) of HERVH endogenous retrovirus. This simple and efficient protocol has been reproduced with multiple hPSC lines, including embryonic and induced pluripotent stem cells, and it takes ∼6 weeks. By using the reporter, homogeneous hPSC cultures can be derived, characterized and maintained for the long term by repeated re-sorting and re-plating steps. The HERVH-expressing cells have a similar, but nonidentical, expression pattern to other naive-like cells, suggesting that alternative pluripotent states might exist.

New Wnt/ß-catenin target genes promote experimental metastasis and migration of colorectal cancer cells through different signals.

OBJECTIVES: We have previously identified a 115-gene signature that characterises the metastatic potential of human primary colon cancers. The signature included the canonical Wnt target gene BAMBI, which promoted experimental metastasis in mice. Here, we identified three new direct Wnt target genes from the signature, and studied their functions in epithelial-mesenchymal transition (EMT), cell migration and experimental metastasis. DESIGN: We examined experimental liver metastases following injection of selected tumour cells into spleens of NOD/SCID mice. Molecular and cellular techniques were used to identify direct transcription target genes of Wnt/ß-catenin signals. Microarray analyses and experiments that interfered with cell migration through inhibitors were performed to characterise downstream signalling systems. RESULTS: Three new genes from the colorectal cancer (CRC) metastasis signature, BOP1, CKS2 and NFIL3, were identified as direct transcription targets of ß-catenin/TCF4. Overexpression and knocking down of these genes in CRC cells promoted and inhibited, respectively, experimental metastasis in mice, EMT and cell motility in culture. Cell migration was repressed by interfering with distinct signalling systems through inhibitors of PI3K, JNK, p38 mitogen-activated protein kinase and/or mTOR. Gene expression profiling identified a series of migration-promoting genes, which were induced by BOP1, CKS2 and NFIL3, and could be repressed by inhibitors that are specific to these pathways. CONCLUSIONS: We identified new direct Wnt/ß-catenin target genes, BOP1, CKS2 and NFIL3, which induced EMT, cell migration and experimental metastasis of CRC cells. These genes crosstalk with different downstream signalling systems, and activate migration-promoting genes. These pathways and downstream genes may serve as therapeutic targets in the treatment of CRC metastasis.

Primate-specific endogenous retrovirus-driven transcription defines naive-like stem cells.

Naive embryonic stem cells hold great promise for research and therapeutics as they have broad and robust developmental potential. While such cells are readily derived from mouse blastocysts it has not been possible to isolate human equivalents easily, although human naive-like cells have been artificially generated (rather than extracted) by coercion of human primed embryonic stem cells by modifying culture conditions or through transgenic modification. Here we show that a sub-population within cultures of human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) manifests key properties of naive state cells. These naive-like cells can be genetically tagged, and are associated with elevated transcription of HERVH, a primate-specific endogenous retrovirus. HERVH elements provide functional binding sites for a combination of naive pluripotency transcription factors, including LBP9, recently recognized as relevant to naivety in mice. LBP9-HERVH drives hESC-specific alternative and chimaeric transcripts, including pluripotency-modulating long non-coding RNAs. Disruption of LBP9, HERVH and HERVH-derived transcripts compromises self-renewal. These observations define HERVH expression as a hallmark of naive-like hESCs, and establish novel primate-specific transcriptional circuitry regulating pluripotency.

Mesenchymal stromal cells (MSCs): science and f(r)iction.

Due to their multi-lineage differentiation capacity, support of haematopoiesis, immunomodulation and secretion of proregenerative factors, mesenchymal stem/stromal cells (MSCs) are in the focus of intense research since decades. The literature is replete with reports on their potential in preclinical model systems. However, the heterogeneity of the primary cell population as starting material and the diverse protocols for isolation and cultivation are hampering progress in their clinical application. Consensus on common standards and harmonised isolation and characterisation protocols are important to ensure safety and efficacy. This review focuses on the recent scientific evidence of clinically relevant properties and on the speculative cardiomyogenic and hepatic differentiation potential of MSCs. Special emphasis is put on the importance of standardisation and harmonisation in clinical-scale manufacturing.

Replicative aging and differentiation potential of human adipose tissue-derived mesenchymal stromal cells expanded in pooled human or fetal bovine serum.

BACKGROUND AIMS: Mesenchymal stromal cells (MSC) are promising candidates for innovative cell therapeutic applications. For clinical-scale manufacturing, different supplements have been evaluated as alternatives for the commonly used fetal bovine serum (FBS). We have reported previously that pooled human AB serum (HS) accelerates the proliferation of adipose tissue-derived MSC (ASC) while maintaining key functions of MSC biology such as differentiation, immune suppression and growth factor secretion. ASC expanded in FBS-supplemented culture media undergo replicative aging that is associated with a progressive loss of differentiation capacity but without indications of cellular transformation. The effects of HS media on ASC long-term culture, however, remain poorly characterized. METHODS: Long-term cultures of ASC in FBS and HS media were analyzed with respect to proliferation, marker expression, differentiation and immune suppression. RESULTS: Despite signs of an accelerated proliferation, extended life span and clonogenic capacity of ASC cultivated in HS-supplemented media, HS and FBS cultures revealed no significant differences with respect to differentiation potential and expression of senescence markers. Anchorage-independent growth, which is indicative of tumorigenic properties, was not observed in either culture conditions. Similarly, immune suppressive activities were maintained. Donor variation regarding differentiation potential and marker expression became apparent in this study independent of the culture supplement or culture duration. CONCLUSIONS: We have demonstrated that the use of pooled allogeneic HS maintains the characteristics of ASC even after long-term expansion, further demonstrating that the use of HS is an alternative to FBS.

Where do you come from; where do you go? Pluripotency, differentiation and malfunction of stem cells.

The international conference 'Stem Cells in Development and Disease' took place in September 2011 at the Max-Delbrück-Center for Molecular Medicine (MDC) in Berlin. It brought together scientists working on different types of stem cell and covered the latest findings in stem cell biology, including the genetic and epigenetic mechanisms of reprogramming, maintenance of pluripotency and differentiation.

E-cadherin is crucial for embryonic stem cell pluripotency and can replace OCT4 during somatic cell reprogramming.

We report new functions of the cell-adhesion molecule E-cadherin in murine pluripotent cells. E-cadherin is highly expressed in mouse embryonic stem cells, and interference with E-cadherin causes differentiation. During cellular reprogramming of mouse fibroblasts by OCT4, SOX2, KLF4 and c-MYC, fully reprogrammed cells were exclusively observed in the E-cadherin-positive cell population and could not be obtained in the absence of E-cadherin. Moreover, reprogrammed cells could be established by viral E-cadherin in the absence of exogenous OCT4. Thus, reprogramming requires spatial cues that cross-talk with essential transcription factors. The cell-adhesion molecule E-cadherin has important functions in pluripotency and reprogramming.

Bone morphogenetic protein-7 release from endogenous neural precursor cells suppresses the tumourigenicity of stem-like glioblastoma cells.

Glioblastoma cells with stem-like properties control brain tumour growth and recurrence. Here, we show that endogenous neural precursor cells perform an anti-tumour response by specifically targeting stem-like brain tumour cells. In vitro, neural precursor cells predominantly express bone morphogenetic protein-7; bone morphogenetic protein-7 is constitutively released from neurospheres and induces canonical bone morphogenetic protein signalling in stem-like glioblastoma cells. Exposure of human and murine stem-like brain tumour cells to neurosphere-derived bone morphogenetic protein-7 induces tumour stem cell differentiation, attenuates stem-like marker expression and reduces self-renewal and the ability for tumour initiation. Neurosphere-derived or recombinant bone morphogenetic protein-7 reduces glioblastoma expansion from stem-like cells by down-regulating the transcription factor Olig2. In vivo, large numbers of bone morphogenetic protein-7-expressing neural precursors encircle brain tumours in young mice, induce canonical bone morphogenetic protein signalling in stem-like glioblastoma cells and can thereby attenuate tumour formation. This anti-tumour response is strongly reduced in older mice. Our results indicate that endogenous neural precursor cells protect the young brain from glioblastoma by releasing bone morphogenetic protein-7, which acts as a paracrine tumour suppressor that represses proliferation, self-renewal and tumour-initiation of stem-like glioblastoma cells.

Two isoforms of human RNA polymerase III with specific functions in cell growth and transformation.

Transcription in eukaryotic nuclei is carried out by DNA-dependent RNA polymerases I, II, and III. Human RNA polymerase III (Pol III) transcribes small untranslated RNAs that include tRNAs, 5S RNA, U6 RNA, and some microRNAs. Increased Pol III transcription has been reported to accompany or cause cell transformation. Here we describe a Pol III subunit (RPC32beta) that led to the demonstration of two human Pol III isoforms (Pol IIIalpha and Pol IIIbeta). RPC32beta-containing Pol IIIbeta is ubiquitously expressed and essential for growth of human cells. RPC32alpha-containing Pol IIIalpha is dispensable for cell survival, with expression being restricted to undifferentiated ES cells and to tumor cells. In this regard, and most importantly, suppression of RPC32alpha expression impedes anchorage-independent growth of HeLa cells, whereas ectopic expression of RPC32alpha in IMR90 fibroblasts enhances cell transformation and dramatically changes the expression of several tumor-related mRNAs and that of a subset of Pol III RNAs. These results identify a human Pol III isoform and isoform-specific functions in the regulation of cell growth and transformation.

The tyrosine phosphatase Shp2 (PTPN11) directs Neuregulin-1/ErbB signaling throughout Schwann cell development.

The nonreceptor tyrosine phosphatase Shp2 (PTPN11) has been implicated in tyrosine kinase, cytokine, and integrin receptor signaling. We show here that conditional mutation of Shp2 in neural crest cells and in myelinating Schwann cells resulted in deficits in glial development that are remarkably similar to those observed in mice mutant for Neuregulin-1 (Nrg1) or the Nrg1 receptors, ErbB2 and ErbB3. In cultured Shp2 mutant Schwann cells, Nrg1-evoked cellular responses like proliferation and migration were virtually abolished, and Nrg1-dependent intracellular signaling was altered. Pharmacological inhibition of Src family kinases mimicked all cellular and biochemical effects of the Shp2 mutation, implicating Src as a primary Shp2 target during Nrg1 signaling. Together, our genetic and biochemical analyses demonstrate that Shp2 is an essential component in the transduction of Nrg1/ErbB signals.

A colorectal cancer expression profile that includes transforming growth factor beta inhibitor BAMBI predicts metastatic potential.

BACKGROUND & AIMS: Much is known about the genes and mutations that cause colorectal cancer (CRC), yet only a few have been associated with CRC metastasis. We performed expression-profiling experiments to identify genetic markers of risk and to elucidate the molecular mechanisms of CRC metastasis. METHODS: We compared gene expression patterns between metastatic and nonmetastatic stage-matched human colorectal carcinomas by microarray analysis. Correlations between BAMBI and metastasis-free survival were examined by quantitative real-time polymerase chain reaction (PCR) using an independent set of human colon carcinomas. Human colon cancer cell lines were analyzed for BAMBI regulation, cell motility, and experimental metastasis. RESULTS: We established a signature of 115 genes that differentiated metastatic from nonmetastatic primary tumors. Among these, the transforming growth factor (TGF) beta inhibitor BAMBI was highly expressed in approximately half of metastatic primary tumors and metastases but not in nonmetastatic tumors. BAMBI is a target of canonical Wnt signaling that involves the beta-catenin coactivator BCL9-2. We observed an inverse correlation between level of BAMBI expression and metastasis-free survival time of patients. BAMBI inhibits TGF-beta signaling and increases migration in colon cancer cells. In mice, overexpression of BAMBI caused colon cancer cells to form tumors that metastasized more frequently to liver and lymph nodes than control cancer cells. CONCLUSIONS: BAMBI regulates CRC metastasis by connecting the Wnt/beta-catenin and TGF-beta-signaling pathways. The metastatic expression signature we describe, along with BAMBI levels, can be used in prognosis. Developmental signaling pathways appear to act in hierarchies and cooperate in tumor cell migration, invasion, and metastasis.

Homogeneity and persistence of transgene expression by omitting antibiotic selection in cell line isolation.

Nonuniform, mosaic expression patterns of transgenes are often linked to transcriptional silencing, triggered by epigenetic modifications of the exogenous DNA. Such phenotypes are common phenomena in genetically engineered cells and organisms. They are widely attributed to features of transgenic transcription units distinct from endogenous genes, rendering them particularly susceptible to epigenetic downregulation. Contrary to this assumption we show that the method used for the isolation of stably transfected cells has the most profound impact on transgene expression patterns. Standard antibiotic selection was directly compared to cell sorting for the establishment of stable cells. Only the latter procedure could warrant a high degree of uniformity and stability in gene expression. Marker genes useful for the essential cell sorting step encode mostly fluorescent proteins. However, by combining this approach with site-specific recombination, it can be applied to isolate stable cell lines with the desired expression characteristics for any gene of interest.

FGF2 signaling in mouse embryonic fibroblasts is crucial for self-renewal of embryonic stem cells.

Human embryonic stem cells (hESCs) can be maintained undifferentiated (pluripotent) or differentiated to basically all functional cell types, depending on the culture conditions used. Culture of hESCs in the presence of medium conditioned by mouse embryonic fibroblasts (MEFs) can be used to keep hESCs undifferentiated. This observation suggests that MEFs produce factors required for the pluripotency of hESCs. The data presented here show that fibroblast growth factor 2 (FGF2) treatment of MEFs is crucial for the production of these factors. To identify the potential factors that are expressed in the presence of FGF2 in MEFs, a global expression profile analysis using microarrays was performed. This analysis indicated that 17 secreted factors are downregulated in the absence of FGF2. These factors include several ligands for known signaling receptors, extracellular proteases and components of the extracellular matrix, that may all be involved in signaling events. Surprisingly, we found that selective blocking of extracellular signal-regulated kinase (ERK) signaling by the MAPK/ERK kinase (MEK) inhibitor U0126 affected the expression of only some of the FGF2-regulated genes, suggesting FGF2-induced pathways that are independent of ERK signaling. It has been shown recently that activation of Activin/Nodal signaling and inhibition of bone morphogenetic protein signaling are required for the maintenance of pluripotency. Accordingly, among the 17 FGF2-regulated genes we found inhibin beta B that can lead to the assembly of Activin B and gremlin 1 that codes for an antagonist of bone morphogenetic proteins. This study identifies potentially important factors involved in the maintenance of pluripotency in hESCs and may allow the development of defined culture conditions without contaminating material from animal cells.

TGFbeta/activin/nodal signaling is necessary for the maintenance of pluripotency in human embryonic stem cells.

Human embryonic stem cells (hESCs) self-renew indefinitely and give rise to derivatives of all three primary germ layers, yet little is known about the signaling cascades that govern their pluripotent character. Because it plays a prominent role in the early cell fate decisions of embryonic development, we have examined the role of TGFbeta superfamily signaling in hESCs. We found that, in undifferentiated cells, the TGFbeta/activin/nodal branch is activated (through the signal transducer SMAD2/3) while the BMP/GDF branch (SMAD1/5) is only active in isolated mitotic cells. Upon early differentiation, SMAD2/3 signaling is decreased while SMAD1/5 signaling is activated. We next tested the functional role of TGFbeta/activin/nodal signaling in hESCs and found that it is required for the maintenance of markers of the undifferentiated state. We extend these findings to show that SMAD2/3 activation is required downstream of WNT signaling, which we have previously shown to be sufficient to maintain the undifferentiated state of hESCs. Strikingly, we show that in ex vivo mouse blastocyst cultures, SMAD2/3 signaling is also required to maintain the inner cell mass (from which stem cells are derived). These data reveal a crucial role for TGFbeta signaling in the earliest stages of cell fate determination and demonstrate an interconnection between TGFbeta and WNT signaling in these contexts.

Expression of nodal, lefty-a, and lefty-B in undifferentiated human embryonic stem cells requires activation of Smad2/3.

Human embryonic stem cells will remain undifferentiated or undergo differentiation when grown in conditioned or non-conditioned medium, respectively. The factors and signaling events that control the maintenance of the undifferentiated state are not well characterized and their identification is of major importance. Based on the data from global expression analyses, we set out to identify genes and the signaling pathways controlling them that are regulated in the early phase of the differentiation process. This study shows that nodal and the inhibitors of Nodal signaling, lefty-A and lefty-B, are down-regulated very early upon differentiation. High expression of these genes in undifferentiated cells is maintained by activation of the transcription factor Smad2/3, downstream of the activin-linked kinases (ALK) 4/5/7. Treatment of differentiating cells with Activin A leads to activation of Smad2/3 and expression of nodal, lefty-A and lefty-B, while inhibition of ALK4/5/7 by the kinase inhibitor SB-431542 blocks activation of Smad2/3 and expression of these genes in the undifferentiated state. In addition, when cells are maintained undifferentiated by treatment with the GSK3-inhibitor, BIO, high expression of nodal, lefty-A, and lefty-B also requires activation of ALK4/5/7. Conversely, BMP signaling leading to Smad1/5/8 activation via ALK2/3/6 is blocked in undifferentiated cells and becomes activated upon differentiation. Taken together, these observations establish that Smad2/3 is activated in undifferentiated hESCs and required for the expression of genes controlling Nodal signaling. Moreover, there appears to be cross-talk between inhibition of GSK3, a hallmark of Wnt signaling and the Activin/Nodal pathway.

Insulin regulates the activity of forkhead transcription factor Hnf-3beta/Foxa-2 by Akt-mediated phosphorylation and nuclear/cytosolic localization.

Hepatocyte nuclear factors 3 alpha, beta, and gamma (Foxa-1, -2, and -3) are transcriptional activators of important metabolic genes in the liver that are suppressed by the actions of insulin. Here, we show that the activation of phosphatidylinositol 3-kinase-Akt by insulin induces Foxa-2 phosphorylation, nuclear exclusion, and inhibition of Foxa-2-dependent transcriptional activity. Foxa-2 physically interacts with Akt, a key mediator of the phosphatidylinositol 3-kinase pathway and is phosphorylated at a single conserved site (T156) that is absent in Foxa-1 and Foxa-3 proteins. This Akt phosphorylation site in Foxa-2 is highly conserved from mammals to insects. Mutant Foxa-2T156A is resistant to Akt-mediated phosphorylation, nuclear exclusion, and transcriptional inactivation of Foxa-2-regulated gene expression. These results implicate an evolutionarily conserved mechanism in the regulation of Foxa-2-dependent transcriptional control by extracellular signals such as insulin.