Determination of the Terbium-152 half-life from mass-separated samples from CERN-ISOLDE and assessment of the radionuclide purity

Terbium-152 is one of four terbium radioisotopes that together form a potential theranostic toolbox for the personalised treatment of tumours. As 152 Tb decay by positron emission it can be utilised for diagnostics by positron emission tomography. For use in radiopharmaceuticals and for activity measurements by an activity calibrator a high radionuclide purity of the material and an accurate and precise knowledge of the half-life is required. Mass-separation and radiochemical purification provide a production route of high purity 152Tb. In the current work, two mass-separated samples from the CERN-ISOLDE facility have been assayed at the National Physical Laboratory to investigate the radionuclide purity. These samples have been used to perform four measurements of the half-life by three independent techniques: high-purity germanium gamma-ray spectrometry, ionisation chamber measurements and liquid scintillation counting. From the four measurement campaigns a half-life of 17.8784(95) h has been determined. The reported half-life shows a significant difference to the currently evaluated half-life (ζ-score = 3.77), with a relative difference of 2.2 % and an order of magnitude improvement in the precision. This work also shows that under controlled conditions the combination of mass-separation and radiochemical separation can provide high-purity 152Tb.

Sufficiency of hypoxia-inducible 2-oxoglutarate dioxygenases to block chemical oxidative stress-induced differentiation of human embryonic stem cells

Hypoxia benefits undifferentiated pluripotent stem cell renewal, and 2-oxoglutarate (2OG) dioxygenases have been implicated in pluripotent stem cell induction and renewal. We show in human embryonic stem cells (hESC) that an ambient oxygen-induced oxidative stress response elicited by culture in a hypoxic atmosphere (0.5% O₂) correlates with the expression of 2OG dioxygenases, which oxidise DNA (TET1, 2, 3) and histone H3 (KDM4C), the former reflected by elevation in genomic 5-hydroxymethylcytosine (5hmC). siRNA-mediated targeting of KDM4C and TET1-3 induces hESC differentiation. Under ambient atmospheric oxygen (21% O₂), exposure to a low inhibitory concentration of sodium arsenite (NaAsO₂, IC₁₀), as a model of chemically-induced oxidative stress, suppresses antioxidant gene expression, reduces mitochondrial membrane potential and induces hESC differentiation. Co-administration of the antioxidant N-acetyl-L-cysteine promoted anti-oxidant, pluripotency and 2OG dioxygenase gene expression, elevated genomic hydroxymethylation and blocked induction of differentiation. Transient ectopic expression of KDM4C or TET1 in ambient atmospheric oxygen achieved the same. Our study substantiates a role for 2OG-dependent dioxygenases in hypoxia's promotion of undifferentiated hESC self-renewal.

A scalable label-free approach to separate human pluripotent cells from differentiated derivatives

The broad capacity of pluripotent human embryonic stem cells (hESC) to grow and differentiate demands the development of rapid, scalable, and label-free methods to separate living cell populations for clinical and industrial applications. Here, we identify differences in cell stiffness, expressed as cell elastic modulus (CEM), for hESC versus mesenchymal progenitors, osteoblast-like derivatives, and fibroblasts using atomic force microscopy and data processing algorithms to characterize the stiffness of cell populations. Undifferentiated hESC exhibited a range of CEMs whose median was nearly three-fold lower than those of differentiated cells, information we exploited to develop a label-free separation device based on the principles of tangential flow filtration. To test the device's utility, we segregated hESC mixed with fibroblasts and hESC-mesenchymal progenitors induced to undergo osteogenic differentiation. The device permitted a throughput of 10(6)-10(7) cells per min and up to 50% removal of specific cell types per single pass. The level of enrichment and depletion of soft, pluripotent hESC in the respective channels was found to rise with increasing stiffness of the differentiating cells, suggesting CEM can serve as a major discriminator. Our results demonstrate the principle of a scalable, label-free, solution for separation of heterogeneous cell populations deriving from human pluripotent stem cells.

Novel Human Embryonic Stem Cell Regulators Identified by Conserved and Distinct CpG Island Methylation State

Human embryonic stem cells (hESCs) undergo epigenetic changes in vitro which may compromise function, so an epigenetic pluripotency “signature” would be invaluable for line validation. We assessed Cytosine-phosphate-Guanine Island (CGI) methylation in hESCs by genomic DNA hybridisation to a CGI array, and saw substantial variation in CGI methylation between lines. Comparison of hESC CGI methylation profiles to corresponding somatic tissue data and hESC mRNA expression profiles identified a conserved hESC-specific methylation pattern associated with expressed genes. Transcriptional repressors and activators were over-represented amongst genes whose associated CGIs were methylated or unmethylated specifically in hESCs, respectively. Knockdown of candidate transcriptional regulators (HMGA1, GLIS2, PFDN5) induced differentiation in hESCs, whereas ectopic expression in fibroblasts modulated iPSC colony formation. Chromatin immunoprecipitation confirmed interaction between the candidates and the core pluripotency transcription factor network. We thus identify novel pluripotency genes on the basis of a conserved and distinct epigenetic configuration in human stem cells.

Dielectrophoresis based discrimination of human embryonic stem cells from differentiating derivatives

Assessment of the dielectrophoresis (DEP) cross-over frequency (f xo), cell diameter, and derivative membrane capacitance (C m) values for a group of undifferentiated human embryonic stem cell (hESC) lines (H1, H9, RCM1, RH1), and for a transgenic subclone of H1 (T8) revealed that hESC lines could not be discriminated on their mean f xo and C m values, the latter of which ranged from 14 to 20 mF/m(2). Differentiation of H1 and H9 to a mesenchymal stem cell-like phenotype resulted in similar significant increases in mean C m values to 41-49 mF/m(2) in both lines (p < 0.0001). BMP4-induced differentiation of RCM1 to a trophoblast cell-like phenotype also resulted in a distinct and significant increase in mean C m value to 28 mF/m(2) (p < 0.0001). The progressive transition to a higher membrane capacitance was also evident after each passage of cell culture as H9 cells transitioned to a mesenchymal stem cell-like state induced by growth on a substrate of hyaluronan. These findings confirm the existence of distinctive parameters between undifferentiated and differentiating cells on which future application of dielectrophoresis in the context of hESC manufacturing can be based.

Screening ethnically diverse human embryonic stem cells identifies a chromosome 20 minimal amplicon conferring growth advantage

The International Stem Cell Initiative analyzed 125 human embryonic stem (ES) cell lines and 11 induced pluripotent stem (iPS) cell lines, from 38 laboratories worldwide, for genetic changes occurring during culture. Most lines were analyzed at an early and late passage. Single-nucleotide polymorphism (SNP) analysis revealed that they included representatives of most major ethnic groups. Most lines remained karyotypically normal, but there was a progressive tendency to acquire changes on prolonged culture, commonly affecting chromosomes 1, 12, 17 and 20. DNA methylation patterns changed haphazardly with no link to time in culture. Structural variants, determined from the SNP arrays, also appeared sporadically. No common variants related to culture were observed on chromosomes 1, 12 and 17, but a minimal amplicon in chromosome 20q11.21, including three genes expressed in human ES cells, ID1, BCL2L1 and HM13, occurred in >20% of the lines. Of these genes, BCL2L1 is a strong candidate for driving culture adaptation of ES cells.

Elasticity of Human Embryonic Stem Cells as Determined by Atomic Force Microscopy

The expansive growth and differentiation potential of human embryonic stem cells (hESCs) make them a promising source of cells for regenerative medicine. However, this promise is off set by the propensity for spontaneous or uncontrolled differentiation to result in heterogeneous cell populations. Cell elasticity has recently been shown to characterize particular cell phenotypes, with undifferentiated and differentiated cells sometimes showing significant differences in their elasticities. In this study, we determined the Young’s modulus of hESCs by atomic force microscopy using a pyramidal tip. Using this method we are able to take point measurements of elasticity at multiple locations on a single cell, allowing local variations due to cell structure to be identified. We found considerable differences in the elasticity of the analyzed hESCs, reflected by a broad range of Young’s modulus (0.05-10 kPa). This surprisingly high variation suggests that elasticity could serve as the basis of a simple and efficient large scale purification/separation technique to discriminate subpopulations of hESCs.

Lineage-specific distribution of high levels of genomic 5-hydroxymethylcytosine in mammalian development

Methylation of cytosine is a DNA modification associated with gene repression. Recently, a novel cytosine modification, 5-hydroxymethylcytosine (5-hmC) has been discovered. Here we examine 5-hmC distribution during mammalian development and in cellular systems, and show that the developmental dynamics of 5-hmC are different from those of 5-methylcytosine (5-mC); in particular 5-hmC is enriched in embryonic contexts compared to adult tissues. A detectable 5-hmC signal appears in pre-implantation development starting at the zygote stage, where the paternal genome is subjected to a genome-wide hydroxylation of 5-mC, which precisely coincides with the loss of the 5-mC signal in the paternal pronucleus. Levels of 5-hmC are high in cells of the inner cell mass in blastocysts, and the modification colocalises with nestin-expressing cell populations in mouse post-implantation embryos. Compared to other adult mammalian organs, 5-hmC is strongly enriched in bone marrow and brain, wherein high 5-hmC content is a feature of both neuronal progenitors and post-mitotic neurons. We show that high levels of 5-hmC are not only present in mouse and human embryonic stem cells (ESCs) and lost during differentiation, as has been reported previously, but also reappear during the generation of induced pluripotent stem cells; thus 5-hmC enrichment correlates with a pluripotent cell state. Our findings suggest that apart from the cells of neuronal lineages, high levels of genomic 5-hmC are an epigenetic feature of embryonic cell populations and cellular pluri- and multi-lineage potency. To our knowledge, 5-hmC represents the first epigenetic modification of DNA discovered whose enrichment is so cell-type specific.

Human embryonic stem cells rapidly take up and then clear exogenous human and animal prions in vitro

Susceptibility to prion infection involves interplay between the prion strain and host genetics, but expression of the host-encoded cellular prion protein is a known prerequisite. Here we consider human embryonic stem cell (hESC) susceptibility by characterizing the genetics and expression of the normal cellular prion protein and by examining their response to acute prion exposure. Seven hESC lines were tested for their prion protein gene codon 129 genotype and this was found to broadly reflect that of the normal population. hESCs expressed prion protein mRNA, but only low levels of prion protein accumulated in self-renewing populations. Following undirected differentiation, up-regulation of prion protein expression occurred in each of the major embryonic lineages. Self-renewing populations of hESCs were challenged with infectious human and animal prions. The exposed cells rapidly and extensively took up this material, but when the infectious source was removed the level and extent of intracellular disease-associated prion protein fell rapidly. In the absence of a sufficiently sensitive test for prions to screen therapeutic cells, and given the continued use of poorly characterized human and animal bioproducts during hESC derivation and cultivation, the finding that hESCs rapidly take up and process abnormal prion protein is provocative and merits further investigation.

Clinically failed eggs as a source of normal human embryo stem cells

The promise of human embryo stem cells (hESCs) for regenerative medicine is offset by the ethical and practical challenges involved in sourcing eggs and embryos for this objective. In this study we sought to isolate an hESC line from clinically failed eggs, the usage of which would not conflict with donor interests to conceive. A total of 8 blastocysts were allocated for hESC derivation from a pool of 579 eggs whose fertilization had been clinically assessed to have occurred abnormally (i.e., three pronuclei) or failed (i.e., no pronuclei) following in vitro insemination or intracytoplasmic sperm injection (ICSI). The latter were subjected to a recovery intervention consisting of either reinsemination by ICSI or parthenogenetic stimulation. One hESC line (RCM1) was obtained from a failed-to-fertilize inseminated egg recovered by parthenogenetic activation. Standard in vitro and in vivo characterization revealed this line to possess all of the properties attributed to a normal euploid hESC line. Whole-genome single-nucleotide polymorphism analysis further revealed that the line was biparental, indicating that sperm penetration had occurred, although parthenogenetic stimulation was required for activation. Our results demonstrate the viability of an alternative strategy to generate normal hESC lines from clinically failed eggs, thereby further minimizing the potential to conflict with donor reproductive interest to conceive.

Nuclear reprogramming of somatic cells by embryonic stem cells is affected by cell cycle stage

Hybrid embryonic stem (ES)-like clones were generated by fusion of murine ES cells with somatic cells that carried a neo resistance gene under the transcriptional control of the Oct-4 promoter. The Oct-4 promoter was reactivated in hybrid ES cells formed by fusion with fetal fibroblasts, and all hybrid colonies were of ES rather than fibroblast phenotype, suggesting efficient reprogramming of fibroblast chromosomes. Like normal diploid murine ES cells, hybrid lines expressed alkaline phosphatase activity and formed differentiated cells derived from the three embryonic germ layers both in vitro and in vivo. Treatments thought to affect nuclear transfer efficiency (ES cell confluence and serum starvation of primary embryonic fibroblasts) were investigated to determine whether they had an effect on reprogramming in cell hybrids. Serum starvation of primary embryonic fibroblasts increased hybrid colony number 50-fold. ES cells were most effective at reprogramming when they contained a high proportion of cells in the S and G2/M phases of the cell cycle. These data suggest that nuclear reprogramming requires an initial round of somatic DNA replication of quiescent chromatin in the presence of ES-derived factors produced during S and G2/M phases.

Quantification of cell fusion by flow cytometry

Cells of different types can be induced to fuse by electroshock. Cells of one type are typically dominant and are able to reprogram the nuclei derived from cells of the other type, in fusion hybrids derived from one cell of each type. Flow cytometry provides a quick and objective technique to assess cell fusion for nuclear reprogramming studies. Two cell types are each stained with a different fluorescent dye and then induced to fuse to form fusion products called heterokaryons. Heterokaryons can be identified and quantified by flow cytometry as double-stained events. Protocols are provided for the optimization of cell staining under conditions that minimize cell clumping and dye leakage. If spectral overlap occurs between emission spectra of the two stained cell types, the data will need to be electronically compensated.

Multipotentiality of neuronal cells after spontaneous fusion with embryonic stem cells and nuclear reprogramming in vitro

Primary mouse brain cells were cultured with HPRT (hypoxanthine phosphoribosyl transferase)-deficient ES (embryonic stem) cells to see if the ES cells could provide cues sufficient to reprogram a pluripotential state. After 5 days of coculture, HPRT-deficient ES cells were killed by selection in HAT (hypoxanthine, aminopterin, thymidine) medium. We observed islands of HAT-resistant ES-like cells surrounded by differentiated cells. Cell lines generated from three such "islands" proved to be spontaneous, pluripotential ES-neural hybrids, and gave rise to a chimera following blastocyst injection. Re-expression of the ES-specific gene Foxd3 from somatic-derived chromosomes suggested that the somatic nucleus had been reprogrammed. Our results raise the intriguing possibility that ASCs shown to contribute to multiple tissues in blastocyst-injection studies may not contribute as a result of pluripotency. Instead contributions may arise from spontaneous fusion events in which phenotype is determined by either cytoplasmic dominance, nuclear reprogramming, or both.

Developmentally-regulated expression of murine K-ras isoforms

The products (p21) of the three mammalian H-, N- and K-ras genes play important roles in intracellular signal transduction, linking membrane receptor kinases to the nuclear pathway through raf and mitogen activated protein kinase. They are involved in the regulation of proliferation and differentiation, and activating mutations of these genes are commonly associated with human cancers. Two p21 proteins are encoded by the K-ras gene (p21K-rasA and p21K-rasB) due to alternative splicing of the last exon. While the four p21ras proteins are highly homologous, their sequences diverge significantly at the C-termini, to which distinct biochemical and perhaps even functional differences may be ascribed. However, H-, N- and K-rasB appear to be ubiquitously expressed, with little evidence of tissue-specific or developmental regulation. In contrast, we now demonstrate that the expression of K-rasA is strikingly different. K-rasA is induced during differentiation of pluripotent embryonal stem cells in vitro. Its expression during early embryogenesis is limited temporally and spatially in a tissue-specific distribution which is largely maintained as an adult. This suggests a distinct biological role for p21K-rasA.

Phenotypic characterization of splenic T cells from mice infected with Plasmodium chabaudi chabaudi

T cells from spleens of mice infected with the erythrocytic stages of Plasmodium chabaudi chabaudi have been analysed with respect to their expression of surface molecules CD3, CD4 and CD8 and T-cell receptor (TCR) alpha beta and gamma delta. The majority of T cells from infected mice were alpha beta TCR+. However, there was an increase of approximately 8-10-fold in the proportion and total number of gamma delta T cells. Immunocytochemical analysis of sections of spleens taken from infected C57BL/6 mice during a primary infection showed that this increase took place particularly in the non-lymphoid areas. Within the alpha beta TCR+ T-cell population, both CD4+ T cells and CD8+ T cells were represented in proportions similar to those observed in normal uninfected mice. Stimulation of splenic T cells from infected mice with P. chabaudi-infected erythrocytes in vitro resulted in a blasted cell population composed predominantly of alpha beta TCR+ T cells with no preferential expansion of gamma delta TCR+ T cells. There was no evidence of superantigen-like stimulation of T cells bearing particular V beta chains of the TCR. The representation of the different V beta chains within the population was not significantly different from that seen in uninfected mice.

Identification and characterization of a novel Bacillus thuringiensis delta-endotoxin entomocidal to coleopteran and lepidopteran larvae

A new class of Bacillus thuringiensis delta-endotoxins, or insecticidal control proteins (ICPs), is defined by an apparently cryptic protein with a unique primary structure and novel entomocidal specificity for certain coleopteran and lepidopteran species. The discovery of a new group of ICPs will extend the use of this natural insecticide in integrated pest-management systems.