Kiyoshi Ohnuma

Integrins Regulate Mouse Embryonic Stem Cell Self-Renewal

Extracellular matrix (ECM) components regulate stem‐cell behavior, although the exact effects elicited in embryonic stem (ES) cells are poorly understood. We previously developed a simple, defined, serum‐free culture medium that contains leukemia inhibitory factor (LIF) for propagating pluripotent mouse embryonic stem (mES) cells in the absence of feeder cells. In this study, we determined the effects of ECM components as culture substrata on mES cell self‐renewal in this culture medium, comparing conventional culture conditions that contain serum and LIF with gelatin as a culture substratum. mES cells remained undifferentiated when cultured on type I and type IV collagen or poly‐d‐lysine. However, they differentiated when cultured on laminin or fibronectin as indicated by altered morphologies, the activity of alkaline phosphatase decreased, Fgf5 expression increased, and Nanog and stage‐specific embryonic antigen 1 expression decreased. Under these conditions, the activity of signal transducer and activator of transcription (STAT)3 and Akt/protein kinase B (PKB), which maintain cell self‐renewal, decreased. In contrast, the extracellular signal‐regulated kinase (ERK)1/2 activity, which negatively controls cell self‐renewal, increased. In the defined conditions, mES cells did not express collagen‐binding integrin subunits, but they expressed laminin‐ and fibronectin‐binding integrin subunits. The expression of some collagen‐binding integrin subunits was downregulated in an LIF concentration‐dependent manner. Blocking the interactions between ECM and integrins inhibited this differentiation. Conversely, the stimulation of ECM‐integrin interactions by overexpressing collagen‐binding integrin subunits induced differentiation of mES cells cultured on type I collagen. The results of the study indicated that inactivation of the integrin signaling is crucial in promoting mouse embryonic stem cell self‐renewal.

Glycome diagnosis of human induced pluripotent stem cells using lectin microarray

Induced pluripotent stem cells (iPSCs) can now be produced from various somatic cell (SC) lines by ectopic expression of the four transcription factors. Although the procedure has been demonstrated to induce global change in gene and microRNA expressions and even epigenetic modification, it remains largely unknown how this transcription factor-induced reprogramming affects the total glycan repertoire expressed on the cells. Here we performed a comprehensive glycan analysis using 114 types of human iPSCs generated from five different SCs and compared their glycomes with those of human embryonic stem cells (ESCs; nine cell types) using a high density lectin microarray. In unsupervised cluster analysis of the results obtained by lectin microarray, both undifferentiated iPSCs and ESCs were clustered as one large group. However, they were clearly separated from the group of differentiated SCs, whereas all of the four SCs had apparently distinct glycome profiles from one another, demonstrating that SCs with originally distinct glycan profiles have acquired those similar to ESCs upon induction of pluripotency. Thirty-eight lectins discriminating between SCs and iPSCs/ESCs were statistically selected, and characteristic features of the pluripotent state were then obtained at the level of the cellular glycome. The expression profiles of relevant glycosyltransferase genes agreed well with the results obtained by lectin microarray. Among the 38 lectins, rBC2LCN was found to detect only undifferentiated iPSCs/ESCs and not differentiated SCs. Hence, the high density lectin microarray has proved to be valid for not only comprehensive analysis of glycans but also diagnosis of stem cells under the concept of the cellular glycome.

BMP4 induction of trophoblast from mouse embryonic stem cells in defined culture conditions on laminin.

Because mouse embryonic stem cells (mESCs) do not contribute to the formation of extraembryonic placenta when they are injected into blastocysts, it is believed that mESCs do not differentiate into trophoblast whereas human embryonic stem cells (hESCs) can express trophoblast markers when exposed to bone morphogenetic protein 4 (BMP4) in vitro. To test whether mESCs have the potential to differentiate into trophoblast, we assessed the effect of BMP4 on mESCs in a defined monolayer culture condition. The expression of trophoblast-specific transcription factors such as Cdx2, Dlx3, Esx1, Gata3, Hand1, Mash2, and Plx1 was specifically upregulated in the BMP4-treated differentiated cells, and these cells expressed trophoblast markers. These results suggest that BMP4 treatment in defined culture conditions enabled mESCs to differentiate into trophoblast. This differentiation was inhibited by serum or leukemia inhibitory factor, which are generally used for mESC culture. In addition, we studied the mechanism underlying BMP4-directed mESC differentiation into trophoblast. Our results showed that BMP4 activates the Smad pathway in mESCs inducing Cdx2 expression, which plays a crucial role in trophoblast differentiation, through the binding of Smad protein to the Cdx2 genomic enhancer sequence. Our findings imply that there is a common molecular mechanism underlying hESC and mESC differentiation into trophoblast.

LEUKEMIA INHIBITORY FACTOR AS AN ANTI-APOPTOTIC MITOGEN FOR PLURIPOTENT MOUSE EMBRYONIC STEM CELLS IN A SERUM-FREE MEDIUM WITHOUT FEEDER CELLS

SummaryWe have developed a serum-free medium, designated ESF7, in which leukemia inhibitory factor (LIF) clearly stimulated murine embryonic stem (ES) cell proliferation accompanied by increased expression of nanog and Rex-1 and decreased FGF-5 expression. These effects were dependent on the concentration of LIF. The ES cells maintained in ESF7 medium for more than 2 yr retained an undifferentiated phenotype, as manifested by the expression of the transcription factor Oct-3/4, the stem cell marker SSEA-1, and alkaline phosphatase. Withdrawal of LIF from ESF7 medium resulted in ES cell apoptosis. Addition of serum to ESF7 medium promoted ES cell differentiation. Addition of MBP4 promoted ES cell differentiation into simple epithelial-like cells. In contrast, FGF-2 promoted ES cell differentiation into neuronal and glial-like cells. Under serum-free culture conditions, LIF was sufficient to stimulate cell proliferation, it inhibited cell differentiation, and it maintained self-renewal of ES cells. Because this simple serum-free adherent monoculture system supports the long-term propagation of pluripotent ES cells in vitro, it will allow the elucidation of ES cell responses to growth factors under defined conditions.

Pdx1-transfected adipose tissue-derived stem cells differentiate into insulin-producing cells in vivo and reduce hyperglycemia in diabetic mice

Insulin-dependent diabetes mellitus (IDDM) is characterized by the rapid development of potentially severe metabolic abnormalities resulting from insulin deficiency. The transplantation of insulin-producing cells is a promising approach for the treatment of IDDM. The transcription factor pancreatic duodenal homeobox 1 (Pdx1) plays an important role in the differentiation of pancreatic beta cells. In this study, the human Pdx1 gene was transduced and expressed in murine adipose tissue-derived stem cells (ASCs). To evaluate pancreatic repair, we used a mouse model of pancreatic damage resulting in hyperglycemia, which involves injection of mice with streptozotocin (STZ). STZ-treated mice transplanted with Pdx1-transduced ASCs (Pdx1-ASCs) showed significantly decreased blood glucose levels and increased survival, when compared with control mice. While stable expression of Pdx1 in ASCs did not induce the pancreatic phenotype in vitro in our experiment, the transplanted stem cells became engrafted in the pancreas, wherein they expressed insulin and C-peptide, which is a marker of insulin-producing cells. These results suggest that Pdx1-ASCs are stably engrafted in the pancreas, acquire a functional beta-cell phenotype, and partially restore pancreatic function in vivo. The ease and safety associated with extirpating high numbers of cells from adipose tissues support the applicability of this system to developing a new cell therapy for IDDM.

Reduction of N-glycolylneuraminic acid in human induced pluripotent stem cells generated or cultured under feeder- and serum-free defined conditions.

Background The successful establishment of human induced pluripotent stem cells (hiPSCs) has increased the possible applications of stem cell research in biology and medicine. In particular, hiPSCs are a promising source of cells for regenerative medicine and pharmacology. However, one of the major obstacles to such uses for hiPSCs is the risk of contamination from undefined pathogens in conventional culture conditions that use serum replacement and mouse embryonic fibroblasts as feeder cells. Methodology/Principal Findings Here we report a simple method for generating or culturing hiPSCs under feeder- and serum-free defined culture conditions that we developed previously for human embryonic stem cells. The defined culture condition comprises a basal medium with a minimal number of defined components including five highly purified proteins and fibronectin as a substrate. First, hiPSCs, which were generated using Yamanakas four factors and conventional undefined culture conditions, adapted to the defined culture conditions. These adapted cells retained the property of self renewal as evaluated morphologically, the expression of self-renewal marker proteins, standard growth rates, and pluripotency as evaluated by differentiation into derivatives of all three primary germ layers in vitro and in vivo (teratoma formation in immunodeficient mice). Moreover, levels of nonhuman N-glycolylneuraminic acid (Neu5Gc), which is a xenoantigenic indicator of pathogen contamination in human iPS cell cultures, were markedly decreased in hiPSCs cultured under the defined conditions. Second, we successfully generated hiPSCs using adult dermal fibroblast under the defined culture conditions from the reprogramming step. For a long therm culture, the generated cells also had the property of self renewal and pluripotency, they carried a normal karyotype, and they were Neu5Gc negative. Conclusion/Significance This study suggested that generation or adaption culturing under defined culture conditions can eliminate the risk posed by undefined pathogens. This success in generating hiPSCs using adult fibroblast would be beneficial for clinical application.

Induction of neural crest cells from mouse embryonic stem cells in a serum-free monolayer culture

The neural crest (NC) is a group of cells located in the neural folds at the boundary between the neural and epidermal ectoderm. NC cells differentiate into a vast range of cells,including neural cells, smooth muscle cells, bone and cartilage cells of the maxillofacial region, and odontoblasts. The molecular mechanisms underlying NC induction during early development remain poorly understood. We previously established a defined serum-free culture condition for mouse embryonic stem (mES) cells without feeders. Here, using this defined condition, we have developed a protocol to promote mES cell differentiation into NC cells in an adherent monolayer culture. We found that adding bone morphogenetic protein (BMP)-4 together with fibroblast growth factor (FGF)-2 shifts mES cell differentiation into the NC lineage. Furthermore, we have established a cell line designated as P0-6 that is derived from the blastocysts of P0-Cre/Floxed-EGFP mice expressing EGFP in an NC-lineage-specific manner. P0-6 cells cultured using this protocol expressed EGFP. This protocol could be used to help clarify the mechanisms by which cells differentiate into the NC lineage and to assist the development of applications for clinical therapy.

Population study of sizes and components of self-reproducing giant multilamellar vesicles.

Population analysis of a system of self-reproducing giant multilamellar vesicles (GMVs) was carried out by means of flow cytometry. The multidimensional distribution of forward light scattering (FS), side light scattering (SS), and fluorescence (FL) intensities originating from each GMV provided information about changes in a population composed of 104 vesicles. FS-FL dot plots indicated that, after the addition of the membrane precursor, the size distribution of the newly generated vesicles was nearly the same as that of the original, but the catalyst content was reduced. This result can be interpreted as evidence for the occurrence of the self-reproduction of GMVs. Moreover, the new GMVs recovered the amount of catalyst to the initial value, keeping their size distribution constant, when a solution of the catalyst was added to the new GMVs. These results are the first experimental evidence for a novel phenomenon on GMV size distribution during their self-reproducing cycle.

Presynaptic target of Ca2+ action on neuropeptide and acetylcholine release in Aplysia californica

1 When buccal neuron B2 of Aplysia californica is co‐cultured with sensory neurons (SNs), slow peptidergic synapses are formed. When B2 is co‐cultured with neurons B3 or B6, fast cholinergic synapses are formed. 2 Patch pipettes were used to voltage clamp pre‐ and postsynaptic neurons and to load the caged Ca2+ chelator o‐nitrophenyl EGTA (NPE) and the Ca2+ indicator BTC into presynaptic neurons. The relationships between presynaptic [Ca2+]i and postsynaptic responses were compared between peptidergic and cholinergic synapses formed by cell B2. 3 Using variable intensity flashes, Ca2+ stoichiometries of peptide and acetylcholine (ACh) release were approximately 2 and 3, respectively. The difference did not reach statistical significance. 4 ACh quanta summate linearly postsynaptically. We also found a linear dose‐response curve for peptide action, indicating a linear relationship between submaximal peptide concentration and response of the SN. 5 The minimum intracellular calcium concentrations ([Ca2+]i) for triggering peptidergic and cholinergic transmission were estimated to be about 5 and 10 μm, respectively. 6 By comparing normal postsynaptic responses to those evoked by photolysis of NPE, we estimate [Ca2+]i at the release trigger site elicited by a single action potential (AP) to be at least 10 μm for peptidergic synapses and probably higher for cholinergic synapses. 7 Cholinergic release is brief (half‐width ≈200 ms), even in response to a prolonged rise in [Ca2+]i, while some peptidergic release appears to persist for as long as [Ca2+]i remains elevated (for up to 10 s). This may reflect differences in sizes of reserve pools, or in replenishment rates of immediately releasable pools of vesicles. 8 Electron microscopy revealed that most synaptic contacts had at least one morphologically docked dense core vesicle that presumably contained peptide; these were often located within conventional active zones. 9 Both cholinergic and peptidergic vesicles are docked within active zones, but cholinergic vesicles may be located closer to Ca2+ channels than are peptidergic vesicles.

Podocalyxin Is a Glycoprotein Ligand of the Human Pluripotent Stem Cell-Specific Probe rBC2LCN

In comprehensive glycome analysis with a high‐density lectin microarray, we have previously shown that the recombinant N‐terminal domain of the lectin BC2L‐C from Burkholderia cenocepacia (rBC2LCN) binds exclusively to undifferentiated human induced pluripotent stem (iPS) cells and embryonic stem (ES) cells but not to differentiated somatic cells. Here we demonstrate that podocalyxin, a heavily glycosylated type 1 transmembrane protein, is a glycoprotein ligand of rBC2LCN on human iPS cells and ES cells. When analyzed by DNA microarray, podocalyxin was found to be highly expressed in both iPS cells and ES cells. Western and lectin blotting revealed that rBC2LCN binds to podocalyxin with a high molecular weight of more than 240 kDa in undifferentiated iPS cells of six different origins and four ES cell lines, but no binding was observed in either differentiated mouse feeder cells or somatic cells. The specific binding of rBC2LCN to podocalyxin prepared from a large set of iPS cells (138 types) and ES cells (15 types) was also confirmed using a high‐throughput antibody‐overlay lectin microarray. Alkaline digestion greatly reduced the binding of rBC2LCN to podocalyxin, indicating that the major glycan ligands of rBC2LCN are presented on O‐glycans. Furthermore, rBC2LCN was found to exhibit significant affinity to a branched O‐glycan comprising an H type 3 structure (Ka, 2.5 × 104 M−1) prepared from human 201B7 iPS cells, indicating that H type 3 is a most probable potential pluripotency marker. We conclude that podocalyxin is a glycoprotein ligand of rBC2LCN on human iPS cells and ES cells.