Lineage Commitment of Conditionally Immortalized Bone Marrow Mesenchymal Stromal Cells from Tetracycline-Regulated SV40 Large T-antigen Transgenic Mice

Adult bone marrow contains a population of mesenchymal stem cells capable to self-renew and to differentiate into haematopoietic-supportive stroma, osteo, adipo- and chondrocytes. However, the identity of mesenchymal stem cells still remains uncertain. The complex population of their descendants, bone marrow mesenchymal stromal cells (BM MSCs), represents a model to study the principles of differentiation and commitment into mesodermal lineages. The experiments using BM MSCs are often hampered by their low proliferative capacity in vitro. In the present study, we established conditionally immortalized BM MSCs from tetracycline-regulated SV40 Large T-antigen transgenic mice. The identity of the conditionally immortalized BM MSCs was confirmed by marker expression, ability to support haematopoiesis and differentiation potential. The advantages of the conditional immortalization are encompassed in (1) indefinite expansion of cell populations, (2) possibility to perform cellular cloning and (3) prevention from spontaneous differentiation. We demonstrated the heterogeneity of BM MSCs and identified at least 6 types of progenitors within BM MSCs population based on their differentiation potential (“OAC”, “OA”, “OC”, “AC”, “O”, “A”). A hypothetical model of BM MSC hierarchy and the relationships between the progenitors has been proposed. We observed that the Wnt/β-catenin signaling pathway and GSK3 activity could modulate the efficiency of osteo- and adipogenic differentiation pathways, but we didn’t find evidence that the lineage commitment of BM MSCs is determined by Wnt. We elucidated the mechanism of transcriptional regulation of the adipogenic induction of BM MSCs in vitro. Our data revealed the key regulatory role of PPARγ1 during adipogenesis in BM MSCs. Furthermore, we assume that PPARγ1 is a potential trigger of the adipogenic commitment of the BM MSCs progenitors. Finally, the non-adipogenic BM MSCs progenitors were converted into the adipogenic lineage using ectopical expression of the transcription factors C/EBPα, C/EBPβ and C/EBPδ. Our findings provide a novel insight into the molecular mechanisms of BM MSCs lineage commitment

Towards consistent generation of pancreatic lineage progenitors from human pluripotent stem cells.

Human pluripotent stem cells can in principle be used as a source of any differentiated cell type for disease modelling, drug screening, toxicology testing or cell replacement therapy. Type I diabetes is considered a major target for stem cell applications due to the shortage of primary human beta cells. Several protocols have been reported for generating pancreatic progenitors by in vitro differentiation of human pluripotent stem cells. Here we first assessed one of these protocols on a panel of pluripotent stem cell lines for capacity to engender glucose sensitive insulin-producing cells after engraftment in immunocompromised mice. We observed variable outcomes with only one cell line showing a low level of glucose response. We, therefore, undertook a systematic comparison of different methods for inducing definitive endoderm and subsequently pancreatic differentiation. Of several protocols tested, we identified a combined approach that robustly generated pancreatic progenitors in vitro from both embryo-derived and induced pluripotent stem cells. These findings suggest that, although there are intrinsic differences in lineage specification propensity between pluripotent stem cell lines, optimal differentiation procedures may consistently direct a substantial fraction of cells into pancreatic specification.This research was supported by European Commission Grant agreement 241883, “BetaCellTherapy”, and by the United Kingdom Medical Research Council.This is the final version of the article. It first appeared from Royal Society Publishing via http://dx.doi.org/10.1098/rstb.2014.036

Capacitation of human naïve pluripotent stem cells for multi-lineage differentiation.

Human naïve pluripotent stem cells (PSCs) share features with the pre-implantation epiblast. They therefore provide an unmatched opportunity for characterising the developmental programme of pluripotency in Homo sapiens Here, we confirm that naïve PSCs do not respond directly to germ layer induction, but must first acquire competence. Capacitation for multi-lineage differentiation occurs without exogenous growth factor stimulation and is facilitated by inhibition of Wnt signalling. Whole-transcriptome profiling during this formative transition highlights dynamic changes in gene expression, which affect many cellular properties including metabolism and epithelial features. Notably, naïve pluripotency factors are exchanged for postimplantation factors, but competent cells remain devoid of lineage-specific transcription. The gradual pace of transition for human naïve PSCs is consistent with the timespan of primate development from blastocyst to gastrulation. Transcriptome trajectory during in vitro capacitation of human naïve cells tracks the progression of the epiblast during embryogenesis in Macaca fascicularis, but shows greater divergence from mouse development. Thus, the formative transition of naïve PSCs in a simple culture system may recapitulate essential and specific features of pluripotency dynamics during an inaccessible period of human embryogenesis.This research was funded by the Medical Research Council of the United Kingdom (G1001028 and MR/P00072X/1), the European Commission Framework 7 (HEALTH-F4-2013-602423, PluriMes) and the UK Regenerative Medicine Platform (MR/L012537/1). The Cambridge Stem Cell Institute receives core funding from the Wellcome Trust and the Medical Research Council. AS is a Medical Research Council Professor

Differential Expression of Surface Markers in Mouse Bone Marrow Mesenchymal Stromal Cell Subpopulations with Distinct Lineage Commitment

Bone marrow mesenchymal stromal cells (BM MSCs) represent a heterogeneous population of progenitors with potential for generation of skeletal tissues. However the identity of BM MSC subpopulations is poorly defined mainly due to the absence of specific markers allowing in situ localization of those cells and isolation of pure cell types. Here, we aimed at characterization of surface markers in mouse BM MSCs and in their subsets with distinct differentiation potential. Using conditionally immortalized BM MSCs we performed a screening with 176 antibodies and high-throughput flow cytometry, and found 33 markers expressed in MSCs, and among them 3 were novel for MSCs and 13 have not been reported for MSCs from mice. Furthermore, we obtained clonally derived MSC subpopulations and identified bipotential progenitors capable for osteo- and adipogenic differentiation, as well as monopotential osteogenic and adipogenic clones, and thus confirmed heterogeneity of MSCs. We found that expression of CD200 was characteristic for the clones with osteogenic potential, whereas SSEA4 marked adipogenic progenitors lacking osteogenic capacity, and CD140a was expressed in adipogenic cells independently of their efficiency for osteogenesis. We confirmed our observations in cell sorting experiments and further investigated the expression of those markers during the course of differentiation. Thus, our findings provide to our knowledge the most comprehensive characterization of surface antigens expression in mouse BM MSCs to date, and suggest CD200, SSEA4 and CD140a as markers differentially expressed in distinct types of MSC progenitors

Retinal Organoids from Pluripotent Stem Cells Efficiently Recapitulate Retinogenesis.

The plasticity of pluripotent stem cells provides new possibilities for studying development, degeneration, and regeneration. Protocols for the differentiation of retinal organoids from embryonic stem cells have been developed, which either recapitulate complete eyecup morphogenesis or maximize photoreceptor genesis. Here, we have developed a protocol for the efficient generation of large, 3D-stratified retinal organoids that does not require evagination of optic-vesicle-like structures, which so far limited the organoid yield. Analysis of gene expression in individual organoids, cell birthdating, and interorganoid variation indicate efficient, reproducible, and temporally regulated retinogenesis. Comparative analysis of a transgenic reporter for PAX6, a master regulator of retinogenesis, shows expression in similar cell types in mouse in vivo, and in mouse and human retinal organoids. Early or late Notch signaling inhibition forces cell differentiation, generating organoids enriched with cone or rod photoreceptors, respectively, demonstrating the power of our improved organoid system for future research in stem cell biology and regenerative medicine

Clonal Analysis Delineates Transcriptional Programs of Osteogenic and Adipogenic Lineages of Adult Mouse Skeletal Progenitors.

Bone, cartilage, and marrow adipocytes are generated by skeletal progenitors, but the relationships between lineages and mechanisms controlling their differentiation are poorly understood. We established mouse clonal skeletal progenitors with distinct differentiation properties and analyzed their transcriptome. Unipotent osteogenic and adipogenic cells expressed specific transcriptional programs, whereas bipotent clones combined expression of those genes and did not show a unique signature. We tested potential regulators of lineage commitment and found that in the presence of interferon-γ (IFNγ) adipogenic clones can be induced to osteogenesis and that their adipogenic capacity is inhibited. Analysis of IFNγ-regulated genes showed that lineage signatures and fate commitment of skeletal progenitors were controlled by EGR1 and EGR2. Knockdown experiments revealed that EGR1 is a positive regulator of the adipogenic transcriptional program and differentiation capacity, whereas EGR2 inhibits the osteogenic program and potency. Therefore, our work revealed transcriptional signatures of osteogenic and adipogenic lineages and mechanism triggering cell fate.This study was supported by the Collaborative Research Grant SFB-655 (German Research Foundation - DFG) to K.A. The Next Generation Sequencing facility was also supported by the SFB-655. P.B. and M. Riminucci are supported by Fondazione Cenci Bolognetti, Telethon (grant GGP15198)

Transposon-mediated BAC transgenesis in human ES cells

Transgenesis is a cornerstone of molecular biology. The ability to integrate a specifically engineered piece of DNA into the genome of a living system is fundamental to our efforts to understand life and exploit its implications for medicine, nanotechnology and bioprospecting. However, transgenesis has been hampered by position effects and multi-copy integration problems, which are mainly due to the use of small, plasmid-based transgenes. Large transgenes based on native genomic regions cloned into bacterial artificial chromosomes (BACs) circumvent these problems but are prone to fragmentation. Herein, we report that contrary to widely held notions, large BAC-sized constructs do not prohibit transposition. We also report the first reliable method for BAC transgenesis in human embryonic stem cells (hESCs). The PiggyBac or Sleeping Beauty transposon inverted repeats were integrated into BAC vectors by recombineering, followed by co-lipofection with the corresponding transposase in hESCs to generate robust fluorescent protein reporter lines for OCT4, NANOG, GATA4 and PAX6. BAC transposition delivers several advantages, including increased frequencies of single-copy, full-length integration, which will be useful in all transgenic systems but especially in difficult venues like hESCs

Lineage Commitment of Conditionally Immortalized Bone Marrow Mesenchymal Stromal Cells from Tetracycline-Regulated SV40 Large T-antigen Transgenic Mice

Adult bone marrow contains a population of mesenchymal stem cells capable to self-renew and to differentiate into haematopoietic-supportive stroma, osteo, adipo- and chondrocytes. However, the identity of mesenchymal stem cells still remains uncertain. The complex population of their descendants, bone marrow mesenchymal stromal cells (BM MSCs), represents a model to study the principles of differentiation and commitment into mesodermal lineages. The experiments using BM MSCs are often hampered by their low proliferative capacity in vitro. In the present study, we established conditionally immortalized BM MSCs from tetracycline-regulated SV40 Large T-antigen transgenic mice. The identity of the conditionally immortalized BM MSCs was confirmed by marker expression, ability to support haematopoiesis and differentiation potential. The advantages of the conditional immortalization are encompassed in (1) indefinite expansion of cell populations, (2) possibility to perform cellular cloning and (3) prevention from spontaneous differentiation. We demonstrated the heterogeneity of BM MSCs and identified at least 6 types of progenitors within BM MSCs population based on their differentiation potential (“OAC”, “OA”, “OC”, “AC”, “O”, “A”). A hypothetical model of BM MSC hierarchy and the relationships between the progenitors has been proposed. We observed that the Wnt/β-catenin signaling pathway and GSK3 activity could modulate the efficiency of osteo- and adipogenic differentiation pathways, but we didn’t find evidence that the lineage commitment of BM MSCs is determined by Wnt. We elucidated the mechanism of transcriptional regulation of the adipogenic induction of BM MSCs in vitro. Our data revealed the key regulatory role of PPARγ1 during adipogenesis in BM MSCs. Furthermore, we assume that PPARγ1 is a potential trigger of the adipogenic commitment of the BM MSCs progenitors. Finally, the non-adipogenic BM MSCs progenitors were converted into the adipogenic lineage using ectopical expression of the transcription factors C/EBPα, C/EBPβ and C/EBPδ. Our findings provide a novel insight into the molecular mechanisms of BM MSCs lineage commitment

Lineage Commitment of Conditionally Immortalized Bone Marrow Mesenchymal Stromal Cells from Tetracycline-Regulated SV40 Large T-antigen Transgenic Mice

Adult bone marrow contains a population of mesenchymal stem cells capable to self-renew and to differentiate into haematopoietic-supportive stroma, osteo, adipo- and chondrocytes. However, the identity of mesenchymal stem cells still remains uncertain. The complex population of their descendants, bone marrow mesenchymal stromal cells (BM MSCs), represents a model to study the principles of differentiation and commitment into mesodermal lineages. The experiments using BM MSCs are often hampered by their low proliferative capacity in vitro. In the present study, we established conditionally immortalized BM MSCs from tetracycline-regulated SV40 Large T-antigen transgenic mice. The identity of the conditionally immortalized BM MSCs was confirmed by marker expression, ability to support haematopoiesis and differentiation potential. The advantages of the conditional immortalization are encompassed in (1) indefinite expansion of cell populations, (2) possibility to perform cellular cloning and (3) prevention from spontaneous differentiation. We demonstrated the heterogeneity of BM MSCs and identified at least 6 types of progenitors within BM MSCs population based on their differentiation potential (“OAC”, “OA”, “OC”, “AC”, “O”, “A”). A hypothetical model of BM MSC hierarchy and the relationships between the progenitors has been proposed. We observed that the Wnt/β-catenin signaling pathway and GSK3 activity could modulate the efficiency of osteo- and adipogenic differentiation pathways, but we didn’t find evidence that the lineage commitment of BM MSCs is determined by Wnt. We elucidated the mechanism of transcriptional regulation of the adipogenic induction of BM MSCs in vitro. Our data revealed the key regulatory role of PPARγ1 during adipogenesis in BM MSCs. Furthermore, we assume that PPARγ1 is a potential trigger of the adipogenic commitment of the BM MSCs progenitors. Finally, the non-adipogenic BM MSCs progenitors were converted into the adipogenic lineage using ectopical expression of the transcription factors C/EBPα, C/EBPβ and C/EBPδ. Our findings provide a novel insight into the molecular mechanisms of BM MSCs lineage commitment

Differential Expression of Surface Markers in Mouse Bone Marrow Mesenchymal Stromal Cell Subpopulations with Distinct Lineage Commitment

Bone marrow mesenchymal stromal cells (BM MSCs) represent a heterogeneous population of progenitors with potential for generation of skeletal tissues. However the identity of BM MSC subpopulations is poorly defined mainly due to the absence of specific markers allowing in situ localization of those cells and isolation of pure cell types. Here, we aimed at characterization of surface markers in mouse BM MSCs and in their subsets with distinct differentiation potential. Using conditionally immortalized BM MSCs we performed a screening with 176 antibodies and high-throughput flow cytometry, and found 33 markers expressed in MSCs, and among them 3 were novel for MSCs and 13 have not been reported for MSCs from mice. Furthermore, we obtained clonally derived MSC subpopulations and identified bipotential progenitors capable for osteo- and adipogenic differentiation, as well as monopotential osteogenic and adipogenic clones, and thus confirmed heterogeneity of MSCs. We found that expression of CD200 was characteristic for the clones with osteogenic potential, whereas SSEA4 marked adipogenic progenitors lacking osteogenic capacity, and CD140a was expressed in adipogenic cells independently of their efficiency for osteogenesis. We confirmed our observations in cell sorting experiments and further investigated the expression of those markers during the course of differentiation. Thus, our findings provide to our knowledge the most comprehensive characterization of surface antigens expression in mouse BM MSCs to date, and suggest CD200, SSEA4 and CD140a as markers differentially expressed in distinct types of MSC progenitors