Cell potency | EPFL Graph Search

Cell potency is a cell's ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum, begins with totipotency to designate a cell with the most differentiation potential, pluripotency, multipotency, oligopotency, and finally unipotency. Totipotency Totipotency (Lat. totipotentia, "ability for all [things]") is the ability of a single cell to divide and produce all of the differentiated cells in an organism. Spores and zygotes are examples of totipotent cells. In the spectrum of cell potency, totipotency represents the cell with the greatest differentiation potential, being able to differentiate into any embryonic cell, as well as any extraembryonic cell. In contrast, pluripotent cells can only differentiate into embryonic cells. A fully differentiated cell can return to a state of totipotency. The conversion to t

Molecular and Functional Characterization of Clonogenic Human Thymic Epithelial Cells

Melissa Maggioni

The thymus is a primary lymphoid organ where bone marrow derived T-cell progenitors come in contact with a unique microenvironment able to sustain their maturation into functional T-cells. This fundamental immunological function of the thymus is supported by thymic epithelial cells, which represent the main component of the thymic stroma. The thymic stroma is organized in a characteristic tridimensional structure that can be distinguished into two main regions, namely, the cortex and medulla. These two regions are responsible for two fundamental processes in the thymus: the positive- and negative- selection of T-cells. The first one involves the selection of T-cells able to react with antigens presented mainly on the surface of cortical cells. T-cell negative selection, meanwhile, is responsible for the elimination of self-reactive T-cells and it is mainly carried out by medullary thymic epithelial cells. The thymic epithelium derives from the primitive endoderm and cortical and medullary thymic epithelial cells have been demonstrated to originate from a common embryonic progenitor population. Currently, the presence of such population has not been described in adult animals and the mechanisms responsible for the maintenance of the post-natal thymus have yet to be clarified. Recently, Bonfanti and colleagues demonstrated that the rat thymus contains a population of clonogenic epithelial cells (rTECs), able to self-renew in the culture system developed in 1975 for epidermal stem cells [Bonfanti et al., 2010, Rheinwald and Green, 1975]. As clonogenicity is a property of skin and other stratified epithelia stem cells, the clonogenic capacity of TECs suggests them as potential thymic epithelial stem cells. Bonfanti and colleagues also demonstrated that rTECs displayed the capacity to integrate into a thymic microenvironment and to express thymic functional markers. The work described in this thesis aims to investigate the stem cell potency and the regenerative capacity of the human thymus. We demonstrated that the human thymus also contains a population of clonogenic thymic epithelial cells (hTECs) able to self-renew and to maintain a general thymic phenotype in the culture system used for skin stem cells and for rTECs. By clonal analysis, we showed that hTECs can be distinguished in three sub-populations, which displayed different molecular phenotypes and different growth and differentiation potentials in vitro. We then investigated the role of Foxn1 transcription factor in hTECs, as Foxn1 is know to be involved in thymic epithelial cells differentiation during development and also in the maintenance of the adult thymus in mice. By experimentally down-regulating Foxn1, we demonstrated that Foxn1 expression is required to sustain the growth of one of the described hTEC sub-populations. We next investigated the differentiation capacity of clonogenic hTECs. Currently, additional experiments are still required to assess hTECs ability to integrate and differentiate in a functional thymic environment. Bonfanti and colleagues also demonstrated that rTECs, if challenged in a hair follicle morphogenetic assay, can be reprogrammed into skin stem cells. Therefore, we decided to investigate the potential of hTECs in an epidermal differentiation assay. In these conditions, hTECs did not show the ability to differentiate into epidermis, probably due to the absence in this assay of the strong morphogenetic signals responsible for the reprogramming process of rTECs into skin stem cells.

EPFL2012

Non-integrating episomal plasmid-based reprogramming of human amniotic fluid stem cells into induced pluripotent stem cells in chemically defined conditions

Lilia Salimova

Amniotic fluid stem cells (AFSC) represent an attractive potential cell source for fetal and pediatric cell-based therapies. However, upgrading them to pluripotency confers refractoriness toward senescence, higher proliferation rate and unlimited differentiation potential. AFSC were observed to rapidly and efficiently reacquire pluripotency which together with their easy recovery makes them an attractive cell source for reprogramming. The reprogramming process as well as the resulting iPSC epigenome could potentially benefit from the unspecialized nature of AFSC. iPSC derived from AFSC also have potential in disease modeling, such as Down syndrome or -thalassemia. Previous experiments involving AFSC reprogramming have largely relied on integrative vector transgene delivery and undefined serum-containing, feeder-dependent culture. Here, we describe non-integrative oriP/EBNA-1 episomal plasmid-based reprogramming of AFSC into iPSC and culture in fully chemically defined xeno-free conditions represented by vitronectin coating and E8 medium, a system that we found uniquely suited for this purpose. The derived AF-iPSC lines uniformly expressed a set of pluripotency markers Oct3/4, Nanog, Sox2, SSEA-1, SSEA-4, TRA-1-60, TRA-1-81 in a pattern typical for human primed PSC. Additionally, the cells formed teratomas, and were deemed pluripotent by PluriTest, a global expression microarray-based in-silico pluripotency assay. However, we found that the PluriTest scores were borderline, indicating a unique pluripotent signature in the defined condition. In the light of potential future clinical translation of iPSC technology, non-integrating reprogramming and chemically defined culture are more acceptable.

Taylor & Francis Inc2016

Bioengineering human bone marrow models to elucidate the triggers of the stem cell niche

Queralt Vallmajó Martín

The bone marrow (BM) microenvironment, or niche, significantly affects behaviors of its resident stem cell populations. Disruptions in the BM niche contribute to a number of severe clinical pathologies. Discovery of novel therapeutic strategies for BM-related diseases necessitates development of superior preclinical models to study parameters affecting BM homeostasis. To address this, a poly(ethylene glycol) hydrogel featuring a particular crosslinking chemistry based on the enzyme transglutaminase factor XIII, dubbed TG-PEG, was utilized to engineer humanized bone marrow models. Its modular nature was exploited throughout this work to systematically evaluate contributions of biophysical, cellular, and biochemical BM niche components to stem cell biology. Stiffness of TG-PEG hydrogels was optimized for each cell type and individual application explored. For bone formation by bone marrow stromal cells (BMSCs), an intermediate stiffness was optimal and significantly improved total bone volume over softer TG-PEG gels or natural materials. Results indicated that stability of the scaffold was more important than their chemical and biological properties. Alternatively, for hematopoietic stem and progenitor cells (HSPCs), softer gels were optimal for preserving multipotency while promoting cell proliferation. A number of BM-specific stem and progenitor cell types with richly diverse functions were explored. Skeletal stem cells (SSCs) encapsulated in TG-PEG hydrogels demonstrated their ability to form de novo bone in healing critically sized calvaria defects in mice. Next, subcutaneous implantation of BMSC-laden gels revealed their significant contribution to formation of ossicles. For some BMSC donors, ossicles could be formed in absence of bone morphogenetic protein (BMP)-2 offering a novel tool to evaluate their intrinsic capacity. Later, titration of BMSC seeding densities and BMP-2 doses yielded optimal conditions for robust BM formation, regardless of donor, enabling reproducibility for follow-on studies involving BM models. In humanized mice, homing of HSPCs to BMSC-laden TG-PEG gels was observed. Finally, humanized xenograft models were employed to determine vulnerability of the BM niche to subversion by cancer cells simulating osteotropism for both leukemia and breast cancer metastasis. Molecular factors known to trigger particular cell reactions within the niche were also investigated. Including RGD cell-adhesion ligands, as well as matrix metalloproteinase (MMP)-susceptible crosslinks to render the gels degradable, were critical for facilitating migration of recruited BM cells from murine hosts in xenograft studies. Hyaluronic acid (HA), when added to the hydrogel backbone, conferred superior engraftment to transplanted BMSCs and afforded reduced immunogenicity. Incorporation of the Notch-signaling ligands Jagged1 or DLL-4 into soft TG-PEG gels during in vitro HSPC expansion substantially stimulated proliferation, but recovered cells could no longer ensure long-term reconstitution. Aging, trauma, or cancer can cause disruptions of the tightly controlled balance between cells and their microenvironment in the BM niche. This body of work presents a number of bioengineered tools optimized for studying how niche components are affected by or contribute to such pathologies. Further work with these or similar models will no doubt highlight key clinically relevant targets and inform novel therapeutic approaches.