Stem cell | EPFL Graph Search

In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each. They are usually distinguished from progenitor cells, which cannot divide indefinitely, and precursor or blast cells, which are usually committed to differentiating into one cell type. In mammals, roughly 50–150 cells make up the inner cell mass during the blastocyst stage of embryonic development, around days 5–14. These have stem-cell capability. In vivo, they eventually differentiate into all of the body's cell types (making them pluripotent). This process starts with the differentiation into the three germ layers – the ectoderm, mesoderm and endoderm – at the gastrulation stage. However, when they are isolated an

Modeling the cornea: an architectural approach

Julien Graber

Nowadays the mechanism regulating the corneal epithelium renewal still remains unclear. Until now it was thought to be the fact of stem cells distributed in the limbus, generating TA cells migrating towards the central cornea and responsible for its renewal. But Majo and Barrandon (Nature Oct 2008) showed the presence of stem cell within the corneal epithelium and the ability of this epithelium to renew without limbal contribution. They prove that the limbal epithelium was involved only in healing processes. To simulate and test the relevance of the different hypothesis a model able to map cells location precisely and analyse or predict their movements in function of the internal forces and tissue biomechanics must be created. In this project I have created a mouse cornea architectural model. It was based on three dimensional reconstruction of a mouse eye using histological cuts. The model include two main parameters; the curvature of the different eye part and their thickness. The techniques developed and used in this project are easily reproducible for the construction of other cornea or eye model of diverse species for instance. This model can be used in clonal analysis to locate cells or groups of cells three-dimensionally. Besides analysis of the corneal structure at the cellular level was performed by the observation of clones (expressing

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-galactosidase), present in the limbus and cornea epithelium. Their location, form and orientation were investigated. This work provides a useful tool in the study of corneal epithelium renewal. Moreover it establishes the basis for the development of a future biomechanical model that will simulate tissue deformation, internal forces or cell movements. Studies of corneal parameters will be performed on enucleated eyes under normal physiological conditions inside an incubator regulating variables such as temperature, intraocular pressure or humidity level, currently develop in the laboratory

2009

Thymic epithelial cells

Paola Bonfanti

As primary lymphoid organ, the thymus provides the essential environment for maturation and selection of functional T lymphocytes. Thymic epithelial (TE) cells derive from the endoderm, and more specifically, from the third pharyngeal pouch. The thymic epithelium is organized in a three-dimensional architecture that does not easily fit into standard classifications of simple or stratified epithelia. Moreover, the mechanisms that maintain the epithelial compartment in the post-natal thymus remain unclear. Although they have been postulated to exist as in all epithelia, thymic stem cells have not been clearly identified to date. One crucial property of adult multipotent stem cells (SCs) in the skin and other stratified epithelia is clonogenicity, i.e the ability of a single cell to give rise to a cell population. Epidermal clonogenic keratinocytes can be propagated for several generations in vitro and can permanently engraft when transplanted onto patients. In the absence of reliable molecular markers to identify and purify multipotent SCs, the demonstration that they can selfrenew in vitro and in vivo represents, to date, the best method to assess stemness. Likewise, the thymus contains epithelial cells that express genes usually only expressed in the skin or other stratified epithelia, thus suggesting the existence of a possible relationship. In the work described in this thesis, we investigated the potentialities of rat primary TE cells through clonal analysis and functional assays. We demonstrate that embryonic and postnatal rat primary TE cells have a clonogenic growth pattern in vitro. We also describe the molecular signature of subtypes of thymic keratinocytes and address the postnatal role of developmentally regulated genes which are commonly expressed in skin and thymus. Clones of rat TE cells have been transplanted onto developing skin in order to evaluate their response to skin morphogenetic signals. Similarly, the response of these clones, as well as of clones obtained from hair follicles, to a thymic environment has been investigated. We demonstrate that cultured TE cells share morphological, phenotypic and functional characteristics with skin multipotent stem cells. When challenged in thymic or skin in vivo assays the clonal progeny of a single TE cell is able to integrate into a functional thymus or give rise to all skin derivatives respectively, i.e. epidermis, hair follicle and sebaceous gland. Conversely skin cells cannot participate to thymic reconstitution. Uncovering the relationship of TE cells with stem cells of stratified epithelia may provide important insights into the molecular basis of diseases involving both thymus and skin.

EPFL2008

Innovative strategy of corneal epithelium regeneration using fabricated soft contact lens containing cavities for stem cells transplantation

Julien Graber

Transplantation of donor cornea is widely performed with a high success rate to treat patients with impaired corneal transparency. However the limited number of donors has led scientists to search for new technologies and treatments, including stem cell therapies. We have developed a device that permits the transplantation of stem cells onto the cornea in order to regenerate a functional epithelium. It is shaped as a contact lens and it possesses cavities in its internal portion that are filled with a cell suspension. The device is used as a carrier to transfer the cells onto the cornea. To test and validate our approach we created an ex vivo system to perform long-term organotypic culture on the cornea of enucleated pig eyes. We seeded corneal epithelial cells onto pig stromas. We demonstrate that 30'000 donor cells can regenerate an entire epithelium in organotypic culture conditions. By using our culture system no living animals were required during the conception and evaluation of the device. We performed preliminary in vivo trials on rabbits, which showed promising results. We aim to create a user-friendly and low cost ocular surface reconstruction procedure that will be an alternative to current treatments. The advantages of our strategy are that it will not require cell culture or tissue preparation, as is the case for usual tissue-based grafts. Hopefully this technique could extend to clinical studies and could one day be used as an ocular surface reconstruction procedure.

EPFL2014

Thymic epithelial cells

Paola Bonfanti

EPFL2008

Modeling the cornea: an architectural approach

Julien Graber

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2009