Epithelium | EPFL Graph Search

Epithelium or epithelial tissue is a thin, continuous, protective layer of compactly packed cells with a little intercellular matrix. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. There are three principal shapes of epithelial cell: squamous (scaly), columnar, and cuboidal. These can be arranged in a singular layer of cells as simple epithelium, either simple squamous, simple columnar, or simple cuboidal, or in layers of two or more cells deep as stratified (layered), or compound, either squamous, columnar or cuboidal. In some tissues, a layer of columnar cells may appear to be stratified due to the placement of the nuclei. This sort of tissue is called pseudostratified. All glands ar

Hormonal regulation of Stat5 in the mammary gland - from signaling to morphogenesis

Sergio Klinke

The mammary gland development is regulated by steroid and peptide hormones and occurs mainly after birth, compared to the majority of the other organs in the body. The principal hormones responsible for the breast development are the estrogen, the progesterone, the growth hormone, the epidermal growth factor and the prolactin. The latter one is of specific interest since it is required for further development of the gland through pregnancy and lactation. During pregnancy and lactation, alveolar structures develop and differentiate into secretory cells. The signal transducer and activator of transcription 5 (Stat5) is known to be the main effector of prolactin signaling during pregnancy, inducing alveologenesis and differentiation of epithelial cells into secretory cells. I investigated if Stat5 has a role before pregnancy. Protein expression as well as mRNA expression analysis of glands from ovariectomized mice which were artificially stimulated with ovarian hormones (estrogen and progesterone) and control vehicle showed evidences that Stat5 expression can be stimulated by these two hormones. Contrary to the role established until now for stat5 in the mammary gland, I found by fluorescence visualization of Stat5-null epithelium as well as whole mount staining of the same glands that Stat5 is required even before pregnancy since null epithelium showed highly reduced growth already in 3 weeks-old virgin mice. This may indicate a new role for this protein in cell proliferation or survival in early stages of mouse mammary development. Furthermore, transplantation experiment of Stat5-null epithelium into wild-type recipient mice showed that pregnancy state was not able to rescue the normal phenotype. This may be due to complete loss of these cells which happened during the 5 weeks left for the transplanted epithelium to expand the cleared fat pad. This discovery opens a new debate on Stat5 role in the mammary gland development.

2008

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

\beta

-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

Deciphering the subcapsular epithelial cells in human fetal and postnatal thymus

Diane Sophie Elodie Hemon

Most papers related to thymus focus on the cortical and medullary epithelial cells whereas the subcapsular layer is ignored. In this thesis, we are providing new informations about the subcapsular thymic epithelial cells (TECs) by comparing them to cortical TECs, medullary TECs, Hassall's corpuscles (HCs) and the epidermis. We have demonstrated that TECs located in the subcapsular region are polarized cells adhering to an organized basement membrane and that they are interconnected in a tridimensional meshwork with all other TECs, including the TECs located in the HCs. We have confirmed that the thymus epithelium has a highly complex architecture that looks like no other epithelium. The 3D structure is certainly important for thymus functionality. However, how the 3D structure impacts T cell instruction remains to be investigated. Additionally, we have demonstrated that the subcapsular TECs express the surface marker EPCAM. Therefore, subcapsular TECs are part of the sorted EPCAM+ TEC population. We have also investigated the expression of proteins important for epidermal morphogenesis and we have unraveled strong similarities between the development of thymic epithelial cells and epidermis. Furthermore, we have shown that epithelial clusters of TP63 positive and Ki67 positive cells are present in the fetal subcortical region. Our work emphasizes that subcapsular TECs are important components of the thymic epithelial network and that they warrant further investigation.

EPFL2017