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Identifier uch.biology.msc//2005papasozomenos
Title Υπερδομική χαρτογράφηση της πρωτεΐνης Fras1 στον εξωκυττάριο χώρο
Author Παπασωζόμενος, Χαράλαμπος
Abstract Basement membranes are thin, sheet like arrangements of extracellular matrix proteins that serve a variety of functions including the physical separation of cell layers and tissues, molecular ultrafiltration and tissue morphogenesis. Electronmicroscopically, typical basement membranes display two distinct zones, the lamina lucida and lamina densa. The lamina lucida contains anchoring filaments that extend to the hemidesmosomes and mediate the attachment of the epithelial cells to the basement membrane. The anchoring of the basement membrane to the mesenchyme is ensured by anchoring fibrils that are associated with the lamina densa and transverse the underlying zone termed sub-lamina densa. Fras1 gene, encodes a putative extracellular matrix multidomain protein (4010 amino acids) expressed from various epithelia of the developing embryo. Fras1 is a putative extracellular matrix protein which has been implicated in the structural adhesion of embryonic epidermis to dermis. Moreover, mutations in Fras1/FRAS1 have been associated with the mouse blebbed phenotype and the human rare genetic disorder Fraser syndrome, respectively. Loss of Fras1 function results in the formation of subepidermal hemorrhagic blisters as well as unilateral or bilateral renal agenesis during mouse embryogenesis. Previous reports demonstrated that dermal-epidermal separation upon blister formation in Fras1-/- mutants occurs below the lamina densa, implying a role for Fras1 at the level of basement membranemesenchymal adherence. In accordance with the previous, other reports indicate that Fras1 is detected underneath the lamina densa of embryonic lung epithelia and exerts its function below the lamina densa. Yet, so far few data exist on the ultrastructual localization of Fras1 within the extracellular space. We therefore performed immunogold labeling experiments in order to study the expression pattern of Fras1 within extracellular space. The aim of the present study was to investigate the ultrastructual immunolocalization of Fras1 within the basement membrane of the developing mouse skin epithelium and to compare with that of a different epithelium such as the esophagus. The epithelium of skin and esophagus that we studied is described as stratified squamous. We used a specific antibody against Fras1 in free floating sections of E14.5 mouse embryos. The protein was subsequently visualized on ultrathin sections as silver intensified gold particles. Ultrastructual immunogold labeling using antibodies raised against the central NG2-like domain of Fras1 detected the protein underneath the lamina densa of embryonic skin and esophagus. This finding is in accordance with the reported indications that Fras1 exerts its function below the lamina densa and is detected within sub-lamina densa of embryonic lung epithelia. Ultrastructual immunogold labeling experiments revealed identical expression pattern of Fras1 in both embryonic skin and esophagus. Notably, the deposition of the protein was also identical to the reported detection of Fras1 in embryonic lung epithelia. The above imply that Fras1 could be an indisputable component of embryonic basement membranes. Fras1 detected in several ultra-thin sections to be anchored on amorphous electron dense structures located underneath lamina densa. The origin and molecular composition of these structures has to be studied in order to evaluate the importance of these finding. We propose that the Fras1 localization may be connected to a well studied component of basal membranes, anchoring fibrils. Recently, Shimizu et al. suggested that 90% of the anchoring fibrils originated and terminated in the lamina densa. Our data suggest that Fras1 is detected in the lower part of anchoring fibrils within sub-lamina densa. Whether there is a potential colocalization between Fras1 and Collagen VII which is the major structural component of the anchoring fibrils, remains to be determined. In conclusion, we demonstrate that Fras1 is an indisputable component of embryonic sub-lamina densa of basal membranes of stratified squamous epithelia.
Language Greek
Issue date 2005-11-28
Date available 2007-11-28
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
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