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|Title:||Immunoelectron Microscopy Provides Evidence for the Extramitchondrial Localization of a Number of Nuclear- and Mitochondrial- DNA Encoded Proteins|
|Advisor:||Gupta, R. S.|
|Abstract:||Mitochondrial proteins are presently believed to reside and function only within the mitochondria, under normal physiological conditions. However, in recent years many examples have come to light where proteins originally identified on the basis of extramitochondrial functions, upon characterization were found to be bonafide mitochondrial proteins. This raises important questions concerning the cellular functions of mitochondrial proteins. To investigate this phenomenon of mitochondrial proteins being present at extramitochondrial locations, we have examined by means of immunoelectron microscopy, the subcellular localization in normal rat tissues of a number of well characterized mitochondrial proteins which are encoded either by the nucleus (chaperonin 10 (Cpn10) and mitochondrial aspartate aminotransferase (mAspAT)), or by mitochondrial DNA (Cytochrome c oxidase subunits I and II (COX I and II)), using highly specific antibodies. Both Cp10 and mAspAT have already been shown to be involved in extramitochondrial functions. Cpn10 has been shown to be identical to early pregnancy factor, which is an immunosuppressant and growth factor found in maternal serum. mAspAT is identical to fatty acid binding protein isolated from plasma membranes of several cell types, involved in the transport of long chain free fatty acids. Immunofluorescent labeling of BS-C-1 African monkey kidney cells with these antibodies showed characteristic mitochondrial labeling. In all tissues examined, the antibodies showed strong labeling of mitochondria, as was expected. In several tissues, the binding was seen exclusively within mitochondria. However, in a variety of tissues such as pancreas, anterior pituitary and kidney, these antibodies showed strong and specific labeling of one or more of the following compartments- pancreatic zymogen granules, growth hormone granules, secretory granules in islet cells, red blood cells, condensing vacuoles in kidney and on the cell surface of different regions of the kidney. All of the observed labeling with these antibodies, both within mitochondria and in other compartments, was abolished upon omitting the primary antibodies or upon adsorption of the Cpn10 antibody (in the case of Cpn10) with purified recombinant protein. The extramitochondrial localization of these proteins, particularly those encoded by mitochondrial DNA provides strong evidence that these proteins have reached these sites by exiting from mitochondria. These observations have important implications concerning the roles of mitochondria and mitochondrial resident proteins in different mitochondrial diseases. Also, the function of these proteins and the precise mechanism by which they reach these extramitochondrial sites is of great interest.|
|Appears in Collections:||Digitized Open Access Dissertations and Theses|
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