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When cells die by apoptosis, cell fragments are engulfed by surrounding cells. It was recently shown that DNA contained in apoptotic bodies may transfer genetic information to the cells that ingest them. Apoptosis was induced in p53-negative rat embryo cells transfected with activated H-ras and human c-myc by irradiation or nutrient deprivation. When apoptotic rat cells were co-cultured with p53-negative mouse embryo fibroblasts, rat chromosomes and rat-mouse fusion chromosomes were found in the mouse cells. Transferred DNA was apparently functional, as mouse fibroblasts showed loss of contact inhibition and acquired a tumorigenic phenotype. If it conferred a strong selective advantage on the mouse cell, rat DNA was maintained and propagated. Apoptotic bodies from non-tumorigenic rat fibroblasts did not transform mouse cells and mouse cells with intact p53 function did not incorporate rat DNA. From these studies, it appears that lateral transfer of genes between cells in an organism can take place and may represent a mechanism for generating genetic diversity in tumors.
Bergsmedh A, Szeles A, Henriksson M, Bratt A, Folkman MJ, Spetz A-L, Holmgren L: Horizontal transfer of oncogenes by uptake of apoptotic bodies. Proc Natl Acad Sci USA 98:6408–6411, 2001.
Type II pneumocytes are the progenitor cells for type I pneumocytes and are the major producers of surfactant. They also undergo pathologic changes in response to a variety of lung insults. Stains such as the modified Papanicolaou and alkaline phosphatase cytochemistry preferentially stain type II cells, but are not highly specific for them. Investigators in Italy recently developed an immunohistochemical stain specific for type II peumocytes based on detection of catalse in peroxisomes using a rabbit polyclonal antibody. The technique works well on paraffin-embedded material using avidin-biotin complex or tyramide amplification techniques; a modified technique can also be used for immunoelectron microscopy. The technique was tested on rat lung. Staining was sufficiently selective and intense to allow automated image analysis.
Farioli-Vecchioli S, Nardacci R, Falciatori I, Stefanini S. Catalase immunocytochemistry allows automatic detection of lung type II alveolar cells. Histochem Cell Biol 115:333–339, 2001.[Medline]
Immunohistochemistry using mouse monoclonal antibodies against the Ki-67 antigen is useful in many species for the detection of proliferating cells. The antigen is expressed in all cells except those in G0 phase of the cell cycle. However, this antibody is not useful in the mouse. Instead, proliferation in mouse tissues is generally assessed immunohistochemically by 5-bromodeoxyuridine (BrdU) incorporation. Limitations of this technique include the need to inject the animals with BrdU ante mortem, BrdU incorporation into DNA undergoing repair, and variability in results due to the timing of BrdU injections. It was recently reported that the mouse monoclonal MIB-5 antibody successfully labeled nuclei of the proliferative fraction of cells in both normal murine tissues and murine tumors. To achieve both sensitivity and low background, antigen retrieval and direct biotinylation of the antibody were required. The results obtained with the MIB-5 antibody were comparable to those using the BrdU technique. Low background allowed computerized image analysis.
Birner P, Ritzi M, Musahi C, Knippers R, Gerdes J, Voightlander, Budka H, Hainfellner JA: Immunohistochemical detection of cell growth fraction in formalin-fixed and paraffin-embedded murine tissue. Am J Pathol 158:1991–1996, 2001.
Listeria moncytogenes is a foodborne pathogen that must cross the epithelium of the host intestine to establish infection. Bacterial internalization is promoted by the bacterial surface protein internalin, the receptor for which is E-cadherin, a host cell adhesion protein. Internalization of Listeria has been difficult to study in experimental systems, because the E-cadherins of mice and rats do not effectively bind internalin and the animals are relatively resistant to experimental infection with the organism via the oral route. Investigators in France have produced transgenic mice that overexpress human E-cadherin in intestinal epithelium. The mice became susceptible to oral infection with Listeria, and internalin-dependent bacterial internalization was demonstrated. It appears that the presence of a proline residue at the sixteenth amino acid position in E-cadherin is essential for the molecule to serve as an internalin receptor. These studies demonstrate that transgenic mice may be useful in studying the pathogenetic mechanisms of bacterial disease when conventional mice are not suitable.
Lecuit M, Vandourmael-Pournin S, Lefort J, Huerre M, Gounon P, Dupuy C, Babinet C, Cossrat P: A transgenic model for listeriosis: role of internalin in crossing the intestinal barrier. Science 292:1722–1725.
Swiss investigators have developed a novel technique that allows cyclic amplification of PrPSc, the conformationally altered form of a normal cell surface protein (PrPC). PrPSc is believed to constitute the infectious agent of the transmissible spongiform encephalopathies. For this assay, brain homogenate containing PrPSc was mix with normal brain homogenate containing PrPC. Each cycle of amplification included an incubation period followed by an episode of sonication. The smaller fragments of PrPSc generated by sonication were able to nucleate additional transformation of PrPC to PrPSc. Using this amplification technique, the authors were able to detect low levels of PrPSc in the brains of infected animals, thus the technique may be useful for disease diagnosis. This technique will also prove useful for studying the mechanisms by which prions cause disease, since the events that ordinarily take months to year to occur in vivo are compressed into a much shorter timeframe.
Saborio GP, Permanne B, Soto C: Sensitive detection of pathological prion protein by cyclic amplification of protein misfolding. Nature 411:810–813, 2001.[CrossRef][Medline]
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