Cytoskeletal changes in epithelial cells during the symbiotic infection of Euprymna scolopes by Vibrio fischeri
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In the study of symbiotic relationships a system with only two species is ideal. The Hawaiian bobtail squid, Euprymna scolopes, and the bioluminescent gram-negative bacteria, Vibrio fischeri, establish such a relationship. V fischeri infects the epithelial crypts of the light organ of E. scolopes within hours after hatching, and confers light emitting ability upon the squid. Changes of the cytoskeleton and volume increases of the epithelial cells lining the crypts are observed as a result of this infection. By using small, fluorescent probe molecules, characterization of cytoskeletal changes and quantitative measurement of the volume increases caused by V. fischeri infection of the epithelial crypt cells in E. scolopes was possible. These probes revealed microfilaments and microtubules in both infected and asymbiotic animals, including the circumferential microfilament bundles characteristic of epithelial cells and the axonemal cores of cilia. Also, tubulin-associated inclusions appeared in the apical regions of epithelial cells of infected crypts.
Previous literature on this symbiotic relationship has described the cell volume increase as cell swelling, an edematous response; however, this has not been empirically determined. As the light producing reaction of the bacteria directly consumes oxygen, it is possible that the bacteria cause local hypoxia during light emission and the cell volume increase of the epithelial crypt cells is a pathological response. An alternative explanation for the cell volume increase of infected epithelial crypt cells is a bacterial mediated hypertrophy. Therefore, I tested the hypothesis if cell volume increase and cytoskeletal reorganization are caused by hypoxia in infected squid, then a relationship should exist among cytoskeletal changes, cell swelling, light production, and oxygen consumption in the light organ crypts. Oxygen uptake rates indicated that hypoxia could exist in the light organ crypts, however, the morphological change, as observed by transmission electron microscopy, was not typical of hypoxia-induced pathology. Epithelial crypt cells enlarged during the diel symbiotic cycle however, the increased volume did not appear as edematous swelling, but rather as hypertrophy of the cytoplasm and/or engorgement resulting from uptake of V. fischeri. The results did not support a role for hypoxiainduced cell swelling, and suggested the hypertrophic changes in the epithelial cells instead result from physiological interactions between the prokaryotic guest and the eukaryotic host.
CitationWhite, P. A. (2001). Cytoskeletal changes in epithelial cells during the symbiotic infection of Euprymna scolopes by Vibrio fischeri (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.
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