Egestion of asbestos fibers in Tetrahymena results in early morphological abnormalities. A step in the induction of heterogeneous cell lines?
In Tetrahymena populations exposed to crocidolite asbestos fibers, many cells develop morphological abnormalities within 1-2 hours. The abnormalities are mainly large or small protrusions or indentations, or flattened parts of the cell surface and most often located in the posterior part of the cell. They are formed repeatedly in all cells but are also continuously repaired so that the fraction of cells affected represents an equilibrium between these two processes. Their formation is connected with egestion of the large bundles of fibers formed by phagocytosis. Such effects of egestion of fibers do not seem to have been reported previously. Egestion of a bundle of fibers is much slower than for other types of undigestible residues. In contrast to normal exocytosis occurring invariably at the cytoproct, egestion of asbestos often occurs in the posterior part of the cell outside the cytoproct. To my knowledge this is the first reported case of either very slow or extra-cytoproctal egestion in Tetrahymena. Cells with large abnormalities have a greater tendency to develop into "early heterogeneous" cells than the average abnormal cell. Some of these give rise to hereditarily stable heterogeneous cell lines of Tetrahymena. The morphological abnormalities are probably caused by mechanical action of the crocidolite fibers resulting in local damage of the cytoskeletal elements responsible for normal cell shape. The heterogenous cell lines may arise when cellular structures carrying non-genic cytotactically inherited information are modified. The relevance of these ideas to the induction of cancer by asbestos is briefly discussed.
Hjelm
K K
KK
Department of Molecular Biology, Odense University, Denmark.
D000818:Animals; D001194:Asbestos / Q000633:toxicity*; D017638:Asbestos, Crocidolite; D002460:Cell Line; D003599:Cytoskeleton / Q000473:pathology; D010587:Phagocytosis; D013768:Tetrahymena / Q000166:cytology*
D017638:Asbestos, Crocidolite; D001194:Asbestos