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Two antibodies against membrane skeleton proteins: epiplasmin B [135kDa] and fenestrin [64 kDa] are markers of the cell polarity of the ciliate Tetrahymena thermophila

Polarity is a common feature of many different cell types (budding yeasts, the C. elegans zygote, the Drosophila oocyte, mammalian epithelia cells). In these cells during a specific stage of cytoskeletal reorganization, the acquisition of cell polarity is associated with a transient immunostaining of the polar region with specific antibodies against either some types of microtubule or membrane skeletal proteins. In this study, the cells of Tetrahymena thermophila were immunostained throughout the cell cycle with an anti-epiplasm antibody directed against B protein, [Williams et al., and with an antibody directed against the fenestrin which co-localizes with the epiplasm-microtubule contact zones in the cortex [Nelsen et al., J. Eukaryot. Microbiol. 41 (1994) 483]. During divisional morphogenesis of T. thermophila, these antibodies showed a number of cell cycle dependent changes in their patterns of cortical disposition of labeling. At late anaphase stage, the anti-fenestrin mAB specifically labeled the cortex of the apical poles of the prospective daughter cells with a weakening of the anti-B label in these areas. It suggested that these antibodies may serve as markers of cell polarity in Tetrahymena. Three lines of evidence indicate that these markers are specifically associated with the acquisition of cell polarity: 1) the anti-fenestrin marker of the apical region appeared during the reorganization of the cytoskeleton even in the absence of cell division, during the so-called oral replacement pathway; 2) it appeared in a proper stage in the phenotypes of a mouthless mutant II8G i.e. in the absence of the microtubular oral apparatus, which in Tetrahymena nearly co-localizes with the apex; and 3) the markers did not appear in phenotypes of the cdaA1 mutant which showed defects in cell polarity. Taken together, these results confirmed that epiplasmin and fenestrin antibodies may serve as specific markers of cell polarity in Tetrahymena thermophila.