Molecular Subdivision of the Cortex of Dividing Tetrahymena Is Coupled with the Formation of the Fission Zone

Abstract

In contrast to a mitotic-spindle-associated bipolar cytokinesis, the cytokinesis of polarized ciliates is preceded by a reorganization of the cortex into dual metameric patterns for prospective daughter cells and then separated by a transverse fission line. This study concerns relations between the generation of cortical metamery and the formation of the fission line in an amicronuclear (i.e., without mitotic spindle) ciliate, Tetrahymena pyriformis. The fission line appears in the division of T. pyriformis as a transverse line formed by equatorial gaps in the meridional ciliary rows, with the second oral structure (OA2) formed posterior to it. It was found that the metamery of cortical morphogenesis is expressed by the appearance of increased MPM2 antibody binding in dividing cells in an apical area and posterior to the fission line gaps, including patterned changes of this binding in both oral apparatuses (OA1 and OA2), and by a reciprocal decrease of binding of an anti-epiplasm antibody. These tested antigens are localized to different cortical structures, but in predividing cells both uniformly show formation of the fission line contrast of labeling. A serine/threonine kinase inhibitor, 6-dimethylaminopurine (6-DMAP), was applied to dividing T. pyriformis at specific stages: (1) if 6-DMAP was added to early dividing cells, it prevented cells from initiating cytokinesis. (2) If 6-DMAP was added to cells at stages close to the physiological transition point of cell division, it yielded either (i) a partial formation of the fission line on the ventral side, combined with modified growth of undivided cortex adjacent to the fission line, with abnormal cytokinesis, or (ii) variable anterior displacement of the complete fission line, which contracted slowly but uniformly. (3) If 6-DMAP was applied during cytokinesis, it did not delay cell division, but daughter cells become abnormal and underwent an incomplete oral reorganization. These results suggest that the generation of metamerism in the cortex of T. pyriformis involves differentiation of the asymmetric fission zone. At least four stage-dependent 6-DMAP-sensitive effects jointly control the progress of cell division and the mutual spatial relations between the generation of metamery and the appearance, completeness, and position of the fission zone in the cortex of polarized T. pyriformis.

Mob1: defining cell polarity for proper cell division

“…This specific polarized localization of Tetrahymena Mob1 points to the importance of basal bodies possessing distinct compositions, creating specialized landmarks inside a singlecelled organism. In fact, the presence of cortical gradients in Tetrahymena was previously postulated based on the spatial patterns of basal body proliferation that precede cleavage furrow constriction (Kaczanowski, 1978;Kaczanowska et al, 1999). In addition, studies of structural pattern mutants (Frankel, 2008) and on fenestrin localization below the fission line and accumulating at the anterior region in dividing cells (Nelsen et al, 1994;Cole et al, 2008) indicate the existence of an asymmetry in the cleavage furrow region.…”

What Do Genic Mutations Tell Us about the Structural Patterning of a Complex Single-Celled Organism?

“…The asymmetry of the developing fission zone has also been documented at the molecular level by the finding that one of the three major membrane-skeletal proteins, the EpiB protein, discovered by Williams and coworkers (162,164), is asymmetrically distributed on opposite sides of the fission zone in predividing and early-dividing cells (84,87), as are other cortical markers (84,85,116).…”

Novel Cytoskeletal Proteins in the Cortex of Tetrahymena1

“…It is predicted that EpiA and EpiB will show a similar behavior, based on previous observations (Honts 1991) and the report by Kaczanowska et al (1999) that describes a reduction in the EpiB staining near the midline. This suggests that there is a general reduction in the amount of these proteins within the membrane skeleton as the cell approaches cleavage.…”