Institute of Environmental Sciences, Jagiellonian University Krakow
Abstract
Summary. During cell cycle of a ciliate Tetrahymena thermophila the divisions of micro- and macronucleus, cortical morphogenesis and '
cytokinesis are temporarily coordinated. Cortical morphogenesis begins with proliferation of the new ciliary basal bodies (BBs) within
meridional cortical rows of ciliary BBs, and with the local proliferation of BBs, which form the new oral apparatus (OA2), positioned subequatorialy
and destined for prospective posterior daughter cell (opisthe). Prior to cytokinesis, two prospective daughter cells are of equal
size and show metamery of their cortical patterns. We studied effects of 20 uM roscovitine (an inhibitor of several cyclin-dependent kinases)
on the cell cycle progression of T. thermophila. We showed that roscovitine delayed cell division, delayed or arrested macronuclear division
and induced increase of cell size and the number of BBs in the cortical rows. The increase in the number of BBs in cortical rows induced
cell elongation which was proportional to the increase in cell surface area. There was uncoupling between this BBs_proliferation which
is continued during prolonged cell cycle and delayed cytokinesis, what resulted in topological alteration of the respective positions of the
OA2 and of the contractile vacuole pores (CVPs). In roscovitine treated cells, the new OA2 was positioned subequatorialy, but the fission
zone was shifted posterior to the equatorial plane of the cell and positioned across and in the extreme cases behind of the new OA2. This
resulted in the formation of a large proter and small size opisthe. The roscovitine treatment induced a formation of a plethora of phenotypes
of postdividing cells. We found that irrespective of changes in divisional morphogenesis induced by roscovitine treatment, all mature BBs
were associated with the cdc!4-like phosphatase. Taken together all these data indicate that during cell cycle of T. thermophila the normal
morphology of the daughter cells depends on the proper division of micro- and macronucleus and on temporal control of BBs proliferation
along the longitudinal rows, during OA2 stomatogenesis and during selection of BBs involved in differentiation of apical BBs (couplets)
and cell division.
Key words: Tetrahymena, roscovitine, basal bodies, morphogenesis, macronucleus, cdc!4p.
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