Microtubule rearrangements during mitosis in multinucleate cells

Abstract

The peroxidase-antiperoxidase (PAP) method for the detection of polymerized tubulin has been used to study the microtubule rearrangements during mitosis in PtK1 and HeLa multinucleate cells obtained by polyethyleneglycol (PEG)-mediated fusion. We demonstrate here that the transition of the microtubular cytoskeleton from interphase to mitosis is an inducible event and independent of the factor(s) responsible for chromatin condensation and nuclear envelope breakdown. However, for the induction of the microtubule rearrangements nuclear envelope breakdown is required. At midprophase, cytoskeletal microtubule rearrangements start for multinucleate PtK1 cells, whereas in HeLa cells such changes are delayed, and a more abrupt transition is observed here. After complete nuclear envelope breakdown (prometaphase) mitotic asters and spindles but no cytoplasmic (interphase) microtubuli can be observed in both systems. Metaphase is characterized by an interaction between the different mitotic poles which show the form of bipolar spindles, but individual separated mitotic poles far removed from the chromatin can also be seen.

Separating centrosomes interact in the absence of associated chromosomes during mitosis in cultured vertebrate cells

“…It, therefore, remains to be determined whether separating centrosomes interact to form a spindle-shaped array of Mts in the absence of chromosomes, and if so whether this structure is stable. In this regard, homokaryons and heterokaryons, formed by fusing the same or different cell types, sometimes enter mitosis with one or more centrosomes that are too far removed from the chromosomes to form an association [e.g., Peterson and Berns, 1979;Armas-Portela et al, 1988]. We reasoned that this system could be used to determine the extent to which free centrosomes interact in the absence of associated chromosomes during mitosis in mammalian cells.…”

Characterization of proteins immunologically related to brain microtubule-associated protein MAP-1B in non-neural cells

“…Perhaps the phosphorylation of the 220K protein may play a role in this process, as it has been reported that phosphorylation of MAP-IB polypeptides may favour their association with microtubules (Dfaz-Nido et al 1988). Furthermore, it has been observed that centrosomes are able to organize the mitotic spindle only after nuclear envelope breakdown (Armas-Portela et al 1988;Vandre et al 1984a,6). This transformation has-been partly ascribed to the binding of nuclear phosphoproteins (Vandre et al 1984a,b).…”