Mitotic errors

Kadura, S., 8c Sazer, S. (2005). SAC-ing mitotic errors How the spindle assembly checkpoint (SAC) plays defense against chromosome mis-segregation. Cell Motility and the Cytoskeleton, 61,145—160. 

Aneuploidy is consequential to mitotic errors malignantly transformed cells frequently commit mitotic errors. In fetal life, the developing human brain suffers of chromosomal segregational defects during mitoses of glial cells and neurons. Aneuploid brain cells are eliminated by apoptosis. Areas not cleared by apoptosis, remain confined to sites of chromosomal mosaicism. The presence of functionally active aneuploid neurons negatively affect neuron-to-neuron and neuron-to-gUal interactions [1291]. 

Several issues needed to be addressed to devise a strategy to address the question of how attachment errors were corrected. First, kinase inhibition should be temporally controlled to experimentally isolate the error correction process, as Aurora kinases have been implicated in multiple mitotic processes. Second, error correction likely involves some regulation of the dynamics of the microtubule fibers that attach chromosomes to the spindle. These dynamics can be analyzed with high temporal and spatial resolution by high-resolution microscopy in living cells. Finally, the dynamics of individual microtubule fibers are difficult to analyze if that fiber is obscured by other microtubules in the spindle. The dynamics can be clearly observed, however, under conditions in which the improperly attached chromosomes are positioned away from the spindle body. 

In addition to Intranuclear effects, DES disrupts mitotic and meiotlc spindles resulting in errors in cell division (JJ2) it is believed that DES acts directly on tubulin within 10 minutes of exposure since DES inhibits the GTP-dependent self-assembly of tubulin (11) and inhibits colchicine binding (12) ihe effect of DES is similar to that of colchicine which also specifically binds to tubulin and prevents the formation of microtubules and spindles. 

Errors in mitotic chromosomal segregation are one pathway for aneuploidy and the deterioration of cells and represent one step towards tumor formation. In this context it is noteworthy that PARP-1 as wells as PARP-3 and probably also TANK-1 are involved in regulation of centtioles and centrosomes. PARP-3 is localized at the dai hter centriole and interacts there vnth PARP-1 PARP-1, on the other hand, has been shown to modify centiosomal proteins, and inhibition of its aaivity leads to hyperamplification of cenuosomes, giving rise to aberrant cell division. ... 

There are several human homonuclear cell lines in culture in which chromosomal deviations from euploidy have been reported (e.g., Huang et aLy 1969). In established heteronuclear cell lines, such as the Chinese hamster cell line that we have used, aneuploidy or deletion of specific chromosomal regions may have occurred through mitotic disjunctional errors or... 

The sporadic failure of leukocyte cultures or occasional low mitotic rates in long-term stationary tissue cultures necessitates experimental replication, preferably on different days. Ideally, all concentrations and exposure times of the agent should be repeated in each experiment. In addition to replicate cultures for each experiment, replicate cytological observations are also important to eliminate possible sampling errors. To this end, multiple slides should be made from each culture and examined on different days. To overcome possible observer bias, the same cells should be evaluated by more than one investigator and the results compared. Such a system would allow comparisons of precision to be made by a single observer at different times as well as by two different observers. 

Figure 26.3 (a) Representative mitotic index assay data for racemic dosabulin and its purified enantiomers. Data points are mean standard error in the mean of an experiment conducted in triplicate. "%PH3 positive cells" refers to the proportion of cells stained with an antibody against phosphor-histone H3. "CPD" = compound... 

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