Microinjection of the active 61-kD catalytic fragment of MLCK into mitotic cells delayed transit time to anaphase onset and increased motile surface activity, but did not prevent cytokinesis.
Does microinjection of the catalytic fragment of MLCK affect mitosis and cytokinesis in dividing cells?
Unregulated MLCK activity affects mitosis and cortical activities but does not alter the rate of cytokinesis, suggesting additional control mechanisms are involved.
Myosin light chain kinase (MLCK) is thought to regulate the contractile activity in smooth and non-muscle cells, and may play an important role in controlling the reorganization of the actin-myosin cytoskeleton during cell division. To test this hypothesis we have microinjected the 61-kD catalytic fragment of MLCK into mitotic cells, and examined the effects of unregulated MLCK activity on cell division. The microinjection of active 61 kD causes both a significant delay in the transit time from nuclear envelope breakdown to anaphase onset, and an increase in motile surface activity during and after metaphase. Control experiments with intact MLCK or with inactive catalytic fragment suggest that these effects are specifically induced by the unregulated myosin light chain kinase activity. Immunofluorescence analysis suggests that delays in mitosis are coupled to disruptions of spindle structures, while increased surface motility may be related to changes in the organization of actin and myosin at the cell cortex. Most importantly, despite the expression of strong phenotypes, 61 kD-injected cells still form functional cleavage furrows that progress through cytokinesis at rates identical to those of control cells. Together, these results suggest that the activity of MLCK can affect mitosis and cortical activities, however additional control mechanisms are likely involved in the regulation of cytokinesis.
Fishkind et al. (Sun,) conducted a other in Mitosis and cytokinesis in dividing cells. Microinjection of the 61-kD catalytic fragment of myosin light chain kinase (MLCK) vs. Intact MLCK or inactive catalytic fragment was evaluated on Effects on mitosis and cytokinesis (transit time to anaphase onset, motile surface activity, cleavage furrow formation). Microinjection of the active 61-kD catalytic fragment of MLCK into mitotic cells delayed transit time to anaphase onset and increased motile surface activity, but did not prevent cytokinesis.
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