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Anaphase onset and dephosphorylation of mitotic phosphoproteins occur concomitantly
1Laboratory of Molecular Biology, University of Wisconsin, Madison 53706.
Abstract:
The cyclical phosphorylation and dephosphorylation of the centrosome during mitosis was analyzed by immunofluorescence methods using the MPM-2 antibody, which reacts with a subset of mitotic phosphoproteins. Quantification of MPM-reactivity indicated that centrosomal phosphorylation attained a maximal level just prior to anaphase onset. This level was maintained in metaphase cells blocked from further mitotic progression with the microtubule depolymerizing agent nocodazole. However, when nocodazole was added to cells that had just initiated anaphase, the level of centrosomal phosphorylation decreased rapidly as in untreated anaphase cells. We conclude that the onset of dephosphorylation of the centrosome coincided with the onset of anaphase and continued in the absence of chromosome movement. Dephosphorylation of MPM-2 reactive phosphoproteins may be taken as a biochemical indicator of anaphase onset.
Insights
Centrosome phosphorylation peaks before anaphase and rapidly decreases upon its onset. This dephosphorylation serves as a key biochemical indicator for the start of anaphase during cell division.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The cell division cycle involves precise regulation of protein modifications.
- Centrosome function and its phosphorylation status are critical for mitosis.
- Mitotic phosphoproteins undergo dynamic changes during cell cycle progression.
Purpose of the Study:
- To investigate the cyclical phosphorylation and dephosphorylation of the centrosome during mitosis.
- To identify a reliable biochemical marker for the onset of anaphase.
Main Methods:
- Immunofluorescence microscopy utilizing the MPM-2 antibody, which targets mitotic phosphoproteins.
- Quantification of MPM-2 reactivity to assess centrosomal phosphorylation levels.
- Experimental manipulation using nocodazole to block or initiate mitotic progression.
Main Results:
- Centrosomal phosphorylation reached maximum levels just before anaphase onset.
- Phosphorylation levels remained high in metaphase-arrested cells but decreased rapidly upon anaphase initiation.
- Dephosphorylation occurred concurrently with anaphase onset, independent of chromosome movement.
Conclusions:
- The dephosphorylation of the centrosome is a key event that coincides with the onset of anaphase.
- MPM-2 reactive phosphoprotein dephosphorylation can serve as a biochemical indicator for anaphase onset.
- This finding provides a new molecular marker for studying cell cycle progression and mitotic regulation.