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Negative regulation of mitosis by two functionally overlapping PTPases in fission yeast
J B Millar1, P Russell, J E Dixon
1Department of Molecular, Scripps Research Institute, La Jolla, CA 92037.
Abstract:
We have identified a third protein tyrosine phosphatase (PTPase) gene in fission yeast, pyp2, encoding an 85 kDa protein. Disruption of pyp2 has no impact on cell viability, but pyp2 is essential in strains lacking the 60 kDa pyp1 PTPase. The two pyp PTPases are approximately 42% identical in their C-terminal catalytic domains and share weak homology in their N-terminal regions. Both genes play a role in inhibiting the onset of mitosis. Disruption of either gene rescues the G2 arrest caused by mutation of the cdc25 mitotic inducer, though the effect of pyp1-disruption is more pronounced. Disruption of pyp1 advances mitosis, suppresses overexpression of the tyrosine kinase encoded by the wee1 mitotic inhibitor, and causes lethal mitotic catastrophe in cdc25 overproducer cells. Cells bearing inactive wee1 are unresponsive to disruption of pyp1. Overexpression of pyp1 or pyp2 delays the onset of mitosis by a wee1-dependent mechanism. These data reveal an unexpected second role for protein tyrosine phosphorylation in the mitotic control that acts by promoting the inhibitory wee1 pathway.
Insights
A new protein tyrosine phosphatase (PTPase) gene, pyp2, was found in fission yeast. It works with pyp1 to control mitosis onset, revealing a new role for protein tyrosine phosphorylation in cell division.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Fission yeast is a model organism for studying cell cycle control.
- Protein tyrosine phosphatases (PTPases) are enzymes that remove phosphate groups from tyrosine residues.
- Mitosis is a crucial process for cell division, regulated by complex signaling pathways.
Purpose of the Study:
- To identify and characterize a novel PTPase gene in fission yeast.
- To investigate the role of this new PTPase, pyp2, in cell cycle regulation, particularly mitosis.
- To elucidate the relationship between pyp2, the known PTPase pyp1, and other cell cycle regulators like cdc25 and wee1.
Main Methods:
- Gene identification and cloning of the pyp2 gene.
- Gene disruption and analysis of cell viability and cell cycle progression.
- Complementation studies with existing mutants.
- Analysis of protein sequence homology between pyp1 and pyp2.
Main Results:
- A third PTPase gene, pyp2, was identified, encoding an 85 kDa protein.
- pyp2 disruption alone had no effect, but was essential in pyp1-deficient strains.
- Both pyp1 and pyp2 inhibit mitosis onset and rescue G2 arrest caused by cdc25 mutations.
- pyp1 disruption advanced mitosis and suppressed wee1 overexpression, while pyp2 overexpression delayed mitosis via wee1.
Conclusions:
- Fission yeast possesses at least two PTPases, pyp1 and pyp2, involved in mitotic control.
- These PTPases function in opposition to the wee1 pathway, promoting mitotic entry.
- Protein tyrosine phosphorylation plays a significant role in regulating the wee1 inhibitory pathway during mitosis.