All posts by Sophie Martin

Cellular ‘speed-dating’: new paper in Current Biology

Cellular ‘speed-dating’: new paper in Current Biology, proposing how fission yeast cells pair during mating. We showed that the dynamic exploratory Cdc42-GTP zones present in early mating cells contain pheromone secretion and perception machineries and that these zone lifetimes scale with pheromone concentration. Computational simulations of fluctuating zones stabilized by pheromone lead to efficient pairing, which relies on zone dynamics, local pheromone release, and short decay length. Experimental assays are consistent with this model. We conclude that efficient cell pairing relies on fluctuating local signal emission and perception, which become locked into place through stimulation.

New paper showing how Pom1 kinase prevents division at cell poles

In this new paper, published in the Journal of Cell Biology, we show that the F-BAR protein Cdc15, a major component of the cytokinetic actomyosin contractile ring, is a direct substrate for Pom1 kinase. Phosphorylation by Pom1 blocks interaction of Cdc15 with several binding partners and destabilizes the ring, allowing it to slide if it assembles at the cell poles. Thus, Pom1 at cell poles protects these regions by blocking ring stabilization.

New paper in PLoS Biology on Cdc42 polarization

Check out our new paper in PLoS Biology, in which we create a first functional Cdc42 GFP-tagged allele. A fast-folding variant of GFP, or mCherry, is inserted in a poorly conserved internal loop, yielding a functional sandwich fusion. We then use this allele to study the localization and dynamics of Cdc42. One of several findings is that Cdc42-GTP is significantly less mobile than Cdc42-GDP, leading to its accumulation at sites of activity.

New lab publication in the Journal of Cell Science

Check our latest publication in the Journal of Cell Science. We show that ectopic localization of Tea4 on cell sides is sufficient to activate Cdc42 and promote growth at this location, yielding cells with a medial bulge. This activity depends on Tea4 binding a catalytic phosphatase 1 subunit, and indeed ectopic targeting of a catalytic subunit to the same location produces the same phenotype. This activity is further dependent on Gef1, a Cdc42 GEF, and Rga4, a Cdc42 GAP.

New lab publication in Cell Cycle

Check our latest publication at Cell Cycle. We show that two distinct levels of Pom1 control cell cycle timing and positioning: partial inhibition of Pom1 promotes faster mitotic entry, but has no effect on the position of the division plane at the cell middle. We further show that Pom1 phosphorylates the C-terminal tail of Cdr2 to negatively regulate its activity, independently of Cdr2 localization. We also show in this publication that Pom1 levels at the medial cortex do not substantially vary in cells of increasing sizes. This raises questions about where Pom1 inhibits Cdr2 activity, and whether Pom1 acts as cell size sensor.

New lab publication at Cell

Check our latest publication at Cell. We describe a complete molecular mechanism by which Pom1 forms concentration gradients at the plasma membrane. This occurs through local dephosphorylation at cell poles, which reveals a Pom1 lipid-binding region allowing plasma membrane binding. At the plasma membrane Pom1 then moves laterally and auto-phosphorylates, weakening lipid binding and promoting plasma membrane detachment. A press release from the University of Lausanne can be found here.

 

New lab publication in Nature

Check our new publication in Nature. We show that the polarity factor Pom1 acts as an inhibitor of mitotic entry, upstream of Wee1 kinase. Pom1 negatively regulates the kinase Cdr2, itself an inhibitor of Wee1. As Pom1 forms concentration gradients from cell poles, and Cdr2 localizes at the medial cortex, this regulatory network may allow cells to measure their own length and delay division until they reach sufficient size. The press release from the University of Lausanne can be found here.