Cell-intrinsic signals for cell polarization

Microtubules often provide spatial signal for cell polarization. In rod-shaped fission yeast cells, microtubules are organized in a dynamic network aligned along the length of the cell and serve to transport polarity landmarks towards the extremities of the cell. Microtubules provide positional information for growth at cell extremities: cells with anomalies in their microtubule network grow at ectopic locations. Our work focuses on one cell polarity landmark transported by microtubules, the protein Tea4, which we had demonstrated binds an actin nucleator of the formin family, For3. This suggested a model in which positional information provided by microtubules directly links to actin assembly to promote polarized cell growth at cell poles.

MT-tea4
Microtubules (purple) and Tea4 (green). The video shows microtubule dynamics.

 

Tea4 function extends beyond formin recruitment. Indeed, Tea4 also functions as type I phosphatase regulatory subunit and modulates the recruitment of regulators of Cdc42, a small Rho-family GTPase critical for cell polarization in eukaryotic cells. We showed that artificial positioning of Tea4 or the phosphatase catalytic subunit on cell sides is sufficient to promote Cdc42 activation and growth at this location. This growth requires both an activator (a guanine-nucleotide exchange factor) and a negative regulator (a GTPase activating protein) of Cdc42, indicating Tea4 phosphatase complex modulates Cdc42 activation cycle. We are interested in further understanding how microtubules through Tea4 promote mark sites for polarized cell growth.

Tea4 phosphatase complex is also essential to nucleate gradients of the protein kinase Pom1. Read more…

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