A Catalytic Role for Mod5 in the Formation of the Tea1 Cell Polarity Landmark

Claudia C Bicho,Kenneth E Sawin,Andrew B Goryachev,David A Kelly,Hilary A Snaith

doi:10.1016/j.cub.2010.08.035

Claudia C Bicho, Kenneth E Sawin + Show 3 more

Open Access

https://doi.org/10.1016/j.cub.2010.08.035

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Abstract

SummaryMany systems regulating cell polarity involve stable landmarks defined by internal cues [1–5]. In the rod-shaped fission yeast Schizosaccharomyces pombe, microtubules regulate polarized vegetative growth via a landmark involving the protein Tea1 [6–9]. Tea1 is delivered to cell tips as packets of molecules associated with growing microtubule ends [10] and anchored at the plasma membrane via a mechanism involving interaction with the membrane protein Mod5 [11, 12]. Tea1 and Mod5 are highly concentrated in clusters at cell tips in a mutually dependent manner, but how the Tea1-Mod5 interaction contributes mechanistically to generating a stable landmark is not understood. Here, we use live-cell imaging, FRAP, and computational modeling to dissect dynamics of the Tea1-Mod5 interaction. Surprisingly, we find that Tea1 and Mod5 exhibit distinctly different turnover rates at cell tips. Our data and modeling suggest that rather than acting simply as a Tea1 receptor or as a molecular “glue” to retain Tea1, Mod5 functions catalytically to stimulate incorporation of Tea1 into a stable tip-associated cluster network. The model also suggests an emergent self-focusing property of the Tea1-Mod5 cluster network, which can increase the fidelity of polarized growth.

Highlights

Tea1 is necessary for accurate restoration of the growth machinery to cell tip centers after stresses that perturb the actin cytoskeleton [6, 7, 11, 13]
Occasional aberrant deposition of Tea1 could lead to undesirable spreading of the Tea1 polarity landmark unless additional factors ensure that only the Tea1 delivered close to cell tip centers becomes ‘‘anchored’’ at the plasma membrane
Because Mod5 is required for Tea1 anchoring at cell tips, and Tea1 is reciprocally required to restrict Mod5 localization to cell tips, it has been proposed that mutually dependent localization of Tea1 and Mod5 acts as a spatial positive-feedback loop in which Mod5 is enriched at the very sites where it is required for correct Tea1 anchoring (Figure S1A, available online) [11, 12]

Summary

Introduction

Mod5 does not merely tether Tea1 to the membrane and acts to promote and interacted with Mod5 but failed to accumulate at cell tips integration of individual incoming Tea1 molecules into the in vivo, whereas mutation of an adjacent dimeric coiled-coil network (Figure 2B; Experimental Procedures). Tea1 and Mod5 associate to form polymeric networks with variable stoichiometry and connectivity (Figures 2C and 2E).

Results

Conclusion