Exploration and stabilization of Ras1 mating zone: A mechanism with positive and negative feedbacks

• DOI: 10.1371/journal.pcbi.1006317
• Publication Date: 2018-07-20T17:24:22Z
• Authors: Bita Khalili; Laura Merlini; Vincent Vincenzetti; Sophie G. Martin; Dimitrios Vavylonis
• Keywords: 0301 basic medicine; Stochastic Processes; QH301-705.5; Reproduction; GTPase-Activating Proteins; Models, Biological; Actins; Pheromones; 03 medical and health sciences; Schizosaccharomyces; ras Proteins; Guanine Nucleotide Exchange Factors; Actins/metabolism; GTPase-Activating Proteins/metabolism; Guanine Nucleotide Exchange Factors/metabolism; Models, Biological; Pheromones/metabolism; Protein Binding; Reproduction; Schizosaccharomyces/enzymology; Schizosaccharomyces/metabolism; Schizosaccharomyces/physiology; Schizosaccharomyces pombe Proteins/metabolism; Signal Transduction; Stochastic Processes; cdc42 GTP-Binding Protein/metabolism; ras Proteins/metabolism; Schizosaccharomyces pombe Proteins; Biology (General); cdc42 GTP-Binding Protein; Research Article; Protein Binding; Signal Transduction

In mating fission yeast cells, sensing and response to extracellular pheromone concentrations occurs through an exploratory Cdc42 patch that stochastically samples the cell cortex before stabilizing towards a mating partner. Active Ras1 (Ras1-GTP), an upstream regulator of Cdc42, and Gap1, the GTPase-activating protein for Ras1, localize at the patch. We developed a reaction-diffusion model of Ras1 patch appearance and disappearance with a positive feedback by a Guanine nucleotide Exchange Factor (GEF) and Gap1 inhibition. The model is based on new estimates of Ras1-GDP, Ras1-GTP and Gap1 diffusion coefficients and rates of cytoplasmic exchange studied by FRAP. The model reproduces exploratory patch behavior and lack of Ras1 patch in cells lacking Gap1. Transition to a stable patch can occur by change of Gap1 rates constants or local increase of the positive feedback rate constants. The model predicts that the patch size and number of patches depend on the strength of positive and negative feedbacks. Measurements of Ras1 patch size and number in cells overexpressing the Ras1 GEF or Gap1 are consistent with the model.