Oscillatory Dynamics of Cdc42 GTPase in the Control of Polarized Growth

Abstract

Cells promote polarized growth by activation of Rho-family protein Cdc42 at the cell membrane. We combined experiments and modeling to study bipolar growth initiation in fission yeast. Concentrations of a fluorescent marker for active Cdc42, Cdc42 protein, Cdc42-activator Scd1, and scaffold protein Scd2, exhibited anti-correlated fluctuations and oscillations with a five-minute average period at polarized cell tips. These dynamics indicate competition for active Cdc42, or its regulators, and the presence of positive and delayed negative feedbacks. Cdc42 oscillations and spatial distribution were sensitive to the amounts of Cdc42-activator Gef1 and to the activity of Cdc42-dependent kinase Pak1, a negative regulator. Feedbacks regulating Cdc42 oscillations and spatial self-organization appear to provide a flexible mechanism for fission yeast cells to explore polarization states and control their morphology.

A novel interplay between GEFs orchestrates Cdc42 activity during cell polarity and cytokinesis

“…In contrast, gef1 mutants become narrower and grow in a monopolar, rather than a bipolar, manner (Coll et al, 2003). Furthermore, Cdc42 activity is reduced at the new end in gef1 mutants (Das et al, 2012). Gef1 shows sparse localization at the cortex, making it difficult to determine whether it oscillates between cell ends (Das et al, 2015).…”

“…Gef1 and Scd1 are partially redundant but exhibit unique phenotypes when deleted (Chang et al, 1994;Coll et al, 2003), indicating that they may regulate Cdc42 in different manners. Cells lacking scd1 appear depolarized (Chang et al, 1994), and Scd1 oscillates between the two cell ends, much like Cdc42 (Das et al, 2012). In contrast, gef1 mutants become narrower and grow in a monopolar, rather than a bipolar, manner (Coll et al, 2003).…”

“…In fission yeast, active Cdc42 displays anti-correlated oscillations between the two ends (Das et al, 2012). These oscillations arise from both positive and time-delayed negative feedback as well as competition between the two ends (Das et al, 2012). This oscillatory pattern regulates cell dimensions and promotes bipolar growth in fission yeast.…”

“…In contrast, fission yeast grows in a bipolar manner, offering a model to understand how a cell regulates polarized growth from multiple sites. In fission yeast, active Cdc42 displays anti-correlated oscillations between the two ends (Das et al, 2012). These oscillations arise from both positive and time-delayed negative feedback as well as competition between the two ends (Das et al, 2012).…”

Analysis ofS. pombeSIN protein SPB-association reveals two genetically separable states of the SIN

“…This is governed by a combination of feedback loops (Das et al, 2012). Given that there is no clear periodicity in the fluctuations GFP-Sid1p signal, it seems unlikely that these mechanisms govern the appearance of GFPSid1p at the SPBs in early mitosis.…”