2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M10: Pattern Formation in Biological Systems
8:00 AM–11:00 AM,
Wednesday, March 8, 2023
Room: Room 202
Sponsoring
Unit:
DBIO
Chair: Andrej Kosmrlj, Princeton University
Abstract: M10.00010 : Cdc42 Mobility and Membrane Flows Regulate Fission Yeast Cell Shape and Survival*
10:36 AM–10:48 AM
Abstract
Presenter:
David M Rutkowski
(Lehigh University)
Authors:
David M Rutkowski
(Lehigh University)
Vincent Vincenzetti
(University of Lausanne)
Dimitrios Vavylonis
(Lehigh University)
Sophie G Martin
(University of Lausanne)
Cdc42 activation directs cell growth by forming membrane associated patches which promote localized exocytosis. Secretion-driven in-plane membrane flow depletes peripheral proteins with low mobilities, including Cdc42 GAPs, away from the region of localized membrane addition/removal. To investigate the self-organizing properties of the Cdc42 secretion-polarization system, we developed a stochastic particle model implementing the reaction-diffusion of Cdc42. The model includes positive feedback by discretely modeled GEFs, hydrolysis by discrete GAPs, and flow-induced displacement by exo/endocytosis targeted towards regions of Cdc42 activity. Our simulations show how stable polarization of wild-type cells relies on flow-induced depletion of low mobility GAP when using Cdc42-GDP and Cdc42-GTP diffusion and membrane dissociation rates estimated from FRAP experiments. To probe the role of Cdc42 mobility, which is fast enough to not be strongly affected by membrane flow in WT cells, we changed its membrane binding properties by replacing its prenylation site with NxRitC, where N is the number of repeats of the Rit1 C terminal membrane binding domain. While Cdc42-3xRitC is inviable, surprisingly, Cdc42-1xRitC and -2xRitC cells survive and polarize, even though the unbinding and diffusion rates for these constructs (as measured from diploid cells also expressing WT Cdc42) are significantly lower than WT-Cdc42. By systematically varying Cdc42 mobility in our model, we find that GEF positive feedback and GAP flow-displacement allows polarization even when membrane flows are strong enough to displace Cdc42 itself away from its activation region. However, lower Cdc42 mobility in the model results in lower Cdc42 activation level and wider patches, in agreement with our experimental observations in haploid and diploid cells. The model predicts that GAP depletion increases Cdc42 activity at the expense of loss of polarization. Experiments confirm this prediction, as deletion of Cdc42 GAPs restores viability to Cdc42-3xRitC cells. Overall, our combined experimental and modeling studies demonstrate how membrane flows are an integral part of Cdc42-driven pattern formation.
*NIH R35GM136372