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Optogenetics reveals Cdc42 local activation by scaffold-mediated positive feedback and Ras GTPase

Published inPLoS biology, vol. 18, no. 1, e3000600
Publication date2020-01-24
First online date2020-01-24
Abstract

Local activity of the small GTPase Cdc42 is critical for cell polarization. Whereas scaffold- mediated positive feedback was proposed to break symmetry of budding yeast cells and produce a single zone of Cdc42 activity, the existence of similar regulation has not been probed in other organisms. Here, we address this problem using rod-shaped cells of fission yeast Schizosaccharomyces pombe, which exhibit zones of active Cdc42-GTP at both cell poles. We implemented the CRY2-CIB1 optogenetic system for acute light-dependent protein recruitment to the plasma membrane, which allowed to directly demonstrate positive feedback. Indeed, optogenetic recruitment of constitutively active Cdc42 leads to co-recruitment of the guanine nucleotide exchange factor (GEF) Scd1 and endogenous Cdc42, in a manner dependent on the scaffold protein Scd2. We show that Scd2 function is dispensable when the positive feedback operates through an engineered interaction between the GEF and a Cdc42 effector, the p21-activated kinase 1 (Pak1). Remarkably, this rewired positive feedback confers viability and allows cells to form 2 zones of active Cdc42 even when otherwise essential Cdc42 activators are lacking. These cells further revealed that the small GTPase Ras1 plays a role in both localizing the GEF Scd1 and promoting its activity, which potentiates the positive feedback. We conclude that scaffold-mediated positive feedback, gated by Ras activity, confers robust polarization for rod-shape formation.

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Citation (ISO format)
LAMAS, Iker et al. Optogenetics reveals Cdc42 local activation by scaffold-mediated positive feedback and Ras GTPase. In: PLoS biology, 2020, vol. 18, n° 1, p. e3000600. doi: 10.1371/journal.pbio.3000600
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ISSN of the journal1544-9173
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