Optogenetic control of receptors reveals distinct roles for actin- and Cdc42-dependent negative signals in chemotactic signal processing

Abstract

During chemotaxis, neutrophils use cell surface G-Protein Coupled Receptors (GPCRs) to detect chemoattractant gradients1-4. The downstream signaling system is wired with multiple feedback loops that amplify weak inputs and promote spatial separation of cell front and rear activities1, 5-8. Positive feedback could promote rapid signal spreading9, yet information from the receptors is transmitted with high spatial fidelity, enabling detection of small differences in chemoattractant concentration across the cell1. How the signal transduction network achieves signal amplification while preserving spatial information remains unclear. The GTPase Cdc42 is a cell-front polarity coordinator that is predictive of cell turning, suggesting an important role in spatial processing10. To directly measure information flow from receptors to Cdc42, we paired zebrafish parapinopsina, an optogenetic GPCR that allows reversible ON/OFF receptor control with a spectrally compatible red/far red Cdc42 FRET biosensor. Using this new toolkit, we show that positive and negative signals downstream of G-proteins shape a rapid, dose-dependent Cdc42 response. Furthermore, F-actin and Cdc42 itself provide two distinct negative signals that limit the duration and spatial spread of Cdc42 activation, maintaining output signals local to the originating receptors.