Regensburg 2013 – scientific programme

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BP: Fachverband Biologische Physik

BP 32: Cell Adhesion and Mechanics

BP 32.1: Talk

Friday, March 15, 2013, 09:30–09:45, H43

Mechanics as second messenger in signal transduction — Roger Hardie and •Kristian Franze — University of Cambridge, Department of Physiology, Development and Neuroscience

Fly eyes have the fastest visual responses in the animal kingdom, but how they achieve this has long been an enigma. Phototransduction in Drosophila microvillar photoreceptors is mediated by a G-protein coupled phospholipase C (PLC) cascade culminating in activation of 'transient receptor potential' (TRP) and TRP-like (TRPL) channels by a still unresolved mechanism. Here we show that these light-sensitive channels are not ligand but mechanically gated. Using atomic force microscopy we found that light exposure evoked rapid contractions of the photoreceptor cells. These contractions were even faster than the cell's electrical response and appeared to be caused directly by PLC activity. Photoreceptor light responses were facilitated by membrane stretch and inhibited by amphipaths, which alter lipid bilayer properties. When we replaced the native light-sensitive channels with mechano-sensitive channels, photoreceptors still generated electrical signals in response to light. These results indicate that splitting of the membrane lipid PIP2 by PLC reduces the membrane area, which leads to an increase in membrane tension, and ultimately causes the contractions of the cells. They furthermore suggest that the resultant mechanical forces contribute to gating the light-sensitive channels, thereby introducing the concept of mechanical force as an intermediate or 'second messenger' in metabotropic signal transduction.

Reference: Roger C. Hardie and Kristian Franze, Photomechanical Responses in Drosophila Photoreceptors, Science 338: 260-263, 2012.