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First published online May 8, 2008
doi: 10.1242/10.1242/jcs.030692

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A spatially restricted increase in receptor mobility is involved in directional sensing during Dictyostelium discoideum chemotaxis

¹ Physics of Life Processes, Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
² Cell Biology, Leiden Institute of Biology, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands

^* Authors for correspondence (e-mails: schmidt{at}physics.leidenuniv.nl; b.e.snaar-jagalska{at}biology.leidenuniv.nl)

Accepted 25 February 2008

The directed cell migration towards a chemotactic source, chemotaxis, involves three complex and interrelated processes: directional sensing, cell polarization and motility. Directional sensing allows migrating eukaryotic cells to chemotax in extremely shallow gradients (<2% across the cell body) of the chemoattractant. Although directional sensing has been observed as spatially restricted responses along the plasma membrane, our understanding of the `compass' of the cell that controls the gradient-induced translocation of proteins during chemotactic movements is still largely lacking. Until now, the dynamical behaviour and mobility of the chemoattractant-receptor molecule has been neglected in models describing the directional sensing mechanisms. Here, we show by single-molecule microscopy an agonist-induced increase in the mobile fraction of cAMP-receptor at the leading edge of chemotacting Dictyostelium discoideum cells. The onset of receptor mobility was correlated to the uncoupling and activation of the G2-protein. A finite-element simulation showed that the increase in mobile fraction of the activated receptor enabled the amplified generation of activated Gβ-dimers at the leading edge of the cell, faithfully representing a primary linear amplification step in directional sensing. We propose here that modulation of the receptor mobility is directly involved in directional sensing and provides a new mechanistic basis for the primary amplification step in current theoretical models that describe directional sensing.

Key words: Single-molecule microscopy, Chemotaxis, Dictyostelium discoideum, G-protein-coupled receptor

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