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J Cell Sci. 2019 Jul 15;132(14). pii: jcs230714. doi: 10.1242/jcs.230714.

Anterior-enriched filopodia create the appearance of asymmetric membrane microdomains in polarizing C. elegans zygotes.

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The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK.
Institute for the Physics of Living Systems, University College London, London WC1E 6BT, UK.
Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, UMR7104, Institut National de la Santé et de la Recherche Médicale, U1258, and Université de Strasbourg, 67404 Illkirch, France.
The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK.


The association of molecules within membrane microdomains is critical for the intracellular organization of cells. During polarization of the C. elegans zygote, both polarity proteins and actomyosin regulators associate within dynamic membrane-associated foci. Recently, a novel class of asymmetric membrane-associated structures was described that appeared to be enriched in phosphatidylinositol 4,5-bisphosphate (PIP2), suggesting that PIP2 domains could constitute signaling hubs to promote cell polarization and actin nucleation. Here, we probe the nature of these domains using a variety of membrane- and actin cortex-associated probes. These data demonstrate that these domains are filopodia, which are stimulated transiently during polarity establishment and accumulate in the zygote anterior. The resulting membrane protrusions create local membrane topology that quantitatively accounts for observed local increases in the fluorescence signal of membrane-associated molecules, suggesting molecules are not selectively enriched in these domains relative to bulk membrane and that the PIP2 pool as revealed by PHPLCδ1 simply reflects plasma membrane localization. Given the ubiquity of 3D membrane structures in cells, including filopodia, microvilli and membrane folds, similar caveats are likely to apply to analysis of membrane-associated molecules in a broad range of systems.


C. elegans; Cell cortex; Cell polarity; Filopodia; PAR proteins; PIP2

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