The multi-FERM-domain-containing protein FrmA is required for turnover of paxillin-adhesion sites during cell migration of Dictyostelium.

FERM domain proteins, including talins, ERMs, FAK and certain myosins, regulate connections between the plasma membrane, cytoskeleton and extracellular matrix. Here we show that FrmA, a Dictyostelium discoideum protein containing two talin-like FERM domains, plays a major role in normal cell shape, cell-substrate adhesion and actin cytoskeleton organisation. Using total internal reflection fluorescence (TIRF) microscopy we show that FrmA-null cells are more adherent to substrate than wild-type cells because of an increased number, persistence and mislocalisation of paxillin-rich cell-substrate adhesions, which is associated with decreased motility. We show for the first time that talinA colocalises with paxillin at the distal ends of filopodia to form cell-substrate adhesions and indeed arrives prior to paxillin. After a period of colocalisation, talin leaves the adhesion site followed by paxillin. Whereas talinA-rich spots turnover prior to the arrival of the main body of the cell, paxillin-rich spots turn over as the main body of the cell passes over it. In FrmA-null cells talinA initially localises to cell-substrate adhesion sites at the distal ends of filopodia but paxillin is instead localised to stabilised adhesion sites at the periphery of the main cell body. This suggests a model for cell-substrate adhesion in Dictyostelium whereby the talin-like FERM domains of FrmA regulate the temporal and spatial control of talinA and paxillin at cell-substrate adhesion sites, which in turn controls adhesion and motility.

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