Talin couples the actomyosin cortex to the plasma membrane during rear retraction and cytokinesis

Abstract

Contraction of the cortical actin cytoskeleton underlies both rear retraction in directed cell migration and cytokinesis. Here, we show that talin, a central component of focal adhesions, has a major role in these processes. We found that Dictyostelium talin A colocalized with myosin II in the rear of migrating cells and the cleavage furrow. During directed cell migration, talin A-null cells displayed a long thin tail devoid of actin filaments, whereas additional depletion of SibA, a transmembrane adhesion molecule that binds to talin A, reverted this phenotype, suggesting a requirement of the link between actomyosin and SibA by talin A for rear retraction. Disruptions of talin A also resulted in detachment of the actomyosin contractile ring from the cell membrane and concomitant regression of the cleavage furrow under certain conditions. The C-terminal actin-binding domain (ABD) of talin A exhibited a localization pattern identical to that of full-length talin A. The N-terminal FERM domain was found to bind phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] and phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] in vitro. In vivo, however, PtdIns(4,5)P2, which is known to activate talin, is believed to be enriched in the rear of migrating cells and the cleavage furrow in Dictyostelium . From these results, we propose that talin A activated by PtdIns(4,5)P2 in the cell posterior or cleavage furrow links actomyosin cytoskeleton to adhesion molecules or other membrane proteins, and that the force is transmitted through these links to retract the tail during cell migration or to cause efficient ingression of the equator during cytokinesis.

Biased localization of actin binding proteins by actin filament conformation

“…Interestingly, common probes for f-actin, including GFP-tagged actin, small actinbinding peptides (lifeact (Riedl et al, 2008), f-tractin (Schell et al, 2001), affimers (Lopata et al, 2018)) and phallotoxins (Yamashiro et al, 2019), do not distribute evenly on different actin cytoskeletal structures (Belin et al, 2014;Melak et al, 2017;Munsie et al, 2009). Similar observations have been made for fluorescent fusions to minimal actin binding domains from different proteins (Tsujioka et al, 2012;Washington and Knecht, 2008). Mechanistically, these results have been ascribed to the complex and competitive interactions between side binding proteins (Christensen et al, 2017;Gateva et al, 2017), the effect of actin nucleators (Mizuno et al, 2018;Risca et al, 2012), and the kinetic properties of the reporting probe (Maiuri et al, 2015;Yamashiro et al, 2019).…”

Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity

“…Dictyostelium cells express several substrate adhesions regulating molecules including Phg1, SadA, and an ortholog of integrin β-subunits designated like integrin βA (SibA) (46)(47)(48)(49). Dictyostelium cells are not known to form stable focal adhesions although they express homologs of talin, vinculin, and paxillin which localize to the basal surface in puncta with F-actin (1,(50)(51)(52). Because Dictyostelium cells need to migrate over a variety of surfaces in their natural environments, their substrate adhesion is thought to be largely nonspecific (53)(54)(55).…”

Talin – the master of integrin adhesions

“…So far, this type of analysis has only been performed in Dictyostelium, which has two talins with partially overlapping functions in cell adhesion and migration (Tsujioka et al, 2008). Dictyostelium does have a family of Sib transmembrane receptors with some integrin-like features and a mutant phenotype that resembles loss of talin (Cornillon et al, 2006;Tsujioka et al, 2012), so it may be that talins always use some form of membrane receptor. However, other organisms have talin and lack both integrins and Sib receptors (our analysis), so talin may not need a transmembrane receptor to function, after all.…”