Ena/VASP proteins mediate repulsion from ephrin ligands

Abstract

Ena/VASP proteins negatively regulate cell motility and contribute to repulsion from several guidance cues; however, there is currently no evidence for a role downstream of Eph receptors. Eph receptors mediate repulsion from ephrins at sites of intercellular contact during several developmental migrations. For example, the expression of ephrin-Bs in posterior halves of somites restricts neural crest cell migration to the anterior halves. Here we show that ephrin-B2 destabilises neural crest cell lamellipodia when presented in a substrate-bound or soluble form. Our timelapse studies show that repulsive events are associated with the rearward collapse and subsequent loss of lamellipodia as membrane ruffles. We hypothesise that Ena/VASP proteins contribute to repulsion from ephrins by destabilising cellular protrusions and show that Ena/VASP-deficient fibroblasts exhibit reduced repulsion from both ephrin-A and ephrin-B stripes compared to wild-type controls. Moreover, when EphB4 and ephrin-B2 were expressed in neighbouring Swiss 3T3 fibroblasts, VASP and Mena co-accumulated with activated Eph receptors at protrusions formed by EphB4-expressing cells. Sequestration of Ena/VASP proteins away from the periphery of these cells inhibited Eph receptor internalisation, a process that facilitates repulsion. Our results suggest that Ena/VASP proteins regulate ephrin-induced Eph receptor signalling events, possibly by destabilising lamellipodial protrusions.

The Caenorhabditis elegans Eph Receptor Activates NCK and N-WASP, and Inhibits Ena/VASP to Regulate Growth Cone Dynamics during Axon Guidance

“…Our finding that VAB-1 negatively regulates UNC-34/Ena is different from a previous report that shows mammalian EphB4 as an activator of Ena/VASP [24]. In fibroblast cells, the EphB4 receptor is thought to activate Ena/VASP to destabilize lamellipodia during cell repulsion and likely does so by promoting elongated actin filaments rather than a branched actin filament network.…”

“…A previous report indicated that Ena/VASP was required for repulsion caused by EphB4 signaling in fibroblasts, but it was unclear how the signal was conveyed [24]. The Ena/VASP family are composed of an N-terminal EVH1 domain, a central PRO region and a C-terminal Ena/VASP homology II domain (EVH2) [16].…”

“…Previous work has shown that Ena/VASP proteins are versatile in their developmental roles and function in both repulsive and attractive cues. For example Ena/VASP are effectors of receptors for repulsive cues such as SAX-3/Robo, UNC-5/Netrin receptor and EphB4, but they can as also act as effectors for attractive cues downstream of receptors such as UNC-40/DCC [21], [22], [23], [24], [25].…”

Reverse Signaling via a Glycosyl-Phosphatidylinositol-Linked Ephrin Prevents Midline Crossing by Migratory Neurons during Embryonic Development inManduca

“…6 K). Only when we applied MsEph-Fc at the onset of migration did we observe a global effect on EP cell motility, akin to the phenomenon of growth cone collapse in vitro (Harbott and Nobes, 2005;Evans et al, 2007). One explanation for this difference is that within the developing ENS, the EP cells may be most sensitive to MsEphrin-dependent signaling during their initial stages of migration, when each neuron extends a wide array of exploratory filopodia before aligning with a particular band pathway (Copenhaver et al, 1996;Wright et al, 1999).…”

DrosophilaPsidin Regulates Olfactory Neuron Number and Axon Targeting through Two Distinct Molecular Mechanisms

“…During targeting, growth cones at axon tips provide a dynamic platform for integration of attractive and repulsive guidance cues (Lowery and Van Vactor, 2009). Through binding to membrane receptors displayed on growth cones, guidance cues orchestrate dynamic changes of the cytoskeleton, in particular of the actin and microtubule networks (Driessens et al, 2001;GordonWeeks, 2004;Kalil and Dent, 2005;Evans et al, 2007;Lowery and Van Vactor, 2009). The growth cone consists of actin-rich structures, finger-like filopodia, and veil-like lamellipodia.…”