micromanipulation-techniques-allowing-analysis-morphogenetic-dynamics

Micromanipulation Techniques Allowing Analysis of Morphogenetic Dynamics and Turnover of Cytoskeletal Regulators

Examining the spatiotemporal dynamics of proteins can reveal their functional importance in various contexts. In this article, it is discussed how ...

Technische Universität Braunschweig

Helmholtz Centre for Infection Research

Migration frequently involves Rac-mediated protrusion of lamellipodia, formed by Arp2/3 complex-dependent branching thought to be crucial for force generation and stability of these networks. The formins FMNL2 and FMNL3 are Cdc42 effectors targeting to the lamellipodium tip and shown here to nucleate and elongate actin filaments with complementary activities in vitro. In migrating B16-F1 melanoma cells, both formins contribute to the velocity of lamellipodium protrusion. Loss of FMNL2/3 function in melanoma cells and fibroblasts reduces lamellipodial width, actin filament density and -bundling, without changing patterns of Arp2/3 complex incorporation. Strikingly, in melanoma cells, FMNL2/3 gene inactivation almost completely abolishes protrusion forces exerted by lamellipodia and modifies their ultrastructural organization. Consistently, CRISPR/Cas-mediated depletion of FMNL2/3 in fibroblasts reduces both migration and capability of cells to move against viscous media. Together, we conclude that force generation in lamellipodia strongly depends on FMNL formin activity, operating in addition to Arp2/3 complex-dependent filament branching.

FMNL formins boost lamellipodial force generation.

Cell migration and cell-cell communication involve the protrusion of actin-rich cell surface projections such as lamellipodia and filopodia. Lamellipodia are networks of actin filaments generated and turned over by filament branching through the Arp2/3 complex. Inhibition of branching is commonly agreed to eliminate formation and maintenance of lamellipodial actin networks, but the regulation of nucleation or elongation of Arp2/3-independent filament populations within the network by, for example, formins or Ena/VASP family members and its influence on the effectiveness of protrusion have been unclear. Here we analyzed the effects of a set of distinct formin fragments and VASP on site-specific, lamellipodial versus cytosolic actin assembly and resulting consequences on protrusion. Surprisingly, expression of formin variants but not VASP reduced lamellipodial protrusion in B16-F1 cells, albeit to variable extents. The rates of actin network polymerization followed a similar trend. Unexpectedly, the degree of inhibition of both parameters depended on the extent of cytosolic but not lamellipodial actin assembly. Indeed, excess cytosolic actin assembly prevented actin monomer from rapid translocation to and efficient incorporation into lamellipodia. Thus, as opposed to sole regulation by actin polymerases operating at their tips, the protrusion efficiency of lamellipodia is determined by a finely tuned balance between lamellipodial and cytosolic actin assembly.

Article	Year
FMNL formins boost lamellipodial force generation. Nature communications\| PubMed ID: 28327544	2017
Efficiency of lamellipodia protrusion is determined by the extent of cytosolic actin assembly. Molecular biology of the cell\| PubMed ID: 28331069	2017

Georgi Dimchev

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