Cofilin Regulates Filopodial Structure and Flexibility in Neuronal Growth Cones

Filopodia are actin-rich cytoskeletal protrusions at the leading edge of motile cells. In neuronal growth cones they function as antennae, guiding axonal growth toward the appropriate cellular targets. Proper brain development relies on robust axonal guidance mechanisms, so it is imperative to understand how the actin cytoskeleton functions in remodeling to meet the demands of growth cone exploration. Here we show by cryo-electron tomography and fluorescence imaging that filopodia in neuronal growth cones switch between fascin-linked and cofilin-decorated states, and that this transition regulates the exclusion of fascin from the cofilactin bundle at the filopodial base by hyper-twisting individual filaments and rearranging their packing. Additionally, we show that cofilactin bundles contribute to the flexibility of filopodial actin networks, thus, likely regulating the efficiency of targeted neurite outgrowth.

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A single tyrosine phosphorylation site in cortactin is important for filopodia formation in neuronal growth cones

Molecular Biology of the Cell ◽

10.1091/mbc.e18-04-0202 ◽

2019 ◽

Vol 30 (15) ◽

pp. 1817-1833 ◽

Cited By ~ 2

Author(s):

Yuan Ren ◽

Yingpei He ◽

Sherlene Brown ◽

Erica Zbornik ◽

Michael J. Mlodzianoski ◽

...

Keyword(s):

Tyrosine Phosphorylation ◽

Phosphorylation Site ◽

Leading Edge ◽

Growth Cones ◽

Neuronal Growth ◽

Src Tyrosine Kinase ◽

Actin Organization ◽

Neuronal Growth Cones ◽

Tyrosine Phosphorylation Site

Cortactin is a Src tyrosine phosphorylation substrate that regulates multiple actin-related cellular processes. While frequently studied in nonneuronal cells, the functions of cortactin in neuronal growth cones are not well understood. We recently reported that cortactin mediates the effects of Src tyrosine kinase in regulating actin organization and dynamics in both lamellipodia and filopodia of Aplysia growth cones. Here, we identified a single cortactin tyrosine phosphorylation site (Y499) to be important for the formation of filopodia. Overexpression of a 499F phospho-deficient cortactin mutant decreased filopodia length and density, whereas overexpression of a 499E phospho-mimetic mutant increased filopodia length. Using an antibody against cortactin pY499, we showed that tyrosine-phosphorylated cortactin is enriched along the leading edge. The leading edge localization of phosphorylated cortactin is Src2-dependent, F-actin–independent, and important for filopodia formation. In vitro kinase assays revealed that Src2 phosphorylates cortactin at Y499, although Y505 is the preferred site in vitro. Finally, we provide evidence that Arp2/3 complex acts downstream of phosphorylated cortactin to regulate density but not length of filopodia. In conclusion, we have characterized a tyrosine phosphorylation site in Aplysia cortactin that plays a major role in the Src/cortactin/Arp2/3 signaling pathway controlling filopodia formation.

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Theoretical Model for Optical Guidance of Neuronal Growth Cones

Biophysical Journal ◽

10.1016/j.bpj.2020.11.1204 ◽

2021 ◽

Vol 120 (3) ◽

pp. 170a

Author(s):

Kahmina R. Ford ◽

Erin M. Craig

Keyword(s):

Theoretical Model ◽

Growth Cones ◽

Neuronal Growth ◽

Neuronal Growth Cones

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Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and Contraction

International Journal of Cell Biology ◽

10.1155/2010/507821 ◽

2010 ◽

Vol 2010 ◽

pp. 1-13 ◽

Cited By ~ 31

Author(s):

Fei Xue ◽

Deanna M. Janzen ◽

David A. Knecht

Keyword(s):

Cell Migration ◽

Actin Polymerization ◽

Myosin Ii ◽

Temporal Distribution ◽

Leading Edge ◽

Distal Portion ◽

Actin Binding ◽

Actin Networks ◽

Motile Cells ◽

A Cell

Numerous F-actin containing structures are involved in regulating protrusion of membrane at the leading edge of motile cells. We have investigated the structure and dynamics of filopodia as they relate to events at the leading edge and the function of the trailing actin networks. We have found that although filopodia contain parallel bundles of actin, they contain a surprisingly nonuniform spatial and temporal distribution of actin binding proteins. Along the length of the actin filaments in a single filopodium, the most distal portion contains primarily T-plastin, while the proximal portion is primarily bound byα-actinin and coronin. Some filopodia are stationary, but lateral filopodia move with respect to the leading edge. They appear to form a mechanical link between the actin polymerization network at the front of the cell and the myosin motor activity in the cell body. The direction of lateral filopodial movement is associated with the direction of cell migration. When lateral filopodia initiate from and move toward only one side of a cell, the cell will turn opposite to the direction of filopodial flow. Therefore, this filopodia-myosin II system allows actin polymerization driven protrusion forces and myosin II mediated contractile force to be mechanically coordinated.

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