Actin cytoskeleton dynamics in the neuronal growth cone

Résumé du document

These slides will review all of the most important actin cytoskeleton regulators inside the neuron and particularly in the growth cone, which is the motile part of it. I mentioned their known functions, molecular interactors and signaling pathways.

Extraits

[...] This function is modulated by interactions with WASH and tubulin subunits WASH can bundle both actin and microtubules in a GTPase regulated manner . Which GTPase ? [...]

[...] Expressed in brain or not ? Secondary Nuclear Promoting Factors (NPFs) Only NPFs regulator expressed in the brain : Cortactin ARP2/3 binding domain Actin binding domain WASP binding domain  Enhance N-WASP mediated activation of ARP2/3  Inhibits the dissociation of ARP2/3-bound filaments branch junctions in vitro  stabilizing Y-branches  Important for cadherin adhesive zone formation Deletion of Cortactin in neurons  alter membrane dynamics affect lamellipodial protrusions or persistence  impaired cell migration Nucleation proteins : Formins Structure : Complex = formin dimerization Around 15 different mammalian formins 7 different subclasses bqsed on FH2 sequence divergence Hot it works : Produce unbranched filaments by addition of actin monomers at the pointed-end Where does it work in the GC : Principal nucleator of filopodia in the GC Formins subclasses • • • • mDIAs (mDIA1-3) FRL DAAM FHOD  Are direct downstream effectors of RhoA, are involved in nucleation inside filopodia and stress fibers  Possess a GTPase Binding Domain : mDIAs can be activated by RhoA and Cdc42 FRL & DAAM are stimulated by high concentrations of Cdc42 FHOD is stimulated by ROCK (RhoA mediated)  stress fibers Formins subclasses • • • • mDIAs (mDIA1-3) FRL DAAM FHOD • FMN  Are direct downstream effectors of RhoA, are involved in nucleation inside filopodia and stress fibers  Possess a GTPase Binding Domain : mDIAs can be activated by RhoA and Cdc42 FRL & DAAM are stimulated by high concentrations of Cdc42 FHOD is stimulated by ROCK (RhoA mediated)  stress fibers  Is a downstream effector of RhoA and Rac1 (activate it) and is involved in filopodia nucleation Formins subclasses • • • • mDIAs (mDIA1-3) FRL DAAM FHOD  Are direct downstream effectors of RhoA, are involved in nucleation inside filopodia and stress fibers  Possess a GTPase Binding Domain : mDIAs can be activated by RhoA and Cdc42 FRL & DAAM are stimulated by high concentrations of Cdc42 FHOD is stimulated by ROCK (RhoA mediated)  stress fibers • FMN  Is a downstream effector of RhoA and Rac1 (activate it) and is involved in filopodia nucleation • Delphilin  Recently discovered . [...]

[...] Not known to interact with RhoGTPases, but is highly expressed in mammalian brain tissue. Unknown function, but Delphilin KO mice  altered synaptic plasticity Other nucleators in the GC SPIRE1 & SPIRE2 (Spire family)  Triggers actin polymerization by capping the barbed-end of actin bundles and inhibiting their depolymerization Other nucleators in the GC SPIRE1 & SPIRE2 (Spire family)  Triggers actin polymerization by capping the barbed-end of actin bundles and inhibiting their depolymerization Cordon-Bleu (COBL) Decreasing COBL expression  suppression of neurite branching Overexpression  increases the number of axonal branch points and dendritic arborization Monomer sequestering proteins Monomer sequestering proteins Profilin  Triggers actin polymerization by sequestration of polymerizable actin monomers at the leading edge of lamellipodia (near the nucleators)  Interacts with N-WASP, and most of the Formins to potentialize their effects  Profilin1 KD leads to moderate decrease of G-actin localization, but strongly affected stucture and dynamicity of GC lamellipodias Monomer sequestering proteins Profilin  Triggers actin polymerization by sequestration of polymerizable actin monomers at the leading edge of lamellipodia (near the nucleators)  Interacts with N-WASP, and most of the Formins to potentialize their effects  Profilin1 KD leads to moderate decrease of G-actin localization, but strongly affected stucture and dynamicity of GC lamellipodias Thymosin–β4  Tβ4 play an important role in the localization of G-actin at the leading edge of lamellipodia  Tβ4 KD essentially eliminated G-actin localization to the leading edge, resulting in structurally normal lamellipodia, but unstable and unable to move and extend efficiently Principal capping proteins • Actin filament elongation & stabilization + • Impairs filament disassembly and turnover CP ARP2/3 Most famous : CP  Promote ARP2/3 dependant actin polymerization  Function in the neuron remains unknown TMOD3/4  ARP2/3 is a capping protein ARP2/3 Other capping proteins in the GC Tropomodulin family : TMOD3 & TMOD4 isoforms are specifically expressed in the brain and present in the GC Their function remains unknown . [...]

[...] This function is modulated by interactions with WASH and tubulin subunits WASH can bundle both actin and microtubules in a GTPase regulated manner . Which GTPase ? [...]

[...] Cdc Rho Ephrins Ephrin-A signalling  Control the topographic projections of retinal ganglion cells  Ehprin-A lead to GC collapse Receptor internalization Vav2 GC collapse and axon repulsion Semaphorin 3A (SEMA3A) signalling  Repels cortical axons in situ and in vitro  Reduces cortical axon granching  Repels retinal neurons  promote branching of their axons Plexin Neuropilin Rac1 sequestering From Kalil et al In cortical neurons : Sema3A reduces axon branching, induces GC collapse, but don't have any effect on axonal length Depolymerization of actin bundles  GC collapse Slit signalling  Prevent commisural axons from recrossing the midline 3 Slit proteins (Slit1-3) binds to Robo receptors  repel axons Robo receptors are highly conserved through evolution Co-expression of different Robo receptors in the GC Abl Robo receptor is regulated by the Abl Filopodia depolymerization, GC turning & axon repulsion Netrin signalling  Attractant cue  Netrin-1 interact with 2 receptors : DCC & Neogenin Netrin-1  DCC = DCC multimerization = GC attraction Axonal growth Fyn P Trio Nck1 Rac1 Pak1 Cdc42 Actin polymerization Tiam1 GC attraction & stimulation of axonal growth Netrin signalling  Attractant cue  Netrin-1 interact with 2 receptors : DCC & Neogenin Netrin-1  DCC = DCC multimerization = GC attraction Axonal growth Netrin-1  DCC + UNC5 = GC repulsion, axon turning GC repulsion & axon turning Netrin signalling  Attractant cue  Netrin-1 interact with 2 receptors : DCC & Neogenin Netrin-1  DCC = DCC multimerization = GC attraction Axonal growth Netrin-1  DCC + UNC5 = GC repulsion, axon turning Slit/ROBO signalling  silence Netrin-1/DCC attraction Filopodia depolymerization, GC turning & axon repulsion Focal adhesion dynamics in the GC Cadherin, Talin, FAK Paxillin, ⍺-actinin Vinculin cin Tenas Fibron ectin Guidance cues + RhoGEF/GAP + RhoGTPases + Integrin ECM Lamin in Integrin PM Integrin Recruitment + intracellular extracellular etc . effectors Focal adhesion dynamics in the GC Cadherin, Talin, FAK Paxillin, ⍺-actinin Vinculin cin Tenas Fibron ectin Guidance cues + RhoGEF/GAP + RhoGTPases + Integrin ECM Lamin in Integrin PM Integrin Recruitment + intracellular extracellular etc . [...]