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Putting the axonal periodic scaffold in order
Christophe Leterrier
To cite this version:
Christophe Leterrier. Putting the axonal periodic scaffold in order. Current Opinion in Neurobiology,
Elsevier, 2021, 69, pp.33-40. �10.1016/j.conb.2020.12.015�. �hal-03110363�
Putting the axonal periodic scaffold in order Christophe Leterrier
Neuronsrelyonauniqueorganizationoftheircytoskeletonto build,maintainandtransformtheirextraordinarilyintricate shapes.Afterdecadesofresearchontheneuronal cytoskeleton,itisexcitingthatnovelassembliesarestill discoveredthankstoprogressincellularimagingmethods.
Indeed,super-resolutionmicroscopyhasrevealedthataxons arelinedwithaperiodicscaffoldofactinrings,spacedevery 190nmbyspectrins.Determiningthearchitecture,
composition,dynamics,andfunctionsofthismembrane- associatedperiodicscaffoldisacurrentconceptualand technicalchallenge,aswellasaveryactiveareaofresearch.
Thisshortreviewaimsatsummarizingthelatestresearchon theaxonalperiodicscaffold,highlightingrecentprogressand openquestions.
Address
AixMarseilleUniversite´,CNRS,INPUMR7051,NeuroCyto,Marseille, France
Correspondingauthor:
Leterrier,Christophe([email protected])
CurrentOpinioninNeurobiology2020,69:33–40
ThisreviewcomesfromathemedissueonMolecularneuroscience EditedbyFrankBradkeandYukikoGoda
https://doi.org/10.1016/j.conb.2020.12.015 0959-4388/ã2021ElsevierLtd.Allrightsreserved.
Introduction
Axonsarethelongcellularextensionsthatconnectneu- rons andform nerve fibers. By aconservative estimate, neuronalinformationrunsthrough160000kmofaxons inourbrainalone,notcountingperipheralaxonsthatcan individuallyreachalengthofonemeter.Developmentof this elaboratecircuitry andmaintenanceduring awhole lifetime is a daunting task, as evidencedby the 40%
drop in total axon length at age 80 [1]. The unique morphologyandfunctionsofaxonsrelyonspecificcyto- skeletal assemblies of microtubules, intermediate filamentsandactin[2–4].Amongthese,theorganization ofactinalongtheaxonshafthaslongbeenoverlooked,as it was unremarkably uniform when seen by optical microscopy,anddifficulttovisualizebyelectronmicros- copy [5]. Only the advent of super-resolution optical microscopy could resolve the unique actin structures
alongaxons,startingwiththediscoveryof thesubmem- branescaffoldofactinringsperiodicallyspacedbyspec- trins [6]. In this short review, I will summarize recent research about the architecture and functions of this membrane-associated periodic scaffold (MPS), as well ashighlightopenquestions:itsmechanismofformation, itsrelationshipwith othercytoskeletalassembliesalong axons, and how progress in cellular imagingcan tackle them.
UbiquityoftheaxonalMPSandhowtolookat it
The MPS is present along the whole axon shaft and composed of submembrane, circumferential actin rings regularly spaced every 190nmby tetramers of spectrin thatconnecttwoadjacentrings(Figure1a)[7].Itcanbe thoughtofasamono-dimensional,tubularanalogtothe bi-dimensional hexagonal pattern of spectrin and short actinfilamentsliningtheerythrocyteplasma membrane [8]. Originally discovered in hippocampal cultured neurons and brain slices [6], the MPS has since been describedinallneuronaltypesandorganismsstudiedso far [9,10]. It is present along unmyelinated but also myelinatedaxons,bothatandbetweennodesofRanvier [9,11,12].Aperiodicorganizationofactinringsspacedby spectrincanalsobedetectedinpartsofdendrites,notably spinenecks, butisfarlesssystematic[13,14,15].
Thecloseappositionofringsevery190nmmakesthem invisibletoclassicalopticalmicroscopy,whichislimited to a250nmresolution(Figure 1b).Theywerevisual- izedforthefirsttimein2013[6]usingSingleMolecule Localization Microscopy (SMLM), a super-resolution technique relying on sequential imaging of single fluorophores to build an image that attains 20nm in resolution[16].Followingthisinitialdescription,SMLM hasremainedamethodofchoicetomapthecomposition and organization of the MPS using variants such as StochasticOpticalReconstructionMicroscopy(STORM, seeFigure2c)[17,18,19],photoactivatedLocalization Microscopy (PALM) that is compatible with live cells [13], or DNA-Point Acquisition in Nanoscale Topogra- phy (PAINT) that allows straightforward multi-color imaging(Figure1c–d)[20,21].
Othersuper-resolutivetechniques[16]havesuccessfully visualizedtheMPS:StructuredIlluminationMicroscopy (SIM),witha120nmtypicalresolution,canimagethe overall190nmperiodicityalongaxonswithlargerfieldsof viewandfasterspeeds(Figure2a)[22,23].Notably,the firstpublishedimageoftheaxonalMPSwasaSIMimage of the scaffold protein ankyrin at the Drosophila
34 Molecularneuroscience
Figure1
(a)
initial segment
α2-spectrin/β4-spectrin α2-spectrin/β2-spectrin
actin ring Tpm3.1
pMLC NMII ankG
dendrites
axon
synapses cell
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adducin
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intensity
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axon initial segment
actin β4-spectrin
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0 200 400 600 800 distance (nm)
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distal axon
actin β2-spectrin
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actin β2-spectrin β4-spectrin
actin β4-spectrin
β2-spectrin (b)
Current Opinion in Neurobiology
Molecularorganizationofthemembrane-associatedperiodicscaffold(MPS).
(a)Cartoonofaneuronshowingitsdendrites,cellbody(topright)andaxonthatmakesynapsesontoadownstreamneuron(topleft).Theaxon comprisestheaxoninitialsegment(AIS,gray)andthedistalaxon.Bottom,organizationoftheMPSintheAIS(bottomleft)anddistalaxon (bottomright).TheMPSismadeofactinrings(gray)spacedevery190nmbyspectrintetramers.IntheAIS,thespectrintetramersaremadefrom a2-spectrin(yellow)andß4-spectrin(lightorange).AnkyrinG(ankG,blue)bindsthecenterofthespectrintetramerandanchorsionchannelsand celladhesionmolecules(lightblue)atthemembrane.Inthedistalaxon,spectrintetramersaremadeofa2-spectrinandß2-spectrin(orange).
TropomyosinTpm3.1(brown)associateswiththeAISactinrings,whileassembliesofphospho-myosinlightchain(pMLC,darkbrown)andmyosin heavychains(brown)cancrosslinkactinrings.Alongthedistalaxon,adducin(brown)associateswiththeactinrings.(b)Diffraction-limitedimage ofamatureculturedhippocampalneuronstainedforß4-spectrin(AIS,arrowheads,yellowonoverlay),ß2-spectrin(distalaxon,outlined arrowheads,orangeonoverlay)andactin(grayonoverlay).(c)Two-colorDNA-PAINTimageactin(gray)andß4-spectrin(yellow)alongtheAIS.
Theß4-spectrinantibodyrecognizestheC-terminusofß4-spectrin,thatis,thecenterofthespectrintetramer.TheresolutionofDNA-PAINT(20 nm)resolvesthe190-nmperiodicappearanceoftheMPS,withactingringsinterspacedbyß4-spectrinbands(zoomimageandintensityprofile alongthegreenlineontheright).(d)Two-colorPointAccumulationinNanoscaleTopography(PAINT)imageactin(gray)andß2-spectrin(yellow) alongthedistalaxon.Theß2-spectrinantibodyrecognizestheC-terminusofß2-spectrin,thatis,thecenterofthespectrintetramer.PAINT resolvesthe190-nmperiodicappearanceoftheMPS,withactingringsinterspacedbyß2-spectrinbands(zoomimageandintensityprofilealong thegreenlineontheright).(b–d)AreadaptedfromRef.[20],withpermission.
neuromuscular junction, resolving a 200-nm structured lattice [24].The60nmresolutionobtainedbyStimu- lated Emission Depletion(STED) microscopy has also beenusedtovisualizetheMPS(Figure2b)[9,14,25–28].
ExpansionMicroscopy(ExM),wherethesampleisphys- ically expandedafter embeddingintoahydrophilic gel, canalsovisualizeperiodicspectrinsalongtheMPS[29].
AlthoughclassicactinlabelsarenotcompatiblewithExM
Figure2
(d)
2 μm 500 nm
actin PREM
200 nm
2 μm 500 nm 200 nm
actin (STORM) (e) PREM
(a) actin (SIM)
2 μm (b) actin (STED)
2 μm (c) actin (STORM)
2 μm
Current Opinion in Neurobiology
Actinringsvisualizedbysuper-resolvedandelectronmicroscopyinlivingorfixedcells.
(a)Imagefroma4-framemovie(1frameevery20s)ofaxonslabeledforactinusingsilicon-rhodamine(SiR)-actinandimagedlivebyStructured IlluminationMicroscopy(SIM).DatafromRef.[34],providedbytheauthorswithpermission.(b)ImageofanaxonlabeledforactinusingSiR-actin andimagedlivebyStimulatedEmission-Depletionmicroscopy(STED).DatafromRef.[24],providedbytheauthorswithpermission.(c)
StochasticOpticalReconstructionMicroscopy(STORM)imageofanaxonfromafixedcelllabeledforactinusingphalloidin.(d)PREMimageof anunroofedandfixedaxonshowingtheMPSwithactinbraids(arrowheadsonzoom,right)embeddedinaspectrinmesh.(e)CorrelativeSTORM ofactin(phalloidinlabeling,orange)andPREMofanunroofedandfixedaxonshowingthattheactinringsimagesbySTORMaretheactinbraids seenbyPREM(arrowheadsonzoom,right).(a–e)Areimagesobtainedfromculturedhippocampalneurons.(d–e)AreadaptedfromRef.[20],with permission.
protocols, new reagents could potentially be used to directlyvisualizeactinringsbyExM [30].
Composition oftheMPS
Inadditiontoactin,anumberofMPScomponentshave been identified (Figure 1a). The spectrins connecting actin rings are head-to-head,190-nm longtetramers of two a-spectrins and two ß-spectrins [31]. The only a-spectrinexpressedinneurons,a2-spectrin,ispresent all along the axon [12,20,32]. At the axon initial segment (AIS, the first 20 50mm of the axon), a2- spectrin associates with ß4-spectrin to form tetramers (Figure 1b–c), whereas in the more distal axon, it associates with ß2-spectrin (Figure 1b & d) [6,17]. In the AIS, membrane proteins (sodium and potassium voltage-gatedchannels,celladhesionmoleculesCAMs) areanchoredto theMPSvia interactionofthe scaffold protein ankyrinG with the spectrin tetramers, and are thusalsoperiodicallyorganizedalong theplasma mem- brane [6,17].
Adducin,whichcapstheshortactinfilamentsfoundinthe spectrinhexagonallatticeoferythrocytes,associateswith actinringsalongtheaxon[6,26],butislesspresentalong its proximal part [21,33]. There, AIS actin rings are decorated bytropomyosinTpm3.1, which couldhavea role in stabilizing them [23]. Actin rings have also recentlybeen characterized as actomyosinstructures: a concentration of phospho-myosin light chain (pMLC), activatorofnon-musclemyosin(NM-II),wasfoundalong theactinringsattheAIS[34],andNM-IIitselfattaches to rings along the whole shaft (Figure 1a) [19,35].
Recentreportshavedescribedtheassociationofactivated membranereceptors(thecannabinoidG-proteincoupled receptor CB1, L1-CAM, receptor tyrosine kinases FGFR1/TrkB) and downstream signalingproteins such as Srcatactin ringsafter theiractivation[18,36].Itis likelythatmoreMPScomponentsandpartnersremainto bediscovered,forexampleusingunbiasedmethodssuch asBioIDtaggingandmassspectrometry[37].
Molecularorganizationofthe MPS
Untilrecently,onlyopticalsuper-resolvedtechniquehad beenabletorevealtheMPS,sothearrangementofMPS componentsatthemolecularscaleremainedspeculative.
By analogy with the actin/spectrin hexagonal lattice of erythrocytes[8],thepresenceofadducinassociatedwith axonalactinringssuggestedthattheseringsweremadeof short, capped filaments bundled into rings [6,7]. Polar- ized-SIM analysis of signal from axonal actin led to proposethattheshortfilamentswerelongitudinalalong the axon, and laterally assembled into rings [38]. The ultrastructuraldetail ofEM isneeded to answersucha question,butdecadesofEMstudiescouldnotdiscernthe submembraneperiodicscaffold[2].Itislikelythatclas- sicalthin-sectionEMcannoteasilycontrastactinassem- bliesmadeofafewfilaments-andmorerecentcryoEM
approachesalsofailedto visualizetheMPSalongaxons [39,40].
AnEMmethodthatcanvisualizethecytoskeletonwith great contrast and resolution is platinum-replica EM (PREM), where the topography of cells is transferred to aplatinum-carbonreplica beforebeingexamined by transmission EM. PREM of axons after membrane extractionbydetergentsonlyrevealedshort,disorganized actinfilamentswithnoperiodicstructures[33].Recently, PREM after mechanical unroofing — removal of the dorsalpartofculturedneuronsandtheiraxonsbyultra- sonicpulses— wasshownto preservetheMPSandits periodic organization [21]. Along the ventral plasma membraneoftheaxon,PREMviewsshowednumerous instancesofsubmembraneactinringfragments,regularly spacedevery190nm,andconnectedbyameshofspec- trin (Figure 2d). Moreover, high magnification views revealed that actin rings are made of two long actin filaments arranged in a braid, with typically 0.5 1mm of continuousbraid beingvisiblewithin adense mesh.
Identification of actin and spectrin by immunogold- PREM and correlative SMLM/PREM confirmed that theactin ringsseen bysuper-resolution microscopyare indeedthebraided,long actinfilamentsseenbyPREM (Figure2e)[21].Unroofingnecessarilybreakringsinto fragments, preventing the visualization of their intact arrangementaroundtheaxoncircumference.Techniques likecryo-electrontomographymayhelpresolvingwhole actinringsattheultrastructurallevelinthefuture[41].
Thebraidsoftwolongfilamentsthatmakeactinringsare uniquestructuresthathaveneverbeenobservedinother cellsorcompartments,openingmanyquestions.Areactin braidsmadeoftwoantiparallelorparallelactinfilaments?
Dotheypolymerizetogether,orarethey assembledfrom individualfilaments?Howcanlong,stiffactinbraids-actin filamentshaveapersistencelengthof10mm-curveinto 1mm diameter rings along the axon circumference?
Invitroworkhasrecentlyshownhowcalponinhomology domains of actin-associated proteins can induce strong individualfilament curvature, andthis could be relevant foraxonalactinrings[42].Ringsmadeoflongfilamentsalso questiontheassumedrole ofadducinatactinrings:more thanaproteincappingshortfilamentslikeinerythrocytes,it could primarily helplateral association of filaments with spectrins[43,44].
Relationshiptoother axonalcytoskeleton assemblies
What is the relationship between the MPS and other cytoskeletalassembliesintheaxon?Interplaywithinter- mediate filaments hasnot been explored, but microtu- bules disassembly can destabilize the MPS at least partially [6,13,22]. Conversely, defect in microtubule bundling and axonal swellings have been observed in drosophila axons lacking an MPS [22]. Disentangling
36 Molecularneuroscience
indirect and direct interplay between axonal actin and microtubulesisdifficult,asdrugstargetingthecytoskel- etonhaveacutepleiotropiceffects,andshRNAorgenetic deletionstrategiescanonly beobservedoverlongterm.
Ideally, localizedand acute strategiessuch as optically- controlledconstructsordrugsshouldbeusedtoovercome this challenge.
AnotheropenquestionistheinterplaybetweentheMPS and dynamic, intra-axonalactin structuressuch as actin hotspots (minute-lived, immobile actin clusters that appear and disappear inside the axon shaft) and actin trails(fast,filamentousassembliesnucleatedfromhotpots that elongate over several mm and disappear within seconds)[45].Interestingly,mostactinhotspotsarecon- tactingtheMPSonaxonalcross-sectionfrom3DSMLM data[46].Moregenerally,itwouldbeimportanttogeta betterunderstandingoftheaxonal‘actineconomy’,that is, the distribution of the available actin pool between dynamic (growth cone, hotspots, trails) and structural (actin rings) assemblies along axons. Finally, the MPS usuallystopsatpresynapses[10,47],buthowisthispause establishedandmaintained,andhowispresynapticactin itselforganized,remainelusive[5].Microtubulesnucle- ationmostlyoccursawayfromthecentrosomeinneurons [48], andtheir nucleationnear atboutons [49,50] could playaroleinshapingtheMPSaroundpresynapses.
Mechanism ofassemblyand dynamics
How is the MPS assembled during development? In neuronal cultures, itappears just after axondifferentia- tion at two days in vitro (div). The first assembled MPS components from 2 div on are ß2-spectrin and actin – notably,actin ringsareeasier todetect in these immature neurons using the actin probe silicon-rhoda- mine (SiR)-actin imaged by STED [25], than using phalloidin imagedbySMLM [6,13]. Actinand spectrin seem mutually interdependent for MPS assembly and integrity:acuteactinperturbationanddepletionofspec- trin bothdisassemble theMPSorprevent itsassembly.
Adducin appears later, at around 6 div [13], and its presence is not necessary for theMPS to form [26]. A fundamentalquestionhereiswhatdrivesMPSassembly.
Consideringthe2Dhexagonallatticeinerythrocytesand the1Dperiodiclatticeinneurons,onecanspeculatethat core component of theMPS are able to auto-organize, driven by the local geometry (flat membrane versus tubular extension). In vitro reconstitution ofa minimal actin/spectrinsystem withindefinedmembranegeome- tries(flat,sphericalortubularmembrane)wouldallowto test auto-assemblyhypotheses ofMPScomponents.
Assembly of theMPS first happensalong the proximal axonat2div,beforespreadingforwardtowardthedistal axon[13].Ofnote,eveninmatureneurons,theverydistal partoftheaxonbeforethegrowthconeisusuallydevoid of a detectable MPS. Beyond this proximo-distal
sequence, notmuchis known about themechanism of MPS assembly: is it continuously propagating like a polymerfromtheassembledparttowardthedistalaxon, or aretheremultipleseedsof proto-MPSthatgrowand coalesce intoasingle scaffold?Live-cell imagingof the MPScouldanswersuchquestionsbutisdifficult,because super-resolution imaging requires high illumination intensitiesthatrestrictthepossibilityoflong-termimag- ing[16].The MPShasbeenobservedinlivingcells by PALMofphotoactivablespectrin[13],orSTED[25]and SIM [35]of actinprobes (Figure 2a–b),but only for a handful of frames and alimited time (seconds to min- utes), precluding the study of slow processes such as assemblyorstructuralplasticity.Moreover,itischalleng- ing to visualizethelow amount ofactinwithinringsin livingcells,aslive-cellactinprobessuchasSiR-actinor LifeAct can over-stabilize filaments and induce actin bundles [15]. A related open question is the nature anddynamicsofMPSassemblyduringaxonregeneration, whichcanbeinducedbystabilizingmicrotubules[51,52].
Live-cell and drug treatment experimentshave never- thelessbroughtkeyinsightsabouttheMPSparadoxical dynamics: on the one hand, the MPS is a static and stablescaffold,assuggestedbythehalf-lifeofspectrins in neuronsthatattains5–10days[53,54].PALMof ß2- spectrin showsnosignificant movementofrings within 30minutes, and FRAP only very slow turnover of spectrins[13].Althoughactinringscanbedisassembled byactin-targetingdrugs,theyareverystableintheAIS [17,21,55]andresistanttoactinassemblyperturbators alongthewholeshaft[19].PREMimagesshowringsas actin braids deeply embedded in a spectrin mesh, in line withtheir highstability and slowturnover. Onthe other hand, the MPS can be profoundly remodeled within a few hours in physiopathological conditions.
MPS disassembly occurs along dorsal root ganglion axons after only three hours of NGF withdrawal, upstream ofthe axonal degeneration eventsthat occur laterin thismodel [56,57].Itwasalso shownthatMPS remodelingcanoccurtoregulatephysiologicalsignaling by GPCRs, CAMs and RTKs [18]. After activation, these membraneproteinsassociate atthecenter ofthe spectrin tetramers in between actin rings, condensing with downstream proteins of the ERK signaling path- way. Signaling itself induces anegative feedback loop ofcalpain-drivendisassemblyoftheMPSafter1hour, drivingsignalingextinction.Evenfasterrearrangements have recently been demonstrated, allowing the trans- portoflargecargoesthroughaxonsofsmallerdiameter:
a myosin-dependent enlargement/opening of rings occurs during cargo passage, before the axon shrinks back to its original diameter within seconds [35].
Theseresultsrevealthatbeyonditslong-termstability, the MPS is exquisitely regulated, and the structural mechanisms of this short-term plasticity remain to be fully explored.
Cellularfunctions oftheMPS
WhatarethecellularrolesoftheMPSfortheaxonphysiol- ogy?GiventheMPSstrikinglyregularorganizationandthe cable-likemorphologyofaxons,oneofthefirstfunctional hypothesiswas mechanicalsupporttoaxons,notablyperiph- eralaxonsthatundergointensestressduringbodymove- ments.The association of rigid actinrings connected by spring-likespectrinsmayformamechanicallyresistant,yet flexible,scaffold[6].Indeed,discoveryoftheMPSprovided astructuralbasistotheearlierfindingthatC.elegansmutant forß-spectrinhave more fragileaxonsthat break dueto animalmovements[58].Carefulmechanobiologicalstudies later showedthatspectrininducesconstitutivetensionalong axons[59],andthattogetherwithmicrotubules,theMPS playsakeyroleinprotectingaxonsagainstmechanicalstress [27].Recently,unfoldingofspectrinrepeatswithintheMPS tetramerswasproposedasamechanismtoreleaselongitu- dinalstressalongstretchedaxons[60].
A molecular view of how the MPS can deform and contractitselfisalsostartingtoemerge.Simulationhave explored how the MPS could provide rigidity to the axonalplasma membrane [61].Actomyosincontractility atthe MPSparticipates in both longitudinaland radial tension along the axon [62], suggesting that myosins could associate with actin rings. Recent studies have located pMLC and NMII heads apposed to the rings at the nanoscale, while heavy chains are preferentially located in-between rings [19,34,35]. The majority of myosin dimers may thus crosslink neighboring rings, a finding confirmed at the ultrastructural level by the localizationofpMLCandmyosinrodsusingimmunogold PREM and correlative SMLM/PREM [21]. How such crosslinking myosins - or a minor population of within-ring associated myosins – can pull along the braidedfilamentsthatformringstogeneratebothradial andaxialcontractilityremainsto beclarified[63,64].
Another widely held hypothesis is that the MPS, by periodically arranging anchored ion channels such as sodium and potassium channels at the AIS, could influencetheway theaction potentialisgenerated and propagated along the axon [7] – but no experimental results have confirmed this so far. It was nevertheless shownthatsurfacediffusionofmembranecomponentsis compartmented bythe submembrane actin rings along the proximal axon [65]. Moreover, the MPS is able to organizesignalingfromaxonalmembraneproteins such as CB1, L1-CAM and FGFR1/TrkB by transiently recruitingactivatedreceptors and intracellulareffectors atthecenterofspectrintetramers(seeabove)[18],and live-cell imaging evidenced activated CB1 receptors immobilization at this location [36]. Beyond receptor signaling,thedensemeshoftheMPSasseenonPREM images is likely to prevent endocytosis from the plasma membrane. Indeed, activated CB1 endocytosis is enhanced in ß2-spectrin depleted neurons [18].
WhethertheMPShasamore generalrolein regulating endo/exocytosis along the axon shaft is an exciting questionfor futureresearch.
Conclusions
One the few truly novel cellular structures discovered bysuper-resolution microscopy so far,theMPS isnow probedusingavarietyofcomplementaryapproachesto understand its architecture, dynamics, and functions.
Yet a lot remains unknown, and new advances will undoubtedlybestimulatedbyprogressintechnologies:
betterspatial andtemporalresolution,bettermolecular identificationcapabilities.Atthestructurallevel,itwill bepossibletogobeyondthelongitudinalperiodicityto zoom on the architecture of single rings, using more elaborate strategies such as SMLM-based single- particle averaging [66]. This in situ structural biology willbecomplemented bymultiplexedapproaches such as automated sequential DNA-PAINT [67] to obtain the molecular arrangement of multiple MPS compo- nents at once. Deep-learning will be instrumental to understand the heterogeneity of patterning between various axonal compartments, quantifying the amount of periodicity and the presence of other actin-based structures[15].Newperturbationstrategieswith bet- ter molecular, spatial and temporal specificity such as optically-driveninhibitors will allowtodissectthe role of the MPS in axonal physiological processes, before zooming out to assess the consequences on neuronal connectivity and information processing. Finally, potential dysfunctions of the MPS in neuropsychiatric diseases, from spectrinopathies [68,69] to Alzheimer’s disease, remain to be explored.
Conflictofintereststatement Nothingdeclared.
Acknowledgements
IwouldliketothankSubhojitRoy,Ste´phaneVassilopoulosandMarie- JeannePapandre´oufordiscussionsandfeedbackonthemanuscript;Tong WangandFredericMeunierforprovidingtheimageinFig.2A,Elisad’Este forprovidingtheimageinFig.2B,FlorianWernertforfeedbackand providingtheimageofFig.2C,andallmembersoftheNeuroCytolab.This workwassupportedbyaCentreNationaldelaRechercheScientifique ATIPgrant(AO2016)toC.Leterrier.
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