CiteULike: lechristophe's neurites_growth

Secretory Outposts for the Local Processing of Membrane Cargo in Neuronal Dendrites.

Cyril Hanus — 2008-07-25T16:20:57-00:00

Traffic (Copenhagen, Denmark) (4 June 2008)

The large size and geometric complexity of neuronal dendrites necessitate specialized mechanisms to both deliver postsynaptic cargo over extended distances and regulate dendritic composition on a submicron scale. Despite the fundamental importance of membrane trafficking in dendrite growth, synapse formation and plasticity, the organelles and cellular rules governing postsynaptic trafficking are only now emerging. Here we review what is currently known about dendritic secretory organelles and their role in the development, maintenance and plasticity of postsynaptic compartments.

Role of Septin cytoskeleton in spine morphogenesis and dendrite development in neurons.

T Tada — 2008-04-30T09:53:48-00:00

Current biology : CB, Vol. 17, No. 20. (23 October 2007), pp. 1752-1758.

Septins are GTP-binding proteins that polymerize into heteromeric filaments and form microscopic bundles or ring structures in vitro and in vivo. Because of these properties and their ability to associate with membrane, F-actin, and microtubules, septins have been generally regarded as cytoskeletal components [1, 2]. Septins are known to play roles in cytokinesis, in membrane trafficking, and as structural scaffolds; however, their function in neurons is poorly understood. Many members of the septin family, including Septin 7 (Sept7), were found by mass-spectrometry analysis of postsynaptic density (PSD) fractions of the brain [3, 4], suggesting a possible postsynaptic function of septins in neurons. We report that Sept7 is localized at the base of dendritic protrusions and at dendritic branch points in cultured hippocampal neurons--a distribution reminiscent of septin localization in the bud neck of budding yeast. Overexpression of Sept7 increased dendrite branching and the density of dendritic protrusions, whereas RNA interference (RNAi)-mediated knockdown of Sept7 led to reduced dendrite arborization and a greater proportion of immature protrusions. These data suggest that Sept7 is critical for spine morphogenesis and dendrite development during neuronal maturation.

MAP kinase pathway-dependent phosphorylation of the L1-CAM ankyrin binding site regulates neuronal growth.

JD Whittard — 2008-02-25T16:46:59-00:00

Mol Biol Cell, Vol. 17, No. 6. (June 2006), pp. 2696-2706.

The growth of neuronal processes depends critically on the function of adhesion proteins that link extracellular ligands to the cytoskeleton. The neuronal adhesion protein L1-CAM serves as a receptor for nerve growth-promoting proteins, a process that is inhibited by the interaction between L1-CAM and the cytoskeleton adaptor ankyrin. Using a novel reporter based on intramolecular bioluminescence resonance energy transfer, we have determined that the MAP kinase pathway regulates the phosphorylation of the FIGQY motif in the adhesion protein L1-CAM and its interaction with ankyrin B. MAP kinase pathway inhibitors block L1-CAM-mediated neuronal growth. However, this blockade is partially rescued by inhibitors of L1-CAM-ankyrin binding. These results demonstrate that the MAP kinase pathway regulates L1-CAM-mediated nerve growth by modulating ankyrin binding, suggesting that nerve growth can be regulated at the level of individual receptors.

Pyramidal neuron polarity axis is defined at the bipolar stage.

F Calderon de Anda — 2008-01-15T10:48:39-00:00

J Cell Sci, Vol. 121, No. Pt 2. (15 January 2008), pp. 178-185.

In situ observations of the development of hippocampal and cortical neurons indicate that final axon-dendrite identity is defined at the time of generation of the first two, oppositely positioned, neurites. Quite differently, in vitro studies demonstrated that axonal fate is defined by the stochastic selection of one of the multiple minor neurites for fast outgrowth. By analyzing the fate of all neurites, starting at the time of emergence from the cell body, we demonstrate that polarity is defined at the bipolar stage, with one of the two first-appearing neurites acquiring axonal fate, irrespective of how many other neurites later form. The first two neurites have, as in vivo, the highest growth potential, as cutting the axon results in the growth of a new axon from the neurite at the opposite pole, and cutting this induces regrowth from the first. This temporal and spatial hierarchical definition of polarized growth, together with the bipolar organization of microtubule dynamics and membrane transport preceding it, is consistent with polarity being initiated by an intrinsic program. In this scenario, molecules required for axon specification would act at one of the first two neurites and extrinsic cues will be required for final commitment of polarity.

Protein kinase Czeta and glycogen synthase kinase-3beta control neuronal polarity in developing rodent enteric neurons, whereas SMAD specific E3 ubiquitin protein ligase 1 promotes neurite growth but does not influence polarity.

BP Vohra — 2008-01-04T09:59:50-00:00

J Neurosci, Vol. 27, No. 35. (29 August 2007), pp. 9458-9468.

Enteric nervous system (ENS) precursors migrate extensively before differentiating to form uni-axonal or multi-axonal neurons. ENS precursor survival, neurite growth, and cell migration are all directed by Ret kinase, but downstream signaling pathways are incompletely understood. We now demonstrate that proteins regulating polarity in other cells including partitioning defective 3 (PAR3), PAR6, protein kinase Czeta (PKCzeta), and glycogen synthase kinase 3beta (GSK3beta) are expressed in developing enteric neurons with a polarized distribution. Blocking PKCzeta or GSK3beta reduces ENS precursor migration and induces the formation of multi-axonal neurons. Axon elongation also depends on SMURF1 (SMAD specific E3 ubiquitin protein ligase 1), which promotes RhoA degradation and associates with polarity proteins. SMURF1 inhibition, however, does not increase the number of multi-axonal neurons in ENS precursors. These data link cell surface Ret activation with molecular machinery controlling cytoskeletal dynamics and suggest that polymorphisms influencing PKCzeta or GSK3beta might alter Hirschsprung disease penetrance or expressivity by affecting ENS precursor migration.

Cell type-specific dendritic polarity in the absence of spatially organized external cues.

AC Horton — 2008-01-03T14:09:30-00:00

Brain Cell Biol, Vol. 35, No. 1. (February 2006), pp. 29-38.

Pyramidal neurons of the hippocampus and cortex have polarized dendritic arbors, but little is known about the cellular mechanisms distinguishing apical and basal dendrites. We used morphometric analysis and time lapse imaging of cultured hippocampal neurons to show that glutamatergic neurons develop progressive dendritic asymmetry in the absence of polarized extrinsic cues. Thus, pyramidal neurons have a cellular program for polarized dendrite growth independent of tissue microenvironment.

NeuriteTracer: A novel ImageJ plugin for automated quantification of neurite outgrowth.

Madeline Pool — 2008-01-03T13:30:51-00:00

J Neurosci Methods (8 September 2007)

In vitro assays to measure neuronal growth are a fundamental tool used by many neurobiologists studying neuronal development and regeneration. The quantification of these assays requires accurate measurements of neurite length and neuronal cell numbers in neuronal cultures. Generally, these measurements are obtained through labor-intensive manual or semi-manual tracing of images. To automate these measurements, we have written NeuriteTracer, a neurite tracing plugin for the freely available image-processing program ImageJ. The plugin analyzes fluorescence microscopy images of neurites and nuclei of dissociated cultured neurons. Given user-defined thresholds, the plugin counts neuronal nuclei, and traces and measures neurite length. We find that NeuriteTracer accurately measures neurite outgrowth from cerebellar, DRG and hippocampal neurons. Values obtained by NeuriteTracer correlate strongly with those obtained by semi-manual tracing with NeuronJ and by using a sophisticated analysis package, MetaXpress. We reveal the utility of NeuriteTracer by demonstrating its ability to detect the neurite outgrowth promoting capacity of the rho kinase inhibitor Y-27632. Our plugin is an attractive alternative to existing tracing tools because it is fully automated and ready for use within a freely accessible imaging program.

A vital role of tubulin-tyrosine-ligase for neuronal organization.

C Erck — 2008-01-03T13:05:22-00:00

Proc Natl Acad Sci U S A, Vol. 102, No. 22. (31 May 2005), pp. 7853-7858.

Tubulin is subject to a special cycle of detyrosination/tyrosination in which the C-terminal tyrosine of alpha-tubulin is cyclically removed by a carboxypeptidase and readded by a tubulin-tyrosine-ligase (TTL). This tyrosination cycle is conserved in evolution, yet its physiological importance is unknown. Here, we find that TTL suppression in mice causes perinatal death. A minor pool of tyrosinated (Tyr-)tubulin persists in TTL null tissues, being present mainly in dividing TTL null cells where it originates from tubulin synthesis, but it is lacking in postmitotic TTL null cells such as neurons, which is apparently deleterious because early death in TTL null mice is, at least in part, accounted for by a disorganization of neuronal networks, including a disruption of the cortico-thalamic loop. Correlatively, cultured TTL null neurons display morphogenetic anomalies including an accelerated and erratic time course of neurite outgrowth and a premature axonal differentiation. These anomalies may involve a mislocalization of CLIP170, which we find lacking in neurite extensions and growth cones of TTL null neurons. Our results demonstrate a vital role of TTL for neuronal organization and suggest a requirement of Tyr-tubulin for proper control of neurite extensions.

RPTPalpha is required for rigidity-dependent inhibition of extension and differentiation of hippocampal neurons.

A Kostic — 2008-01-03T12:49:58-00:00

J Cell Sci, Vol. 120, No. Pt 21. (1 November 2007), pp. 3895-3904.

Receptor-like protein tyrosine phosphatase alpha (RPTPalpha)-knockout mice have severe hippocampal abnormalities similar to knockouts of the Src family kinase Fyn. These enzymes are linked to the matrix-rigidity response in fibroblasts, but their function in neurons is unknown. The matrix-rigidity response of fibroblasts appears to differ from that of neuronal growth cones but it is unknown whether the rigidity detection mechanism or response pathway is altered. Here, we report that RPTPalpha is required for rigidity-dependent reinforcement of fibronectin (FN)-cytoskeleton bonds and the rigidity response in hippocampal neuron growth cones, like in fibroblasts. In control neurons, rigid FN surfaces inhibit neurite extension and neuron differentiation relative to soft surfaces. In RPTPalpha(-/-) neurons, no inhibition of extension and differentiation is found on both rigid and soft surfaces. The RPTPalpha-dependent rigidity response in neurons is FN-specific, and requires clustering of alpha(v)beta(6) integrin at the leading edge of the growth cones. Further, RPTPalpha is necessary for the rigidity-dependent concentration of Fyn and p130Cas phosphorylation at the leading edge of the growth cone, like it is in fibroblasts. Although neurons respond to rigid FN surfaces in the opposite way to fibroblasts, we suggest that the mechanism of detecting FN rigidity is similar and involves rigidity-dependent RPTPalpha recruitment of Fyn.

Cordon-bleu is an actin nucleation factor and controls neuronal morphology.

R Ahuja — 2008-01-03T10:10:00-00:00

Cell, Vol. 131, No. 2. (19 October 2007), pp. 337-350.

Despite the wealth of different actin structures formed, only two actin nucleation factors are well established in vertebrates: the Arp2/3 complex and formins. Here, we describe a further nucleator, cordon-bleu (Cobl). Cobl is a brain-enriched protein using three Wiskott-Aldrich syndrome protein homology 2 (WH2) domains for actin binding. Cobl promotes nonbundled, unbranched filaments. Filament formation relies on barbed-end growth and requires all three Cobl WH2 domains and the extended linker L2. We suggest that the nucleation power of Cobl is based on the assembly of three actin monomers in cross-filament orientation. Cobl localizes to sites of high actin dynamics and modulates cell morphology. In neurons, induction of both neurites and neurite branching is dramatically increased by Cobl expression-effects that critically depend on Cobl's actin nucleation ability. Correspondingly, Cobl depletion results in decreased dendritic arborization. Thus, Cobl is an actin nucleator controlling neuronal morphology and development.

Filopodia are required for cortical neurite initiation

Erik Dent — 2007-12-03T17:43:21-00:00

Nature Cell Biology, Vol. 9, No. 12. (18 November 2007), pp. 1347-1359.

Extension of neurites from a cell body is essential to form a functional nervous system; however, the mechanisms underlying neuritogenesis are poorly understood. Ena/VASP proteins regulate actin dynamics and modulate elaboration of cellular protrusions. We recently reported that cortical axon-tract formation is lost in Ena/VASP-null mice and Ena/VASP-null cortical neurons lack filopodia and fail to elaborate neurites. Here, we report that neuritogenesis in Ena/VASP-null neurons can be rescued by restoring filopodia formation through ectopic expression of the actin nucleating protein mDia2. Conversely, wild-type neurons in which filopodia formation is blocked fail to elaborate neurites. We also report that laminin, which promotes the formation of filopodia-like actin-rich protrusions, rescues neuritogenesis in Ena/VASP-deficient neurons. Therefore, filopodia formation is a key prerequisite for neuritogenesis in cortical neurons. Neurite initiation also requires microtubule extension into filopodia, suggesting that interactions between actin-filament bundles and dynamic microtubules within filopodia are crucial for neuritogenesis.

Emerging aspects of membrane traffic in neuronal dendrite growth.

Bor Luen Tang — 2008-01-02T18:39:28-00:00

Biochim Biophys Acta (4 December 2007)

Polarized growth of the neuron would logically require some form of membrane traffic to the tip of the growth cone, regulated in conjunction with other trafficking processes that are common to both neuronal and non-neuronal cells. Unlike axons, dendrites are endowed with membranous organelles of the exocytic pathway extending from the cell soma, including both rough and smooth endoplasmic reticulum (ER) and the ER-Golgi intermediate compartment (ERGIC). Dendrites also have satellite Golgi-like cisternal stacks known as Golgi outposts that have no membranous connections with the somatic Golgi. Golgi outposts presumably serve both general and specific local trafficking needs, and could mediate membrane traffic required for polarized dendritic growth during neuronal differentiation. Recent findings suggest that dendritic growth, but apparently not axonal growth, relies very much on classical exocytic traffic, and is affected by defects in components of both the early and late secretory pathways. Within dendrites, localized processes of recycling endosome-based exocytosis regulate the growth of dendritic spines and postsynaptic compartments. Emerging membrane traffic processes and components that contribute specifically to dendritic growth are discussed.

The relations between neurite development and the subcellular structures of hippocampal neuron somata

Zhang Yingge — 2007-09-13T10:34:43-00:00

Journal of Structural Biology, Vol. 144, No. 3. (December 2003), pp. 327-336.

The relations between neurite development and the subcellular structures of the hippocampal neuron somata have been studied with atomic force microscopy (AFM). The conformation of the neuron was achieved by the synapse-like structures found by AFM scanning along a neurite of the cell. Hippocampal neuron somata were divided into two or three subcellular parts by one or two horizontal grooves. The upper parts increased while the middle and the lower parts decreased with the number and the length of the neurites and the formation of the neurosynapse-like structures. When neurites sufficiently developed, the middle parts were lost and the lower parts became very small. Mitosis inhibitors could prevent the formation of such subcellular structures of hippocampal neuron somata, which was accompanied by the loss of ability to form synapse-like structures. These results suggest that the upper parts are responsible for neuritogenesis while the middle and the lower parts only have indirect effect on it.

Growing Dendrites and Axons Differ in Their Reliance on the Secretory Pathway

Bing Ye — 2007-08-24T11:28:41-00:00

Cell, Vol. 130, No. 4. (24 August 2007), pp. 717-729.

Summary Little is known about how the distinct architectures of dendrites and axons are established. From a genetic screen, we isolated dendritic arbor reduction (dar) mutants with reduced dendritic arbors but normal axons of Drosophila neurons. We identified dar2, dar3, and dar6 genes as the homologs of Sec23, Sar1, and Rab1 of the secretory pathway. In both Drosophila and rodent neurons, defects in Sar1 expression preferentially affected dendritic growth, revealing evolutionarily conserved difference between dendritic and axonal development in the sensitivity to limiting membrane supply from the secretory pathway. Whereas limiting ER-to-Golgi transport resulted in decreased membrane supply from soma to dendrites, membrane supply to axons remained sustained. We also show that dendritic growth is contributed by Golgi outposts, which are found predominantly in dendrites. The distinct dependence between dendritic and axonal growth on the secretory pathway helps to establish different morphology of dendrites and axons.

Design and validation of a tool for neurite tracing and analysis in fluorescence microscopy images

E Meijering — 2007-01-26T11:27:22-00:00

Cytometry Part A, Vol. 58A, No. 2. (2004), pp. 167-176.

For the investigation of the molecular mechanisms involved in neurite outgrowth and differentiation, accurate and reproducible segmentation and quantification of neuronal processes are a prerequisite. To facilitate this task, we developed a semiautomatic neurite tracing technique. This article describes the design and validation of the technique.The technique was compared to fully manual delineation. Four observers repeatedly traced selected neurites in 20 fluorescence microscopy images of cells in culture, using both methods. Accuracy and reproducibility were determined by comparing the tracings to high-resolution reference tracings, using two error measures. Labor intensiveness was measured in numbers of mouse clicks required. The significance of the results was determined by a Student t-test and by analysis of variance.Both methods slightly underestimated the true neurite length, but the differences were not unanimously significant. The average deviation from the true neurite centerline was a factor 2.6 smaller with the developed technique compared to fully manual tracing. Intraobserver variability in the respective measures was reduced by a factor 6.0 and 23.2. Interobserver variability was reduced by a factor 2.4 and 8.8, respectively, and labor intensiveness by a factor 3.3.Providing similar accuracy in measuring neurite length, significantly improved accuracy in neurite centerline extraction, and significantly improved reproducibility and reduced labor intensiveness, the developed technique may replace fully manual tracing methods. © 2004 Wiley-Liss, Inc.

Recycling endosomes in neuronal membrane traffic.

Michael R Schmidt — 2007-05-29T14:07:20-00:00

Biol Cell, Vol. 99, No. 6. (1 June 2007), pp. 333-342.

Neurons are highly polarized cells with axonal and somatodendritic membrane surfaces that spatially separate signal-sending from signal-receiving membrane domains. As found in many other cell types, different populations of endosomes are involved in the sorting of synaptic and other membrane cargo in neurons. The exact source of the membrane for neurite extension and process remodelling during neuronal differentiation has remained uncertain, and we do not know exactly how polarized sorting of neuronal membrane proteins is achieved. In the present article, we will provide a brief overview of endosomes and their putative or proven functions in fibroblasts, epithelial cells and neurons. On the basis of insights from non-neuronal cell types and recent studies on the function of recycling endosomes during synaptic plasticity-induced membrane remodelling, we postulate a speculative model regarding the role of recycling endosomes in neuronal differentiation.

NeuronMetrics: software for semi-automated processing of cultured neuron images.

ML Narro — 2007-05-29T13:38:18-00:00

Brain Res, Vol. 1138 (23 March 2007), pp. 57-75.

Using primary cell culture to screen for changes in neuronal morphology requires specialized analysis software. We developed NeuronMetrics for semi-automated, quantitative analysis of two-dimensional (2D) images of fluorescently labeled cultured neurons. It skeletonizes the neuron image using two complementary image-processing techniques, capturing fine terminal neurites with high fidelity. An algorithm was devised to span wide gaps in the skeleton. NeuronMetrics uses a novel strategy based on geometric features called faces to extract a branch number estimate from complex arbors with numerous neurite-to-neurite contacts, without creating a precise, contact-free representation of the neurite arbor. It estimates total neurite length, branch number, primary neurite number, territory (the area of the convex polygon bounding the skeleton and cell body), and Polarity Index (a measure of neuronal polarity). These parameters provide fundamental information about the size and shape of neurite arbors, which are critical factors for neuronal function. NeuronMetrics streamlines optional manual tasks such as removing noise, isolating the largest primary neurite, and correcting length for self-fasciculating neurites. Numeric data are output in a single text file, readily imported into other applications for further analysis. Written as modules for ImageJ, NeuronMetrics provides practical analysis tools that are easy to use and support batch processing. Depending on the need for manual intervention, processing time for a batch of approximately 60 2D images is 1.0-2.5 h, from a folder of images to a table of numeric data. NeuronMetrics' output accelerates the quantitative detection of mutations and chemical compounds that alter neurite morphology in vitro, and will contribute to the use of cultured neurons for drug discovery.

High-Content Microscopy Identifies New Neurite Outgrowth Regulators.

Vibor Laketa — 2006-12-05T11:52:42-00:00

Mol Biol Cell (8 November 2006)

Monitoring Editor: Anne Ridley Neurons, with their long axons and elaborate dendritic arbour, establish the complex circuitry that is essential for the proper functioning of the nervous system. While a catalogue of structural, molecular and functional differences between axons and dendrites is accumulating, the mechanisms involved in early events of neuronal differentiation, such as neurite initiation and elongation, are less well understood, mainly because the key molecules involved remain elusive. Here we describe the establishment and application of a microscopy-based approach designed to identify novel proteins involved in neurite initiation and/or elongation. We identified 21 proteins that affected neurite outgrowth when ectopically expressed in cells. Complementary time-lapse microscopy allowed us to discriminate between early and late effector proteins. Localization experiments with GFP-tagged proteins in fixed and living cells revealed a further 14 proteins that associated with neurite tips either early or late during neurite outgrowth. Coexpression experiments of the new effector proteins provide a first glimpse on a possible functional relationship of these proteins during neurite outgrowth. Altogether, we demonstrate the potential of the systematic microscope-based screening approaches described here to tackle the complex biological process of neurite outgrowth regulation.

A critical role for a Rho-associated kinase, p160ROCK, in determining axon outgrowth in mammalian CNS neurons.

H Bito — 2006-07-27T16:48:06-00:00

Neuron, Vol. 26, No. 2. (May 2000), pp. 431-441.

We tested the contribution of the small GTPase Rho and its downstream target p160ROCK during the early stages of axon formation in cultured cerebellar granule neurons. p160ROCK inhibition, presumably by reducing the stability of the cortical actin network, triggered immediate outgrowth of membrane ruffles and filopodia, followed by the generation of initial growth cone-ike membrane domains from which axonal processes arose. Furthermore, a potentiation in both the size and the motility of growth cones was evident, though the overall axon elongation rate remained stable. Conversely, overexpression of dominant active forms of Rho or ROCK was suggested to prevent initiation of axon outgrowth. Taken together, our data indicate a novel role for the Rho/ROCK pathway as a gate critical for the initiation of axon outgrowth and the control of growth cone dynamics.

Actin cytoskeleton regulation in neuronal morphogenesis and structural plasticity.

L Luo — 2006-07-27T16:14:36-00:00

Annu Rev Cell Dev Biol, Vol. 18 (2002), pp. 601-635.

The actin cytoskeleton plays a major role in morphological development of neurons and in structural changes of adult neurons. This article reviews the myriad functions of actin and myosin in axon initiation, growth, guidance and branching, in morphogenesis of dendrites and dendritic spines, in synapse formation and stability, and in axon and dendrite retraction. Evidence is presented that signaling pathways involving the Rho family of small GTPases are key regulators of actin polymerization and myosin function in the context of different aspects of neuronal morphogenesis. These studies support an emerging theme: Different aspects of neuronal morphogenesis may involve regulation of common core signaling pathways, in particular the Rho GTPases.

Rho GTPases and phosphoinositide 3-kinase organize formation of branched dendrites.

J Leemhuis — 2006-07-27T13:39:58-00:00

J Biol Chem, Vol. 279, No. 1. (2 January 2004), pp. 585-596.

Neurons receive information from other neurons via their dendritic tree. Dendrites and their branches result from alternating outgrowth and retraction. The Rho GTPases Rac and Cdc42 (cell division cycle 42) facilitate the outgrowth of branches, whereas Rho attenuates it. The mechanism of neurite retraction is unknown. Because the adenylyl cyclase activator forskolin causes numerous branched extensions in NG108-15 cells, we have investigated the underlying mechanism in this cell line. In additional studies, we used cultured hippocampal neurons in which forskolin induces branched dendrites. In both cell types, forskolin enhanced the activity of Cdc42, but not that of Rac, although both GTPases were necessary for the formation of branched extensions. Time lapse microscopy showed that forskolin did not increase the rate of addition of new extensions or branches, but it reduced the rate of the retraction so that more branched extensions persisted. Inhibition of phosphoinositide 3-kinase activity by wortmannin or LY294002 also reduced the rate of retraction and thus facilitated dendritic arborization. Forskolin diminished the activity of phosphoinositide 3-kinases. Inhibitors of phosphoinositide 3-kinases not only reduced the retraction but also the addition of new dendrites and branches. This reduction was no longer present when Rho kinase was simultaneously inactivated, suggesting an interaction of phosphoinositide 3-kinases and Rho kinase. The present results show a central role of phosphoinositide 3-kinases in dendrite formation. In neuronal cells, increased levels of cAMP can support dendritic arborization by modulating the activity of the lipid kinase.

RhoA/ROCK regulation of neuritogenesis via profilin IIa-mediated control of actin stability.

JS Da Silva — 2006-07-27T13:36:47-00:00

J Cell Biol, Vol. 162, No. 7. (29 September 2003), pp. 1267-1279.

Neuritogenesis, the first step of neuronal differentiation, takes place as nascent neurites bud from the immediate postmitotic neuronal soma. Little is known about the mechanisms underlying the dramatic morphological changes that characterize this event. Here, we show that RhoA activity plays a decisive role during neuritogenesis of cultured hippocampal neurons by recruiting and activating its specific kinase ROCK, which, in turn, complexes with profilin IIa. We establish that this previously uncharacterized brain-specific actin-binding protein controls neurite sprouting by modifying actin stability, a function regulated by ROCK-mediated phosphorylation. Furthermore, we determine that this novel cascade is switched on or off by physiological stimuli. We propose that RhoA/ROCK/PIIa-mediated regulation of actin stability, shown to be essential for neuritogenesis, may constitute a central mechanism throughout neuronal differentiation.