Participation of structural microtubule-associated proteins (MAPs) in the development of neuronal polarity

Protein aggregation: A detrimental symptom or an adaptation mechanism?

Protein quality control mechanisms oversee numerous aspects of protein lifetime. From the point of protein synthesis, protein homeostasis machineries take part in folding, solubilization, and/or degradation of impaired proteins. Some proteins follow an alternative path upon loss of their solubility, thus are secluded from the cytosol and form protein aggregates. Protein aggregates differ in their function and composition, rendering protein aggregation a complex phenomenon that continues to receive plenty of attention in the scientific and medical communities. Traditionally, protein aggregates have been associated with aging and a large spectrum of protein folding diseases, such as neurodegenerative diseases, type 2 diabetes, or cataract. However, a body of evidence suggests that they may act as an adaptive mechanism to overcome transient stressful conditions, serving as a sink for the removal of misfolded proteins from the cytosol or storage compartments for machineries required upon stress release. In this review, we present examples and evidence elaborating different possible roles of protein aggregation and discuss their potential roles in stress survival, aging, and disease, as well as possible anti-aggregation interventions.

Insights into role of microRNA in Alzheimer's disease: From contemporary research to bedside perspective

One of the most prevalent neurodegenerative disorders is Alzheimer's disease (AD). Despite the pervasiveness of AD being considerable, the rates of both diagnosis and therapy are comparatively less and still lacking. For the treatment of AD, acetylcholinesterase inhibitors and NMDA receptor antagonists (Memantine) have received clinical approval. The approved drugs are only capable of mitigating the symptoms; however, halting the progression of the disease remains a matter of substantial concern. MicroRNAs (miRs) are a subclass of non-coding single-stranded RNA molecules that target mRNAs to control the expression of genes in certain tissues. Dysregulation in the expression and function of miRs contributes to a neurodegeneration-like pathogenesis seen in Alzheimer's disease (AD), featuring hallmark characteristics such as Aβ aggregation, hyper-phosphorylation of Tau proteins, mitochondrial dysfunction, neuroinflammation, and apoptosis. These factors collectively underpin the cognitive deterioration and learning disabilities associated with AD. According to the research, numerous miRs have considerably different expression patterns in AD patients compared to healthy people. Due to these attributes, miRs prove to be effective diagnostic and therapeutic agents for AD. This review will examine clinical and preclinical data concerning the potential of miRs as diagnostic and therapeutic agents, utilizing various techniques (such as miR antagonists or inhibitors, miR agonists or mimics, miR sponges, and miR antisense oligonucleotides) to target specific pathogenic mechanisms in AD.

Bridging the gap of axonal regeneration in the central nervous system: A state of the art review on central axonal regeneration

Neuronal regeneration in the central nervous system (CNS) is an important field of research with relevance to all types of neuronal injuries, including neurodegenerative diseases. The glial scar is a result of the astrocyte response to CNS injury. It is made up of many components creating a complex environment in which astrocytes play various key roles. The glial scar is heterogeneous, diverse and its composition depends upon the injury type and location. The heterogeneity of the glial scar observed in different situations of CNS damage and the consequent implications for axon regeneration have not been reviewed in depth. The gap in this knowledge will be addressed in this review which will also focus on our current understanding of central axonal regeneration and the molecular mechanisms involved. The multifactorial context of CNS regeneration is discussed, and we review newly identified roles for components previously thought to solely play an inhibitory role in central regeneration: astrocytes and p75NTR and discuss their potential and relevance for deciding therapeutic interventions. The article ends with a comprehensive review of promising new therapeutic targets identified for axonal regeneration in CNS and a discussion of novel ways of looking at therapeutic interventions for several brain diseases and injuries.

MicroRNAs in Alzheimer's disease: Potential diagnostic markers and therapeutic targets

Alzheimer's disease (AD) is the most common neurodegenerative disease, with cognitive decline as the primary clinical feature. According to epidemiological statistics, 50 million people worldwide are currently affected by Alzheimer's disease. Although new drugs such as aducanumab have been approved for use in the treatment of AD, none of them have reversed the progression of AD. MicroRNAs (miRNAs) are small molecule RNAs that exert their biological functions by regulating the expression of intracellular proteins, and differential abundance and varieties are found between the central and peripheral tissues of AD patients and healthy controls. This article will summarise the changes of miRNAs in the AD process, and the potential role of diagnostic markers and therapeutic targets in AD will be explored.

Bridging the Gap: The Importance of TUBA1A α-Tubulin in Forming Midline Commissures

Developing neurons undergo dramatic morphological changes to appropriately migrate and extend axons to make synaptic connections. The microtubule cytoskeleton, made of α/β-tubulin dimers, drives neurite outgrowth, promotes neuronal growth cone responses, and facilitates intracellular transport of critical cargoes during neurodevelopment. TUBA1A constitutes the majority of α-tubulin in the developing brain and mutations to TUBA1A in humans cause severe brain malformations accompanied by varying neurological defects, collectively termed tubulinopathies. Studies of TUBA1A function in mammalian cells have been limited by the presence of multiple genes encoding highly similar tubulin proteins, which leads to α-tubulin antibody promiscuity and makes genetic manipulation challenging. Here, we test mutant tubulin levels and assembly activity and analyze the impact of TUBA1A reduction on growth cone composition, neurite extension, and commissural axon architecture during brain development. We present a novel tagging method for studying and manipulating TUBA1A in cells without impairing tubulin function. Using this tool, we show that a TUBA1A loss-of-function mutation TUBA1A N102D (TUBA1A ND ), reduces TUBA1A protein levels and prevents incorporation of TUBA1A into microtubule polymers. Reduced Tuba1a α-tubulin in heterozygous Tuba1a ND/+ mice leads to grossly normal brain formation except a significant impact on axon extension and impaired formation of forebrain commissures. Neurons with reduced Tuba1a as a result of the Tuba1a ND mutation exhibit slower neuron outgrowth compared to controls. Neurons deficient in Tuba1a failed to localize microtubule associated protein-1b (Map1b) to the developing growth cone, likely impacting stabilization of microtubules. Overall, we show that reduced Tuba1a is sufficient to support neuronal migration and cortex development but not commissure formation, and provide mechanistic insight as to how TUBA1A tunes microtubule function to support neurodevelopment.

Insight Into Seeded Tau Fibril Growth From Molecular Dynamics Simulation of the Alzheimer's Disease Protofibril Core

Aggregates of the microtubule associated tau protein are a major constituent of neurofibrillary lesions that define Alzheimer’s disease (AD) pathology. Increasing experimental evidence suggests that the spread of tau neurofibrillary tangles results from a prion-like seeding mechanism in which small oligomeric tau fibrils template the conversion of native, intrinsically disordered, tau proteins into their pathological form. By using atomistic molecular dynamics (MD) simulations, we investigate the stability and dissociation thermodynamics of high-resolution cryo-electron microscopy (cryo-EM) structures of both the AD paired-helical filament (PHF) and straight filament (SF). Non-equilibrium steered MD (SMD) center-of-mass pulling simulations are used to probe the stability of the protofibril structure and identify intermolecular contacts that must be broken before a single tau peptide can dissociate from the protofibril end. Using a combination of exploratory metadynamics and umbrella sampling, we investigate the complete dissociation pathway and compute a free energy profile for the dissociation of a single tau peptide from the fibril end. Different features of the free energy surface between the PHF and SF protofibril result from a different mechanism of tau unfolding. Comparison of wild-type tau PHF and post-translationally modified pSer356 tau shows that phosphorylation at this site changes the dissociation free energy surface of the terminal peptide. These results demonstrate how different protofibril morphologies template the folding of endogenous tau in distinct ways, and how post-translational modification can perturb the folding mechanism.

Manipulation of Axonal Outgrowth via Exogenous Low Forces

Neurons are mechanosensitive cells. The role of mechanical force in the process of neurite initiation, elongation and sprouting; nerve fasciculation; and neuron maturation continues to attract considerable interest among scientists. Force is an endogenous signal that stimulates all these processes in vivo. The axon is able to sense force, generate force and, ultimately, transduce the force in a signal for growth. This opens up fascinating scenarios. How are forces generated and sensed in vivo? Which molecular mechanisms are responsible for this mechanotransduction signal? Can we exploit exogenously applied forces to mimic and control this process? How can these extremely low forces be generated in vivo in a non-invasive manner? Can these methodologies for force generation be used in regenerative therapies? This review addresses these questions, providing a general overview of current knowledge on the applications of exogenous forces to manipulate axonal outgrowth, with a special focus on forces whose magnitude is similar to those generated in vivo. We also review the principal methodologies for applying these forces, providing new inspiration and insights into the potential of this approach for future regenerative therapies.

Mechanisms of Pathogenic Tau and Aβ Protein Spreading in Alzheimer's Disease

Alzheimer’s disease (AD) is pathologically defined by extracellular accumulation of amyloid-β (Aβ) peptides generated by the cleavage of amyloid precursor protein (APP), strings of hyperphosphorylated Tau proteins accumulating inside neurons known as neurofibrillary tangles (NFTs) and neuronal loss. The association between the two hallmarks and cognitive decline has been known since the beginning of the 20th century when the first description of the disease was carried out by Alois Alzheimer. Today, more than 40 million people worldwide are affected by AD that represents the most common cause of dementia and there is still no effective treatment available to cure the disease. In general, the aggregation of Aβ is considered an essential trigger in AD pathogenesis that gives rise to NFTs, neuronal dysfunction and dementia. During the process leading to AD, tau and Aβ first misfold and form aggregates in one brain region, from where they spread to interconnected areas of the brain thereby inducing its gradual morphological and functional deterioration. In this mini-review article, we present an overview of the current literature on the spreading mechanisms of Aβ and tau pathology in AD since a more profound understanding is necessary to design therapeutic approaches aimed at preventing or halting disease progression.

3β, 6β-dichloro-5-hydroxy-5α-cholestane facilitates neuronal development through modulating TrkA signaling regulated proteins in primary hippocampal neuron

Potentiating neuritogenesis through pharmacological intervention might hold therapeutic promise in neurodegenerative disorders and acute brain injury. Here, we investigated the novel neuritogenic potentials of a steroidal chlorohydrin, 3β, 6β-dichloro-5-hydroxy-5α-cholestane (hereafter, SCH) and the change in cellular proteome to gain insight into the underlying mechanism of its neurotrophic activity in hippocampal neurons. Morphometric analysis showed that SCH promoted early neuronal differentiation, dendritic arborization and axonal maturation. Proteomic and bioinformatic analysis revealed that SCH induced upregulation of several proteins, including those associated with neuronal differentiation and development. Immunocytochemical data further indicates that SCH-treated neurons showed upregulation of Hnrnpa2b1 and Map1b, validating their proteomic profiles. In addition, a protein-protein interaction network analysis identified TrkA as a potential target connecting most of the upregulated proteins. The neurite outgrowth effect of SCH was suppressed by TrkA inhibitor, GW441756, verifying TrkA-dependent activity of SCH, which further supports the connection of TrkA with the upregulated proteins. Also, the computational analysis revealed that SCH interacts with the NGF-binding domain of TrkA through Phe327 and Asn355. Collectively, our findings provide evidence that SCH promotes neuronal development via upregulating TrkA-signaling proteins and suggest that SCH could be a promising therapeutic agent in the prevention and treatment of neurodegenerative disorders.

Neuronal polarization: From spatiotemporal signaling to cytoskeletal dynamics

Neuronal polarization establishes distinct molecular structures to generate a single axon and multiple dendrites. Studies over the past years indicate that this efficient separation is brought about by a network of feedback loops. Axonal growth seems to play a major role in fueling those feedback loops and thereby stabilizing neuronal polarity. Indeed, various effectors involved in feedback loops are pivotal for axonal growth by ultimately acting on the actin and microtubule cytoskeleton. These effectors have key roles in interconnecting actin and microtubule dynamics - a mechanism crucial to commanding the growth of axons. We propose a model connecting signaling with cytoskeletal dynamics and neurite growth to better describe the underlying processes involved in neuronal polarization. We will discuss the current views on feedback loops and highlight the current limits of our understanding.

Microtubule-regulating proteins and cAMP-dependent signaling in neuroblastoma differentiation

Neurons are highly differentiated cells responsible for the conduction and transmission of information in the nervous system. The proper function of a neuron relies on the compartmentalization of their intracellular domains. Differentiated neuroblastoma cells have been extensively used to study and understand the physiology and cell biology of neuronal cells. Here, we show that differentiation of N1E-115 neuroblastoma cells is more pronounced upon exposure of a chemical analog of cyclic AMP (cAMP), db-cAMP. We next analysed the expression of key microtubule-regulating proteins in differentiated cells and the expression and activation of key cAMP players such as EPAC, PKA and AKAP79/150. Most of the microtubule-promoting factors were up regulated during differentiation of N1E-115 cells, while microtubule-destabilizing proteins were down regulated. We observed an increase in tubulin post-translational modifications related to microtubule stability. As expected, db-cAMP increased PKA- and EPAC-dependent signalling. Consistently, pharmacological modulation of EPAC activity instructed cell differentiation, number of neurites, and neurite length in N1E-115 cells. Moreover, disruption of the PKA-AKAP interaction reduced these morphometric parameters. Interestingly, PKA and EPAC act synergistically to induce neuronal differentiation in N1E-115. Altogether these results show that the changes observed in the differentiation of N1E-115 cells proceed by regulating several microtubule-stabilizing factors, and the acquisition of a neuronal phenotype is a process involving concerted although independent functions of EPAC and PKA.

Intracellular and extracellular microtubule associated protein tau as a therapeutic target in Alzheimer disease and other tauopathies

INTRODUCTION

Microtubule associated protein tau, a protein mainly expressed in neurons, plays an important role in several diseases related to dementia, named tauopathies. Alzheimer disease is the most relevant tauopathy. The role of tau protein in dementia is now a topic under discussion, and is the focus of this review.

AREAS COVERED

We have covered two major areas: tau pathology and tau as a therapeutic target. Tau pathology is mainly related to a gain of toxic function due to an abnormal accumulation, aberrant modifications (such as hyperphosphorylation and truncation, among others) and self-aggregation of tau into oligomers or larger structures. Also, tau can be found extracellularly in a toxic form. Tau-based therapy is mainly centered on avoiding the gain of these toxic functions of tau.

EXPERT OPINION

Tau therapies are focused on lowering tau levels, mainly of modified tau species that could be toxic for neurons (phosphorylated, truncated or aggregated tau), in intracellular or extracellular form. Decreasing the levels of those toxic species is a possible therapeutic strategy.

The role of microtubule-associated protein 1B in axonal growth and neuronal migration in the central nervous system

In this review, we discuss the role of microtubule-associated protein 1B (MAP1B) and its phosphorylation in axonal development and regeneration in the central nervous system. MAP1B exhibits similar functions during axonal development and regeneration. MAP1B and phosphorylated MAP1B in neurons and axons maintain a dynamic balance between cytoskeletal components, and regulate the stability and interaction of microtubules and actin to promote axonal growth, neural connectivity and regeneration in the central nervous system.

The Ubiquitin-Proteasome System and Molecular Chaperone Deregulation in Alzheimer's Disease

One of the shared hallmarks of neurodegenerative diseases is the accumulation of misfolded proteins. Therefore, it is suspected that normal proteostasis is crucial for neuronal survival in the brain and that the malfunction of this mechanism may be the underlying cause of neurodegenerative diseases. The accumulation of amyloid plaques (APs) composed of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles (NFTs) composed of misfolded Tau proteins are the defining pathological markers of Alzheimer's disease (AD). The accumulation of these proteins indicates a faulty protein quality control in the AD brain. An impaired ubiquitin-proteasome system (UPS) could lead to negative consequences for protein regulation, including loss of function. Another pivotal mechanism for the prevention of misfolded protein accumulation is the utilization of molecular chaperones. Molecular chaperones, such as heat shock proteins (HSPs) and FK506-binding proteins (FKBPs), are highly involved in protein regulation to ensure proper folding and normal function. In this review, we elaborate on the molecular basis of AD pathophysiology using recent data, with a particular focus on the role of the UPS and molecular chaperones as the defensive mechanism against misfolded proteins that have prion-like properties. In addition, we propose a rational therapy approach based on this mechanism.

Serum-induced neurite retraction in CAD cells--involvement of an ATP-actin retractile system and the lack of microtubule-associated proteins

Cultured catecholamine-differentiated cells [which lack the microtubule-associated proteins (MAPs): MAP1B, MAP2, Tau, STOP, and Doublecortin] proliferate in the presence of fetal bovine serum, and, in its absence, cease dividing and generate processes similar to the neurites of normal neurons. The reintroduction of serum induces neurite retraction, and proliferation resumes. The neurite retraction process in catecholamine-differentiated cells was partially characterized in this study. Microtubules in the cells were found to be in a highly dynamic state, and tubulin in the microtubules consisted primarily of the tyrosinated and deacetylated isotypes. Increased levels of acetylated or Δ2-tubulin (which are normally absent) did not prevent serum-induced neurite retraction. Treatment of differentiated cells with lysophosphatidic acid or adenosine deaminase induced neurite retraction. Inhibition of Rho-associated protein kinase, ATP depletion and microfilament disruption each (individually) blocked serum-induced neurite retraction, suggesting that an ATP-dependent actomyosin system underlies the mechanism of neurite retraction. Nocodazole treatment induced neurite retraction, but this effect was blocked by pretreatment with the microtubule-stabilizing drug paclitaxel (Taxol). Paclitaxel did not prevent serum-induced or lysophosphatidic acid-induced retraction, suggesting that integrity of microtubules (despite their dynamic state) is necessary to maintain neurite elongation, and that paclitaxel-induced stabilization alone is not sufficient to resist the retraction force induced by serum. Transfection with green fluorescent protein-Tau conferred resistance to retraction caused by serum. We hypothesize that, in normal neurons (cultured or in vivo), MAPs are necessary not only to stabilize microtubules, but also to establish interactions with other cytoskeletal or membrane components to form a stable structure capable of resisting the retraction force.

The MAP1B case: an old MAP that is new again

The functions of microtubule-associated protein 1B (MAP1B) have historically been linked to the development of the nervous system, based on its very early expression in neurons and glial cells. Moreover, mice in which MAP1B is genetically inactivated have been used extensively to show its role in axonal elongation, neuronal migration, and axonal guidance. In the last few years, it has become apparent that MAP1B has other cellular and molecular functions that are not related to its microtubule-stabilizing properties in the embryonic and adult brain. In this review, we present a systematic review of the canonical and novel functions of MAP1B and propose that, in addition to regulating the polymerization of microtubule and actin microfilaments, MAP1B also acts as a signaling protein involved in normal physiology and pathological conditions in the nervous system.

Wnt signaling through the Ror receptor in the nervous system

The receptor tyrosine kinase-like orphan receptor (Ror) proteins are conserved tyrosine kinase receptors that play roles in a variety of cellular processes that pattern tissues and organs during vertebrate and invertebrate development. Ror signaling is required for skeleton and neuronal development and modulates cell migration, cell polarity, and convergent extension. Ror has also been implicated in two human skeletal disorders, brachydactyly type B and Robinow syndrome. Rors are widely expressed during metazoan development including domains in the nervous system. Here, we review recent progress in understanding the roles of the Ror receptors in neuronal migration, axonal pruning, axon guidance, and synaptic plasticity. The processes by which Ror signaling execute these diverse roles are still largely unknown, but they likely converge on cytoskeletal remodeling. In multiple species, Rors have been shown to act as Wnt receptors signaling via novel non-canonical Wnt pathways mediated in some tissues by the adapter protein disheveled and the non-receptor tyrosine kinase Src. Rors can either activate or repress Wnt target expression depending on the cellular context and can also modulate signal transduction by sequestering Wnt ligands away from their signaling receptors. Future challenges include the identification of signaling components of the Ror pathways and bettering our understanding of the roles of these pleiotropic receptors in patterning the nervous system.

Dab2ip regulates neuronal migration and neurite outgrowth in the developing neocortex

Dab2ip (DOC-2/DAB2 interacting protein) is a member of the Ras GTPase-activating protein (GAP) family that has been previously shown to function as a tumor suppressor in several systems. Dab2ip is also highly expressed in the brain where it interacts with Dab1, a key mediator of the Reelin pathway that controls several aspects of brain development and function. We found that Dab2ip is highly expressed in the developing cerebral cortex, but that mutations in the Reelin signaling pathway do not affect its expression. To determine whether Dab2ip plays a role in brain development, we knocked down or over expressed it in neuronal progenitor cells of the embryonic mouse neocortex using in utero electroporation. Dab2ip down-regulation severely disrupts neuronal migration, affecting preferentially late-born principal cortical neurons. Dab2ip overexpression also leads to migration defects. Structure-function experiments in vivo further show that both PH and GRD domains of Dab2ip are important for neuronal migration. A detailed analysis of transfected neurons reveals that Dab2ip down- or up-regulation disrupts the transition from a multipolar to a bipolar neuronal morphology in the intermediate zone. Knock down of Dab2ip in neurons ex-vivo indicates that this protein is necessary for proper neurite development and for the expression of several major neuronal microtubule associated proteins (MAPs), which are important for neurite growth and stabilization. Thus, our study identifies, for the first time, a critical role for Dab2ip in mammalian cortical development and begins to reveal molecular mechanisms that underlie this function.

L1CAM increases MAP2 expression via the MAPK pathway to promote neurite outgrowth

The neural cell adhesion molecule L1 (L1CAM) promotes neurite outgrowth via mechanisms that are not completely understood, but are known to involve the cytoskeleton. Here, we show that L1 binds directly to the microtubule associated protein 2c (MAP2c). This isoform of MAP2 is predominantly expressed in developing neurons. We found that the mRNA and protein levels of MAP2c, but not of MAP2a/b, are reduced in brains of young adult L1-deficient transgenic mice. We show via ELISA, that MAP2c, but not MAP2a/b, binds directly to the intracellular domain of L1. Remarkably, all these MAP2 isoforms co-immunoprecipitate with L1, suggesting that MAP2a/b associates with L1 via intermediate binding partners. The expression levels of MAP2a/b/c correlate with those of L1 in different brain regions of early postnatal mice, while expression levels of heat shock cognate protein 70 (Hsc70) or actin do not. L1 enhances the expression of MAP2a/b/c in cultured hippocampal neurons depending on activation of the mitogen-activated protein kinase (MAPK) pathway. Deficiency in both L1 and MAP2a/b/c expression results in reduced neurite outgrowth in vitro. We propose that the L1-triggered increase in MAP2a/b/c expression is required to promote neurite outgrowth.

DDA3 stabilizes microtubules and suppresses neurite formation

We have previously shown that DDA3 - also known as proline/serine-rich coiled-coil protein 1 (PSRC1) - is a microtubule-associated protein that promotes cell growth by stimulating the β-catenin pathway. Here, we report that DDA3 can bundle and stabilize microtubules in vivo and in vitro. We found that overexpression of DDA3 increased the abundance of acetylated and tyrosinated microtubules. We employed PC12 and N2a cell lines, as well as cultured hippocampal neurons, and demonstrated that overexpression of DDA3 suppressed neurite/axon outgrowth, whereas its depletion accelerated neurite/axon formation and elongation. Knockdown of DDA3 reduced β3-tubulin levels in N2a cells, which contributed to the spontaneous neurite formation caused by DDA3 depletion. Consistent with its role in suppressing neuritogenesis, DDA3 was downregulated during induced neuronal differentiation. Moreover, expression of DDA3 was detected in the rat brain at embryonic (E) day E15 and in the cortical region at E17, the period of active neurogenesis. Levels of cortical DDA3 decreased at the beginning of E19, when active neuritogenesis is completed. Overall our results demonstrate that DDA3 is a so-far-unknown microtubule-stabilizing protein that is involved in regulating neurite formation and elongation.

Tau protein is involved in morphological plasticity in hippocampal neurons in response to BDNF

Tau protein, a microtubule-associated protein involved in a number of neurological disorders such as Alzheimer's disease (AD), may undergo modifications under both physiological and pathological conditions. However, the signaling pathways that couple tau protein to neuronal physiology such as synaptic plasticity have not yet been elucidated. Here we report that tau protein is involved in morphological plasticity in response to brain derived neurotrophic factor (BDNF). Stimulation of the cultured rat hippocampal neurons with BDNF resulted in increased tau protein expression, as detected by Western blotting. Furthermore, tau protein accumulated in the distal region of the neurite when treated with taxol or taxol plus BDNF. The increased tau protein also protected neurons against nocodazole-induced dendrite loss. Moreover, BDNF promoted spine growth as well as tau protein over-expression. Knockdown of tau protein using specific short-hairpin RNA (shRNA) significantly decreased the spine density. And BDNF could not increase the spine density of tau-knockdown neurons. These results highlight a possible role for tau protein in the dynamic rearrangement of cytoskeletal fibers vital for BDNF-induced synaptic plasticity.

MAP1B and clathrin are novel interacting partners of the giant cyto-linker dystonin

Dystonin is a large multidomain cytoskeletal-associated protein that plays an essential role in the nervous system. Loss of dystonin results in neuromuscular dysfunction and early death in a mouse mutant called dystonia musculorum. Conserved among related proteins, the plakin domain is a defining feature of all major dystonin isoforms, yet its interactions have not been explored in detail. The purpose of the present study was to identify novel interacting partners of the plakin domain of the neuronal isoform of dystonin (dystonin-a). Newly identified interacting proteins discovered through a pull-down assay were validated using coimmunoprecipitation, coimmunofluorescence, and proximity ligation assays. Microtubule associated protein 1B (MAP1B), a microtubule stabilizing protein, and clathrin heavy chain, the major component of the clathrin triskelion, were identified as interaction partners for dystonin-a. Increased levels of phosphorylated MAP1B suggest a misregulation of MAP1B and a potentially novel component of the dt pathology. This work will further facilitate our understanding of how cytoskeletal proteins can affect and regulate neurodegenerative disorders.

Kidins220/ARMS modulates the activity of microtubule-regulating proteins and controls neuronal polarity and development

In order for neurons to perform their function, they must establish a highly polarized morphology characterized, in most of the cases, by a single axon and multiple dendrites. Herein we find that the evolutionarily conserved protein Kidins220 (kinase D-interacting substrate of 220-kDa), also known as ARMS (ankyrin repeat-rich membrane spanning), a downstream effector of protein kinase D and neurotrophin and ephrin receptors, regulates the establishment of neuronal polarity and development of dendrites. Kidins220/ARMS gain and loss of function experiments render severe phenotypic changes in the processes extended by hippocampal neurons in culture. Although Kidins220/ARMS early overexpression hinders neuronal development, its down-regulation by RNA interference results in the appearance of multiple longer axon-like extensions as well as aberrant dendritic arbors. We also find that Kidins220/ARMS interacts with tubulin and microtubule-regulating molecules whose role in neuronal morphogenesis is well established (microtubule-associated proteins 1b, 1a, and 2 and two members of the stathmin family). Importantly, neurons where Kidins220/ARMS has been knocked down register changes in the phosphorylation activity of MAP1b and stathmins. Altogether, our results indicate that Kidins220/ARMS is a key modulator of the activity of microtubule-regulating proteins known to actively regulate neuronal morphogenesis and suggest a mechanism by which it contributes to control neuronal development.

The microtubule network and neuronal morphogenesis: Dynamic and coordinated orchestration through multiple players

Nervous system function and plasticity rely on the complex architecture of neuronal networks elaborated during development, when neurons acquire their specific and complex shape. During neuronal morphogenesis, the formation and outgrowth of functionally and structurally distinct axons and dendrites require a coordinated and dynamic reorganization of the microtubule cytoskeleton involving numerous regulators. While most of these factors act directly on microtubules to stabilize them or promote their assembly, depolymerization or fragmentation, others are now emerging as essential regulators of neuronal differentiation by controlling tubulin availability and modulating microtubule dynamics. In this review, we recapitulate how the microtubule network is actively regulated during the successive phases of neuronal morphogenesis, and what are the specific roles of the various microtubule-regulating proteins in that process. We then describe the specific signaling pathways and inter-regulations that coordinate the different activities of these proteins to sustain neuronal development in response to environmental cues.

Tubulin tyrosination is required for the proper organization and pathfinding of the growth cone

Background

During development, neuronal growth cones integrate diffusible and contact guidance cues that are conveyed to both actin and microtubule (MT) cytoskeletons and ensure axon outgrowth and pathfinding. Although several post-translational modifications of tubulin have been identified and despite their strong conservation among species, their physiological roles during development, especially in the nervous sytem, are still poorly understood.

Methodology/Findings

Here, we have dissected the role of a post-translational modification of the last amino acid of the α-tubulin on axonal growth by analyzing the phenotype of precerebellar neurons in Tubulin tyrosin ligase knock-out mice (TTL^−/−) through in vivo, ex vivo and in vitro analyses. TTL^−/− neurons are devoid of tyrosinated tubulin. Their pathway shows defects in vivo, ex vivo, in hindbrains open-book preparations or in vitro, in a collagen matrix. Their axons still orient toward tropic cues, but they emit supernumerary branches and their growth cones are enlarged and exhibit an emission of mis-oriented filopodia. Further analysis of the TTL^−/− growth cone intracellular organization also reveals that the respective localization of actin and MT filaments is disturbed, with a decrease in the distal accumulation of Myosin IIB, as well as a concomitant Rac1 over-activation in the hindbrain. Pharmacological inhibition of Rac1 over-activation in TTL^−/− neurons can rescue Myosin IIB localization.

Conclusions/Significance

In the growth cone, we propose that tubulin tyrosination takes part in the relative arrangement of actin and MT cytoskeletons, in the regulation of small GTPases activity, and consequently, in the proper morphogenesis, organization and pathfinding of the growth cone during development.

Antisense suppression of tau in cultured rat oligodendrocytes inhibits process formation

The microtubule-associated protein tau is integral to neuronal process development and has a role in the pathogenesis of several neurodegenerative conditions. We examined possible roles for tau in cultured oligodendrocyte process formation by using antisense oligonucleotide treatment. Inhibition of tau synthesis with single oligonucleotides resulted in decreased tau protein levels and significantly shorter cellular processes. Simultaneous use of two nonoverlapping oligonucleotides caused a major reduction in tau levels and severely inhibited process outgrowth. The timing of oligonucleotide addition to oligodendrocyte cultures was important, with addition of antisense at the time of plating into culture having the most significant effect on morphology through reduction of tau expression.

Direct AKAP-mediated protein-protein interactions as potential drug targets

A-kinase-anchoring proteins (AKAPs) are a diverse family of about 50 scaffolding proteins. They are defined by the presence of a structurally conserved protein kinase A (PKA)-binding domain. AKAPs tether PKA and other signalling proteins such as further protein kinases, protein phosphatases and phosphodiesterases by direct protein-protein interactions to cellular compartments. Thus, AKAPs form the basis of signalling modules that integrate cellular signalling processes and limit these to defined sites. Disruption of AKAP functions by gene targeting, knockdown approaches and, in particular, pharmacological disruption of defined AKAP-dependent protein-protein interactions has revealed key roles of AKAPs in numerous processes, including the regulation of cardiac myocyte contractility and vasopressin-mediated water reabsorption in the kidney. Dysregulation of such processes causes diseases, including cardiovascular and renal disorders. In this review, we discuss AKAP functions elucidated by gene targeting and knockdown approaches, but mainly focus on studies utilizing peptides for disruption of direct AKAP-mediated protein-protein interactions. The latter studies point to direct AKAP-mediated protein-protein interactions as targets for novel drugs.

Peripheral site acetylcholinesterase blockade induces RACK1-associated neuronal remodeling

BACKGROUND

Peripheral anionic site (PAS) blockade of acetylcholinesterase (AChE) notably affects neuronal activity and cyto-architecture, however, the mechanism(s) involved are incompletely understood.

OBJECTIVE

We wished to specify the PAS extracellular effects on specific AChE mRNA splice variants, delineate the consequent cellular remodeling events, and explore the inhibitory effects on interchanging RACK1 interactions.

METHODS

We exposed rat hippocampal cultured neurons to BW284C51, the peripheral anionic site inhibitor of AChE, and to the non-selective AChE active site inhibitor, physostigmine for studying the neuronal remodeling of AChE mRNA expression and trafficking.

RESULTS

BW284C51 induced overexpression of both AChE splice variants, yet promoted neuritic translocation of the normally rare AChE-R, and retraction of AChE-S mRNA in an antisense-suppressible manner. BW284C51 further caused modest decreases in the expression of the scaffold protein RACK1 (receptor for activated protein kinase betaII), followed by drastic neurite retraction of both RACK1 and the AChE homologue neuroligin1, but not the tubulin-associated MAP2 protein. Accompanying BW284C51 effects involved decreases in the Fyn kinase and membrane insertion of the glutamate receptor NR2B variant and impaired glutamatergic activities of treated cells. Intriguingly, molecular modeling suggested that direct, non-catalytic competition with Fyn binding by the RACK1-interacting AChE-R variant may be involved.

CONCLUSIONS

Our findings highlight complex neuronal AChE-R/RACK1 interactions and are compatible with the hypothesis that peripheral site AChE inhibitors induce RACK1-mediated neuronal remodeling, promoting suppressed glutamatergic neurotransmission.

Changes in neurogenesis in dementia and Alzheimer mouse models: are they functionally relevant?

Alzheimer's disease and related dementias are devastating disorders that lead to the progressive decline of cognitive functions. Characteristic features are severe brain atrophy, paralleled by accumulation of beta amyloid and neurofibrillary tangles. With the discovery of neurogenesis in the adult brain, the hopes have risen that these neurodegenerative conditions could be overcome, or at least ameliorated, by the generation of new neurons. The location of the adult neurogenic zones in the hippocampus and the lateral ventricle wall, close to corpus callosum and neocortex, indicates strategic positions for potential repair processes. However, we also need to consider that the generation of new neurons is possibly involved in cognitive functions and could, therefore, be influenced by disease pathology. Moreover, aberrant neurogenic mechanisms could even be a part of the pathological events of neurodegenerative diseases. It is the scope of this review to summarize and analyze the recent data from neurogenesis research with respect to Alzheimer's disease and its animal models.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

GSK3 alpha and GSK3 beta are necessary for axon formation

The mechanisms that underlie axon formation are still poorly understood. GSK3 has been recently implicated in establishing the axon and in its elongation. We have used four different GSK3 inhibitors to determine the role of GSK3 activity in hippocampal neurons at different periods of time. Inhibition of GSK3 activity impairs axon formation. The "critical period" of this activity of GSK3 is at least the first 24h since afterwards the inhibition of GSK3 does not compromise the process of elongation, although it exacerbates axon branching. Moreover, interference RNAs impeding the expression of the GSK3 alpha or beta isoforms in hippocampal neurons prevents an axon from forming.

Differentiation of human adult skin-derived neuronal precursors into mature neurons

The isolation of autologous neuronal precursors from skin-derived precursor cells extracted from adult human skin would be a very efficient source of neurons for the treatment of various neurodegenerative diseases. The purpose of this study was to demonstrate that these neuronal precursors were able to differentiate into mature neurons. We isolated neuronal precursors from breast skin and expanded them in vitro for over ten passages. We showed that 48% of these cells were proliferating after the first passage, while this growth rate decreased after the second passage. We demonstrated that 70% of these cells were nestin-positive after the third passage, while only 17% were neurofilament M-positive after 7 days of differentiation. These neuronal precursors expressed betaIII tubulin, the dendritic marker MAP2 and the presynaptic marker synaptophysin after 7 days of in vitro maturation. They also expressed the postsynaptic marker PSD95 and the late neuronal markers NeuN and neurofilament H after 21 days of differentiation, demonstrating they became terminally differentiated neurons. These markers were still expressed after 50 days of culture. The generation of autologous neurons from an accessible adult human source opens many potential therapeutic applications and has a great potential for the development of experimental studies on normal human neurons.

Characterization of MAP1B heavy chain interaction with actin

Microtubule-associated protein 1B is an essential protein during brain development and neurite outgrowth and was studied by several assays to further characterize actin as a major interacting partner. Tubulin and actin co-immunoprecipitated with MAP1B at similar ratios throughout development. Their identity was identified by mass spectrometry and was confirmed by Western blots. In contrast to previous reports, the MAP1B-actin interaction was not dependent on the MAP1B phosphorylation state, since actin was precipitated from brain tissue throughout development at similar ratios and equal amounts were precipitated before and after dephosphorylation with alkaline phosphatase. MAP1B heavy chain was able to bind actin directly and therefore the N-terminal part of MAP1B heavy chain must also contain an actin-binding site. The binding force of this interaction was measured by atomic force microscopy and values were in the same range as those of MAP1B binding to tubulin or that measured in MAP1B self-aggregation. Aggregation was confirmed by negative staining and electron microscopy. Experiments including COS-7 cells, PC12 cells, cytochalasin D and immunocytochemistry with subsequent confocal laser microscopy, suggested that MAP1B may bind to actin but has no obvious microfilament stabilizing effect. We conclude, that the MAP1B heavy chain has a microtubule-stabilization effect, and contains an actin-binding site that may play a role in the crosslinking of actin and microtubules, a function that may be important in neurite elongation.

Microtubule-associated protein 1B, a growth-associated and phosphorylated scaffold protein

Microtubule-associated protein 1B, MAP1B, is one of the major growth associated and cytoskeletal proteins in neuronal and glial cells. It is present as a full length protein or may be fragmented into a heavy chain and a light chain. It is essential to stabilize microtubules during the elongation of dendrites and neurites and is involved in the dynamics of morphological structures such as microtubules, microfilaments and growth cones. MAP1B function is modulated by phosphorylation and influences microtubule stability, microfilaments and growth cone motility. Considering its large size, several interactions with a variety of other proteins have been reported and there is increasing evidence that MAP1B plays a crucial role in the stability of the cytoskeleton and may have other cellular functions. Here we review molecular and functional aspects of this protein, evoke its role as a scaffold protein and have a look at several pathologies where the protein may be involved.

COUP-TFI is required for the formation of commissural projections in the forebrain by regulating axonal growth

The transcription factor COUP-TFI (NR2F1), an orphan member of the nuclear receptor superfamily, is an important regulator of neurogenesis, cellular differentiation and cell migration. In the forebrain, COUP-TFI controls the connectivity between thalamus and cortex and neuronal tangential migration in the basal telencephalon. Here, we show that COUP-TFI is required for proper axonal growth and guidance of all major forebrain commissures. Fibres of the corpus callosum, the hippocampal commissure and the anterior commissure project aberrantly and fail to cross the midline in COUP-TFI null mutants. Moreover, hippocampal neurons lacking COUP-TFI have a defect in neurite outgrowth and show an abnormal axonal morphology. To search for downstream effectors, we used microarray analysis and showed that, in the absence of COUP-TFI, expression of various cytoskeleton molecules involved in neuronal morphogenesis is affected. Diminished protein levels of the microtubule-associated protein MAP1B and increased levels of the GTP-binding protein RND2 were confirmed in the developing cortex in vivo and in primary hippocampal neurons in vitro. Therefore, based on morphological studies, gene expression profiling and primary cultured neurons, the present data uncover a previously unappreciated intrinsic role for COUP-TFI in axonal growth in vivo and supply one of the premises for COUP-TFI coordination of neuronal morphogenesis in the developing forebrain.

Brain site-specific gene expression analysis in Alzheimer's disease patients

BACKGROUND

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that is characterized by a progressive loss of higher cognitive functions. The brain of an individual with AD exhibits extracellular senile plaques (SPs) of aggregated amyloid-beta peptide (Abeta) and intracellular neurofibrillary tangles (NFTs). Given the critical role of neuronal transport of both proteins and organelles, it is not surprising that perturbation of microtubule-based transport may play a major role in the pathogenesis of AD.

MATERIALS AND METHODS

We used the cDNA subtraction methodology and in vitro neural cell culture analyses to study the meaning of the brain site-specific gene expression pattern in cerebral tissue obtained from AD patients and also from control subjects at autopsy.

RESULTS

We observed that cytoskeleton-associated proteins were down-regulated in AD subjects. We also noted an altered expression of the microtubule-associated protein 1B (MAP1B), the heat-shock protein (HSP)-90 (a key chaperone molecule), the tripartite motif-containing proteins (TRIM)-32/37 (an anti apoptotic enzyme with ubiquitin-protein ligase activity) and the Reticulon-3 (a modulator of the amyloid-precursor-protein (APP) cleavage) in AD brains. Additional molecular- and cell-biological studies revealed that small interfering RNA (siRNA)-mediated down-regulation of MAP1B expression leads to neuronal cell death in vitro.

CONCLUSION

Altered expression of MAP1B, HSP90, TRIM32/37 and Reticulon-3 provides new clues by which the ubiquitin-proteasome-, the protein-chaperon- and the APP-processing systems are disturbed in AD, thus, leading to neuritic amyloid plaques and neurofibrillary tangles.

Tau protects microtubules in the axon from severing by katanin

Microtubules in the axon are more resistant to severing by katanin than microtubules elsewhere in the neuron. We have hypothesized that this is because of the presence of tau on axonal microtubules. When katanin is overexpressed in fibroblasts, the microtubules are severed into short pieces, but this phenomenon is suppressed by the coexpression of tau. Protection against severing is also afforded by microtubule-associated protein 2 (MAP2), which has a tau-like microtubule-binding domain, but not by MAP1b, which has a different microtubule-binding domain. The microtubule-binding domain of tau is required for the protection, but within itself, provides less protection than the entire molecule. When tau (but not MAP2 or MAP1b) is experimentally depleted from neurons, the microtubules in the axon lose their characteristic resistance to katanin. These results, which validate our hypothesis, also suggest a potential explanation for why axonal microtubules deteriorate in neuropathies involving the dissociation of tau from the microtubules.

Microtubule-associated protein 2 (MAP2) is a neurosteroid receptor

The neurosteroid pregnenolone (PREG) and its chemically synthesized analog 3beta-methoxypregnenolone (MePREG) bind to microtubule-associated protein 2 (MAP2) and stimulate the polymerization of microtubules. PREG, MePREG, and progesterone (PROG; the physiological immediate metabolite of PREG) significantly enhance neurite outgrowth of nerve growth factor-pretreated PC12 cells. However, PROG, although it binds to MAP2, does not increase the immunostaining of MAP2, contrary to PREG and MePREG. Nocodazole, a microtubule-disrupting agent, induces a major retraction of neurites in control cultures, but pretreatment with PREG/MePREG is protective. Decreasing MAP2 expression by RNA interference does not modify PROG action, but it prevents the stimulatory effects of PREG and MePREG on neurite extension, showing that MAP2 is their specific receptor.

Neurite extension in central neurons: a novel role for the receptor tyrosine kinases Ror1 and Ror2

Neurite elongation and branching are key cellular events during brain development as they underlie the formation of a properly wired neuronal network. Here we report that the receptor tyrosine kinases Ror1 and Ror2 modulate the growth of neurites as well as their branching pattern in hippocampal neurons. Upon Ror1 or Ror2 suppression using antisense oligonucleotides or RNA interference (RNAi), neurons extended shorter and less branched minor processes when compared to those in control cells. In addition, Ror-depleted cells elongated longer, albeit less branched, axons than seen in control cells. Conversely, Ror overexpression both in non-neuronal cells and in hippocampal neurons resulted in the enhanced extension of short and highly branched processes. These phenotypes were accompanied by changes in the microtubule-associated proteins MAP1B and MAP2. Taken together, these results support a novel role for Ror receptors as modulators of neurite extension in central neurons.

Acute inactivation of MAP1b in growing sympathetic neurons destabilizes axonal microtubules

Microtubule-associated-protein 1b (MAP1b) is abundant in neurons actively extending axons. MAP1b is present on microtubules throughout growing axons, but is preferentially concentrated on microtubule polymer in the distal axon and growth cone. Although MAP1b has been implicated in axon growth and pathfinding, its specific functions are not well understood. Biochemical and transfection studies suggest that MAP1b has microtubule-stabilizing activity, but recent studies with neurons genetically deficient in MAP1b have not confirmed this. We have explored MAP1b functions in growing sympathetic neurons using an acute inactivation approach. Neurons without axons were injected with polyclonal MAP1b antibodies and then stimulated to extend axons. Injected cells were compared to controls in terms of axon growth behavior and several properties of axonal microtubules. The injected antibodies rapidly and quantitatively sequestered MAP1b in the cell body, making it unavailable to perform its normal functions. This immunodepletion of MAP1b had no statistically significant effect on axon growth, the amount of microtubule polymer in the axon, and the relative tyrosinated tubulin content of this polymer, and this was true in sympathetic neurons from rat, wild type mice, and tau knockout mice. Thus, robust axon growth can occur in the absence of MAP1b alone or both MAP1b and tau. However, immunodepletion of MAP1b significantly increased the sensitivity of microtubules in the distal axon and growth cone to nocodazole-induced depolymerization. These results indicate that MAP1b has microtubule-stabilizing activity in growing axons. This stabilizing activity may be required for some axonal functions, but it is not necessary for axon growth.

Regulation of tau isoform expression and dementia

In the central nervous system (CNS), aberrant changes in tau mRNA splicing and consequently in protein isoform ratios cause abnormal aggregation of tau and neurodegeneration. Pathological tau causes neuronal loss in Alzheimer's disease (AD) and a diverse group of disorders called the frontotemporal dementias (FTD), which are two of the most common forms of dementia and afflict more than 10% of the elderly population. Autosomal dominant mutations in the tau gene cause frontotemporal dementia with parkinsonism-chromosome 17 type (FTDP-17). Just over half the mutations affect tau protein function and decrease its affinity for microtubules (MTs) or increase self-aggregation. The remaining mutations occur within exon 10 (E10) and intron 10 sequences and alter complex regulation of E10 splicing by multiple mechanisms. FTDP-17 splicing mutations disturb the normally balanced levels of distinct protein isoforms that result in altered biochemical and structural properties of tau. In addition to FTDP-17, altered tau isoform levels are also pathogenically associated with other FTD disorders such as progressive supranuclear palsy (PSP), corticobasal degeneration and Pick's disease; however, the mechanisms remain undefined and mutations in tau have not been detected. FTDP-17 highlights the association between splicing mutations and the pronounced variability in pathology as well as phenotype that is characteristic of inherited disorders.

MAP2c, but not tau, binds and bundles F-actin via its microtubule binding domain

BACKGROUND

MAP2 and tau are abundant microtubule-associated proteins (MAPs) in neurons. The development of neuronal dendrites and axons requires a dynamic interaction between microtubules and actin filaments. MAPs represent good candidates to mediate such interactions. Although MAP2c and tau have similar, well-characterized microtubule binding activities, their actin interaction is poorly understood.

RESULTS

Here, we show by using a cosedimentation assay that MAP2c binds F-actin. Upon actin binding, MAP2c organizes F-actin into closely packed actin bundles. Moreover, we show by using a deletion approach that MAP2c's microtubule binding domain (MTBD) is both necessary and sufficient for both F-actin binding and bundling activities. Surprisingly, even though the MAP2 and tau MTBDs share high sequence homology and possess similar microtubule binding activities, tau is unable to bind or bundle F-actin. Furthermore, experiments with chimeric proteins demonstrate that the actin binding activity fully correlates with the ability to promote neurite initiation in neuroblastoma cells.

CONCLUSIONS

These results provide the first demonstration that the MAP2c and tau MTBD domains exhibit distinct properties, diverging in actin binding and neurite initiation activities. These results implicate a novel actin function for MAP2c in neuronal morphogenesis and furthermore suggest that actin interactions could contribute to functional differences between MAP2 and tau in neurons.

Role of tau protein in both physiological and pathological conditions

The morphology of a neuron is determined by its cytoskeletal scaffolding. Thus proteins that associate with the principal cytoskeletal components such as the microtubules have a strong influence on both the morphology and physiology of neurons. Tau is a microtubule-associated protein that stabilizes neuronal microtubules under normal physiological conditions. However, in certain pathological situations, tau protein may undergo modifications, mainly through phosphorylation, that can result in the generation of aberrant aggregates that are toxic to neurons. This process occurs in a number of neurological disorders collectively known as tauopathies, the most commonly recognized of which is Alzheimer's disease. The purpose of this review is to define the role of tau protein under normal physiological conditions and to highlight the role of the protein in different tauopathies.

Microtubule-associated protein 1B function during normal development, regeneration, and pathological conditions in the nervous system

Microtubule-associated protein 1B is the first MAP to be expressed during the development of the nervous system. Several different approaches have revealed that MAP1B function is associated with microtubule and actin microfilament polymerization and dynamics. In recent years, the generation of molecular models to inactivate MAP1B function in invertebrates and mammals has sparked some controversy about the real role of MAP1B. Despite discrepancies between some studies, it is clear that MAP1B plays a principal role in the development of the nervous system. In this article, we summarize the evidence for MAP1B function in a wide variety of cellular processes implicated in the proper construction of the nervous system. We also discuss the role of MAP1B in pathological processes.