Reactive oxygen: its sources and significance in Alzheimer disease

Over the past decade, oxidative stress has been established as the earliest cytological feature of Alzheimer disease and an attractive therapeutic target. The major challenges now are establishing the source of the reactive oxygen and what oxidative stress tells us about the etiology of Alzheimer disease. These are complex issues since a variety of enzymatic and non-enzymatic processes are involved in reactive oxygen formation and damage to macromolecules. In this review, we consider disease mechanisms that show the greatest promise for future research.

Regulation of neuronal cytoskeleton by lysophosphatidic acid: role of GSK-3

Neurite retraction is a crucial process during nervous system development and neurodegeneration. This process implies reorganization of the neuronal cytoskeleton. Some bioactive lipids such as lysophosphatidic acid (LPA) induce neurite retraction. The reorganization of the actin cytoskeleton during neurite retraction is one of the best-characterized effects of LPA. However, less information is available regarding the reorganization of the microtubule (MT) network in response to LPA in neuronal cells. Here, we first give an overview of the roles of cytoskeleton during neurite outgrowth, and subsequently, we review some of the data from different laboratories concerning LPA-induced cytoskeletal rearrangement in neuronal cells. We also summarize our own recent results about modifications of MTs during LPA-induced neurite retraction. We have shown that LPA induces changes in tubulin pools and increases in the phosphorylation levels of microtubule-associated proteins (MAPs), such as Tau. Tau hyperphosphorylation in response to LPA is mediated by the activation of glycogen synthase kinase-3 (GSK-3). The upregulation of GSK-3 activity by LPA seems to be a general process as it occurs in diverse neuronal cells of different species in correlation with the neurite retraction process.

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

Several lines of evidence have indicated that changes in the structure of neuronal cytoskeleton provide the support for the dramatic morphological changes that occur during neuronal differentiation. It has been proposed that microtubule-associated proteins can contribute to the development of this phenomenon by controlling the dynamic properties of microtubules. In this report we have characterized the effect of the combined suppression of MAP1B and tau, and MAP1B and MAP2 on neuronal polarization in cultured hippocampal cells grown on a laminin-containing substrate. We have taken advantage of the use of a mouse line deficient in MAP1B expression obtained by the gene trapping approach. In addition to this engineered mice line we used the antisense oligonucleotide approach to induce the suppression of tau or MAP2, in wild type and MAP1B-deficient neurons. Together these results show a synergistic role for MAP1B/MAP2 and MAP1B/TAU.

Microtubule-associated protein 2 phosphorylation is decreased in the human epileptic temporal lobe cortex

Microtubule-associated protein 2 (MAP2) is an abundant component of the neuronal cytoskeleton whose function is related to the outgrowth and stability of neuronal processes, to synaptic plasticity and neuronal cell death. We have sought to study whether abnormal patterns of neuronal activity which are characteristic of epileptic patients are associated to alterations of MAP2 phosphorylation. An antibody (305) that selectively recognizes a phosphorylated epitope in a proline-rich region of the MAP2 molecule has been used to analyze neocortical biopsy samples from temporal lobe epileptic patients, whose electrocorticogram activity had been previously monitored. Immunoblot analysis showed that samples with greater spiking activity displayed significantly diminished MAP2 phosphorylation. Immunocytochemical analysis revealed the occurrence of discrete areas in the neocortex with highly decreased or no immunostaining for antibody 305, which showed a clear, although non-significant, tendency to appear more frequently in areas with greater spiking activity. To further support an association between epileptiform activity and MAP2 dephosphorylation an experimental model of epileptiform activity in cultures of rat hippocampal neurons was used. Neurons were cultured during 15 days in the presence of kynurenic acid, an antagonist of glutamate receptors. At this time, kynurenic acid was removed from the culture medium and neurons developed seizure-like activity. Using antibody 305, we found a decrease of MAP2 phosphorylation that was already visible after 15 min of kynurenic acid withdrawal. We therefore propose that MAP2 phosphorylation is decreased in the neocortex of epileptic patients and that this decrease is a likely consequence of seizure activity. Also, MAP2 dephosphorylation may lead to alterations of the neuronal cytoskeleton and eventually to neuronal damage and loss, which is typical of epileptic patients.

FTDP-17 mutations in tau transgenic mice provoke lysosomal abnormalities and Tau filaments in forebrain

The tauopathies, which include Alzheimer's disease (AD) and frontotemporal dementias, are a group of neurodegenerative disorders characterized by filamentous Tau aggregates. That Tau dysfunction can cause neurodegeneration is indicated by pathogenic tau mutations in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). To investigate how Tau alterations provoke neurodegeneration we generated transgenic mice expressing human Tau with four tubulin-binding repeats (increased by FTDP-17 splice donor mutations) and three FTDP-17 missense mutations: G272V, P301L, and R406W. Ultrastructural analysis of mutant Tau-positive neurons revealed a pretangle appearance, with filaments of Tau and increased numbers of lysosomes displaying aberrant morphology similar to those found in AD. Lysosomal alterations were confirmed by activity analysis of the marker acid phosphatase, which was increased in both transgenic mice and transfected neuroblastoma cells. Our results show that Tau modifications can provoke lysosomal aberrations and suggest that this may be a cause of neurodegeneration in tauopathies.

Proteasomal-dependent aggregate reversal and absence of cell death in a conditional mouse model of Huntington's disease

Neuronal intranuclear inclusions are a histopathological hallmark of Huntington's disease. Nevertheless, the precise mechanism by which they are formed and their relevance to neuronal cell death and/or dysfunction remains unclear. We recently generated a conditional mouse model of Huntington's disease (HD94) in which silencing expression of mutated huntingtin led to the disappearance of intranuclear aggregates and amelioration of the behavioral phenotype. Here, we analyze primary striatal neuronal cultures from HD94 mice to explore the dynamics of aggregate formation and reversal, the possible mechanisms involved, and the correlation between aggregates and neuronal death. In parallel, we examine symptomatic adult HD94 mice in similar studies and explored the relationship between aggregate clearance and behavioral reversal. We report that, in culture, aggregate formation and reversal were rapid processes, such that 2 d of transgene expression led to aggregate formation, and 5 d of transgene suppression led to aggregate disappearance. In mice, full reversal of aggregates and intranuclear mutant huntingtin was more rapid than reported previously and preceded the motor recovery by several weeks. Furthermore, the proteasome inhibitor lactacystin inhibited the aggregate clearance observed in culture, thus indicating that aggregate formation is a balance between the rate of huntingtin synthesis and its degradation by the proteasome. Finally, neither expression of the mutant huntingtin nor aggregates compromised the viability of HD94 cultures. This correlated with the lack of cell death in symptomatic HD94 mice, thus demonstrating that neuronal dysfunction, and not cell loss, triggered by mutant huntingtin underlies symptomatology.

Distribution of the phosphorylated form of microtubule associated protein 1B in the fish visual system during optic nerve regeneration

Microtubule associated proteins are a heterogeneous group of proteins that have been implicated in regulating microtubule stability. They play an important role in the organisation of the neuronal cytoskeleton during neurite outgrowth, plasticity and regeneration. The fish visual system presents a considerable degree of plasticity. Thus, the retina grows continually throughout life and the optic nerve regenerates after crush. In the present study, we compared the distribution of the microtubule associated protein 1B in its phosphorylated form (MAP1B-phos) in the normal adult fish visual system with that observed during optic nerve regeneration after adult optic nerve crush using a specific monoclonal antibody mAb-150. Expression of MAP1B-phos was observed in some ganglion cell somata and in developing, growing axons within the control optic nerve. Few immunoreactive terminals were seen in the control optic tectum. After optic nerve crush, we found additional MAP1B-phos expression in regenerating axons throughout the visual system. Our results demonstrate that MAP1B-phos is present in growing and regenerating axons of fish retinal ganglion cells, which suggests that the phosphorylated form of MAP1B may play an important role in developmental and regeneration processes within the fish central nervous system.

The inhibition of phosphatidylinositol-3-kinase induces neurite retraction and activates GSK3

It has been extensively described that neuronal differentiation involves the signalling through neurotrophin receptors to a Ras-dependent mitogen-activated protein kinase (MAPK) cascade. However, signalling pathways from other neuritogenic factors have not been well established. It has been reported that cAMP may activate protein kinase (PKA), and it has been shown that PKA-mediated stimulation of MAPK pathway regulates not only neuritogenesis but also survival. However, extracellular regulated kinases (ERKs) mediated pathways are not sufficient to explain all the processes which occur in neuronal differentiation. Our present data show that: in cAMP-mediated neuritogenesis, using the SH-SY5Y human neuroblastoma cell line, there exists a link between the activation of PKA and stimulation of phosphatidylinositol 3-kinase (PI3K). Both kinase activities are essential to the initial elongation steps. Surprisingly, this neuritogenic process appears to be independent of ERKs. While the activity of PI3K is essential for elongation and maintenance of neurites, its inhibition causes retraction. In this neurite retraction process, GSK3 is activated. Using both a pharmacological approach and gene transfer of a dominant negative form of GSK3, we conclude that this induced retraction is a GSK3-dependent process which in turn appears to be a common target for transduction pathways involved in lysophosphatidic acid-mediated and PI3K-mediated neurite retraction.

Review: postchaperonin tubulin folding cofactors and their role in microtubule dynamics

The microtubule cytoskeleton consists of a highly organized network of microtubule polymers bound to their accessory proteins: microtubule-associated proteins, molecular motors, and microtubule-organizing proteins. The microtubule subunits are heterodimers composed of one alpha-tubulin polypeptide and one beta-tubulin polypeptide that should undergo a complex folding processing before they achieve a quaternary structure that will allow their incorporation into the polymer. Due to the extremely high protein concentration that exists at the cell cytoplasm, there are alpha- and beta-tubulin interacting proteins that prevent the unwanted interaction of these polypeptides with the surrounding protein pool during folding, thus allowing microtubule dynamics. Several years ago, the development of a nondenaturing electrophoretic technique made it possible to identify different tubulin intermediate complexes during tubulin biogenesis in vitro. By these means, the cytosolic chaperonin containing TCP-1 (CCT or TriC) and prefoldin have been demonstrated to intervene through tubulin and actin folding. Various other cofactors also identified along the alpha- and beta-tubulin postchaperonin folding route are now known to have additional roles in tubulin biogenesis such as participating in the synthesis, transport, and storage of alpha- and beta-tubulin. The future characterization of the tubulin-binding sites to these proteins, and perhaps other still unknown proteins, will help in the development of chemicals that could interfere with tubulin folding and thus modulating microtubule dynamics. In this paper, current knowledge of the above postchaperonin folding cofactors, which are in fact chaperones involved in tubulin heterodimer quaternary structure achievement, will be reviewed.

[The microtubule-associated protein tau in neurodegenerative diseases. Tauopathies]

INTRODUCTION

Microtubules are the essential components of the cytoskeleton, they are responsible for the formation and maintenance of the neuronal morphology and their specific connections. The microtubule associated proteins (MAPs) contribute to regulate the dynamism and stability of the microtubules, and therefore they are essential to maintain the correct function of the microtubules. Among them, tau is a protein that seems to be crucial in stabilizing the neuronal polarity.

DEVELOPMENT

In this paper, factors affecting the affinity of tau to bind microtubules are reviewed, giving special attention to the processes that take place in the neurodegenerative diseases that present neurofibrillary tangles (NFTs), aggregates composed of modified tau in form of paired helical filaments (PHFs). One of the most important tau modification in this aberrant aggregates is the hyperphosphorylation. Thus, kinases and phosphatases responsible for tau modification could be altered in certain pathologies, leading to a decrease in the affinity of tau to bind microtubules and carrying out its self assembling and aberrant aggregation in the neurons of the affected nervous system regions. Those pathologies presenting a tau disfunction are known as tauopathies.

Evidence for the role of MAP1B in axon formation

Cultured neurons obtained from a hypomorphous MAP1B mutant mouse line display a selective and significant inhibition of axon formation that reflects a delay in axon outgrowth and a reduced rate of elongation. This phenomenon is paralleled by decreased microtubule formation and dynamics, which is dramatic at the distal axonal segment, as well as in growth cones, where the more recently assembled microtubule polymer normally predominates. These neurons also have aberrant growth cone formation and increased actin-based protrusive activity. Taken together, this study provides direct evidence showing that by promoting microtubule dynamics and regulating cytoskeletal organization MAP1B has a crucial role in axon formation.

In Vitro Assembly of Tau Protein: Mapping the Regions Involved in Filament Formation

Unraveling the mechanism of self-assembly of the protein tau into paired helical filaments (PHFs) is a crucial step toward the understanding of Alzheimer's and other neuropathological diseases at the molecular level. In an effort to map the role of different regions of tau in the mechanism of self-assembly, we have studied the polymerization ability of different tau fragments using an in vitro assay. Our results indicate that the N-terminal domain interferes with tau's ability to polymerize in vitro. The effect seems to be size dependent. Particularly, an isoform of tau from the peripheral nervous system, which has a much larger N-terminal domain, was found unable to form filaments in our in vitro assay. This finding can explain why in Alzheimer's patients PHFs only accumulate in the neurons from the central nervous system. We also report that a short segment of tau located in the third microtubule binding repeat (residues 317 to 335, peptide 1/2R) is probably the minimal segment of that region able to grow into filaments in vitro and in the presence of heparin. In contrast with whole peptide 1/2R, peptides corresponding to either the N-terminal or C-terminal halves of this segment were unable to form filaments. Finally, our polymerization studies of peptides from the C-terminal domain reveal a short sequence spanning residues 391 to 407 that grows into filaments in vitro. This tau segment forms filaments regardless of whether is incubated with heparin. Moreover, such filaments differ in diameter and morphology, suggesting a different mechanism of self-assembly.

Apolipoprotein E4 stimulates sulfation of glycosaminoglycans in neural cells

Apolipoprotein E externally added to neuroblastoma cells in culture stimulates [35S]sulfate incorporation on cell and extracellular matrix glycosaminoglycans (sGAG). This stimulation is mainly observed for ApoE4 compared to ApoE3. The increase in sulfation is not due to increased synthesis as there is no corresponding increase in the [3H]glucosamine incorporation. Since the presence of ApoE is a risk factor for Alzheimer's disease (AD) and the presence of sGAG could facilitate the assembly of the main components, beta-amyloid and tau proteins, of the aberrant structures found in AD, the present study indicates a possible relation between those factors.

Microtubule-associated protein-2 located in growth regions of rat hippocampal neurons is highly phosphorylated at its proline-rich region

Neuronal morphogenesis is regulated, among other factors, by microtubule-associated proteins (MAPs). A family of these proteins, MAP2, which is very abundant in the mammalian nervous system, has been associated with the formation of neurites at early developmental stages and with the dendritic scaffold upon maturation. The function of MAP2 is regulated by its phosphorylation state. One of the phosphorylation sites that has been described is located in the proline-rich region of the protein. It comprises of the residues 1616-1626 and is specifically recognized by the antibody 305. However, little is known about the functional consequences of its modification in vivo. To gain insight into this, we have analysed the expression levels and intracellular distribution of MAP2 phosphorylated at this site (MAP2-P), in primary cultures of rat hippocampal neurons at different developmental stages. Western blot analysis of hippocampal neuron protein extracts revealed that the ratio of MAP2-P:MAP2 was 4:1 at early developmental stages and became 1:4 at later developmental stages, suggesting a role of such phosphorylated forms of the protein in neuritogenesis. Consistent with this view, immunofluorescence microscopy analysis showed that the ratio MAP2-P:MAP2 was 2 in the neurite growth cones, sites where net elongation takes place. A higher presence of phosphorylated MAP2 was observed in growth regions with higher levels of microfilaments, which may be related with the growth region stability. Indeed, when growth-cone collapse was induced in hippocampal neurons after cytochalasin D treatment, which depolymerizes microfilaments, the ratio MAP2-P:MAP2 in these growing regions decreased down to 1. Finally, acceleration of neuronal maturation induced by the activation of glutamate-receptors triggered a dramatic decrease in the phosphorylation of MAP2 at the site recognized by antibody 305. From these results we suggest that the phosphorylation of MAP2 at its proline-rich region is an important event during neuritogenesis.

Phosphorylated, but not native, tau protein assembles following reaction with the lipid peroxidation product, 4-hydroxy-2-nonenal

A correlation between hyperphosphorylation of tau protein and its aberrant assembly into paired helical filaments has lead to suggestions that phosphorylation controls assembly, but lacked a mechanistic basic. In this work, we have found that phosphorylated, but not native, tau protein is able to form polymers after the reaction with 4-hydroxy-2-nonenal, a highly toxic product of lipid peroxidation. Phosphorylation of tau by both proline or non-proline directed kinases, was able to assemble it into polymers.

Role of the PI3K regulatory subunit in the control of actin organization and cell migration

Cell migration represents an important cellular response that utilizes cytoskeletal reorganization as its driving force. Here, we describe a new signaling cascade linking PDGF receptor stimulation to actin rearrangements and cell migration. We demonstrate that PDGF activates Cdc42 and its downstream effector N-WASP to mediate filopodia formation, actin stress fiber disassembly, and a reduction in focal adhesion complexes. Induction of the Cdc42 pathway is independent of phosphoinositide 3-kinase (PI3K) enzymatic activity, but it is dependent on the p85alpha regulatory subunit of PI3K. Finally, data are provided showing that activation of this pathway is required for PDGF-induced cell migration on collagen. These observations show the essential role of the PI3K regulatory subunit p85alpha in controlling PDGF receptor-induced cytoskeletal changes and cell migration, illustrating a novel signaling pathway that links receptor stimulation at the cell membrane with actin dynamics.

Perinatal lethality of microtubule-associated protein 1B-deficient mice expressing alternative isoforms of the protein at low levels

Microtubule-associated protein 1B (MAP1B) has been implicated in axogenesis in cultured cells. To gain insight into the functions that MAP1B plays in vivo, we analyzed a strain of Map1B mutant mice generated by a gene trapping approach. Homozygous mice die on the first day after birth, probably due to a severe abnormal development of the nervous system. They present alterations in the structure of several brain regions. The normal Map1B gene yields different protein isoforms from alternatively spliced transcripts. The smaller isoforms were present in wild type, hetero-, and homozygous mice, but their expression was higher in the mutants than in the wild-type. Moreover, trace amounts of MAP1B protein were also observed in Map1B homozygous mutants, indicating an alternative splicing around the gene trap insertion. Thus, the Map1B gene trapped mutation reported in this work did not generated a null mutant, but a mouse with a drastic deficiency in MAP1B expression. Analyses of these mice indicate the presence of several neural defects and suggest the participation of MAP1B in neuronal migration.

Molecular genetic approaches to microtubule-associated protein function

Protein function in vivo can be studied by deleting (knock-out) the gene that encodes it, and search for the consequences. This procedure involves different technologies, including recombinant DNA procedures, cell biology methods and histological and immunocytochemical analysis. In this work we have reviewed these procedures when they have been applied to ascertain the function of several microtubule-associated proteins. These proteins have been previously involved, through in vitro experiments, in having a role in the microtubule stabilization. Here, we will summarize the generation and characterization of different microtubule-associated protein knock-out mice. Special attention will be paid to MAP1B knock-out mice. Amongst the different MAPs knock-out mice these show the strongest phenotype, the most likely for being MAP1B, the MAP that is expressed earliest in neurogenesis. Molecular genetics could be considered as a valid and useful procedure to truly establish the in vivo functions of a protein, although it is necessary to be aware of possible artifacts such as the generation of some kinds of RNA alternative splicing. To avoid this the best strategy to be used must consider the deletion of the exon that contains the functional domains of the protein.

Cloning, sequencing, and expression of H.a.YNR1 and H.a.YNI1, encoding nitrate and nitrite reductases in the yeast Hansenula anomala

A single Hansenula anomala genomic DNA fragment containing the genes H.a.YNR1 (yeast nitrate reductase) and H.a.YNI1 (yeast nitrite reductase) encoding nitrate and nitrite reductase, respectively, was isolated from a lambda EMBL3 genomic DNA library. As probe, a 3.2 kb DNA fragment isolated from a lambda gt11 H. anomala genomic DNA library screened with antiserum anti-NR from H. anomala was used. H. a.YNR1 and H.a.YNI1 genes are separated by 473 bp and encode putative proteins of 870 and 1077 amino acids, respectively, with great similarity to nitrate and nitrite reductases from other organisms. Northern blot analysis revealed that both genes are highly expressed in nitrate, very low in nitrate plus ammonium, and no expression was detected in ammonium or nitrogen-free media. Levels of nitrate reductase and nitrite reductase were very low or undetectable by Western blot analysis in nitrogen-free and ammonium media, whereas both proteins were present in nitrate and ammonium plus nitrate media. The nucleotide sequence Accession No. is AF123281.

A study of the response of Y3Al5O12:Ce phosphor powder screens in the vacuum ultraviolet and soft X-ray regions using synchrotron radiation

Phosphor screens find application in many fields because of their ability to convert incident radiation to wavelengths that are readily measured by modern detectors. While the response of such screens in the X-ray region has been widely studied, much work still remains to be done regarding their response in the vacuum ultraviolet and soft X-ray regions, where the response is predicted to be non-linear owing to the presence of elemental absorption edges. Here, an experiment using synchrotron radiation to determine the response of thin Y(3)Al(5)O(12):Ce (1-21 mg cm(-2)) and Y(2)O(3):Eu (2.64 mg cm(-2)) powder phosphor screens in the spectral range 20-900 A (13.8-620 eV) is reported. Also, a custom-built camera is described which permits simultaneous collection of the forward- and backward-emitted light and that enables measurements to be made at various positions across the screens and at several screen/incident beam angles. Finally, features in the response spectra are identified, and efficiencies across the spectral range indicated for different screen thicknesses and operating modes are plotted, before a curve of the intrinsic radiant efficiency of Y(3)Al(5)O(12):Ce is produced. The results are discussed in the context of other measurements.

Tau aggregation into fibrillar polymers: taupathies

Different neurological disorders, known as taupathies have been recently described. In these disorders it has been suggested that modifications in the microtubule-associated protein tau could cause neural degeneration in specific regions. Although these regions are different in the different taupathies, some common features appear to occur in all of them: abnormal hyperphosphorylation of tau and aberrant tau aggregation. These two features are commented upon in this review.

Regulated expression of p14 (cofactor A) during spermatogenesis

The correct folding of tubulins and the generation of functional alpha beta-tubulin heterodimers require the participation of a series of recently described molecular chaperones and CCT (or TRiC), the cytosolic chaperonin containing TCP-1. p14 (cofactor A) is a highly conserved protein that forms stable complexes with beta-tubulin which are not apparently indispensable along the in vitro beta-tubulin folding route. Consequently, the precise role of p14 is still unknown, though findings on Rb12p (its yeast homologue) suggest p14 might play a role in meiosis and/or perhaps to serve as an excess beta-tubulin reservoir in the cell. This paper investigates the in vivo possible role of p14 in testis where mitosis, meiosis, and intense microtubular remodeling processes occur. Our results confirm that p14 is more abundantly expressed in testis than in other adult mammalian tissues. Northern blot, Western blot, in situ hybridization, and immunocytochemical analyses have all demonstrated that p14 is progressively upregulated from the onset of meiosis through spermiogenesis, being more abundant in differentiating spermatids. The close correlation observed between the mRNA expression waves for p14 and testis specific tubulin isotypes beta 3 and alpha 3/7, together with the above results, suggest that p14 role in testis would presumably be associated to beta-tubulin processing rather than meiosis itself. Additional in vitro beta 3-tubulin synthesis experiments have shown that p14 plays a double role in beta-tubulin folding, enhancing the dimerization of newly synthesized beta-tubulin isotypes as well as capturing excess beta-tubulin monomers. The above evidence suggests that p14 is a chaperone required for the actual beta-tubulin folding process in vivo and storage of excess beta-tubulin in situations, such as in testis, where excessive microtubule remodeling could lead to a disruption of the alpha-beta balance. As seen for other chaperones, p14 could also serve as a route to lead excess beta-tubulin or replaced isotypes towards degradation.

Phosphorylation of microtubule-associated protein 2 (MAP2) and its relevance for the regulation of the neuronal cytoskeleton function

Neurons, the basic information processing units of the nervous system, are characterized by a complex polar morphology which is essential for their function. To attain their precise morphology, neurons extend cytoplasmatic processes (axons and dendrites) and establish synaptic connections in a highly regulated way. Additionally, neurons are also subjected to small plastic changes at the adult stage which serve to regulate synaptic transmission. Every step of neuronal development is genetically controlled by endogenous determinants, as well as by environmental signals including intercellular contacts, extracellular matrix and diffusible signals. Cytoskeletal components are among the main protein targets modified in response to most of those extracellular signals which ultimately determine neuronal morphology. One of the major mechanisms controlling the neuronal cytoskeleton is the modification of the phosphorylation state of cytoskeletal proteins via changes in the relative activities of protein kinases and phosphatases within neurons. In particular, the microtubule-associated protein 2 (MAP2) family of proteins is an abundant group of cytoskeletal components which are predominantly expressed in neurons and serve as substrates for most of protein kinases and phosphatases present in neurons. MAP2 phosphorylation seems to control its association with the cytoskeleton and it is developmentally regulated. Moreover, MAP2 may perform many functions including the nucleation and stabilization of microtubules (and maybe microfilaments), the regulation of organelle transport within axons and dendrites, as well as the anchorage of regulatory proteins such as protein kinases which may be important for signal transduction. These putative functions of MAP2 have also been proposed to play important roles in the outgrowth of neuronal processes, synaptic plasticity and neuronal cell death. Thus, MAP2 constitutes an interesting case to understand the regulation of neuronal function by the alteration of the phosphorylation state of cytoskeletal proteins in response to different extracellular signals. Here we will review the current knowledge about the regulation of MAP2 function through phosphorylation/dephosphorylation and its relevance in the broader context of neuronal functions.