Molecular and functional characteristics of MAP-2a: ability of MAP-2a versus MAP-2b to induce stable microtubules in COS cells

Neuronal Differentiation and Outgrowth Effect of Thymol in Trachyspermum ammi Seed Extract via BDNF/TrkB Signaling Pathway in Prenatal Maternal Supplementation and Primary Hippocampal Culture

Reviving the neuronal functions in neurodegenerative disorders requires the promotion of neurite outgrowth. Thymol, which is a principal component of Trachyspermum ammi seed extract (TASE), is reported to have neuroprotective effects. However, the effects of thymol and TASE on neuronal differentiation and outgrowth are yet to be studied. This study is the first report investigating the neuronal growth and maturation effects of TASE and thymol. Pregnant mice were orally supplemented with TASE (250 and 500 mg/kg), thymol (50 and 100 mg/kg), vehicle, and positive controls. The supplementation significantly upregulated the expression of brain-derived neurotrophic factor (BDNF) and early neuritogenesis markers in the pups' brains at post-natal day 1 (P1). Similarly, the BDNF level was significantly upregulated in the P12 pups' brains. Furthermore, TASE (75 and 100 µg/mL) and thymol (10 and 20 µM) enhanced the neuronal polarity, early neurite arborization, and maturation of hippocampal neurons in a dose-dependent manner in primary hippocampal cultures. The stimulatory activities of TASE and thymol on neurite extension involved TrkB signaling, as evidenced by attenuation via ANA-12 (5 µM), which is a specific TrkB inhibitor. Moreover, TASE and thymol rescued the nocodazole-induced blunted neurite extension in primary hippocampal cultures, suggesting their role as a potent microtubule stabilizing agent. These findings demonstrate the potent capacities of TASE and thymol in promoting neuronal development and reconstruction of neuronal circuitry, which are often compromised in neurodegenerative diseases and acute brain injuries.

Genome-Wide Association Analyses of Fertility Traits in Beef Heifers

The ability of livestock to reproduce efficiently is critical to the sustainability of animal agriculture. Antral follicle count (AFC) and reproductive tract scores (RTS) can be used to estimate fertility in beef heifers, but the genetic mechanisms influencing variation in these measures are not well understood. Two genome-wide association studies (GWAS) were conducted to identify the significant loci associated with these traits. In total, 293 crossbred beef heifers were genotyped on the Bovine GGP 50K chip and genotypes were imputed to 836,121 markers. A GWAS was performed with the AFC phenotype for 217 heifers with a multi-locus mixed model, conducted using the year, age at time of sampling and principal component analysis groupings as the covariates. The RTS GWAS was performed with 289 heifers using an additive correlation/trend test comparing prepubertal to pubertal heifers. The loci on chromosomes 2, 3 and 23 were significant in the AFC GWAS and the loci on chromosomes 2, 8, 10 and 11 were significant in the RTS GWAS. The significant region on chromosome 2 was similar between both analyses. These regions contained genes associated with cell proliferation, transcription, apoptosis and development. This study proposes candidate genes for beef cattle fertility, although future research is needed to elucidate the precise mechanisms.

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

Neurons are particularly susceptible to microtubule (MT) defects and deregulation of the MT cytoskeleton is considered to be a common insult during the pathogenesis of neurodegenerative disorders. Evidence that dysfunctions in the MT system have a direct role in neurodegeneration comes from findings that several forms of neurodegenerative diseases are associated with changes in genes encoding tubulins, the structural units of MTs, MT-associated proteins (MAPs), or additional factors such as MT modifying enzymes which modulating tubulin post-translational modifications (PTMs) regulate MT functions and dynamics. Efforts to use MT-targeting therapeutic agents for the treatment of neurodegenerative diseases are underway. Many of these agents have provided several benefits when tested on both in vitro and in vivo neurodegenerative model systems. Currently, the most frequently addressed therapeutic interventions include drugs that modulate MT stability or that target tubulin PTMs, such as tubulin acetylation. The purpose of this review is to provide an update on the relevance of MT dysfunctions to the process of neurodegeneration and briefly discuss advances in the use of MT-targeting drugs for the treatment of neurodegenerative disorders.

Participation of EML6 in the regulation of oocyte meiotic progression in mice

The generation of a high-quality egg for reproduction requires faithful segregation of chromosome during oocyte meiosis. Here, we report that echinoderm microtubule-associated protein like 6 (EML6) is highly expressed in oocytes, and responsible for accurate segregation of homologous chromosomes in mice. Quantitative real-time RT-PCR and immunohistochemistry analyses revealed that EML6 was predominantly expressed by oocytes in the ovaries. Whole mount immunofluorescent staining showed that EML6 was colocalized with spindle microtubules in oocytes at various stages after meiotic resumption. This specialized localization was disrupted by nocodazole, the microtubule destabilizer, while enhanced by Taxol, a microtubule stabilizing reagent. In vivo knockdown of Eml6 expression by the specific siRNA resulted in chromosome misalignment and alteration in spindle dimension at both metaphase Ⅰ and Ⅱ stages, as well as the increased aneuploidy in the mature oocytes. Thus, these data suggest that EML family proteins participate in the control of oocyte meiotic division.

Modulation of Synaptic Plasticity by Exercise Training as a Basis for Ischemic Stroke Rehabilitation

In recent years, rehabilitation of ischemic stroke draws more and more attention in the world, and has been linked to changes of synaptic plasticity. Exercise training improves motor function of ischemia as well as cognition which is associated with formation of learning and memory. The molecular basis of learning and memory might be synaptic plasticity. Research has therefore been conducted in an attempt to relate effects of exercise training to neuroprotection and neurogenesis adjacent to the ischemic injury brain. The present paper reviews the current literature addressing this question and discusses the possible mechanisms involved in modulation of synaptic plasticity by exercise training. This review shows the pathological process of synaptic dysfunction in ischemic roughly and then discusses the effects of exercise training on scaffold proteins and regulatory protein expression. The expression of scaffold proteins generally increased after training, but the effects on regulatory proteins were mixed. Moreover, the compositions of postsynaptic receptors were changed and the strength of synaptic transmission was enhanced after training. Finally, the recovery of cognition is critically associated with synaptic remodeling in an injured brain, and the remodeling occurs through a number of local regulations including mRNA translation, remodeling of cytoskeleton, and receptor trafficking into and out of the synapse. We do provide a comprehensive knowledge of synaptic plasticity enhancement obtained by exercise training in this review.

Systematic analysis of neuronal wiring of the rodent deep cerebellar nuclei reveals differences reflecting adaptations at the neuronal circuit and internuclear levels

A common view of the architecture of different brain regions is that, despite their heterogeneity, they have optimized their wiring schemes to make maximal use of space. Based on experimental findings, computational models have delineated how about two-thirds of the neuropil is filled out with dendrites and axons optimizing cable costs and conduction time while keeping the connectivity at the highest level. However, whether this assumption can be generalized to all brain regions has not yet been tested. Here we quantified and charted the components of the neuropil in the four deep cerebellar nuclei (DCN) of the rat's brain. We segmented and traced the neuropil stained with one of two antibodies, one antibody against dendritic microtubule-associated proteins (MAP2a,b) and the second against the Purkinje cell axons (PCP2). We compared fiber length density, average fiber diameter, and volume fraction within different components of the DCN in a random, systematic fashion. We observed differences in dendritic and axonal fiber length density, average fiber diameters, and volume fraction within the four different nuclei that make up the DCN. We observe a relative increase in the length density of dendrites and Purkinje cell axons in two of the DCN, namely, the posterior interposed nucleus and the lateral nucleus. Furthermore, the DCN have a surprisingly low volume fraction of their dendritic length density, which we propose is related to their special circuitry. In summary, our results show previously unappreciated functional adaptations among these nuclei.

Expression of vascular endothelial growth factor receptor-3 mRNA in the rat developing forebrain and retina

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, is expressed in neural progenitor cells, but there has been no comprehensive study of its distribution in the developing brain. Here, the temporal and cell-specific expression of VEGFR-3 mRNA was studied in the developing rat forebrain and eye. Expression appeared along the ventricular and subventricular zones of the lateral and third ventricles showing ongoing neurogenesis as early as embryonic day 13 but was progressively down-regulated during development and remained in the subventricular zone and rostral migratory stream of the adult forebrain. VEGFR-3 expression was also detectable in some differentiating and postmitotic neurons in the developing cerebral cortex, including Cajal-Retzius cells, cortical plate neurons, and subplate neurons. Expression in the subplate increased significantly during the early postnatal period but was absent by postnatal day 14. It was also highly expressed in nonneural tissues of the eye during development, including the retinal pigment epithelium, the retinal ciliary margin, and the lens, but persisted in a subset of cells in the pigmented ciliary epithelium of the adult eye. In contrast, there was weak or undetectable expression in the early neural retina, but a subset of retinal neurons in the postnatal and mature retina showed intense signals. These unique spatiotemporal mRNA expression patterns suggest that VEGFR-3 might mediate the regulation of both neurogenesis and adult neuronal function in the rat forebrain and eye.

Oncogenic BRAFV600E induces expression of neuronal differentiation marker MAP2 in melanoma cells by promoter demethylation and down-regulation of transcription repressor HES1

MAP2 is a neuron-specific microtubule-associated protein that binds and stabilizes dendritic microtubules. Previously, we showed that MAP2 expression is (a) activated in cutaneous primary melanoma and (b) inversely associated with melanoma tumor progression. We also showed that ectopic expression of MAP2 in metastatic melanoma cells inhibits cell growth by inducing mitotic spindle defects and apoptosis. However, molecular mechanisms of regulation of MAP2 gene expression in melanoma are not understood. Here, we show that in melanoma cells MAP2 expression is induced by the demethylating agent 5-aza-2'-cytidine, and MAP2 promoter is progressively methylated during melanoma progression, indicating that epigenetic mechanisms are involved in silencing of MAP2 in melanoma. In support of this, methylation of MAP2 promoter DNA in vitro inhibits its activity. Because MAP2 promoter activity levels in melanoma cell lines also correlated with activating mutation in BRAF, a gene that is highly expressed in neurons, we hypothesized that BRAF signaling is involved in MAP2 expression. We show that hyperactivation of BRAF-MEK signaling activates MAP2 expression in melanoma cells by two independent mechanisms, promoter demethylation or down-regulation of neuronal transcription repressor HES1. Our data suggest that BRAF oncogene levels can regulate melanoma neuronal differentiation and tumor progression.

Differential expression of microtubule-associated protein 2 in melanocytic skin lesions

Neoplastic melanocytes may exhibit certain differentiation characteristics of other neural-crest derivatives. We aimed to study the expression of microtubule-associated protein 2 (MAP-2) in different types of melanocytic skin lesions. Paraffin-embedded sections of 42 benign nevi (BN), 22 dysplastic nevi (DN), 45 superficial spreading melanomas (SSMs), and 15 subcutaneous melanoma metastases were immunohistologically assessed using the monoclonal mouse MAP-2ab antibody (Zytomed, Berlin, Germany). The percentage MAP-2 expression of DN and SSMs was significantly increased compared with BN. Moreover, subcutaneous melanoma metastases showed significantly decreased MAP-2 expression compared with DN and SSMs. In SSMs, MAP-2 expression significantly correlated with the Breslow vertical tumor thickness, Clark level, and stage of disease. We observed that MAP-2 is differentially expressed during the development and progression of benign and malignant melanocytic skin lesions. In contrast with the findings of previous studies, our data indicate that MAP-2 is a moderately positive predictor of the progression of SSMs.

Involvement of microtubule-associated protein 2 (MAP2) in oral cancer cell motility: a novel biological function of MAP2 in non-neuronal cells

Microtubule-associated protein 2 (MAP2) has been better known for its well-defined role primarily in neurite outgrowth during neuronal development. However, the biological functions of MAP2 in non-neuronal cells, such as epithelial cells, remain largely unknown. In the present study, we sought to investigate the cellular functions of MAP2 by separately establishing stable expression of two MAP2 isoforms, MAP2A and MAP2C, in oral squamous cell carcinoma, Ca9-22. Ectopic expression of MAP2A or MAP2C results in microtubule bundling predominantly at the cell periphery. Remarkably, overexpression of MAP2A but not MAP2C significantly promotes migration of Ca9-22 cells, whereas knockdown of MAP2A expression by specific siRNA oligos dramatically decreases cell migration of HaCaT, an immortalized keratinocyte cell line with abundant endogenous MAP2A. Furthermore, by immunohistochemical studies, MAP2A was shown to highly and selectively express in invasive oral cancer tissues, consistent with its motility-promoting cellular function revealed through in vitro assays. Thus, our findings have not only identified a novel role of MAP2 in non-neuronal cells, but also provided the first implication of MAP2 in malignant oral cancer tissues.

Microtubule-associated proteins as targets in cancer chemotherapy

Natural and synthetic compounds that disrupt microtubule dynamics are among the most successful and widely used cancer chemotherapeutic agents. However, lack of reliable markers that predict sensitivity of cancers to these agents and development of resistance remain vexing issues. There is accumulating evidence that a family of cellular proteins that are associated with and alter the dynamics of microtubules can determine sensitivity of cancer cells to microtubule-targeting agents and play a role in tumor cell resistance to these agents. This growing family of microtubule-associated proteins (MAP) includes products of oncogenes, tumor suppressors, and apoptosis regulators, suggesting that alteration of microtubule dynamics may be one of the critical events in tumorigenesis and tumor progression. The objective of this review is to integrate the knowledge on these seemingly unrelated proteins that share a common function and examine their relevance to microtubule-targeting therapies and highlight MAPs-tubulin-drug interactions as a novel avenue for new drug discovery. Based on the available evidence, we propose that rational microtubule-targeting cancer therapeutic approaches should ideally include proteomic profiling of tumor MAPs before administration of microtubule-stabilizing/destabilizing agents preferentially in combination with agents that modulate the expression of relevant MAPs.

Echinoderm microtubule-associated protein like protein 4, a member of the echinoderm microtubule-associated protein family, stabilizes microtubules

Echinoderm microtubule-associated protein (EMAP) is the major microtubule binding protein in dividing sea urchin (Strongylocentrotus purpuratus) eggs. Echinoderm microtubule-associated protein like protein 4 (Eml4, restrictedly overexpressed proliferation-associated protein 120 kDa (Ropp120)) is one of the five mammalian EMAP homologues, the cellular function of which remains to be elucidated. In our first set of experiments we determined the spatio-temporal expression pattern of Eml4 in mouse brain. Our results demonstrate that Eml4 is a highly developmentally regulated gene with high expression levels in the developing nervous system of E11 embryos declining to low levels in adult. Spatially, Eml4 expression becomes restricted to the olfactory bulb, hippocampus and cerebellum. Transient transfection of a fusion construct of full-length mouse Eml4 with green fluorescent protein (GFP-Eml4) into Cos7 and HeLa cells resulted in colocalization of GFP-Eml4 with microtubules. This colocalization was observed both with microtubules of non-dividing cells and with the mitotic spindle of dividing cells. In addition, transient overexpression of GFP-Eml4 in Cos7 cells resulted in microtubules that were resistant to nocodazole treatment suggesting that Eml4 stabilizes microtubules. A consequence of microtubule stabilization is a net reduction in the amount of free tubulin. Microtubule stabilizing proteins therefore are expected to indirectly decrease the microtubule growth rate. Indeed, transient transfection of GFP-Eml4 resulted in a marked decrease in the microtubule growth rate, which is in line with our hypothesis that Eml4 functions as a microtubule stabilizing protein. In summary, our results suggest that Eml4 is a developmentally regulated protein that colocalizes with and stabilizes microtubules.

Microtubule-associated protein 2, a marker of neuronal differentiation, induces mitotic defects, inhibits growth of melanoma cells, and predicts metastatic potential of cutaneous melanoma

Dynamic instability of microtubules is critical for mitotic spindle assembly and disassembly during cell division, especially in rapidly dividing tumor cells. Microtubule-associated proteins (MAPs) are a family of proteins that influence this property. We showed previously that MAP2, a neuron-specific protein that stabilizes microtubules in the dendrites of postmitotic neurons, is induced in primary cutaneous melanoma but is absent in metastatic melanomas. We proposed that induction of a microtubule-stabilizing protein in primary melanoma could disrupt the dynamic instability of microtubules, inhibit cell division and prevent or delay tumor progression. Here we show, by Kaplan-Meier survival and multivariate Cox regression analysis, that patients diagnosed with MAP2+ primary melanomas have significantly better metastatic disease-free survival than those with MAP2- disease. Investigation of the mechanisms that underlie the effect of MAP2 on melanoma progression showed that MAP2 expression in metastatic melanoma cell lines leads to microtubule stabilization, cell cycle arrest in G2-M phase and growth inhibition. Disruption of microtubule dynamics by MAP2 resulted in multipolar mitotic spindles, defects in cytokinesis and accumulation of cells with large nuclei, similar to those seen in vivo in MAP2+ primary melanomas cells. These data suggest that ectopic activation of a neuronal differentiation gene in melanoma during early tumor progression inhibits cell division and correlates with inhibition or delay of metastasis.

Fyn phosphorylates human MAP-2c on tyrosine 67

The Src homology 3 (SH3) domain of Fyn binds to a conserved PXXP motif on microtubule-associated protein-2. Co-transfections into COS7 cells and in vitro kinase assays performed with Fyn and wild-type, or mutant MAP-2c, determined that Fyn phosphorylated MAP-2c on tyrosine 67. The phosphorylation generated a consensus sequence for the binding of the SH2 domain of Grb2 (pYSN). Pull-down assays with SH2-Grb2 from human fetal brain homogenates, and co-immunoprecipitation of Grb2 and MAP-2 confirmed the interaction in vivo, and demonstrated that MAP-2c is tyrosine-phosphorylated in human fetal brain. Filter overlay assays confirmed that the SH2 domain of Grb2 binds to human MAP-2c following incubation with active Fyn. Enzyme-linked immunosorbent assays confirmed the interaction between the SH2 domain of Grb2 and a tyrosine-phosphorylated MAP-2 peptide spanning the pY(67)SN motif. Thus, MAP-2c can directly recruit multiple signaling proteins important for central nervous system development.

MAP-2e, a novel MAP-2 isoform, is expressed in gliomas and delineates tumor architecture and patterns of infiltration

The MAP-2 isoform containing exon 13 (MAP-2e) is expressed in human fetal development as early as 15 gestational weeks and parallels oligodendrocyte maturation. MAP-2e is down-regulated following myelination and is expressed in few cells in the adult central nervous system (CNS). To determine whether CNS tumors express MAP-2e, we screened 122 archival, paraffin-embedded adult and pediatric tumors of the CNS and non-CNS. All oligodendrogliomas were positive and extensive staining was observed in glioblastomas, various malignant gliomas and dysembryoplastic neuroepithelial tumors. MAP-2e was not expressed in non-CNS tumors or neuroblastomas. Thus. neuroectodermal tumors that have glial characteristics express this developmental marker of immature glia. Analysis of oligodendrogliomas demonstrated numerous cell morphologies from round cells with no processes to cells with single or multiple processes. MAP-2e immunostaining also delineated tumor invasion into adjacent gray and white matter, indicating that MAP-2e appears to be a useful marker for examining the infiltration of malignant cells into surrounding tissue.

Regulation of microtubule-associated proteins

Microtubule-associated proteins (MAPs) function to regulate the assembly dynamics and organization of microtubule polymers. Upstream regulation of MAP activities is the major mechanism used by cells to modify and control microtubule assembly and organization. This review summarizes the functional activities of MAPs found in animal cells and discusses how these MAPs are regulated. Mechanisms controlling gene expression, isoform-specific expression, protein localization, phosphorylation, and degradation are discussed. Additional regulatory mechanisms include synergy or competition between MAPs and the activities of cofactors or binding partners. For each MAP it is likely that regulation in vivo reflects a composite of multiple regulatory mechanisms.

Binding of Fyn to MAP-2c through an SH3 binding domain. Regulation of the interaction by ERK2

Microtubule-associated protein 2 (MAP-2) isoforms are developmentally expressed in the nervous system and contain a number of functional domains. Adjacent to the first repeat of the microtubule-binding domain is an RTPPKSP motif for binding SH3 domains. To identify SH3-containing proteins that interact with MAP-2, transfections, filter overlay assays, glutathione S-transferase (GST)-mediated binding assays, co-immunoprecipitations and enzyme-linked immunosorbent assays were performed. Transfections of MAP-2a, MAP-2b, and MAP-2c constructs into COS7 cells, followed by incubation of the cell lysates with SH3-GST fusion proteins, determined that the strongest interaction was between MAP-2c and the non-receptor tyrosine kinase Fyn; however, MAP-2b and MAP-2c also bound to Grb2. Co-immunoprecipitation of Fyn and MAP-2c from human fetal homogenates confirmed the interaction in vivo. MAP-2 synthetic peptides spanning the RTPPKSP motif bound to Fyn, and the interaction was regulated by phosphorylation. Co-transfections with MAP-2c and the extracellular signal-regulated kinase 2 (ERK2) demonstrated that MAP-2c is threonine/serine-phosphorylated on its RTPPKSP motif and that threonine phosphorylation abolished the MAP-2c/Fyn binding. Kinase assays and co-transfection of MAP-2c and Fyn confirmed that Fyn tyrosine kinase phosphorylates MAP-2c. Thus, the activation of signaling pathways may regulate cytoskeletal dynamics by altering the state of phosphorylation of MAP-2 by both ERK2 and Fyn kinase.

GSK3beta-mediated phosphorylation of the microtubule-associated protein 2C (MAP2C) prevents microtubule bundling

A major determinant of neuronal morphology is the cytoskeleton. And one of the main regulatory mechanisms of cytoskeletal proteins is the modification of their phosphorylation state via changes in the relative activities of protein kinases and phosphatases in neurons. In particular, the microtubule-associated protein 2 (MAP2) family of proteins are abundant cytoskeletal components predominantly expressed in neurons and have been found to be substrates for most of protein kinases and phosphatases present in neurons, including glycogen-synthase kinase 3 (GSK3). It has been suggested that changes in GSK3-mediated MAP phosphorylation may modify MT stability and could control neuronal development. We have previously shown that MAP2 is phosphorylated in vitro and in situ by GSK3 at Thr1620 and Thr1623, located in the proline-rich region of MAP2 and recognized by antibody 305. However, the function of the phosphorylation of this site of MAP2 is still unknown. In this study, non-neuronal COS-1 cells have been co-transfected with cDNAs encoding MAP2C and either wild type or mutated GSK3beta to analyze possible effects on microtubule stability and on the association of MAP2 with microtubules. We have found that GSK3beta phosphorylates MAP2C in co-transfected cells. Moreover, this phosphorylation is inhibited by the specific GSK3 inhibitor lithium chloride. Additionally, the formation of microtubule bundles, which is observed after transfection with MAP2C, was decreased when MAP2C was co-transfected with GSK3beta wild type. Microtubule bundles were not observed in cells expressing MAP2C phosphorylated at the site recognized by antibody 305. The absence of microtubule bundles was reverted after treatment of MAP2C/GSK3beta wild type transfected cells with lithium chloride. Highly phosphorylated MAP2C species, which were phosphorylated at the site recognized by antibody 305, appeared in cells co-transfected with MAP2C and GSK3beta wild type. Interestingly, these MAP2C species were enriched in cytoskeleton-unbound protein preparations. These data suggests that GSK3-mediated phosphorylation of MAP2 may modify its binding to microtubules and regulate microtubule stability.

Effects of euxanthone on neuronal differentiation

The growth inhibitory and differentiation inducing effects of euxanthone (1,7-dihydroxyxanthone) from the medicinal plant Polygala caudata on the neuroblastoma (Neural 2A, subclone BU-1) were investigated. At the concentration range of 0-100 microM, euxanthone inhibits the growth of BU-1 cells in a dose dependent manner. The 50% growth inhibitory concentration (IC50) was 41 microM. Significant induction of morphological differentiation and neurite growth was observed at the concentration of 100 microM. Frequency of proliferative neuroblastoma cells was determined after induction of differentiation. The frequency of proliferating BU-1 cells was markedly reduced from 1/1.1 to <1/99. Confocal microscopy also confirmed that the morphological differentiation of BU-1 was associated with the expression of neurite specific marker MAP-2 protein in neurites. These data suggest that euxanthone may be one of the neuropharmacological active compounds in the medicinal plant Polygala caudata.

Functional roles for fatty acylated amino-terminal domains in subcellular localization

Several membrane-associating signals, including covalently linked fatty acids, are found in various combinations at the N termini of signaling proteins. The function of these combinations was investigated by appending fatty acylated N-terminal sequences to green fluorescent protein (GFP). Myristoylated plus mono/dipalmitoylated GFP chimeras and a GFP chimera containing a myristoylated plus a polybasic domain were localized similarly to the plasma membrane and endosomal vesicles, but not to the nucleus. Myristoylated, nonpalmitoylated mutant chimeric GFPs were localized to intracellular membranes, including endosomes and the endoplasmic reticulum, and were absent from the plasma membrane, the Golgi, and the nucleus. Dually palmitoylated GFP was localized to the plasma membrane and the Golgi region, but it was not detected in endosomes. Nonacylated GFP chimeras, as well as GFP, showed cytosolic and nuclear distribution. Our results demonstrate that myristoylation is sufficient to exclude GFP from the nucleus and associate with intracellular membranes, but plasma membrane localization requires a second signal, namely palmitoylation or a polybasic domain. The similarity in localization conferred by the various myristoylated and palmitoylated/polybasic sequences suggests that biophysical properties of acylated sequences and biological membranes are key determinants in proper membrane selection. However, dual palmitoylation in the absence of myristoylation conferred significant differences in localization, suggesting that multiple palmitoylation sites and/or enzymes may exist.

Making sense of the multiple MAP-2 transcripts and their role in the neuron

Microtubule-associated protein-2 (MAP-2) is a family of heat-stable, phosphoproteins expressed predominantly in the cell body and dendrites of neurons. Three major MAP-2 isoforms, (MAP-2a, MAP-2b, MAP-2c) are differentially expressed during the development of the nervous system and have an important role in microtubule dynamics. Several MAP-2 cDNA clones that correspond to the major MAP-2 transcripts and additional, novel MAP-2 transcripts expressed in the CNS and PNS have been characterized. The transcripts result from the alternative splicing of a single MAP-2 gene consisting of 20 exons. Studies are now being directed toward understanding the role of the multiple MAP-2 forms that contain novel exons in the nervous system. The expression, localization, and possible functions of the newly identified spliced forms are the focus of this review.