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At least 109 records · Page 6Linked to original sources
PubMed2006

MUTYH-associated polyposis--from defect in base excision repair to clinical genetic testing.

Established predisposition genes account for only a small proportion of familial colorectal cancer. Recently, it has been shown that germline mutations in MUTYH predispose to MUTYH-associated polyposis (MAP), an autosomal recessive disorder characterised by multiple colorectal adenomas and carcinomas. MUTYH functions as a base excision repair DNA glycosylase that excises adenines misincorporated opposite 8-oxo-7,8-dihydro-2'-deoxyguanosine, one of the most stable products of oxidative DNA damage. It is the failure to correct this mispair that is thought to give rise to the characteristic signature of G:C-->T:A mutations found in MAP-associated tumours. Here, we review the germline mutation spectrum at the MUTYH locus (comprising 30 truncating and 55 missense/inframe insertion/deletion variants) and the molecular mechanism and biochemical defect(s) underlying this disorder. We also discuss the application of molecular genetic analysis of MUTYH in clinical practice.

Adenoma↗
PubMed2026

Gastric amphicrine carcinoma in the stomach: an unexpected presentation of MUTYH-associated polyposis.

Amphicrine carcinomas of the stomach, defined by dual exocrine and neuroendocrine differentiation within the same neoplastic cell, are exceedingly rare. MUTYH-associated polyposis (MAP) is an autosomal recessive polyposis syndrome characterized by multiple colorectal adenomas and variable upper gastrointestinal involvement; however, amphicrine carcinomas have not been previously documented in this setting. We report a gastric amphicrine carcinoma arising in the background of extensive fundic gland polyposis in a patient with MAP. Endoscopy revealed a 3.5-cm flat elevated lesion in the gastric fundus amid extensive fundic gland polyposis. Histologically, the tumor consisted of a single population of cells exhibiting combined glandular and neuroendocrine differentiation without zonal or biphasic architecture, and many of these cells demonstrated true amphicrine morphology. Immunohistochemistry confirmed co-expression of cytokeratin and the neuroendocrine markers chromogranin A and synaptophysin in the same cell population. Germline targeted next-generation sequencing identified biallelic MUTYH variants in trans (c.733C>T, p.Arg245Cys [likely pathogenic]; c.842C>T, p.Ala281Val [variant of uncertain significance]), supporting a diagnosis of MAP. To our knowledge, this is the first reported case of a gastric amphicrine carcinoma in a MAP patient, expanding the spectrum of MAP-associated upper gastrointestinal neoplasia and underscoring the importance of vigilant endoscopic surveillance in hereditary polyposis syndromes.

Carcinoma↗
PubMed1986

Cellular distribution of a protein related to neuronal microtubule-associated protein MAP-2 in Leydig cells.

A monoclonal antibody to neuronal microtubule-associated protein MAP-2 was produced. Immunoblotting of lysates of cultured cells revealed that the antibody, called MA-01, bound to a protein of Mr 210 kDa. Double immunofluorescence microscopy showed that the antibody stained microtubules. No fibrillar structures were observed in cells treated with Colcemid, but the antibody stained vinblastine paracrystals. In cytochalasin B-treated Leydig cells, MA-01 antibody stained star-like structures that codistributed with actin patches and with a star-like arrangement of vimentin. These observations indicate that the protein immunologically related to MAP-2 in Leydig cells could be involved in the interaction of microtubules with intermediate filaments or microfilaments.

Actins↗
PubMed1987

Binding of mammalian brain microtubule-associated proteins (MAPs) to insect ovarian microtubules.

In this study we have applied microtubule-associated proteins (MAPs) from mammalian brain to both native and reassembled insect ovarian microtubules. Such microtubules, which are normally smooth walled, become decorated with projections similar to those observed when mammalian brain MAPs are added back to assembling or assembled mammalian brain microtubules. The mammalian MAPs were also detected as components of insect microtubules when analyzed by polyacrylamide gel electrophoresis. Our observations suggest that mammalian brain MAPs have common binding sites on microtubules from two widely different sources and indicate the degree of evolutionary conservation of such sites.

Animals↗
PubMed2001

Characterization of two promoters that regulate alternative transcripts in the microtubule-associated protein (MAP) 1A gene.

We cloned and characterized the mouse gene for microtubule-associated protein (MAP) 1A, an important protein for neuronal morphology and mitotic spindle formation. We also investigated the 5' untranslated region of the gene to characterize the promoter units. Two alternative transcripts different in the 5' region were identified by 5' RACE. Both transcripts were principally observed in the brain. Genomic cloning revealed that exons 1, 2, and 4 generate the 5' part of a long transcript, whereas exons 3 and 4 generate a short transcript. Putative 5' and intronic promoters flanking exons 1 and 3, respectively, are GC-rich and lack a canonical TATA box. DNase I footprinting from mouse cells revealed that several potential cis-elements were occupied by nuclear proteins. A reporter assay system in conjunction with a number of deletion and mutation constructs was used to test the two putative promoters. Both putative promoters showed transactivity and their function was dependent upon Sp1 sites. In addition, an NF-1 site, an HNF3B site, and an AP-1/ATF site were necessary for basal promoter activity of the intronic promoter. Our data provide insight into the regulatory mechanisms that govern the expression of the MAP1A gene.

3T3 Cells↗
PubMed1997

Differential expression of microtubule associated protein MAP-2 in developing cochleovestibular neurons and its modulation by neurotrophin-3.

Microtubule associated proteins (MAPs) are essential cytoskeletal proteins in developing neurons. The present study was undertaken to analyze the expression of MAP2 and its isoforms (a,b,c) during the embryonal and early post-hatching development of chicken cochleovestibular ganglion (CVG) neurons. Moreover, we have investigated MAP2 expression in primary cultures of CVG neurons, and whether it is regulated by neurotrophin-3 (NT3). The expression of MAP2 immunoreactivity (IR) was studied using both Western blot and immunohistochemistry on tissue sections and primary cultures. In vivo MAP2c was expressed from incubation day 4 (E4) to E10, and MAP2b was found in all embryonal stages studied and at post-hatching day 10 (P10), whereas MAP2a was restricted to the post-hatching periods. The cellular localization of IR was in the neuronal perikarya and their peripheral processes (dendrites) but not in axons. Primary cultures matched the in vivo pattern of MAP2 expression, and IR was localized in neuronal cell bodies and the initial segment of the neuronal processes. Exogenous NT3 regulated the expression of MAP2 isoforms in a dose dependent manner. At the survival dose of 0.5 ng/ml NT3, the main MAP2 expression was MAP2c. Conversely, at the neuritogenic dose of 5 ng/ml NT3 increased MAP2b and MAP2a expression, but not MAP2c. The present results demonstrate that MAP2 isoforms are developmentally regulated, thus suggesting that each isoform is specifically involved in CVG neuron maturation. Furthermore, we provide evidence of MAP2 regulation in culture by the neurotrophic factor NT3.

Animals↗
PubMed1999

E-MAP-115 (ensconsin) associates dynamically with microtubules in vivo and is not a physiological modulator of microtubule dynamics.

Microtubule-associated proteins (MAPs) have been hypothesized to regulate microtubule dynamics and/or functions. To test hypotheses concerning E-MAP-115 (ensconsin) function, we prepared stable cell lines expressing conjugates in which the full-length MAP (Ensc) or its microtubule-binding domain (EMTB) was conjugated to one or more green fluorescent protein (GFP) molecules. Because both distribution and microtubule-binding properties of GFP-Ensc, GFP-EMTB, and 2x, 3x, or 4xGFP-EMTB chimeras all appeared to be identical to those of endogenous E-MAP-115 (ensconsin), we used the 2xGFP-EMTB molecule as a reporter for the behavior and microtubule-binding function of endogenous MAP. Dual wavelength time-lapse fluorescence imaging of 2xGFP-EMTB in cells microinjected with labeled tubulin revealed that this GFP-MAP chimera associated with the lattice of all microtubules immediately upon polymerization and dissociated concomitant with depolymerization, suggesting that dynamics of MAP:microtubule interactions were at least as rapid as tubulin:microtubule dynamics in the polymerization reaction. Presence of both GFP-EMTB chimeras and endogenous E-MAP-115 (ensconsin) along apparently all cellular microtubules at all cell cycle stages suggested that the MAP might function in modulating stability or dynamics of microtubules, a capability shown previously in transiently transfected cells. Although cells with extremely high expression levels of GFP-EMTB chimera exhibited stabilized microtubules, cells expressing four to ten times the physiological level of endogenous MAP exhibited microtubule dynamics indistinguishable from those of untransfected cells. This result shows that E-MAP-115 (ensconsin) is unlikely to function as a microtubule stabilizer in vivo. Instead, this MAP most likely serves to modulate microtubule functions or interactions with other cytoskeletal elements.

Female↗
PubMed2003

Localization of microtubule-associated protein (MAP) 1B in the postsynaptic densities of the rat cerebral cortex.

1. Although microtubule-associated protein (MAP) 1B and its phosphorylation have been suggested to be important for synapse formation among cortical neurons, the localization of MAP1B in synapses has not yet been confirmed. In this report, we examine the localization of MAP1B in synaptic regions. 2. The localization of MAP1B was observed by immunohistochemical and electron microscopic techniques using specific antibodies against MAP1B. 3. MAP1B immunoreactivities were widely distributed in the cerebral cortex and were observed in the postsynaptic area but not in presynaptic terminals. 4. These synapses were classified as the asymmetrical type. 5. Only some synapses exhibited MAP1B immunoreactivities. MAP1B-immunopositive synapses accounted for about half of the total synapses. 6. Such a localization suggests MAP1B's important roles in synaptic functions.

Animals↗
PubMedDate not supplied

Retrograde transport by the microtubule-associated protein MAP 1C.

Microtubules are involved in several forms of intracellular motility, including mitosis and organelle movement. Fast axonal transport is a highly ordered form of organelle motility that operates in both the anterograde (outwards from the cell body) and retrograde (from the periphery towards the cell body) direction. Similar microtubule-associated movement is observed in non-neuronal cells, and might be involved in secretion, endocytosis and the positioning of organelles within the cell. Kinesin is a mechanochemical protein that produces force along microtubules in an anterograde direction. We recently found that the brain microtubule-associated protein MAP 1C (ref. 7) is a microtubule-activated ATPase and, like kinesin, can translocate microtubules in an in vitro assay for microtubule-associated motility. MAP 1C seemed to be related to the ciliary and flagellar ATPase, dynein, which is thought to produce force in a direction opposite to that observed for kinesin. Here we report that MAP 1C, in fact, acts in a direction opposite to kinesin, and has the properties of a retrograde translocator.

Animals↗
PubMed1991

Dependency of microtubule-associated proteins (MAPs) for tubulin stability and assembly; use of estramustine phosphate in the study of microtubules.

Microtubule-associated proteins (MAPs) were separated from tubulin with several different methods. The ability of the isolated MAPs to reinduce assembly of phosphocellulose purified tubulin differed markedly between the different methods. MAPs isolated by addition of 0.35 M NaCl to taxol-stabilized microtubules stimulated tubulin assembly most effectively, while addition of 0.6 M NaCl produced MAPs with a substantially lower ability to stimulate tubulin assembly. The second best preparation was achieved with phosphocellulose chromatographic separation of MAPs with 0.6 M NaCl elution. The addition of estramustine phosphate to microtubules reconstituted of MAPs prepared by 0.35 M NaCl or phosphocellulose chromatography, induced less disassembly than for microtubules assembled from unseparated proteins, and was almost without effect on microtubules reconstituted from MAPs prepared by taxol and 0.6 M NaCl. Estramustine phosphate binds to the tubulin binding part of the MAPs, and the results do therefore indicate that the MAPs are altered by the separation methods. Since the MAPs are regarded as highly stable molecules, one probable alteration could be aggregation of the MAPs, as also indicated by the results. The purified tubulin itself seemed not to be affected by the phosphocellulose purification, since the microtubule proteins were unchanged by the low buffer strenght used during the cromatography. However, the assembly competence after a prolonged incubation of the microtubule proteins at 4 degrees C was dependent on intact bindings between the tubulin and MAPs.

Alkaloids↗
PubMed1985

Expression of microtubule-associated proteins, MAP-1 and MAP-2, in human neuroblastomas and differential diagnosis of immature neuroblasts.

The expression of microtubule-associated proteins, MAP-1 and MAP-2, was studied in human neuroblastomas at various developmental stages using the immuno-alkaline-phosphatase technique and immunofluorescence microscopy. Of 15 cases examined, including grade I, grade II, and grade III neuroblastomas (M. Hughes, H. B. Marsden, and M. K. Palmer, Cancer 34:1706, 1974), rabbit antibodies raised against individual MAP-1 and MAP-2 from mammalian brain showed strong reactions with the whole spectrum of tumor cells including the immature small neuroblasts, partially mature neuroblasts, neurofibrils, and ganglion cells. Antibodies to alpha- and beta-tubulin showed similar staining patterns. In contrast, antibodies to the Mr = 200.000 neurofilament protein were reactive only with the mature and partially mature tumor cells, as well as with neurofibrils, but not with immature "round-cell" neuroblasts. Other types of round-cell tumors examined, including several cases of Ewing's sarcoma, undifferentiated rhabdomyosarcoma, and malignant lymphoma, showed no reaction with antibodies to MAP-1 and MAP-2. These tumors were reactive, however, with antibodies to various other tumor-specific as well as nonspecific antigens. It is concluded that antibodies to neuronal MAPs provide a valuable new tool for the differential diagnosis of neuroblastomas.

Adolescent↗
PubMed1990

Common antigenic determinants of the tubulin binding domains of the microtubule-associated proteins MAP-2 and tau.

The structural-functional aspects of the tubulin binding domain on the microtubule-associated protein MAP-2, and its relationship with the tubulin binding domain on tau, were studied using anti-idiotypic antibodies that react specifically with the epitope(s) on MAPs involved in their interaction with tubulin in addition to other tau and MAP-2 specific antibodies. Previous studies showed that MAP-2 and tau share common binding sites on tubulin defined by the peptide sequences alpha (430-441) and beta (422-434) of tubulin subunits. Furthermore, binding experiments revealed the existence of multiple sites for the interaction of the alpha- and beta-tubulin peptides with MAP-2 and tau. Most recent studies showed that the synthetic tau peptide Val187-Gly204 (VRSKIGSTENLKHQPGGG) from the repetitive sequence on tau defines a tubulin binding site on tau. Our present immunological studies using anti-idiotypic antibodies which interact with the synthetic tau peptide and antibodies against the Val187-Gly204 tau peptide indicate that MAP-2 and tau share common antigenic determinants at the level of their respective tubulin binding domains. These antigenic determinants appear to be present in the 35 kDa tubulin binding fragment of MAP-2 and in 18-20 kDa chymotryptic fragments containing the tubulin binding site(s) on MAP-2. These findings, along with structural information on these proteins, provide strong evidence in favor of the hypothesis that tubulin binding domains on MAP-2 and tau share similar structural features.

Amino Acid Sequence↗
PubMed1992

Estramustine-phosphate binds to a tubulin binding domain on microtubule-associated proteins MAP-2 and tau.

Estramustine-phosphate (EMP), a phosphorylated conjugate of estradiol and nor-nitrogen mustard binds to microtubule-associated proteins MAP-2 and tau. It was shown that this estramustine derivative inhibits the binding of the C-terminal tubulin peptide beta-(422-434) to both MAP-2 and tau. This tubulin segment constitutes a main binding domain for these microtubule-associated proteins. Interestingly, estramustine-phosphate interacted with the synthetic tau peptides V187-G204 and V218-G235, representing two major repeats within the conserved microtubule-binding domain on tau and also on MAP-2. This observation was corroborated by the inhibitory effects of estramustine-phosphate on the tau peptide-induced tubulin assembly into microtubules. On the other hand, the nonphosphorylated drug estramustine failed to block the MAP peptide-induced assembly, indicating that the negatively charged phosphate moiety of estramustine-phosphate is of importance for its inhibitory effect. These findings suggest that the molecular sites for the action of estramustine-phosphate are located within the microtubule binding domains on tau and MAP-2.

Amino Acid Sequence↗
PubMed1993

Organization of microtubules in axonal growth cones: a role for microtubule-associated protein MAP 1B.

Neuronal growth cones guide growing axons and dendrites (neurites) through developing embryos by detecting extrinsic guidance cues and transducing the signal into changes in motile behaviour. In this brief review, the role of the growth cone cytoskeleton in these events, in particular the microtubules, is discussed. Microtubules in the neurite are mainly bundled into fascicles whereas on entering the growth cone they diverge from each other and traverse the central (C)-domain of the growth cone. Occasionally, individual microtubules extend as far as the peripheral (P)-domain and may even enter filopodia. Microtubules in the growth cone are probably dynamically unstable, exchanging dimer with a large pool of soluble tubulin. It is proposed that the 'capture' of dynamically unstable microtubules by filopodial actin filament bundles is a crucial step underlying directed growth. Localised assembly of microtubules at the growth cone, rather than at the cell body followed by transport of polymer to the growth cone, may facilitate the delivery of material to specific regions of the growth cone and hence allow vectorial growth. Bundling of microtubules and capture of microtubules by filopodia both imply roles for microtubule-associated proteins (MAPs). Several microtubule-associated proteins are present within growth cones, including MAP 1B, MAP2 and tau. Recent experiments point toward a phosphorylated form of MAP 1B as an important component in neurite elongation and in particular in the bundling of microtubules in the growth cone.

Animals↗
PubMed1981

Microtubule-associated proteins (MAPs) and the organization of actin filaments in vitro.

When purified muscle actin was mixed with microtubule-associated proteins (MAPs) prepared from brain microtubules assembled in vitro, actin filaments were organized into discrete bundles, 26 nm in diameter. MAP-2 was the principal protein necessary for the formation of the bundles. Analysis of MAP-actin bundle formation by sedimentation and electrophoresis revealed the bundles to be composed of approximately 20% MAP-2 and 80% actin by weight. Transverse striations were observed to occur at 28-nm intervals along negatively stained MAP-actin bundles, and short projections, approximately 12 nm long and spaced at 28-nm intervals, were resolved by high-resolution metal shadowing. The formation of MAP-actin bundles was inhibited by millimolar concentrations of ATP, AMP-PCP (beta, gamma-methylene-adenosine triphosphate), and pyrophosphate but not by AMP, ADP, or GTP. The addition of ATP to a solution containing MAP-actin bundles resulted in the dissociation of the bundles into individual actin filaments; discrete particles, presumably MAP-2, were periodically attached along the splayed filaments. These results demonstrate that MAPs can bind to actin filaments and can induce the reversible formation of actin filament bundles in vitro.

Actins↗
PubMed2003

Selection and evaluation of tagging SNPs in the neuronal-sodium-channel gene SCN1A: implications for linkage-disequilibrium gene mapping.

Association studies are widely seen as the most promising approach for finding polymorphisms that influence genetically complex traits, such as common diseases and responses to their treatment. Considerable interest has therefore recently focused on the development of methods that efficiently screen genomic regions or whole genomes for gene variants associated with complex phenotypes. One key element in this search is the use of linkage disequilibrium to gain maximal information from typing a selected subset of highly informative single-nucleotide polymorphism (SNP) markers, now often called "tagging SNPs" (tSNPs). Probably the most common approach to linkage-disequilibrium gene mapping involves a three-step program: (1) characterization of the haplotype structure in candidate genes or genomic regions of interest, (2) identification of tSNPs sufficient to represent the most common haplotypes, and (3) typing of tSNPs in clinical material. Early definitions of tSNPs focused on the amount of haplotype diversity that they explained. To select tSNPs that would have maximal power in a genetic association study, however, we have developed optimization criteria based on the r2 measure of association and have compared these with other criteria based on the haplotype diversity. To evaluate the full program and to assess how well the selected tags are likely to perform, we have determined the haplotype structure and have assessed tSNPs in the SCN1A gene, an important candidate gene for sporadic epilepsy. We find that as few as four tSNPs are predicted to maintain a consistently high r2 value with all other common SNPs in the gene, indicating that the tags could be used in an association study with only a modest reduction in power relative to direct assays of all common SNPs. This implies that very large case-control studies can be screened for variation in hundreds of candidate genes with manageable experimental effort, once tSNPs are identified. However, our results also show that tSNPs identified in one population may not necessarily perform well in another, indicating that the preliminary study to identify tSNPs and the later case-control study should be performed in the same population. Our results also indicate that tSNPs will not easily identify discrepant SNPs, which lie on importantly discriminating but apparently short genealogical branches. This could significantly complicate tagging approaches for phenotypes influenced by variants that have experienced positive selection.

Adult↗
PubMed1998

Morphological transformation of liposomes caused by assembly of encapsulated tubulin and determination of shape by microtubule-associated proteins (MAPs).

To examine the role of cytoskeletons in cellular morphogenesis, we generated liposomes encapsulating tubulin, with or without microtubule-associated proteins (MAPs), and observed their transformation using dark-field microscopy. When tubulin was polymerized with MAPs in liposomes, liposomes were transformed into a "bipolar" shape with a central sphere and two tubular membrane protrusions that aligned in a straight line. On the other hand, when pure tubulin was polymerized in liposomes without MAPs, they initially transformed into a bipolar shape but subsequently re-transformed into a "monopolar" shape, i.e. a sphere with only one straight tubular portion. This re-transformation occurred in two ways: first, by shortening of one of the tubular portions due to microtubule disassembly; or second, by fluctuation of the central sphere toward one of the ends without shortening of the tube portion. MAPs prevented this re-transformation, and their role in stabilizing the shape of transformed liposomes was studied by the co-sedimentation method. The results show that MAPs, particularly MAP1 and MAP2, mediate binding between microtubules and the liposomal membrane. However, MAP2 by itself did not bind to liposomes, but was able to stabilize bipolar liposomes. This stabilization is caused not only by direct links between microtubules and liposomes, but also by prevention of Brownian motion of microtubules through an increase in friction.

Liposomes↗