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PubMed1987

Choroid plexus tumors. An immunocytochemical study with particular reference to the coexpression of intermediate filament proteins.

Sixteen choroid plexus tumors (CPTs) have been investigated for the localization of different immunocytochemical markers of epithelial and nonepithelial nature, namely, simple epithelial-type cytokeratins, vimentin, glial fibrillary acidic protein (GFAP), a panepithelial antigen defined by the lu-5 monoclonal antibody (lu-5 antigen), S-100 protein, and epithelial membrane antigen (EMA). Intermediate filament proteins have been identified in paraffin sections of 14 of 16 cases (87.5%). In all these tumors, cytokeratins and vimentin were constantly coexpressed by the neoplastic cells, in a manner similar to that of the cells lining normal choroid plexus. In 7 of these 14 cases, in addition to cytokeratins and vimentin, the neoplastic cells were shown to coexpress GFAP, which is not synthesized by their normal cell counterpart. The appearance of GFAP immunoreactivity in CPTs might be related to an ependymal differentiation of the neoplastic cells, because normal ependyma and ependymomas constantly coexpress GFAP and vimentin. The simultaneous expression of three distinct intermediate filament proteins by the same neoplastic cells is an exceedingly rare phenomenon, which has never been reported by double labeling technique in neoplasms of the central nervous system. Despite the complex antigenic profile of the CPT, which includes immunoreactivity for lu-5 antigen, S-100 protein, and EMA in most of the cases, positivity for three different epithelial markers indicates that these tumors have an epithelial nature. Moreover, the immunocytochemical typing of CPT with the panel of antibodies used in the current investigation allows differentiation from other primary and metastatic central nervous system tumors.

Antibodies, Monoclonal↗
PubMed1993

The 47-kD lens-specific protein phakinin is a tailless intermediate filament protein and an assembly partner of filensin.

In previous studies we have characterized a lens-specific intermediate filament (IF) protein, termed filensin. Filensin does not self-assemble into regular IFs but is known to associate with another 47-kD lens-specific protein which has been suggested to represent its assembly partner. To address this possibility, we cloned and sequenced the cDNA coding for the bovine 47-kD protein which we have termed phakinin (from the greek phi alpha kappa omicron sigma = phakos = lens). The predicted sequence comprises 406 amino acids and shows significant similarity (31.3% identity over 358 residues) to type I cytokeratins. Phakinin possesses a 95-residue, non-helical domain (head) and a 311 amino acid long alpha-helical domain punctuated with heptad repeats (rod). Similar to cytokeratin 19, phakinin lacks a COOH-terminal tail domain and it therefore represents the second known example of a naturally tailless IF protein. Confocal microscopy on frozen lens sections reveals that phakinin colocalizes with filensin and is distributed along the periphery of the lens fiber cells. Quantitative immunoblotting with whole lens fiber cell preparations and fractions of washed lens membranes suggest that the natural stoichiometry of phakinin to filensin is approximately 3:1. Under in vitro conditions, phakinin self-assembles into metastable filamentous structures which tend to aggregate into thick bundles. However, mixing of phakinin and filensin at an optimal ratio of 3:1 yields stable 10-nm filaments which have a smooth surface and are ultrastructurally indistinguishable from "mainstream" IFs. Immunolabeling with specific antibodies shows that these filaments represent phakinin/filensin heteropolymers. Despite its homology to the cytokeratins, phakinin does not coassemble with acidic (type I), or basic (type II) cytokeratins. From these data we conclude that filensin and phakinin are obligate heteropolymers which constitute a new membrane-associated, lens-specific filament system related to, but distinct from the known classes of IFs.

Amino Acid Sequence↗
PubMed1997

Spatial distribution of cytoskeleton intermediate filaments during fetal rat hepatocyte differentiation.

The construction of the liver parenchyma throughout fetal development depends on the elaboration of intercellular contacts between epithelial cells and between epithelial and mesenchymal cells. During this time, the spatial distribution of cytokeratins in hepatocytes shows a striking evolution as demonstrated by confocal microscopy and image analysis. In the early stages of fetal rat development, the liver is mainly a hematopoietic organ and hepatocytes represent fewer than 40% of all liver cells. At this time, cytokeratin filaments are scarce and are randomly distributed inside the cytoplasm. A coexpression of desmin and cytokeratin is found in some cells. Intercellular contacts between epithelial and mesenchymal cells are more numerous than between epithelial cells. Later in development, hepatocytes are arranged in a "muralium duplex" architecture (two-cell-thick sheets). Contacts between hepatocytes become more numerous and bile canaliculi become well developed. The density of cytokeratin filaments increases and appears to be very high near the bile canaliculi. In adult liver, hepatocytes are arranged in a "muralium simplex" architecture. Cytokeratin filaments show a symmetrical distribution in relation to the nuclear region. The highest density of filaments is found near the cytoplasmic membrane. Variations of the spatial distribution of intermediate filaments throughout hepatocyte differentiation were investigated in a pilot study using computerized image analysis. We found significant differences between the filament networks in fetal and adult hepatocytes.

Animals↗
PubMed1983

Effect of microtubules and intermediate filaments on mitochondrial distribution.

The laser dye rhodamine 123 specifically stains mitochondria in living cells and facilitates the observation of changes in mitochondrial distribution in single cells under a variety of experimental conditions. Visualization of mitochondria in a number of cell lines followed by processing of these cells to study different cytoskeletal elements by indirect immunofluorescence, revealed good but not absolute correlation between mitochondria and microtubules or intermediate filaments. Mitochondria and microfilament distribution within the same cell did not show such a correlation. On the basis of observations made by various experimental approaches, we suggest that mitochondrial distribution is under the strong influence of the two systems, microtubules and intermediate filaments. Neither plays an absolute role but one seems able to play a more dominant role in the absence of the other.

Animals↗
PubMed1991

Modifications of the intermediate filament and nuclear matrix networks by the extracellular matrix.

The tissue matrix system is a dynamic, interacting structural network directly linking the nuclear matrix, cytoskeleton and the extracellular matrix. We report here that interaction of normal rat kidney epithelial cells (NRK) and Kirsten-ras transformed rat kidney cells, with an extracellular matrix secreted by tumor cells, causes modifications to the protein composition of the intermediate filament and nuclear matrix networks. The matrix networks are different between normal and transformed cells; however, these alterations by the tumor extracellular matrix are similar in both cell types. These data represent the first report that modification of the extracellular matrix environment can have an effect on the protein composition of the nuclear matrix.

Animals↗
PubMed1988

Modulation of desmin intermediate filament assembly by a monoclonal antibody.

We have used a monoclonal antibody against desmin to examine the assembly of intermediate filaments (IF) from their building blocks, the tetrameric protofilaments. The antibody, designated D76, does not cross react with any other IF proteins (Danto, S.I., and D.A. Fischman. 1984. J. Cell Biol. 98:2179-2191). It binds to a region amino-terminal to cys-324 of avian desmin that is resistant to chymotrypsin and trypsin digestion, and in the electron microscope appears to bind to the ends of tetrameric protofilaments. In combination, these findings suggest that the epitope of the antibody resides at the amino-terminal end of the alpha-helical rod domain. Preincubation of desmin protofilaments with an excess of D76 antibodies blocks their subsequent assembly into IF. In the presence of sub-stoichiometric amounts of antibodies, IF are assembled from protofilaments but they are morphologically aberrant in that (a) they are capped by IgG molecules at one or both ends; (b) they are unraveled to varying degree, revealing a characteristic right-handed helical arrangement of sub-filamentous strands of different diameters. The antibody binds only to the ends but not along the length of desmin IF. The most straightforward explanation for this is that the epitope resides in a part of the desmin molecule that becomes buried within the core of the filament upon polymerization and is therefore inaccessible to the antibody.

Animals↗
PubMed1989

Selective distribution of the 57 kDa neural intermediate filament protein in the rat CNS.

In order to determine the CNS distribution of the 57 kDa neural intermediate filament protein (NIFP), a specific antiserum was used in immunofluorescence studies on serial sections taken from each spinal cord level and at 300-microns intervals through the rat brain. The labeling pattern was recorded onto camera lucida tracings of adjacent sections stained with hematoxylin and eosin/luxol fast blue. Three major immunolocalization patterns were revealed. (1) Both large-caliber and fine-caliber axons of optic and all brain stem cranial nerves and their tracts except for the auditory portion of the VIIIth nerve. (2) An extensive array of fine-caliber fibers in the cerebellar white matter and brain stem with region-specific variation in pattern and density. Prominent among the regions with dense arrays of labeled processes were selective cerebellar afferent systems, particularly olivocerebellar fibers, visual afferents arising in the retina, and selective regions of reticular formation. In contrast to the brain stem, the telencephalon contained rare label. (3) Filamentous labeling of neuronal cytokarya in sensory ganglia and a small number of CNS nuclear groups, including all autonomic nuclei and the cholinergic pontine nuclei. On sections of selected CNS regions, distribution patterns of the 57 kDa NIFP were correlated to results obtained by in situ hybridization of a cDNA probe for the 57 kDa NIFP. The data suggest the possible existence of neuronal IF proteins specifically related to selective anatomic and/or neurotransmitter systems.

Animals↗
PubMed1991

Interactions of intermediate filament proteins from wool.

Filaments of wool are heteropolymers formed by interaction of type I and type II intermediate filament (IF) proteins. There are four proteins in each of these two classes. Interaction of the reduced wool IF proteins was studied by two-dimensional electrophoresis which showed that complexes between type I and type II proteins were formed in solution at urea concentrations below 6 M. Complex formation between the carboxymethyl derivatives of wool IF proteins was studied using a filter binding assay in which radio-labelled individual components were allowed to react under various conditions with SDS-PAGE separated components after transfer to nitrocellulose. The results suggested that (i) absolute type specificity of interaction was maintained, (ii) fine specificity, i.e. preferential reaction between specific components is observed, (iii) wool IF proteins (hard keratins) also react, with the same type specificity, with soft keratins isolated from cow snout, (iv) the initial step in the polymerization sequence that leads to filament formation yields heterodimers.

Animals↗
PubMed1987

Esthesioneuroblastoma. Intermediate filaments, neuroendocrine, and tissue-specific antigens.

Esthesioneuroblastoma (EN), a malignant neuroblastic tumor arising in the superior portion of the nasal cavity, shares histologic similarities with a number of primary malignant tumors that arise in this region, including rhabdomyosarcoma, lymphoepithelioma, and lymphoma. To establish an antigenic profile of EN as an aid in the differential diagnosis of these histologically similar nasal tumors, immunostaining was performed for the following intermediate filaments: keratin, neurofilament, glial fibrillary acidic protein, and desmin; neuron-specific enolase (NSE), S-100 protein, chromogranin, human common leukocyte antigen (HLE), epithelial membrane antigen (EMA), myoglobin, and carcinoembryonic antigen (CEA) on 21 primary nasal tumors: eight EN, five lymphoepitheliomas, two small cell carcinomas, three lymphomas, and three rhabdomyosarcomas. Keratin and CEA stained only the carcinomas (6/7+, 4/7+), respectively; desmin and myoglobin only rhabdomyosarcoma (3/3+, 1/3+); and HLE only lymphomas (3/3+). Chromogranin and neurofilament staining occurred exclusively in one case each of EN. S-100 and NSE commonly stained EN (5/8+, 6/8+), but carcinomas (1/7+, 2/7+) and rhabdomyosarcomas (1/3+, 3/3+) were also positive. Despite the apparent nonspecificity of NSE and S-100, an antigenic profile of positive NSE of S-100 staining with negative epithelial, muscle, and lymphoid antigens uniquely identified six of eight EN. Chromogranin and neurofilament positivity was further evidence for EN in two cases. This antigenic profile is a helpful adjunct in the diagnosis of EN and other primary malignant nasal tumors.

Antigens, Neoplasm↗
PubMed1986

A monoclonal antibody to chicken gizzard desmin that recognizes intermediate filaments and nuclear granules in BHK21/C13 cells.

One hybridoma (AC54), which produces monoclonal antibody (MAb) that recognizes both intermediate filaments (IFs) and nuclear granules in BHK21/C13 cells, and two hybridomas (AC19 and AC36) which produce MAbs that recognize IFs only, were obtained by using a crude actin preparation from chicken gizzard as an antigen. In immunoblotting, both the AC54 and AC19 MAbs reacted with the 52 kD protein (desmin) and some other proteins in gizzard and BHK21/C13 cells. Indirect immunofluorescent microscopy of BHK21/C13 cells showed that the cytoplasmic filaments stained by these MAbs were IFs based on their colchicine-induced whorl formation. The ability of AC54 MAb to recognize IFs was more limited than that of AC19 MAb. The nuclear granules recognized by AC54 MAb were in a different location than the cytoplasmic IFs and sometimes were concentrated in the nucleolus. These results indicate that AC54 MAb is an anti-desmin MAb that reacts with some desmin-related proteins; that it recognizes IFs differently than AC19 MAb, another anti-desmin MAb; and that it recognizes nuclear granules in locations where desmin or desmin-related protein has not yet been reported.

Animals↗
PubMed1987

Rearrangement of the vimentin cytoskeleton during adipose conversion: formation of an intermediate filament cage around lipid globules.

During adipose conversion of murine 3T3-L1 cells, the arrangement of vimentin intermediate filaments (IFs) changes from an extended fibrillar state to a complex cage formation tightly associated with the forming lipid globules. The fully developed cage complex surrounding the lipid globule consists of a monolayer of groups of regularly spaced vimentin IFs that in turn is closely ensheathed by a special endoplasmic reticulum cisterna. The same IF cage is also seen in other adipocytes in culture and in tissues. The specificity of the association of lipid globules with vimentin IFs during adipose conversion is discussed as a special form of compartmentalization supporting adipogenesis and is taken as an example of a possible IF function in relation to a cell differentiation process.

Adipose Tissue↗
PubMed1993

Plexiform schwannoma. Immunohistochemistry of Schwann cell markers, intermediate filaments and extracellular matrix components.

An immunohistochemical study using a comprehensive panel of antibodies to Schwann cell markers, intermediate filaments and extracellular matrix components has been performed on three cases of plexiform schwannoma. All tumour cells expressed S 100 protein, Leu 7-HNK 1 antigen and vimentin; glial fibrillary acidic protein was detected in many tumour cells. In addition, expression of cytokeratin was also demonstrated in one case. The associated extracellular matrix was found to be reactive with antibodies to laminin, heparan sulfate proteoglycan, fibronectin, type I, III, IV and VI collagen. It is concluded that Schwann cells producing their own extracellular matrix are the main components of these tumours. The significance of the cytokeratin expression and the possible role of the extracellular matrix in regulating Schwann cells' proliferation in peripheral nerve tumours are discussed.

Adult↗
PubMed1985

Intermediate filaments in Merkel cell tumors.

A series of ten Merkel cell tumors is described, with special emphasis on intermediate filament expression. The presence of cytoskeletal proteins was studied with a polyclonal antiserum directed against cytokeratin and with monoclonal antibodies against cytokeratin, neurofilament, and vimentin by the immunoperoxidase technique. Cytokeratin was demonstrated in nine of ten tumors. Neurofilament was observed in the two snap-frozen tissues tested and in three of the eight formalin-fixed, paraffin-embedded tissues. No reactivity for vimentin was found. By electron microscopy desmosomes were found to be present in all cases, while tonofilaments were found in only a few cases. neurosecretory granules, although seen in all tumors, were generally present in low numbers. The results of this study indicate that the Merkel cell tumor is a poorly differentiated small cell carcinoma that has the ability to express some neuroendocrine features.

Adenocarcinoma↗
PubMed1995

A nuclear dot-like structure that has a relationship with perinuclear intermediate filaments.

A new type of nuclear dot-like structure was found that seems to associate with perinuclear intermediate filaments (IFs). A monoclonal antibody AP435 MAb (IgM), reactive with desmin and vimentin, recognized from several to dozens of small nuclear dots (AP435 dots) as well as cytoplasmic IFs in various mammalian cells under immunofluorescence microscopy. AP435 dots were sensitive to treatment with 0.5% Triton X-100 while IFs were resistant. The dots disappeared during mitosis in some cells. They colocalized with neither centromeres nor structures involved in RNA processing. Many AP435 dots seem to associate with perinuclear IFs, though they were observed even in cells with no IFs. In cells possessing IFs AP435 dots separated from the bulk of the IFs and remained in the nuclear region both after treatment with colchicin and after treatment with cytochalasin B followed by centrifugation. Confocal laser-scanning fluorescence microscopy revealed the dots to be inside the nucleus. AP435 dots are small intranuclear structures that seem to interact directly or indirectly with perinuclear IFs.

Animals↗
PubMed2002

Expression profiles of the essential intermediate filament (IF) protein A2 and the IF protein C2 in the nematode Caenorhabditis elegans.

The multigene family of intermediate filament (IF) proteins in Caenorhabditis elegans covers 11 members of which four (A1-3, B1) are essential for development. Suppression of a fifth gene (C2) results in a dumpy phenotype. Expression patterns of three essential genes (A1, A3, B1) were already reported. To begin to analyze the two remaining RNAi phenotypes we followed the expression of the A2 and C2 proteins. Expression of A2 mRNA starts in larval stage L1 and continues in the adult. Transgenic A2 promoter/gfp larvae strongly display GFP in the main body hypodermis but not in seam cells. This pattern and the muscle displacement/paralysis induced by RNAi silencing are consistent with the role of this protein in keeping the correct hypodermis/muscle relationship during development. IF protein C2 occurs in the cytoplasm and desmosomes of intestinal cells and in pharynx desmosomes. Expression of C2 starts in the late embryo and persists in all further stages.

Animals↗
PubMed1990

Neuronal intermediate filament expression during neurite outgrowth from explanted goldfish retina: effect of retinoic acid.

Regulation of the goldfish neuronal intermediate filament proteins ON1 and ON2 was investigated in a retinal explant system. The synthesis of these proteins in explanted retina decreased with increasing time in culture, despite continuing neurite outgrowth. Thus, ON1/ON2 neurofilament expression is regulated independently from neurite outgrowth. During regeneration of the goldfish optic nerve in vivo, the expression of these proteins increased during the later phase of the process, when growing axons make contact with the optic tectum. The declining synthesis of ON1 and ON2 during neurite outgrowth in culture suggests that factors extrinsic to the retina are necessary to support synthesis of these proteins. Treating retinal explants with retinoic acid stimulated the synthesis of the ON1/ON2 proteins in a dose-dependent manner. This stimulation was effective during a period of declining synthesis of the ON1/ON2 proteins, restoring their synthesis towards initial levels of expression. These results show that retinoic acid serves as a modulator of neurofilament expression in this in vitro model of nerve regeneration.

Animals↗
PubMed1987

Modulation of intermediate-filament expression in developing cochlear epithelium.

The present study was designed to characterize the expression and distribution of intermediate filaments (IFs) in the diverse cellular elements of inner-ear epithelium in guinea pig and man. Using immunofluorescence microscopy with a battery of IF-specific monoclonal antibodies, we show that the epithelium of the otocyst expresses cytokeratin (CK) polypeptides typical of simple epithelia. Cells in the early otic ganglion were also positively labelled for cytokeratins, suggesting that they are of otocystic epithelial origin. Cytokeratin distribution was largely homogeneous in the early cochlear duct as the epithelium differentiated, differences in the distribution of cytokeratin between the various cell types became detectable. Characteristically, cochlear hair cells became devoid of cytokeratin labelling, and remained unlabelled with antibodies specific for all other IF classes. The neural tissue of the inner ear was also devoid of cytokeratins and was typically positive for neurofilaments. Vimentin IFs were abundant in the mesenchymal tissues around the membranous labyrinth. Desmin and glial fibrillary acidic protein were not detectable in the cochlea. The apparent absence of all IFs from the cochlear hair cells in both guinea pig and man, as revealed by immunofluorescence and electron microscopy, and the possible significance of their absence for cochlear physiology, are discussed.

Animals↗
PubMed1995

Disruption of intermediate filament organization leads to structural defects at the intersomite junction in Xenopus myotomal muscle.

In mature striated muscle, intermediate filaments (IFs) are associated with the periphery of Z-discs and sites of myofibril-membrane attachment. Previously T. Schultheiss, Z. X. Lin, H. Ishikawa, I. Zamir, C. J. Stoeckert and H. Holtzer (1991) J. Cell Biol. 114, 953) reported that the disruption of IF organization in cultured chick myotubes had no detectable effect on muscle cell structure. Cultured muscle is not, however, under the mechanical loads characteristic of muscle in situ. The dorsal myotomal muscle (DMM) of the Xenopus tadpole provides an accessible model system in which to study the effects of mutant IF proteins on an intact, functional muscle. DNAs encoding truncated forms of Xenopus vimentin or desmin were injected into fertilized Xenopus eggs. Embryos were allowed to develop to the tadpole stage and then examined by confocal or electron microscopy. DMM cells containing the truncated IF polypeptides displayed disorganized IF systems. While the alignment of Z-lines appeared unaffected, cells accumulating mutant IF polypeptides displayed abnormal organization at the intersomite junction. Myocyte termini are normally characterized by deep invaginations of the sarcolemma. In myocytes expressing mutated IF polypeptides, these membrane invaginations were reduced or completely absent. Furthermore, the attachment of myofibrils to the junctional membrane was often aberrant or completely disrupted. These results suggest that in active muscle IFs play an important role in the organization and/or stabilization of myofibril-membrane attachment sites.

Animals↗