Drebrin is a widespread actin-associating protein enriched at junctional plaques, defining a specific microfilament anchorage system in polar epithelial cells

Using immunoblotting, immunprecipitation with subsequent fragment mass spectrometry, and immunolocalization techniques, we have detected the actin-binding ca. 120-kDa protein drebrin, originally identified in - and thought to be specific for - neuronal cells, in diverse kinds of human and bovine non-neuronal cells. Drebrin has been found in numerous cell culture lines and in many tissues of epithelial, endothelial, smooth muscle and neural origin but not in, for example, cardiac, skeletal and certain types of smooth muscle cells, in hepatocytes and in the human epithelium-derived cell culture line A-431. By double-label fluorescence microscopy we have found drebrin enriched in actin microfilament bundles associated with plaques of cell-cell contact sites representing adhering junctions. These drebrin-positive, adhering junction-associated bundles, however, are not identical with the vinculin-containing, junction-attached bundles, and in the same cell both subtypes of microfilament-anchoring plaques are readily distinguished by immunolocalization comparing drebrin and vinculin. The intracellular distribution of the drebrin- and the vinculin-based microfilament systems has been studied in detail by confocal fluorescence laser scanning microscopy in monolayers of the polar epithelial cell lines, MCF-7 and PLC, and drebrin has been found to be totally and selectively absent in the notoriously vinculin-rich focal adhesions. The occurrence and the possible functions of drebrin in non-neuronal cells, notably epithelial cells, and the significance of the existence of two different actin-anchoring junctional plaques is discussed.

Detection of new DNA polymerase genes of known and potentially novel herpesviruses by PCR with degenerate and deoxyinosine-substituted primers

A consensus primer PCR approach was used to (i) investigate the presence of herpesviruses in wild and zoo equids (zebra, wild ass, tapir) and to (ii) study the genetic relationship of the herpesvirus of pigeons (columbid herpesvirus 1) to other herpesvirus species. The PCR assay, based on degenerate primers targeting highly conserved regions of the DNA polymerase gene of herpesviruses, was modified by using a mixture of degenerate and deoxyinosine-substituted primers. The applicability of the modification was validated by amplification of published DNA polymerase genes of 16 herpesvirus species and of the previously uncharacterized DNA polymerase genes of equine herpesvirus 3 (EHV-3) and equine herpesvirus 5 (EHV-5). The modified assay was then used for partial amplification of the polymerase of columbid herpesvirus 1 which is presently classified as a beta-herpesvirus based on biological criteria. Sequence analysis of amplicons obtained from four different viral strains revealed a close relationship of columbid herpesvirus 1 to members of the subfamily Alphaherpesvirinae, especially to Marek's disease herpesvirus. This was confirmed by characterization of additional 1.6kb of the columbid herpesvirus 1 polymerase. Consensus PCR analysis of blood samples from zebras, a wild ass and a tapir revealed amplicons showing high percentages ( > 50%) of sequence identity to DNA polymerases of gamma-herpesviruses. In particular, the zebra and the wild ass sequence were closely related to each other and to the polymerases of the equine gamma-herpesviruses EHV-2 and EHV-5 with sequence identities of > 80%. This is a first indication that novel gamma-herpesviruses are present in wild and zoo equids.

The arm-repeat protein NPRAP (neurojungin) is a constituent of the plaques of the outer limiting zone in the retina, defining a novel type of adhering junction

In the retina, special plaque-bearing adhering junctions are aligned to form a planar system (the "outer limiting zone," OLZ) of heterotypic connections between the photoreceptor cells and the surrounding glial cells ("Müller cells"), together with homotypic junctions. In the plaques of these junctions, which contain N-cadherin-and possibly also related cadherins-we have identified, by immunolocalization techniques, a recently discovered neural tissue-specific protein, neurojungin, a member of the plakoglobin/armadillo protein family. In these plaques we have also detected other adherens plaque proteins, such as alpha- and beta-catenin, protein p120, and vinculin, as well as proteins known as constituents of tight junction plaques, such as symplekin and protein ZO-1, and the desmosomal plaque protein plakophilin 2. This unusual combination of proteins and the demonstrated absence of plakoglobin define the OLZ junctions as a new and distinct category of adhering junction, which probably has special architectural functions.

[Reovirus infection of pheasants (Phasianus colchicus)]

In this case report we discribe clinic, pathology and diagnostic of an avian reovirus-infection in pheasants. The disease was observed 1993 in a flock of game-pheasants in the western part of Turkey. Of a live-stock of 100 animals, 27 were affected most of them being three to five months old. Beside a general disorder, sick pheasants showed signs of shortness of breath as well as greenish, watery diarrhoea and died within a week. The pathologic findings were dominated by an extreme hepatopathia. In addition a fibrinous tracheitis, a catarrhal inflammation of the gut and a perihepatitis fibrinosa could be observed. From organs of affected pheasants a pathogen could be isolated, which was characterized anti-genetically, by physico-chemical properties an by electronmicroscopy as avian reovirus.

Lessons from keratin 18 knockout mice: formation of novel keratin filaments, secondary loss of keratin 7 and accumulation of liver-specific keratin 8-positive aggregates

Here, we report on the analysis of keratin 18 null mice. Unlike the ablation of K8, which together with K18 is expressed in embryonic and simple adult epithelia, K18 null mice are viable, fertile, and show a normal lifespan. In young K18 null mice, hepatocytes were completely devoid of keratin filaments. Nevertheless, typical desmosomes were formed and maintained. Old K18 null mice, however, developed a distinctive liver pathology with abnormal hepatocytes containing K8-positive aggregates. These stained positively for ubiquitin and MM120-1 and were identified as Mallory bodies, one hallmark of human alcoholic hepatitis. This is the first demonstration that the ablation of one keratin leads to the accumulation of its single partner. Another striking finding was the absence or drastic down regulation of K7 in several tissues despite its ongoing transcription. Moreover, K18 null mice revealed new insights in the filament-forming capacity of the tail-less K19 in vivo. Due to the unexpected secondary loss of K7, only K8/19 are expressed in the uterine epithelium of K18 null mice. Immunoelectron microscopy of this tissue demonstrated the presence of typical K8/19 IF, thus highlighting in vivo that K19 is a fully competent partner for K8.

Excretion of the anabolic steroid boldenone by racing pigeons

OBJECTIVES

To detect the anabolic steroid bolden-one and to monitor its elimination in the droppings (hereafter referred to as feces) of pigeons treated with the drug.

ANIMALS

8 female pigeons ("Texas" race, 500 +/- 20 g).

PROCEDURE

4 pigeons were given boldenone-17-undecylenate (10 mg/kg of body weight, IM). Feces were collected over defined periods, freeze-dried, extracted with buffer (pH 7.2), and centrifuged. Total immunoreactivity in the supernatant was determined directly by use of an ELISA, and individual boldenone concentration was measured by use of a high-performance liquid chromatography (HPLC)/ELISA after solvent extraction of the aqueous phase. An additional 4 pigeons received a 1-mg/kg dose of the drug.

RESULTS

Screening of feces from boldenone-treated pigeons revealed detection of the drug up to 49 days after its administration. The free parent compound was detected during the same period at a constant value of 12 ng/g of lyophilized feces. Positive results predicted by screening were reliably confirmed by the HPLC/ ELISA. Treatment of pigeons with a lower dosage (1 mg/kg) yielded positive results for 31 days.

CONCLUSIONS

Illegal medication of pigeons with the anabolic steroid boldenone can be uncovered by screening of feces, using a specific ELISA. Confirmation analysis by use of 2 HPLC systems combined with ELISA reliably yields evidence of drug misuse. Owing to the multiple immunoreactive material, the apparent boldenone concentrations registered by screening markedly exceeded the immunoreactivity attributed to boldenone recovered by HPLC/ELISA. Because the test yields positive results in pigeons for at least 31 days after a single treatment, even at a low dosage of the 17-undecylenate preparation (1 mg/kg), the proposed boldenone test procedure is recommended for doping control in racing pigeons.

Targeted mutation of plakoglobin in mice reveals essential functions of desmosomes in the embryonic heart

Plakoglobin (gamma-catenin), a member of the armadillo family of proteins, is a constituent of the cytoplasmic plaque of desmosomes as well as of other adhering cell junctions, and is involved in anchorage of cytoskeletal filaments to specific cadherins. We have generated a null mutation of the plakoglobin gene in mice. Homozygous -/- mutant animals die between days 12-16 of embryogenesis due to defects in heart function. Often, heart ventricles burst and blood floods the pericard. This tissue instability correlates with the absence of desmosomes in heart, but not in epithelia organs. Instead, extended adherens junctions are formed in the heart, which contain desmosomal proteins, i.e., desmoplakin. Thus, plakoglobin is an essential component of myocardiac desmosomes and seems to play a crucial role in the sorting out of desmosomal and adherens junction components, and consequently in the architecture of intercalated discs and the stabilization of heart tissue.

[Detection of doping compounds in the racing pigeon]

To overcome the doping problems in racing pigeons it requires reliable methods to detect illegally medicated drugs. Difficulties applying specifically to pigeons caused the present investigation, since urine and blood commonly analyzed cannot be gathered from pigeons. Drug detection is complicated by those compounds exhibiting an extremely high potency such as the anabolic boldenone, the glucocorticoid prednisolone, and the bronchodilator clenbuterol. The material for analysis selected was faeces of pigeons treated with the doping substances under investigation. The freeze-dried material was subjected to liquid/liquid extraction (Extrelut), and the extracts were submitted to high performance liquid chromatography. Identification of drugs present in the fractions was carried out by specific antibodies (ELISA), and their relative chromatographic retentions were calculated by means of internal standards. The results obtained provide an overall information about elimination kinetics of the three drugs examined. Thus, boldenone, prednisolone, and clenbuterol were detected in the faeces up to 7 weeks, 2 and 1 day, respectively (limits of detection amounted to 0.1-4 ng per g of the freeze-dried faeces.) The detection periods correspond to the periods of pharmacological action of the individual compounds. The results reported here exemplify the proof of doping by examination of faeces from pigeons treated with very potent drugs. High performance liquid chromatography combined with ELISA turned out to be a suitable technique to detect illegal medication in racing pigeons.

Symplekin, a novel type of tight junction plaque protein

Using a monoclonal antibody we have identified and cDNA-cloned a novel type of protein localized, by light and electron microscopy, to the plaque associated with the cytoplasmic face of the tight junction-containing zone (zonula occludens) of polar epithelial cells and of Sertoli cells of testis, but absent from the junctions of vascular endothelia. The approximately 3.7-kb mRNA encodes a polypeptide of 1142 amino acids (calculated molecular weight 126.5 kD, pI 6.25), for which the name "symplekin" (from Greek sigma upsilon mu pi lambda epsilon kappa epsilon iota, nu, to tie together, to weave, to be intertwined) is proposed. However, both the mRNA and the protein can also be detected in a wide range of cell types that do not form tight junctions or are even completely devoid of any stable cell contacts. Careful analyses have revealed that the protein occurs in all these diverse cells in the nucleoplasm, and only in those cells forming tight junctions is it recruited, partly but specifically, to the plaque structure of the zonula occludens. We discuss symplekin as a representative of a group of dual residence proteins which occur and probably function in the nucleus as well as in the plaques exclusive for either tight junctions, adherens junctions, or desmosomes.

Continual assembly of half-desmosomal structures in the absence of cell contacts and their frustrated endocytosis: a coordinated Sisyphus cycle

It is widely assumed that the coordinate assembly of desmosomal cadherins and plaque proteins into desmosome-typical plaque-coated membrane domains, capable of anchoring intermediate-sized filaments (IF), requires cell-to-cell contacts and a critical extracellular Ca2+ concentration. To test this hypothesis we studied several cell lines grown for years in media with less than 0.1 mM Ca2+ to steady-state low Ca2+ medium (LCM) conditions, particularly the human keratinocyte line HaCaT devoid of any junctional cell contact (HaCaT-L cells). Using immunolocalization and vesicle fractionation techniques, we found that the transmembrane glycoprotein, desmoglein (Dsg), colocalized with the plaque proteins, desmoplakin and plakoglobin. The sites of coassembly of desmosomal molecules in HaCaT-L cells as well as in HaCaT cells directly brought into LCM were identified as asymmetric plaque-coated plasma membrane domains (half-desmosomes) or as special plaque-associated cytoplasmic vesicles, most of which had formed endocytotically. The surface exposure of Dsg in these half-desmosomes was demonstrated by the binding, in vivo, of antibodies specific for an extracellular Dsg segment which also could cross-bridge them into symmetric quasi-desmosomes. Otherwise, these half-desmosomes were shown in LCM to be taken up endocytotically. Half-desmosomal assemblies were also seen in uncoupled cells in normal Ca2+ medium. We conclude that, in the absence of intercellular contacts, assembly of desmosomal proteins at the cell surface takes place, resulting in transient half-desmosomes which then, in LCM and without a stable partner connection to the adjacent cell, can be endocytotically resumed. This frustrated cycle of synthesis and assembly maintains an ensemble of molecules characteristic of epithelial differentiation and the potential to form desmosomes, even when the final junctional structure cannot be formed. We propose that these half-desmosomal structures are general cell structures of epithelial and other desmosome-forming cells.

Contactus adherens, a special type of plaque-bearing adhering junction containing M-cadherin, in the granule cell layer of the cerebellar glomerulus

In the glomeruli of the granule cell layer of mammalian cerebellum, neuronal extensions are interconnected by numerous small, nearly isodiametric (diameters up to 0.1 micron), junctions previously classified as puncta adherentia related to the vinculin-containing, actin microfilament-anchoring junctions of the zonula adherens of epithelial and certain other cells. Using immunofluorescence and immunoelectron microscopy, we have found, however, that these junctions are negative for E- and VE-cadherin, for desmosomal cadherins, and also for vinculin, alpha-actinin, and desmoplakin, but they do contain, in addition to the protein plakoglobin common to all forms of adhering junctions, the plaque proteins alpha- and beta-catenin and the transmembrane glycoprotein M-cadherin previously found as a spread--i.e., not junction bound--plasma membrane protein in certain fetal and regenerating muscle cells and in satellite cells of adult skeletal muscle. We conclude that these M-cadherin-containing junctions of the granule cell layer represent a special type of adhering junction, for which we propose the term contactus adherens (from the Latin contactus, for touch, site of bordering upon, also influence), and we discuss the differences between the various adhering junctions on the basis of their molecular constituents.

Sorting of synaptophysin into special vesicles in nonneuroendocrine epithelial cells

Synaptophysin is a major transmembrane glycoprotein of a type of small vesicle with an electron-translucent content (SET vesicles), including the approximately 50-nm presynaptic vesicles in neuronal cells, and of similar, somewhat larger (< or = approximately 90 nm) vesicles (SLMV) in neuroendocrine (NE) cells. When certain epithelial non-NE cells, such as human hepatocellular carcinoma PLC cells, were cDNA transfected to synthesize synaptophysin, the new molecules appeared in specific SET vesicles. As this was in contrast to other reports that only NE cells were able to sort synaptophysin away from other plasma membrane proteins into presynaptic- or SLMV-type vesicles, we have further characterized the vesicles containing synaptophysin in transfected PLC cells. Using fractionation and immunoisolation techniques, we have separated different kinds of vesicles, and we have identified a distinct type of synaptophysin-rich, small (30-90-nm) vesicle that contains little, if any, protein of the constitutive secretory pathway marker hepatitis B surface antigen, of the fluid phase endocytosis marker HRP, and of the plasma membrane recycling endosomal marker transferrin receptor. In addition, we have found variously sized vesicles that contained both synaptophysin and transferrin receptor. A corresponding result was also obtained by direct visualization, using double-label immunofluorescence microscopy for the endocytotic markers and synaptophysin in confocal laser scan microscopy and in double-immunogold label electron microscopy. We conclude that diverse non-NE cells of epithelial nature are able to enrich the "foreign" molecule synaptophysin in a category of SET vesicles that are morphologically indistinguishable from SLMV of NE cells, including one type of vesicle in which synaptophysin is sorted away from endosomal marker proteins. Possible mechanisms of this sorting are discussed.

Detection of G-protein heterotrimers on large dense core and small synaptic vesicles of neuroendocrine and neuronal cells

Heterotrimeric G proteins, initially believed to be exclusively present in the plasma membrane, have also been found to be associated with intracellular membrane compartments. There they are involved in various membrane trafficking processes including regulated secretion (reviewed in Bomsel, M., K. Mostov, Mol. Biol. Cell 3, 1317-1328 (1992)). Vesicles of two distinct types enter the regulated secretory pathway, i.e. large dense core vesicles and small synaptic vesicles, which differ in their membrane composition and content. Little is known about an association of heterotrimeric G proteins with regulated secretory vesicles, that would explain some aspects of the role heterotrimeric G proteins have during secretion. By immunofluorescence microscopy and immunoreplica analysis, we provide the first demonstration of the presence of complete sets of heterotrimeric G proteins, consisting of alpha-, beta-, and gamma-subunits, on large dense core vesicles from bovine adrenal medulla (chromaffin granules) and small synaptic vesicles from rodent and bovine brain. Each of the two types of secretory vesicles contains beta-subunits (at least beta 1 and beta 2), as well as gamma-subunits (at least gamma 2 or gamma 3). Interestingly, they differ in their composition of alpha-subunits. On small synaptic vesicles, we found two G(o) alpha-subunits (alpha o1 and alpha o2) and two Gi alpha-subunits (alpha i1 and alpha i2). In contrast, on chromaffin granules so far only one alpha o-subunit but no alpha i-subunits could be detected. Functional properties such as transmitter storage and/or exocytotic membrane fusion may be modulated by the various G-protein subunits associated with chromaffin granules and small synaptic vesicles.

Amyloid-like properties of peptides flanking the epitope of amyloid precursor protein-specific monoclonal antibody 22C11

Alzheimer's disease is one of the prevalent forms of human dementia. Its pathology is distinguished by proteinaceous deposits ("amyloid") in the brain. They contain a peptide (beta A4) that is proteolytically derived from a larger transmembrane protein. To follow the different metabolic pathways of this Amyloid Precursor Protein (APP) may thus lead to the elucidation of the molecular basis of Alzheimer's disease. Specific antibodies are necessary tools for this task. Using synthetic peptides, we have characterized the epitope of the APP-specific monoclonal antibody 22C11; it is localized between residues 66 and 81 of APP. Some of the peptides flanking this site exhibited properties generally associated with amyloid, i.e. low solubility, filament formation, and birefringence after Congo Red staining. Exploiting differences in the peptides' aggregational properties, we present evidence that the two dyes Eosin and Direct Red 254, in conjunction with classical amyloid staining by Congo Red, can be used to characterize aggregating, amyloid-like peptides in vitro.

Rescue of mice homozygous for lethal albino deletions: implications for an animal model for the human liver disease tyrosinemia type 1

Mice homozygous for specific deletions around the albino locus on chromosome 7 die within the first few hours of birth. They have a complex phenotype in liver and kidney, which includes multiple changes in gene expression and ultrastructural abnormalities. On the basis of this phenotype, it was proposed that these deletions remove a regulatory locus, alf or hsdr-1. Recently, we and others showed that the gene for fumarylacetoacetate hydrolase (Fah), an enzyme involved in tyrosine catabolism, was disrupted by the lethal albino deletion c14CoS. The finding that the Fah gene in wild-type mice is highly expressed only in cell types that develop a phenotype in mutants, and the fact that Fah deficiency determines the human liver disease hereditary tyrosinemia type 1 (HT1), suggested that disruption of the Fah gene was responsible for the lethal albino phenotype. To test this hypothesis, we have created lines of mice carrying Fah transgenes. We find that c14CoS homozygotes which express transgenic Fah are complemented for all aspects of the complex lethal albino phenotype. Moreover, the degree to which the phenotype is corrected depends on the level of transgenic Fah expression. These results unequivocally establish Fah as the gene mapping at alf/hsdr-1 and prove that the phenotype depends ultimately on the blockage of tyrosine metabolism. Finally, they suggest lethal albino mice as an animal model for HT1.

Temperature-sensitive intermediate filament assembly. Alternative structures of Xenopus laevis vimentin in vitro and in vivo

In assembly assays of intermediate filaments (IFs) from vimentin of the amphibian species Xenopus laevis we have observed the formation of so far unknown structures at temperatures above 28 degrees C. Upon assembly in vitro at temperatures above 34 degrees C massive aggregates, partly with a protofilamentous substructure, were found and their formation correlated with drastically reduced end-viscosity. Large spheroidal, dense aggregates with a complex suborganization were also seen to form at 37 degrees C in the cytoplasm of living mammalian cells devoid of endogenous vimentin upon transfection with cDNA encoding the amphibian vimentin, and this was also true for vimentin forced to accumulate in the nucleoplasm by the introduction of a "nuclear localization signal". Upon shift from the non-permissive (37 degrees C) to the permissive (28 degrees C) temperature, such aggregates of non-IF vimentin structures gradually disappeared and a normal-looking IF meshwork formed. The results, which are discussed in relation to other structures assembled by IF proteins, indicate a marked thermosensitivity in the amino acid sequence of the vimentin which seems to have been reduced during evolution of warm-blooded animals. They further show that members of the multigene gene family of IF proteins can occur in structures totally different from IFs.

An amphicrine pancreatic cell line: AR42J cells combine exocrine and neuroendocrine properties

The permanent cell culture line AR42J, derived from a rat pancreatic acinar carcinoma, is widely used for functional studies of exocrine pancreatic acinar cells. We now present evidence that these cells are amphicrine in that they contain zymogen granules as well as small (40-80 nm) neuroendocrine (NE) vesicles and typical neurotransmitters. Using the small NE vesicle-specific markers synaptophysin and "protein S.V.2", including synaptophysin cDNA probes, we have found that AR42J cells synthesize these proteins and contain vesicles harboring these proteins with biophysical properties similar to those of small NE vesicles. NE properties of these cells are further indicated by the presence of considerable amounts of stored amino acids (gamma-aminobutyric acid (GABA), glycine, glutamate) and by the presence of the GABA-synthesizing enzyme, glutamic acid decarboxylase. Finally, intermediate filament (IF) protein typing showed only cytokeratins 8 and 18, indicating that AR42J cells possess an IF protein complement indistinguishable from that of acinar and islet cells. Our results document the unusual case of a permanent cell line with combined exocrine and neuroendocrine properties that may be indicative of a derivation from a cell with multipotential character.

Suprabasal marker proteins distinguishing keratinizing squamous epithelia: cytokeratin 2 polypeptides of oral masticatory epithelium and epidermis are different

Terminal differentiation of squamous epithelia is usually characterized by the synthesis of a subset of cytokeratins (CKs) in suprabasal cell layers which become major components of the intermediate filament (IF) bundle cytoskeleton of the maturing cells. We have examined the significance, molecular nature and pattern of synthesis of the elusive human CK 2 by analyzing mRNAs from certain stratified epithelia, using in vitro translation, cDNA cloning. Northern blotting and in situ hybridization. We show that genuine polypeptides with the typical gel electrophoretic mobility of CK 2 exist but that the CK 2 present in the masticatory epithelia of hard palate and gingiva (CK 2p) differs from that found in epidermis (CK 2e) by its amino acid sequence and is encoded by a different gene. The two CKs 2 show only limited sequence homology (71% identical amino acid positions in the rod domain), and the oral CK 2p is more closely related to the corneal CK 3 (86%), as is also indicated by the cross-reaction of monoclonal antibody AE5. By in situ hybridization and immunocytochemistry, we further show that both CK 2e and CK 2p are expressed only in suprabasal cell layers of the specific epithelia where they can accumulate to represent major cytoskeletal proteins. We discuss this tissue-type specificity of CK 2 synthesis in otherwise morphologically and biochemically similar epithelia in relation to differences of IF appearance and packing in upper strata between epidermal and masticatory epithelia as well as to tissue formation and differentiation during development.

Biochemical and structural aspects of transiently and stably expressed mutant desmin in vimentin-free and vimentin-containing cells

Using immunoelectron microscopy it is demonstrated that desmin subunits missing their complete carboxy-terminal domain are incapable of homopolymeric filament formation in vivo. Furthermore it is shown that, in vimentin-containing cells, desmin integrates into preexisting vimentin filaments resulting in desmin/vimentin heteropolymers. Removal of the amino-terminal or both nonhelical end domains of desmin increases Triton X-100 solubility of the mutant desmin subunits. Expression of desmin mutants containing deletions in the C-terminal part of the rod in vimentin-free cells results in an increase of the Triton X-100 solubility too. In contrast, if expressed in vimentin-containing cells, these mutant subunits remain in the Triton X-100 insoluble fraction. Deletion of the nonhelical carboxy-terminal domain only has no effect on solubility. In vimentin-free cells, stably expressed desmin subunits missing their amino-terminal domains display a slightly higher turnover rate compared to wild-type desmin. Transiently expressed desmin subunits missing 18 or more carboxy-terminal residues of the rod domain are rapidly degraded in vimentin-free cells. In vimentin-containing cells, turnover rates were much less pronounced. Finally, by using site-directed mutagenesis, we were able to map specific residues important for de novo filament assembly within the amino-terminal domain and in the conserved part at the C-terminus of the alpha-helical domain.

Characterization of the mcrBC region of Escherichia coli K-12 wild-type and mutant strains

We have carried out an analysis of the Escherichia coli K-12 mcrBC locus in order to (1) elucidate its genetic organization, (2) to identify the proteins encoded by this region, and (3) to characterize their involvement in the restriction of DNA containing methylated cytosine residues. In vitro expression of recombinant plasmids carrying all or portions of the mcrBC region revealed that the mcrB and mcrC genes are organized as an operon. The mcrBC operon specifies five proteins, as evident from parallel in vitro and in in vivo expression studies. Three proteins of 53, 35 and 34 kDa originate from mcrB expression, while two proteins of 37 and 16 kDa arise from mcrC expression. Products of both the mcrB and mcrC genes are required to restrict the methylated substrate DNA used in this study. We also determined the nature of mutant mcrBC loci in comparison to the E. coli K-12 wild-type mcrBC locus. A major goal of these studies was to clarify the nature of the mcrB-1 mutation, which is carried by some strains employed in previous analyses of the E. coli K-12 McrBC system. Based on our analyses the mutant strains investigated could be divided into different complementation groups. The mcrB-1 mutation is a nonsense or frameshift mutation located within mcrB. It causes premature termination of mcrB gene product synthesis and reduces the level of mcrC gene expression. This finding helps to understand an existing conflict in the literature. We also describe temperature-sensitive McrA activity in some of the strains analysed and its relationship to the previously defined differences in the tolerance levels of E. coli K-12 mcrBC mutants to cytosine methylation.

Expression of nef, vpu, CA and CD4 during the infection of lymphoid and monocytic cell lines with HIV-1

The expression of the capsid antigen (CA) and the two regulatory proteins nef and vpu as well as the CD4 cell surface receptor was followed in HIV-infected lymphoid and promonocytic cells. In the lytic phase of infection all three viral proteins were expressed; production of these proteins coincided with the increase of CA antigen and infectious virus in culture supernatants and with prominent cytopathic effects. After selection of persistently infected cells, the number of lymphoid cells expressing detectable levels of nef decreased to zero; the number of cells positive for CA ranged between 40 to 70%. In chronically infected promonocytic cells nef and vpu expression was reduced to undetectable levels, whereas most of the cells accumulated CA intracellularly. Infectious cell free virus and CA in the supernatant of promonocytic cells had low titers. CD4 surface expression declined in all cell lines investigated before cell free virus was detectable.

Immunolocalization of lamins in the thick nuclear lamina of human synovial cells

While in the great majority of cells the nuclear lamina is not resolved as a distinct structure separating the chromatin from the nuclear envelope, a demonstrable nuclear lamina ("fibrous lamina") of 30 to 300 nm thickness, interposed between the inner nuclear membrane and the peripheral chromatin, is characteristic for certain types of cells of vertebrates and invertebrates. We have examined whether the thick (50-70 nm) fibrous lamina of human synovial cells from patients suffering from rheumatoid arthritis indeed contains the lamins found in the indiscernible lamina structures present in most normal cells. We have observed, by electron microscopic immunolocalization, that both the A and the B type lamins occur throughout the entire nuclear lamina of these cells and that this structure is also resistant to treatments with nucleases and high salt buffers. This shows that the thick fibrous lamina only seen in certain vertebrate cells is compositionally related to the "masked" nuclear lamina of most other cells which usually is identified only upon removal of the adjacent nuclear structures.

Extensive changes in cytokeratin expression patterns in pathologically affected human gingiva

The stratified squamous epithelium of the oral gingiva and the hard palate is characterized by a tissue architecture and a cytoskeletal composition similar to, although not identical with, that of the epidermis and fundamentally different from that of the adjacent non-masticatory oral mucosa. Using immunocytochemistry with antibodies specific for individual cytokeratins, in situ hybridization and Northern blots of RNA with riboprobes specific for individual cytokeratin mRNAs, and gel electrophoresis of cytoskeletal proteins of microdissected biopsy tissue samples, we show changes in the pattern of expression of cytokeratins and their corresponding mRNAs in pathologically altered oral gingiva. Besides a frequently, although not consistently, observed increase in the number of cells producing cytokeratins 4 and 13 (which are normally found as abundant components in the sulcular epithelium and the alveolar mucosa but not in the oral gingiva) and a reduction in the number of cells producing cytokeratins 1, 10 and 11, the most extensive change was noted for cytokeratin 19, a frequent cytokeratin in diverse one-layered and complex epithelia. While in normal oral gingiva cytokeratin 19 is restricted to certain, sparsely scattered cells of --or near--the basal cell layer, probably neuroendocrine (Merkel) cells, in altered tissue of inflamed samples it can appear in larger regions of the basal cell layer(s) and, in apparently more advanced stages, also in a variable number of suprabasal cells. Specifically, our in situ hybridization experiments show that this altered suprabasal cytokeratin 19 expression is more extended at the mRNA than at the protein level, indicating that cytokeratin 19 mRNA synthesis may be a relatively early event during the alteration. These changes in cytokeratin expression under an external pathological influence are discussed in relation to other factors known to contribute to the expression of certain cytokeratins and with respect to changes occurring during dysplasia and malignant transformation of oral epithelia.