Effects of long-term portal hypertension on structure, active force and content of contractile and structural proteins in smooth muscle of the rat portal vein

Growth of the smooth muscle cells in the rat portal vein was induced by a partial ligation of the vessel. The ligation caused an increase in the transmural pressure and segments of the portal vein were investigated 6 weeks after the ligation. The spontaneous contractile activity of the ligated veins was similar to that of the control veins. In the ligated vessels the active force at optimal length for force development was doubled, 22.8 +/- 1.3 compared with 12.5 +/- 1.4 mN for the controls. The cross-sectional area of the media in the ligated veins, determined on transverse sections, increased from the control value of 0.10 +/- 0.01 to 0.19 +/- 0.01 mm2. Electron microscopy revealed that the mean cross-sectional area of the smooth muscle cells in the ligated portal vein was doubled (controls: 6.4 +/- 0.6, hypertrophic: 13.6 +/- 1.8 microns2). This suggests hypertrophy of the smooth muscle cells in the vessel wall as the cause for the increase in cross-sectional area of the ligated veins. An increase in the number of intermediate filaments was observed in the hypertrophied smooth muscle. The relative contents of contractile (myosin and actin) and structural (desmin and vimentin) proteins were determined with SDS-polyacrylamide gel electrophoresis. The actin/myosin and vimentin/actin ratios were unaltered by hypertrophy. The hypertrophied veins showed an increase in the desmin/actin ratio (control: 0.20 +/- 0.01, hypertrophied: 0.27 +/- 0.03). The increased amounts of desmin correlates with the increased number of intermediate filaments observed by electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

A conserved region in the tail domain of vimentin is involved in its assembly into intermediate filaments

Although the head and rod domains of intermediate filament (IF) proteins are known to play significant roles in filament assembly, the role of the tail domain in this function is unclear and the available information supports contradictory conclusions. We examined this question by comparing transfection of the same cDNA constructs, encoding vimentins with modified tail domains, into cell lines that do and do not contain endogenous IF proteins. By this approach, we were able to distinguish between the ability of a mutant IF protein to initiate assembly de novo, from that of incorporating into existing filament networks. Vimentins with modifications at or near a highly conserved tripeptide, arg-asp-gly (RDG), of the tail domain incorporated into existing IF networks in vimentin-expressing (vim+) cells, but were assembly-incompetent in cells that did not express IF proteins (vim-). The failure of the RDG mutant vimentins to assemble into filament arrays in vim- cells was reversible by re-introducing a wild-type vimentin cDNA, whereupon both wild-type and mutant vimentins coassembled into one and the same IF network. We conclude that the function of the tail domain of type III IF proteins, and possibly of keratins K8 and K18, in IF assembly is distinct from those of other domains; a region encompassing the RDG tripeptide appears to be important in the assembly process.

Intermediate filament proteins and epithelial differentiation in the embryonic ovary of the rat

The development and sexual differentiation of gonads in female rat embryos and fetuses between the ages of 11 and 17 days was studied by immunocytochemical analysis of intermediate filament proteins and laminin by light and electron microscopy. In the 11-day-old pregonadal embryo, the surface epithelial cells in the ventral cortex of the mesonephros contained desmin but not cytokeratin or vimentin. The development of the gonad began on the following day by proliferative growth of the mesonephric surface cells, which like the subepithelial cells soon expressed vimentin in addition to desmin. The differentiation continued by formation of separate epithelial cell clusters, which joined into cords, irregular in shape and size. Desmin disappeared from the cord cells and cytokeratins appeared while vimentin remained in all somatic cell types. Desmin was especially abundant in some stromal cells adjacent to the epithelial tissues. After the segration of the basic ovarian tissues, vimentin and desmin decreased and cytokeratins appeared in the surface epithelial cells. New changes in cytokeratin expression appeared with the differentiation of the embryonic cords in a sex-specific manner with gradual decrease of reactivity for cytokeratin 18. No immunoreaction to the neurofilament proteins was found at the present ages, and the germ cells were negative for intermediate filaments. The results show that desmin is expressed in several primitive ovarian and mesonephric cells even though they are not myogenic.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal incisor-tooth differentiation in transgenic mice expressing the muscle-specific desmin gene

Immunocytochemistry and electron microscopic observations on the incisor-tooth organ of transgenic mice expressing the muscle-specific desmin gene under the direction of the vimentin promoter, reveal that the expression of the hybrid transgene occurs both in mesenchymal cells and differentiating odontoblasts. The muscle-specific desmin, as estimated by fluorescence intensity, is more expressed in immature mesenchymal cells than in postmitotic differentiated odontoblasts. The expression of the transgene generates alteration of the odontoblast-intermediate filament network and interferes with the secretory activity of both odontoblasts and ameloblasts. Our results are consistent with the hypothesis that odontoblasts have inductive properties on the differentiation of ameloblasts and that intermediate filaments among other factors play the role of cell and tissue organizer.

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.

Transient requirement for vimentin in neuritogenesis: intracellular delivery of anti-vimentin antibodies and antisense oligonucleotides inhibit neurite initiation but not elongation of existing neurites in neuroblastoma

Vimentin is initially expressed by nearly all neuronal precursors in vivo, and is gradually replaced by neurofilaments shortly after the immature neurons become postmitotic (Cochard and Paulin, 1984, J Neurosci 4:2080; Tapscott et al., 1981, Dev Biol 86:40). A transient increase in neuritic vimentin filaments occurs within the first day of dbcAMP-mediated neurite induction in NB2a/d1 neuroblastoma, after which vimentin levels rapidly decline and neurofilaments increase (Shea, 1990, Brain Res 521:343). In the present study, we tested the possibility that vimentin filaments may function in neurite elaboration by inducing neuritogenesis under conditions where vimentin expression and assembly was inhibited. Intracellular delivery of anti-vimentin antiserum into transiently permeabilized NB2a/d1 cells prevented the initial elaboration of neurites, but did not retract existing neurites. By contrast, intracellular delivery of antiserum directed against the low molecular weight neurofilament subunit or normal rabbit antiserum did not affect neurite outgrowth. Treatment with vimentin antisense oligonucleotides reversibly depleted vimentin synthesis and steady-state levels, and prevented neurite initiation, but did not induce retraction of existing neurites. These findings point toward an hitherto undetected role for vimentin in the initiation of neurite outgrowth.

The lipoxygenase metabolite, 12(S)-HETE, induces a protein kinase C-dependent cytoskeletal rearrangement and retraction of microvascular endothelial cells

We previously reported that a lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], induced large vessel endothelial cell (EC) retraction and increased tumor cell adhesion to exposed extracellular matrix (Honn et al., FASEB J. 3, 2285-2293, 1989). Here, we present evidence that 12(S)-HETE induces the retraction of microvascular ECs in a time- and concentration-dependent manner. The EC retraction was observed 15 min after 12(S)-HETE treatment and reached a peak level between 1 and 2 h. The monolayer reformed by 24 h. Silver staining and "gap-FRAP" experiments suggest that 12(S)-HETE altered the normally apposed cell junctions and impaired gap junction-mediated cell-cell communication. It appears that the 12(S)-HETE effect was mediated by cytoskeletal alteration. The first observed alteration in EC cytoskeleton following 12(S)-HETE stimulation is vimentin bundling, followed by the rearrangement and disruption of vinculin-containing adhesion plaques and/or simultaneous redistribution of alpha-actinin and disruption of spectrin. These changes are accompanied by progressive microfilament dissolution. During the same time interval, alpha-actinin is mobilized to the cell periphery at cell "ruffles." However, 12(S)-HETE showed little or no effects on actin-binding proteins filamin and tropomyosin or on microtubules. 12(S)-HETE effects on these cytoskeletal elements were fully reversible by 24 h and appeared to be mediated through enhancing protein phosphorylation. Following 12(S)-HETE (0.1 microM) treatment increased phosphorylation of proteins that comigrated with myosin light chain (20 kDa), actin (42 kDa), and vimentin (57 kDa) were observed. The enhanced phosphorylation of these cytoskeletal proteins was confirmed by 2D gel analysis. The phosphorylation-promoting effect of 12(S)-HETE on cytoskeletal proteins could be totally abolished by calphostin C, partially inhibited by staurosporine, but was not influenced by N-[2-(methylamine)ethyl]-5-isoquinolinesilfonamide dihydrochloride (HS), suggesting that the 12(S)-HETE effect was mediated via protein kinase C. This was further substantiated by quantitative experiments demonstrating that calphostin C, but not H8, inhibited 12(S)-HETE-induced EC retraction.

The roles of the rod end and the tail in vimentin IF assembly and IF network formation

Using mutagenesis, we investigated the importance of two vimentin domains: (a) a highly conserved segment near the carboxy end of the alpha-helical rod, and (b) the tail, with which the rod end is known to interact. As judged by in vitro filament assembly and expression in transiently transfected cells lacking an endogenous vimentin network, the rod-tail interaction is not essential for 10 nm filament structure in vitro or for formation of fibrous arrays in culture. However, when mutated, amino acid residues within the rod and the tail segments can cause perturbations in IF assembly and in IF network formation. Finally, our studies show that the vimentin tail seems to play a role both in thermodynamically stabilizing IF structure in vitro and in establishing proper IF networks in vivo.

[Immunohistochemical study in acquired cystic disease of the kidney--expression of vimentin, epidermal growth factor, epidermal growth factor receptor and c-erb B2 gene product]

Acquired cystic disease of the kidney (ACDK) reveals abnormal epithelial cell growth which suggests a cotinuum of cyst, adenoma and renal cell carcinoma (RCC). In the present study, we examined potential role of vimentin and growth factors for cyst growth and proliferation in 20 cases with ACDK by immunoperoxidase staining method. 1281 cysts with single-layered epithelia and 89 cysts with multi-layered epithelia (atypical cyst) were studied. Intermediated filament, vimentin was positive in staining in 41.6% of cysts with single-layered epithelia, in 73.1% of cyst with multi-layered epithelia and in 100% of adenomas and RCCs. Vimentin expression, therefore, may be considered as an indication of cellular differentiation among proliferating tubular or intracystic cells. In order to evaluate the growth and/or proliferative capabilities of cyst epithelia, epidermal growth factor (EGF), epidermal growth factor receptor (EGFR) and c-erb B2 gene product were determined in cyst epithelia, adenoma and adenocarcinoma. EGF showed positive staining in 49.1% of cyst with single-layered epithelia, in 68.4% of cyst with multi-layered epithelia, in 2 of 3 adenomas and in 5 of 8 RCCs. EGFR expression was observed in 61.7% of cyst with single-layered epithelia, in 94.7% of cyst with multi-layered epithelia, in 100% of adenomas and RCCs. Co-expression of EGF and EGFR was observed in 40.3% of cyst with single-layered epithelia and in 67.1% of cyst with multi-layered epithelia. C-erb B2 gene product was positive in 9.7% of cyst with single-layered epithelia, in 100% of cyst with multi-layered epithelia and in 3 of 7 RCCs. These findings indicate that the expression of vimentin and overexpression of these growth factors and receptors appear to be one of the mechanisms operating in potentiating the abnormal growth of cyst epithelia, including potential for oncogenesis of RCC.

Identification of a vimentin-like function associated molecule (FAM) on rat NK cells: evidence for receptor function

Monoclonal antibody (MoAb) 5C6 specifically binds to fish, rat and human NK cells and inhibits cytotoxicity. The molecule recognized by this MoAb is a 50-53-kDa membrane protein on rat leukaemic NK (CRC) cells. In the present study, we have obtained a partial internal amino acid sequence from a purified 42-kDa fragment of the CRC-function associated molecule (FAM). Three tryptic peptide fragments were sequenced and each showed homology to intermediate filament vimentin sequences as deduced from (GenBank) mouse cDNA sequences. Amino acid composition analysis indicated that similar to cytoskeletal vimentin, the FAM contained a high percentage of non-polar amino acids. To further assess the similarities between this protein and vimentin, two commercially available anti-vimentin MoAbs and one anti-vimentin polyclonal antibody were tested for binding and inhibition of NK cytotoxicity. All anti-vimentin MoAbs inhibited killing by rat NWNA cells of appropriate targets. Anti-vimentin MoAb 13.2 bound to 41% of NWNA cells compared with approximately 58% binding for MoAb 5C6. Capping and sequential binding experiments showed that MoAb 5C6 effectively removed, from CRC-cell membranes, the protein recognized by MoAb V9. Sequential addition of these two MoAbs (MoAb 13.2 followed by MoAb V9) to CRC cells did not produce competitive binding. Biochemical and Western blot analysis of the vimentin-like protein obtained from CRC cells indicated that this protein has a molecular weight of 48-50 kDa, with an isoelectric point of pH 6.1-6.3. This protein is cross-reactive by Western blot analysis with anti-vimentin and anti-intermediate filament (IFA) antigen MoAbs but not with anti-desmin or anti-actin MoAbs. The molecular weight heterogeneity (43 versus 48-50 kDa) of the CRC protein was also examined. Western blot analysis of the CRC extract after different in vitro incubation times at 37 degrees C and 4 degrees C demonstrated that the 50-53-kDa 'native' protein degraded to a 42-kDa protein by 24 and 48 h respectively. This degradation was inhibitable by 10 mM EGTA. Evidence is presented which indicates that a vimentin-like protein on transformed rat NK cells may be an antigen binding receptor which initiates target cell lysis.

A functional role for vimentin intermediate filaments in the metabolism of lipoprotein-derived cholesterol in human SW-13 cells

Numerous studies have indicated that cytoplasmic intermediate filaments (cIFs) can associate with cellular lipids. To determine if these interactions might have functional consequences, we have studied the lipid metabolism of human SW-13 adrenal tumor cell lines that either contain vimentin-type cIFs (vim+) or lack any detectable cIF network (vim-). Although there were no significant differences in phospholipid or glyceride synthesis, vim- cell lines had elevated levels of cholesterol synthesis and decreased cholesterol esterification, compared with vim+ cells. These differences in cholesterol synthesis and esterification were found to be due to an impaired ability of vim- cells to utilize low density lipoprotein (LDL)-derived cholesterol, although receptor-mediated endocytosis of LDL and the capacity of these cells to esterify endogenously produced cholesterol were not affected. Expression of a mouse vimentin cDNA in stably transfected cell lines, derived from vim- cells, restored the capacity of these cells to utilize LDL cholesterol. The uptake and metabolism of [3H]cholesterol linoleate-loaded LDL showed that the impaired ability of vim- cells to esterify LDL cholesterol was not associated with an accumulation of cellular free cholesterol but rather an increase in the appearance of [3H]cholesterol in the culture medium. These studies indicate that in SW-13 cells, the intracellular movement of LDL-derived cholesterol from the lysosome to the site of esterification is a vimentin-dependent process.

Involvement of the consensus sequence motif at coil 2b in the assembly and stability of vimentin filaments

Nearly all intermediate filament (IF) proteins share two sequence motifs located at the N- and the C-terminal ends of their helical rod domain (‘coil 1a’ and ‘coil 2b’, respectively). To examine the structural role of the coil 2b motif, we have performed in vitro assembly studies and in vivo microinjection experiments employing two site-specific reagents: (a) a 20-residue synthetic peptide (C-2) representing the conserved motif itself and (b) a monoclonal antibody (anti-IFA) that recognises an epitope within the conserved coil 2b sequence. We demonstrate here that vimentin protofilaments, when induced to assemble in the presence of C-2 or anti-IFA, show a lower propensity to polymerise and yield various abberant structures. The few filaments that are formed under these conditions appear much shorter than normal IFs and are unravelled or aggregated. Furthermore, when preformed vimentin filaments are exposed to C-2 or anti-IFA, most of the normal IFs are converted into shorter filamentous forms that possess an abberant morphology. None of these effects is seen when vimentin subunits are coincubated with control peptides. Microinjection of anti-IFA into the cytoplasm of interphasic 3T3 cells provokes collapse of vimentin IFs into a juxtanuclear mass and formation of numerous amorphous aggregates distributed throughout the cytoplasm. These two effects are not seen when the anti-IFA is microinjected into the cell nucleus. Our results provide experimental evidence supporting previous suggestions for a role for the conserved coil 2b sequence in filament assembly. We propose that this region is interacting with other sites along the vimentin molecule and that these interactions are essential for proper protofilament-protofilament alignment and filament stability.

Desmin/vimentin intermediate filaments are dispensable for many aspects of myogenesis

An expression vector was prepared containing a cDNA coding for a truncated version of the intermediate filament (IF) protein desmin. The encoded truncated desmin protein lacks a portion of the highly conserved alpha-helical rod region as well as the entire nonhelical carboxy-terminal domain. When transiently expressed in primary fibroblasts, or in differentiating postmitotic myoblasts and multinucleated myotubes, the truncated protein induces the complete dismantling of the preexisting vimentin or desmin/vimentin IF networks, respectively. Instead, in both cell types vimentin and desmin are packaged into hybrid spheroid bodies scattered throughout the cytoplasm. Despite the complete lack of intact IFs, myoblasts and myotubes expressing truncated desmin assemble and laterally align normal striated myofibrils and contract spontaneously in a manner indistinguishable from that of control myogenic cells. In older cultures the spheroid bodies shift from a longitudinal to a predominantly transverse orientation and loosely align along the I-Z-I-regions of striated myofibrils (Bennett, G.S., S. Fellini, Y. Toyama, and H. Holtzer. 1979. J. Cell Biol. 82:577-584), analogous to the translocation of intact desmin/vimentin IFs in control muscle. These results suggest the need for a critical reexamination of currently held concepts regarding the functions of desmin IFs during myogenesis.

Sorting out IF networks: consequences of domain swapping on IF recognition and assembly

Vimentin and keratin are coexpressed in many cells, but they segregate into two distinct intermediate filament (IF) networks. To understand the molecular basis for the sorting out of these IF subunits, we genetically engineered cDNAs encoding hybrid IF proteins composed of part vimentin and part type I keratin. When these cDNAs were transiently expressed in cells containing vimentin, keratin, or both IFs, the hybrid IF proteins all recognized one or the other or both networks. The ability to distinguish networks was dependent upon which segments of IF proteins were present in each construct. Constructs containing sequences encoding either helix 1B or helix 2B seemed to be the most critical in conferring IF recognition. At least for type I keratins, recognition was exerted at the level of dimer formation with wild-type type II keratin, as demonstrated by anion exchange chromatography. Interestingly, despite the fact that swapping of helical domains was not as deleterious to IF structure/function as deletion of helical domains, keratin/vimentin hybrids still caused structural aberrations in one or more of the cytoplasmic IF network. Thus, sequence diversity among IF proteins seems to influence not only coiled-coil but also higher ordered associations leading to 10-nm filament formation and/or IF interactions with other cellular organelles/proteins.

Assembly of amino-terminally deleted desmin in vimentin-free cells

To study the role of the amino-terminal domain of the desmin subunit in intermediate filament (IF) formation, several deletions in the sequence encoding this domain were made. The deleted hamster desmin genes were fused to the RSV promoter. Expression of such constructs in vimentin-free MCF-7 cells as well as in vimentin-containing HeLa cells, resulted in the synthesis of mutant proteins of the expected size. Single- and double-label immunofluorescence assays of transfected cells showed that in the absence of vimentin, desmin subunits missing amino acids 4-13 are still capable of filament formation, although in addition to filaments large numbers of desmin dots are present. Mutant desmin subunits missing larger portions of their amino terminus cannot form filaments on their own. It may be concluded that the amino-terminal region comprising amino acids 7-17 contains residues indispensable for desmin filament formation in vivo. Furthermore it was shown that the endogenous vimentin IF network in HeLa cells masks the effects of mutant desmin on IF assembly. Intact and mutant desmin colocalized completely with endogenous vimentin in HeLa cells. Surprisingly, in these cells endogenous keratin also seemed to colocalize with endogenous vimentin, even if the endogenous vimentin filaments were disturbed after expression of some of the mutant desmin proteins. In MCF-7 cells some overlap between endogenous keratin and intact exogenous desmin filaments was also observed, but mutant desmin proteins did not affect the keratin IF structures. In the absence of vimentin networks (MCF-7 cells), the initiation of desmin filament formation seems to start on the preexisting keratin filaments. However, in the presence of vimentin (HeLa cells) a gradual integration of desmin in the preexisting vimentin filaments apparently takes place.

Characterization of dominant and recessive assembly-defective mutations in mouse neurofilament NF-M

We have generated a set of amino- and carboxy-terminal deletions of the neurofilament NF-M gene and determined the molecular consequences of forced expression of these mutant constructs in mouse fibroblasts. To follow the expression of mutant NF-M subunits in transfected cells, a 12 amino acid epitope (from the human c-myc protein) was expressed at the carboxy terminus of each mutant. We show that NF-M molecules missing up to 90 or 70% of the nonhelical carboxy-terminal tail or amino-terminal head domains, respectively, incorporate readily into an intermediate filament network comprised either of vimentin or NF-L, whereas deletions into either the amino- or carboxy-terminal alpha-helical rod region generate assembly-incompetent polypeptides. Carboxy-terminal deletions into the rod domain invariably yield dominant mutants which rapidly disrupt the array of filaments comprised of NF-L or vimentin. Accumulation of these mutant NF-M subunits disrupts vimentin filament arrays even when present at approximately 1% the level of the wild-type subunits. In contrast, the amino-terminal deletions into the rod produce pseudo-recessive mutants that perturb the wild-type NF-L or vimentin arrays only modestly. The inability of such amino-terminal mutants to disrupt wild-type subunits defines a region near the amino-terminal alpha-helical rod domain (residues 75-126) that is required for the earliest steps in filament assembly.

Induction of differentiation of the human histiocytic lymphoma cell line U937 in the absence of vimentin expression

We have studied the expression of vimentin in the human histiocytic lymphoma cell line U937, induced to differentiate along the monocyte/macrophage pathway. Normal monocytes possess a network of vimentin intermediate filaments (IFs) at all stages of maturation. The undifferentiated U937 leukemia cells contain very low amounts of vimentin, but express a conspicuous IF network when exposed to phorbol myristate acetate. In parallel, they acquire functional properties typical of cells of the monocyte lineage. These concomitant variations suggest that vimentin IFs could play a role in the process of differentiation. However, we observed that all-trans-retinoic acid and 1,25-dihydroxyvitamin D3 confer monocyte-like properties upon U937 cells without inducing vimentin expression. We obtained increased phenotypic changes, yet in the absence of a vimentin network, by combining the effects of both inducers. These results show that vimentin expression is not crucial for the acquisition of some of the functions characteristic of the monocyte/macrophage lineage.

Vimentin downregulation is an inherent feature of murine erythropoiesis and occurs independently of lineage

In mammalian erythropoiesis, the mature cells of the primitive lineage remain nucleated while those of the definitive lineage are anuclear. One of the molecular and structural changes that precedes enucleation in cells of the definitive lineage is the cessation in the expression of the gene for the intermediate filament (IF) protein vimentin and the removal of all vimentin filaments from the cytoplasm. We show here that in immature primitive cells vimentin is synthesized and forms a cytoplasmic network of IFs. As differentiation proceeds in vivo, vimentin gene expression is downregulated in these cells; this is accompanied by the loss of vimentin filaments from the cytoplasm. This loss temporally coincides with the nucleus becoming freely mobile within the cytoplasm, suggesting that, while IF removal is not directly linked to the physical process of enucleation, it may be a prerequisite for the initiation of nuclear mobility in both lineages. These changes are also observed in early primitive cells cultured in vitro, suggesting that they constitute an intrinsic part of the murine erythroid differentiation program independent of lineage and hematopoietic microenvironment.

Intermediate filament assembly and stability in vitro: effect and implications of the removal of head and tail domains of vimentin by the human immunodeficiency virus type 1 protease

The intermediate filament subunit protein vimentin is efficiently cleaved in vitro by purified human immunodeficiency virus type 1 protease. Immunological data confirm that identical sites are cleaved when vimentin is polymerized into filaments or occurs as protofilaments. The primary cleavage gives rise to a molecule lacking most of the tail domain and which not only remains in preformed filaments, but is also capable of polymerizing into essentially normal 10 nm filaments. However, these filaments show a propensity to form large lateral aggregates. The three secondary cleavage products of vimentin additionally lack portions of the head domain, are almost quantitatively (greater than 95%) released from preformed filaments and are not capable of forming filaments de novo. These results extend the limits of the head and tail domains of vimentin that play a role in filament formation and stability.

Effects of thrombospondin antibody on the recovery of endothelial cells from hyperthermia

In addition to the increased synthesis of the classical heat-shock proteins (28,000, 71,000, 73,000, 90,000 and 100,000 Mr polypeptides) there is also an increase of thrombospondin in the growth medium of endothelial cells exposed to hyperthermia. The effect of a monoclonal antibody to thrombospondin on the recovery of endothelial cells from hyperthermia as it relates to cytoskeletal organization and cell spreading was assessed. The antibody interacts with the heparin-binding domain of thrombospondin in the extracellular matrix of cells. We report that during recovery from thermal insult at 37 degrees C, intermediate filaments, stress fibres and microtubules show distinct time-recovery characteristics in bovine aortic endothelial cells; that in the presence of this antibody the cytoskeleton is notably altered; that this antibody causes retraction of endothelial cell processes; and that the recovery of the cytoskeleton in endothelial cells exposed to hyperthermia is prevented by the thrombospondin antibody in the time frame examined. Our data suggest that the recovery of cells from heat shock requires the integrity of thrombospondin and its interactions.

Membrane Ig-cytoskeletal interactions. III. Receptor cross-linking results in the formation of extensive filamentous arrays of vimentin

The proposed function of intermediate filaments is to provide a cell type-specific structural framework that maintains cell shape and organelle distribution and mediates signal transduction through its connections with the plasma membrane and the nucleus. Vimentin is the intermediate filament protein expressed in B lymphocytes. Immunocytochemical analysis of the high salt-stable cytoskeletons from B cells stimulated with anti-Ig revealed an increased accumulation of vimentin in the cytoskeleton compared to nontreated controls. This increased accumulation of vimentin in the cytoskeleton was manifested by the organization of vimentin into extensive filamentous arrays (EFA) as viewed in the fluorescent microscope. In contrast to the effects of anti-Ig, activation of B cells with LPS did not induce the organization of vimentin into EFA. This suggested that signals unique to anti-Ig directed EFA formation. Immunocytochemical results were verified by biochemical analysis showing that vimentin was more abundant in isolated cytoskeletons from anti-Ig activated B cells, than cytoskeletons isolated from LPS-activated B cells. These observations established a relationship between increased content of vimentin in the cytoskeleton and the formation of EFA. By testing a wide variety of activating agents, we were able to correlate increased vimentin expression in the cytoskeleton to activating agents that cross-link membrane Ig. It appeared that treatment of B cells with LPS prohibited the induction of EFA by anti-Ig because cotreatment with both anti-Ig and LPS resulted in decreased vimentin accumulation in the cytoskeleton to a level less than that in resting cells. The significance of these results with regard to B cell biology is discussed.

[The cytokeratin skeleton of the human organ of Corti and its functional significance]

In the adult human organ of Corti cytokeratin (CK) is expressed by all supporting cells enclosing it like a shell. The pattern of immunoreactivity clearly demonstrates a quantitative gradient in the expression of CK, with more CK at the apex than at the base of the cochlea. Predominantly in the apical cochlear turns, the CK-shell separates the compartment of the inner hair cells from that of the outer hair cells. Ultrastructurally, the supporting cells contain a loose fibrillary network which apically is oriented toward the desmosome chain and which can be clearly distinguished from the well-known tubular filaments (microtubuli). Some supporting cells show centrioles. Both the expression of CK and the presence of centrioles indicate a possible potential for cell regeneration. Ultrastructurally, outer hair cells and Deiters' cells show features of a specialized contact zone which might be of functional significance regarding the contractile abilities of the outer hair cells. In the human organ of Corti, vimentin is expressed only by the inner and outer pillar cells. These cells thus express CK together with vimentin. The distinct shell configuration of the CK network in the organ of Corti gives it a tonotopically related difference in rigidity which not only must be of importance for cochlear perception of sound but also could explain the reduced vulnerability of the ear to low frequencies.

The role of the vimentin intermediate filaments in rat 3Y1 cells elucidated by immunoelectron microscopy and computer-graphic reconstruction

The three-dimensional arrangement of vimentin intermediate filaments (IF) was studied in 3Y1, rat fibroblastic cell line, to elucidate its biological role in the cell. While actin filaments were observed exclusively in the superficial part of the cell, vimentin IF were found to be abundantly present in the inside of the cell where microtubules were occasionally discovered. By whole-mount immunoelectron microscopy and computer-graphic reconstruction of serial thin sections, it was observed in more detail that vimentin IF are located very close to the nucleus, endoplasmic reticulum, and mitochondria. Vimentin IF were observed to be attached to these organelles laterally or terminally. Thus, we can reasonably assume that vimentin IF are major cytoskeletal structures deep inside the cell and that they play an important role in supporting the location of the organelles. This is the first report which has visualized the three-dimensional relationship between vimentin IF and the organelles of the cell.

Overexpression of the vimentin gene in transgenic mice inhibits normal lens cell differentiation

To investigate the role of the intermediate filament protein vimentin in the normal differentiation and morphogenesis of the eye lens fiber cells, we generated transgenic mice bearing multiple copies of the chicken vimentin gene. In most cases, the vimentin transgene was overexpressed in the lenses of these animals, reaching up to 10 times the endogenous levels. This high expression of vimentin interfered very strongly with the normal differentiation of the lens fibers. The normal fiber cell denucleation and elongation processes were impaired and the animals developed pronounced cataracts, followed by extensive lens degeneration. The age of appearance and extent of these abnormalities in the different transgenic lines were directly related to the vimentin level. Electron microscopic analysis revealed that the accumulated transgenic protein forms normal intermediate filaments.

Epstein-Barr virus latent membrane protein: induction of B-cell activation antigens and membrane patch formation does not require vimentin

The latent membrane protein (LMP) of Epstein-Barr virus (EBV) forms patches associated with the vimentin intermediate filament system in EBV-transformed lymphoblastoid cell lines, EBV-infected Burkitt's lymphoma cells, and LMP-transfected, EBV-negative Burkitt's lymphoma cells. By gene transfer, LMP induces the expression of vimentin and B-cell activation antigens in EBV-negative Burkitt's lymphoma cells. We have now expressed LMP in an EBV-positive Burkitt's lymphoma cell line, Daudi, which does not express any LMP or vimentin. In these Daudi transfectants, LMP still formed plasma membrane patches in the absence of vimentin. LMP did not resist nonionic detergent extraction in Daudi cells as it does in vimentin-expressing cells. LMP still retained functional activity as judged by induction of B-cell activation antigens. These data indicate that LMP can form plasma membrane patches and induce B-lymphocyte activation independent of vimentin association.

Immunohistochemical investigation of different cytokeratins and vimentin in the human epididymis from the fetal period up to adulthood

The anatomical distribution of cytokeratins and vimentin was investigated by means of immunohistochemistry in the human epididymis. Epithelial cells of the ductuli efferentes and the corpus epididymidis were positive for cytokeratins and vimentin. The expression of epithelial vimentin decreased toward the cauda epididymidis, whereas cytokeratins remained unchanged. The epithelium of the ductus deferens was negative when antibodies against vimentin were used. With monoclonal antibodies to individual cytokeratins, the presence of cytokeratins 7, 8, 18, and 19 was demonstrated histochemically throughout the epithelium of the epididymis. Monoclonal antibodies specific for cytokeratin 17 allowed immunohistochemical differentiation between the ductuli efferentes and the ductus epididymidis.

Mechano-chemical control of human endothelium orientation and size

Human umbilical vein endothelial cells (EC) were grown on elastic silicone membranes subjected to cyclic stretch, simulating arterial wall motion. Stretching conditions (20% amplitude, 52 cycle/min) stimulated stress fiber formation and their orientation transversely to the strain direction. Cell bodies aligned along the same axis after the actin cytoskeleton. EC orientation response was inhibited by the adenylate cyclase activator, forskolin (10(-5) M), which caused stress fiber disassembly and the redistribution of F-actin to the cortical cytoplasm. Preoriented EC depleted of stress fibers by forskolin treatment retained their aligned state. Thus, stress fibers are essential for the process of EC orientation induced by repeated strain, but not for the maintenance of EC orientation. The monolayer formed by EC grown to confluence in conditions of intermittent strain consisted of uniform elongated cells and was resistant to deformation. In contrast, the monolayer assembled in stationary conditions was less compliant and exposed local denudations on initiation of stretching. When stretched in the presence of 10(-5) M forskolin it rapidly (3-4 h) reestablished integrity but gained a heterogeneous appearance since denuded areas were covered by giant cells. The protective effect of forskolin was because of the stimulation of EC spreading. This feature of forskolin was demonstrated while studying its action on EC spreading and repair of a scratched EC monolayer in conventional culture. Thus mechanical deformation and adenylate cyclase activity may be important factors in the control of endothelium morphology in human arteries.

Opioid peptides modulate the organization of vimentin filaments, phagocytic activity, and expression of surface molecules in monocytes

It is theorized that intermediate filaments are important in the modulation of membrane activity and cell motility; however, their functions are unknown. The assembly and organization of these filaments are under hormonal regulation. We investigated in human monocytes the in vitro effects of Met-enkephalin, Leu-enkephalin, and beta-endorphin on the expression of immunoreactive cytoskeletal vimentin filaments. We simultaneously examined their effect on the phagocytosis of Candida albicans and on the membrane display of surface molecules. The three opioid peptides markedly reduced the expression of vimentin filaments, the phagocytic activity, and the display of HLA-DR molecules at concentrations of 10(-6), 10(-8), and 10(-10) M. On the other hand, the intravenous administration of fentanyl, a synthetic opiate agonist, to patients undergoing surgery induced similar changes in monocytes. In other experiments, 10(-8) M beta-endorphin also decreased the expression of CR3 but did not influence the display of CD13, a surface protein of unknown function. Expression of vimentin filaments correlated directly with the display of HLA-DR antigens and CR3 and with the phagocytic activity. The results of this paper indicate that opiates and opioids, neuropeptides known to be released during stress, can directly depress several monocyte functions. Furthermore, from these data it may be speculated that intermediate filaments may regulate the membrane expression of some surface molecules and the phagocytic process.

Association of mRNA and eIF-2 alpha with the cytoskeleton in cells lacking vimentin

The human bladder carcinoma cell lines RT4 and T24 and the human breast adenocarcinoma cell line MCF-7 were found to be negative for vimentin when studied by means of immunofluorescence and immunoblotting. Northern blot analysis revealed that these cells lacked detectable levels of vimentin mRNA with the exception of T24, which contains trace amounts of vimentin mRNA compared to the RNA level in vimentin-containing HeLa cells. CAT assays performed on these cells showed that a hamster vimentin promoter is inactive in RT4 and MCF-7 cells. In the vimentin-lacking cells, the binding of polyribosomes, specific mRNAs, and translation factor eIF-2 alpha to the cytoskeletal fraction was examined. Our results indicate that the presence of a vimentin network is not crucial for the association of the translation machinery with the cytoskeleton. Furthermore, in these vimentin-negative cell lines the immunofluorescence staining pattern of eIF-2 alpha shows a fibro-granular structure that has no resemblance to the cytokeratin or actin cytoskeleton present in these cells.

Involvement of vimentin in the reverse transformation reaction

An organized cytoskeleton is required for the cAMP-induced reverse transformation reaction in CHO-K1 cells. In the course of the reaction a considerable fraction of the genome changes its nuclease sensitivity. The current paper presents the following evidence that cAMP-induced phosphorylation of vimentin is an early step in this reaction complex. (i) Vimentin is only slightly phosphorylated in transformed CHO-K1 cells but is heavily phosphorylated in normal fibroblasts. (ii) cAMP addition almost triples the vimentin phosphorylation of CHO-K1 cells but does not change that of normal cells. (iii) Vimentin phosphorylation is one of the earliest phenomena to occur after addition of cAMP to CHO-K1 cells, preceding the cell-stretching reaction and other manifestations of reverse transformation. (iv) Indirect immunofluorescence experiments demonstrate that vimentin appears as a condensed mass in transformed CHO-K1 cells but cAMP addition restores the filamentous structure characteristic of the normal fibroblast. (v) Other transformed cells unresponsive to reverse transformation by cAMP failed to demonstrate increased phosphorylation of vimentin on treatment with cAMP. These results support the proposed scheme that phosphorylation of cytoskeletal elements initiates a large-scale genetic regulatory action in which a substantial change in the spectrum of genome exposure and sequestration occurs. A function for intermediate filaments in reverse transformation is implied.

Ultrastructural immunogold labelling of vimentin filaments on postembedding ultrathin sections of arachnoid villi and meningiomas

An immunoelectron microscopic technique for the labelling of vimentin intermediate filaments on postembedding ultrathin sections is reported. Arachnoid villi obtained at autopsy and meningiomas at surgery were fixed in 1% paraformaldehyde for 30 minutes, embedded without postfixation in Epon-Araldite mixture and polymerized at 37 degrees C for 3 weeks. Ultrathin sections were etched in 2% KOH for 3 minutes and incubated with anti-vimentin monoclonal antibodies which were subsequently labelled with goat anti-mouse IgG coupled to colloidal golds. All of these labelling procedures were consistently performed within 4 hours. In both arachnoidal and meningioma cells, immunogolds preferentially decorated the intermediate filaments in proportion to the concentration. Very few gold particles were seen over the nucleus, Golgi zone, mitochondria and the extracellular connective tissue fibres. The present technique may be applied to the immunogold labelling of intermediate filaments on postembedding ultrathin sections.

Vimentin: changes in distribution during brain development

This paper examines both the anatomical changes in the distribution of vimentin intermediate filament protein and the biochemical changes in vimentin and its degradative enzyme during postnatal brain development in the tree shrew (Tupaia belangeri). A pattern of multiple immunoreactive bands at birth (postnatal day 0, or P0) was revealed in nitrocellulose blots of polyacrylamide gels ("Western blots"). These multiple bands gradually disappear during development, and in the adult a single band at the published molecular weight for vimentin (57 kD) is seen. This pattern of bands probably reflects shifts in the activity of a calcium-activated vimentin protease. The changes in the anatomical distribution of vimentin-immunoreactive (vimentin+) cells and their fine processes parallel the biochemical shifts seen in immunoblots. We have examined the neocortex, lateral geniculate nucleus (LGN), and hippocampus in detail. During the first postnatal week, vimentin+ glia, especially radial glia, are prominent in both neocortex and hippocampus. In contrast, only a few vimentin+ radial glia remain in the thalamus at this age. Vimentin+ glia appear to coincide with bundles of axons and often seem to outline subdivisions of thalamic nuclei. Additionally, cellular layers of the lateral geniculate nucleus (LGN) appear to stain with antibodies to vimentin several days before the characteristic neuronal cell layers appear in this area. During the second postnatal week, vimentin+ cells appear in "patches" throughout the cortex. Some subdivisions of the thalamus and hippocampus (as defined by cytoarchitectonic differences in the adult) are distinct when the tissue is stained with an antibody to vimentin, even though a conventional Nissl stain at this age shows no apparent delineation in these same regions. Finally, in the adult, only a few vimentin+ cells remain, primarily in the white matter. Taken together, these results suggest that the remodeling of vimentin+ intermediate filaments in immature glial cells (including radial glia) is paralleled by the action of the enzyme which breaks down these filaments. The apparent activity of this enzyme is high early in development as radial and other glia are rapidly dividing and undergoing morphological changes, with a decrease in activity in the juvenile and adult brain, as immature glial cells are supplanted by mature forms.

Changing patterns of cytokeratins and vimentin in the early chick embryo

The distribution of cytokeratins and vimentin intermediate filaments in the first 48 h of chick development has been determined using immunofluorescent labelling. During formation of the germ layers, cytokeratin expression is associated with the appearance of an integral epithelium (ectoderm), whereas vimentin expression is associated with cells that detach and migrate from this epithelium to form endoderm and mesoderm. Subsequently, vimentin persists in the endoderm and mesoderm and the tissues derived therefrom, such as the somites and developing heart, throughout the period of study. The appearance of cytokeratins at later stages of development occurs in some epithelia such as the ectoderm, endoderm, lateral plate and epimyocardium but not others including the neural plate, neural tube and somites. Expression of cytokeratins in endoderm and mesenchymal tissues occurs in tandem with vimentin. In conclusion, vimentin expression is related to its distribution in the epiblast before germ layer formation. Its initial appearance may be related to the motile behaviour of cells about to ingress through the primitive streak. The appearance of cytokeratin filaments, however, does not reflect germ layer derivation but rather the need for an epithelial sheet.

Immunocytochemical identification of non-neuronal intermediate filament proteins in the developing Xenopus laevis nervous system

Intermediate filament proteins in the postmetamorphic Xenopus laevis nervous system were identified by their crossreactivities on Western blots with a pan-specific intermediate filament antibody (anti-IFA). These intermediate filament protein bands on Western blots were characterized as 3 cytokeratin-like proteins (49, 55, and 58 kDa), one vimentin-like protein (53 kDa), two distinct glial fibrillary acidic protein (GFAP)-like proteins (60 and 67 kDa), and 3 neurofilament proteins (73, 175, and 200 kDa) by evaluation of their crossreactivities with specific antibodies directed against the mammalian forms of these proteins. This panel of antibodies to mammalian proteins, and two additional antibodies directed against a Xenopus GFAP-like protein and a Xenopus neurofilament (NF-M) protein, were used in immunocytochemical studies to determine the developmental expression of these proteins in the Xenopus nervous system. The first antigen to be detected during development was cytokeratin immunoreactivity, which was located in the inner lining of the embryonic neural tube as early as stage 19, and which in immunocytochemical studies in postmetamorphic frogs was abundant in meninges and processes forming the ventricular lining of the ependymal zone. Vimentin immunoreactivity was found in numerous neuroepithelial cell processes in the rhombencephalon and anterior spinal cord by stage 22, in the prosencephalon by stage 33/34, and in the retina by stage 29/30. In the postmetamorphic frog, vimentin immunoreactivity was found to be abundant in radial processes throughout the brain and spinal cord. NF-M protein immunoreactivity was first detected in neurons in the developing neural tube between stages 22 and 24, in the retina by stages 29/30, and continued to increase throughout development. GFAP-like immunoreactivity was detected very early in radial cells in the neural tube (stage 24), and by stage 42 was found throughout the nervous system. This early appearance of GFAP-like immunoreactivity implies that the onset of glial cell differentiation is a relatively early event in Xenopus.

Keratin and vimentin expression in early organogenesis of the rabbit embryo

The expression of vimentin and keratins is analysed in the early postimplantation embryo of the rabbit at 11 days post conceptionem (d.p.c.) using a panel of monoclonal antibodies specific for single intermediate filament polypeptides (keratins 7, 8, 18, 19 and vimentin) and a "pan-epithelial" monoclonal keratin antibody. Electrophoretic separation of cytoskeletal preparations obtained from embryonic tissues, in combination with immunoblotting of the resulting polypeptide bands, demonstrates the presence of the rabbit equivalents of human keratins 8, 18, and vimentin in 11-day-old rabbit embryonic tissues. Immunohistochemical staining shows that several embryonic epithelia such as notochord, surface ectoderm, primitive intestinal tube, and mesonephric duct, express keratins, while others (neural tube, dermomyotome) express vimentin, and a third group (coelomic epithelia) can express both. Similarly, of the mesenchymal tissues sclerotomal mesenchyme expresses vimentin, while somatopleuric mesenchyme (abdominal wall) expresses keratins, and splanchnopleuric mesenchyme (dorsal mesentery) expresses both keratins and vimentin. While these results are in accordance with most results of keratin and vimentin expression in embryos of other species, they stand against the common concept of keratin and vimentin specificity in adult vertebrate tissues. Furthermore, keratin and vimentin are not expressed in accordance with germ layer origin of tissues in the mammalian embryo; rather the expression of these proteins seems to be related to cellular function during embryonic development.

A functional role for intermediate filaments in the formation of frog virus 3 assembly sites

During the course of frog virus 3 (FV3) infection in baby hamster kidney 21 (BHK) cells, vimentin-type intermediate filaments reorganize to surround the virus's cytoplasmic assembly sites. To determine whether the association between vimentin filaments and viral assembly sites has a functional role in the virus life-cycle, we treated cells with the antimicrotubule drugs taxol or colchicine, or injected them with monoclonal antivimentin antibodies prior to FV3 infection. Each of these reagents caused the collapse of the normally extended BHK intermediate filament system. In the case of taxol-treated or antivimentin-injected cells, the collapsed vimentin filaments were unable to reorganize around the newly forming viral assembly sites. The viral assembly sites that did form were aberrant and there was a significant reduction in the number of mature virions present. Colchicine, which also caused the collapse of vimentin filament organization, did not block the reorganization of vimentin filaments in response to viral infection and viral assembly sites appeared normal. These results suggest that intermediate filaments play an important role in maintaining the structural and functional integrity of FV3 assembly sites.

Organizational fate of vimentin during redistribution of surface immunoglobulin in mouse splenic lymphocytes

We have used immunofluorescence to examine the organizational fate of vimentin and its spatial relationship to the microtubule system during antibody-induced redistribution of surface immunoglobulin (sIg) in control and drug-treated mouse splenic lymphocytes. In control cells, vimentin is relocalized as a diffuse accumulation underneath the site of the cap during sIg redistribution. Observations on cells that were treated with colcemid or taxol prior to induction of sIg redistribution have further shown that vimentin accumulation corresponds to a dynamic rearrangement of this filamentous system which is related to, but is not required for, the energy-dependent translocation of sIg.

Expression of glial fibrillary acidic protein in rat C6 glioma relates to vimentin and is independent of cell-cell contact

Glial fibrillary acidic protein (GFAP) was induced in rat C6 glioma cells grown in M199 and HAM F10 media by addition of 1 mM dibutyryl cyclic AMP. The amount of GFAP per cell increased 7- and 33-fold in M199 and HAM F10 media, respectively. GFAP could be induced in each phase of the cell culture except for the lag phase, where GFAP synthesis was delayed until the onset of the logarithmic growth. The induction took place under conditions where the total protein content of the cell decreased. Measurement of the amount of vimentin indicated that GFAP was induced under conditions of low vimentin concentration. Our results do not support the hypothesis that GFAP induction depends on cell-cell contact or cell proliferation. They indicate a shift from vimentin to GFAP synthesis by an as yet unknown mechanism.

IgG binding to cytoskeletal intermediate filaments activates the complement cascade

The cellular plasma membrane becomes permeable to macromolecules during the cell injury process. This results in exposure of the interior of the cell to plasma proteins and to high-affinity binding of the Fc part of IgG to intermediate filaments (Hansson, G K, Starkebaum, G A, Benditt, E P & Schwartz, S M, Proc natl acad sci USA 81 (1984) 3103). Such IgG binding could be an early step in a process that serves to eliminate the injured cell. We have now identified its effect on the complement system. Intermediate filaments were reconstituted in vitro from purified vimentin, and incubated with plasma proteins. Cross-linker experiments showed binding of the heavy chain of IgG to vimentin, indicating that the vimentin protein carries an Fc-binding site. In contrast, no direct binding of complement factor Clq to vimentin could be detected. Binding of both IgG and Clq could, however, be detected by immunofluorescence when cytoskeletons of cultured endothelial cells were incubated with fresh serum. Therefore, IgG binding to filaments in the presence of serum is accompanied by Clq binding to IgG. This was in turn followed by fixation of C4 and C3 to intermediate filaments in a process that was dependent on both Ca2+, Mg2+ and Clq, indicating that it was part of a complement activation via the classical pathway. Exposure of fresh serum to intermediate filaments also resulted in production of the anaphylatoxic complement cleavage fragment. C3a, with a dose-response relationship between the amount of filaments present and the amount of C3a generated. Chemotactic activity towards granulocytes and monocytes was also generated by exposure of serum to intermediate filaments, and this activity was dependent on the presence of complement factor C5 and on the classical complement activation cascade, implying that it was due to the C5a peptide. Exposure of the interior of the cell to plasma proteins thus results in binding of IgG to intermediate filaments and activation of the complement cascade via the classical pathway. This, in turn generates bioactive mediators which may recruit leukocytes to the injured cell (C5a) and have profound effects on vascular permeability (C3a, C5a). We propose that this is part of a scavenger mechanism for the elimination of damaged cells.

Wound healing of human skin transplanted onto the nude mouse. II. An immunohistological and ultrastructural study of the epidermal basement membrane zone reconstruction and connective tissue reorganization

The reconstruction of human epidermis during healing of human skin wounded after grafting onto the nude mouse was described in a previous paper (M. Démarchez, P. Sengel, and M. Pruniéras, 1986, Dev. Biol. 113, 90-96). The regeneration of the epidermal basement membrane zone (BMZ) and the reorganization of the connective tissue are the subjects of the present study. They were investigated by two complementary methods: electron microscopy to analyze the BMZ reorganization, and indirect immunofluorescence with species-specific and cross-reacting antibodies directed against laminin, bullous pemphigoid antigen, mouse or human collagens of types I or IV, human elastic fibers, fibronectin, fibrin, actin, and human vimentin, to examine the species origin and distribution of BMZ and connective tissue components during the regeneration process. It is reported that grafted human skin preserves its own immunological markers not only in the epidermis but also in the BMZ and dermis as well, and that, after injury, its regeneration proceeds according to the following sequence of overlapping events: production of a mouse granulation tissue; reepidermization by human cells; reconstruction of a BMZ with human characteristics; formation of a human neodermis. It is concluded that human skin grafted onto the nude mouse is able to regenerate its three structural compartments, namely, the epidermis, BMZ, and dermis. Interestingly, it appeared, also, that the connective tissue regeneration would be a two-step mechanism including the sequential formation of two tissues of distinct sources, namely, a granulation tissue and a neodermis.

Influence of phospholipids on the formation and stability of vimentin-type intermediate filaments

The interaction of vesicles produced from individual phospholipids and mixtures thereof with preformed vimentin filaments as well as the influence of these vesicles on filament assembly were investigated employing negative stain electron microscopy and sucrose density gradient equilibrium centrifugation. Liposomes with a phospholipid composition characteristic of Ehrlich ascites tumor cells were able to bind efficiently to vimentin filaments without significantly affecting their morphology at higher concentrations. However, in sucrose density gradient centrifugation partial disintegration of the filaments was observed. In addition, larger quantities of phospholipid mixture totally blocked intermediate filament (IF) formation. Using vesicles of individual phospholipids, these effects could be shown to be due to the presence of negatively charged lipid species in the phospholipid mixture. While these were highly active in preventing filament assembly and in dissociating preformed filaments, electrically uncharged phospholipids were virtually inactive. The highest efficiency was shown by phosphatidylinositol-4,5-diphosphate. These results demonstrate that a negative surface charge of liposomes is an essential prerequisite for their successful and tight association with vimentin filaments. However, the high susceptibility of these filaments to photoaffinity labeling with the membrane-penetrating reagent 1-azidopyrene in the presence of phospholipid vesicles, points to additional interactions between hydrophobic regions of both reactants. Finally, the data also suggest a direct relationship between IFs and the lipid bilayer as the active principle underlying the association of IFs with natural membranes as observed by electron and immunofluorescence microscopy.

Transient coexpression of cytokeratin and vimentin in differentiating rat Sertoli cells

The expression of cytokeratin and vimentin type intermediate filaments were studied in fetal, postnatal, and adult rat testes. Immunocytochemical observations were correlated with the light and electron microscopic analysis of the developing organs. The Sertoli cell precursors in 15-day-old fetal testes contained both cytokeratin and vimentin. A gradual reorganization of both filaments, accompanied by a decrease of cytokeratin-positivity, was observed toward the end of the fetal period. The simultaneous presence of cytokeratin and vimentin in the same cells was shown by double immunofluorescence of newborn testes and the primary culture of dissociated testicular cells. In postnatal Sertoli cells, cytokeratin-positivity continued to decrease and disappeared by the age of 14 days. The increase in vimentin content and the appearance of axially oriented vimentin filaments coincided with the acquisition of the columnar shape of the Sertoli cells. The presence of cytokeratin and vimentin in fetal and newborn testes, and only vimentin in the adult testes was confirmed by immunoblotting. The present results suggest that major qualitative changes in the expression of intermediate filament proteins can take place during the embryonic development. The expression of cytokeratin in developing Sertoli cells, although only transient, supports the epithelial origin of these cells and can be applied as a marker for embryonic and early postnatal Sertoli cells.

Epithelial and mesenchymal cell differentiation in the fetal rat genital ducts: changes in the expression of cytokeratin and vimentin type of intermediate filaments and desmosomal plaque proteins

Mesonephric and paramesonephric ducts develop in different ways in male and female fetuses. We have analyzed the changes in the expression of cytokeratin and vimentin type of intermediate filaments and desmosomal plaque proteins in progressing and regressing genital ducts of rat fetuses. The concomitant changes in the basement membranes were detected by laminin antibody. Epithelial cells of the indifferent (Day 15) male and female mesonephric and paramesonephric ducts contained faint vimentin positivity which, however, later disappeared. Indifferent mesonephric duct epithelium stained strongly for cytokeratin, whereas in the corresponding paramesonephric duct only a weak and spotty positivity was seen. Immunocytochemical localization of cytokeratin filaments and desmosomal plaque proteins correlated with the ultrastructural differences in the apical junctional complexes of the mesonephric and paramesonephric ducts. Regardless of the ongoing regression of the male paramesonephric duct, cytokeratin positivity increased in the disorganizing epithelium; the most weak and a granular immunoreaction was seen in the cells found in the intensively vimentin-positive periductal mesenchyme. In the regressing female mesonephric duct cytokeratin positivity was lost before the final dissolution of the basement membrane. Immunoblotting analysis of cytokeratin and vimentin polypeptides of the individual genital ducts were in agreement with the immunocytochemical results obtained in 15- and 16-day-old fetuses. The results suggest that the expression of vimentin type intermediate filaments is an indication of the mesothelial origin of the genital ducts. The increase in cytokeratin positivity of the regressing paramesonephric duct epithelium suggests that the degenerative changes are initiated by the mesenchyme. Cytokeratin-positive cells found in the periductal mesenchyme of the male paramesonephric duct may be epithelial cells transforming into mesenchyme. The results emphasize a close relationship between the changes of the intermediate filament system and extracellular matrix upon differentiation of the fetal genital ducts.

Role of cytoskeletal elements in the retractile activity of human skin fibroblasts

Giant axonal neuropathy skin fibroblasts, which are characterized by a selective and partial disorganization of vimentin filaments [1] exhibited, when compared with normal skin fibroblasts, less fibrin clot retractile (FCR) activity and spreading within the fibrin clot both during active growth and resting stage. Skin fibroblasts derived from patients affected with adenomatosis of the colon and rectum, which display a disorganized actin network [2], exhibited reduced FCR activity and spreading within the fibrin clot only during resting stage. FCR inhibition was also obtained by treating the cells with colcemid, cytochalasin B (CB) and dihydrocytochalasin B. The data suggest that FCR activity is under the control of different cytoskeletal structures. For the first time, a direct involvement of intermediate-sized filaments could be demonstrated in the interaction between fibroblasts and an organic substratum.