Cell density and cell shape-related regulation of vimentin and cytokeratin synthesis. Inhibition of vimentin synthesis and appearance of a new 45 kD cytokeratin in dense epithelial cell cultures

L1-mediated colon cancer cell metastasis does not require changes in EMT and cancer stem cell markers

Aberrant activation of Wnt/β-catenin signaling is common in most sporadic and inherited colorectal cancer (CRC) cells leading to elevated β-catenin/TCF transactivation. We previously identified the neural cell adhesion molecule L1 as a target gene of β-catenin/TCF in CRC cells. Forced expression of L1 confers increased cell motility, invasion, and tumorigenesis, and the induction of human CRC cell metastasis to the liver. In human CRC tissue, L1 is exclusively localized at the invasive front of such tumors in a subpopulation of cells displaying nuclear β-catenin. We determined whether L1 expression confers metastatic capacities by inducing an epithelial to mesenchymal transition (EMT) and whether L1 cosegregates with cancer stem cell (CSC) markers. We found that changes in L1 levels do not affect the organization or expression of E-cadherin in cell lines, or in invading CRC tissue cells, and no changes in other epithelial or mesenchymal markers were detected after L1 transfection. The introduction of major EMT regulators (Slug and Twist) into CRC cell lines reduced the levels of E-cadherin and induced fibronectin and vimentin, but unlike L1, Slug and Twist expression was insufficient for conferring metastasis. In CRC cells L1 did not specifically cosegregate with CSC markers including CD133, CD44, and EpCAM. L1-mediated metastasis required NF-κB signaling in cells harboring either high or low levels of endogenous E-cadherin. The results suggest that L1-mediated metastasis of CRC cells does not require changes in EMT and CSC markers and operates by activating NF-κβ signaling.

Bioreactor for mammalian cell culture

Purpose of this article is to review the current status of bioreactor design for mammalian cell culture. Morphological and biochemical features of two major mammalian cell groups, anchorage-dependent and independent cells are proposed as a basis for different behavior at their cultivation. Different bioreactor configurations are systematically discussed through enumerating elementary physical phenomena and through stressing their physiological significance. Special considerations are given to those areas which are inherent to mammalian cell bioreactor.

Basal cytokeratins and their relationship to the cellular origin and functional classification of breast cancer

Recent publications have classified breast cancers on the basis of expression of cytokeratin-5 and -17 at the RNA and protein levels, and demonstrated the importance of these markers in defining sporadic tumours with bad prognosis and an association with BRCA1-related breast cancers. These important observations using different technology platforms produce a new functional classification of breast carcinoma. However, it is important in developing hypotheses about the pathogenesis of this tumour type to review the nomenclature that is being used to emphasize potential confusion between terminology that defines clinical subgroups and markers of cell lineage. This article reviews the lineages in the normal breast in relation to what have become known as the 'basal-like' carcinomas.

Functional and molecular characterisation of mammary side population cells

BACKGROUND

Breast cancer is thought to arise in mammary epithelial stem cells. However, the identity of these stem cells is unknown.

METHODS

Studies in the haematopoetic and muscle systems show that stem cells have the ability to efflux the dye Hoechst 33342. Cells with this phenotype are referred to as the side population (SP). We have adapted the techniques from the haematopoetic and muscle systems to look for a mammary epithelial SP.

RESULTS

Of mammary epithelial cells isolated from both the human and mouse mammary epithelia, 0.2-0.45% formed a distinct SP. The SP was relatively undifferentiated but grew as typical differentiated epithelial clones when cultured. Transplantation of murine SP cells at limiting dilution into cleared mammary fat pads generated epithelial ductal and lobuloalveolar structures.

CONCLUSION

These data demonstrate the existence of an undifferentiated SP in human and murine mammary epithelium. Purified SP cells are a live single-cell population that retain the ability to differentiate in vitro and in vivo. Studies of haematopoetic cells have suggested that the SP phenotype constitutes a universal stem cell marker. This work therefore has implications for mammary stem cell biology.

Functional and molecular characterisation of mammary side population cells

It has been brought to our attention that there was an inaccuracy in the above article [1]. In the discussion section the authors state that "One of the assumptions underlying mammary transplant studies is that mammary outgrowths at limiting dilution are clonal (14,000–20,000 cells per cleared fat pad)" and they attribute this to reference 21 "Smith GH: Experimental mammary epithelial morphogenesis in an in vivo model: evidence for distinct cellular progenitors of the ductal and lobular phenotype. Breast Cancer Res Treat 1996, 39:21–31" [2]. In the paper by Smith no claim of clonality is made, rather it is stated that it is not known whether the simultaneous development of both lobular and ductal phenotypes indicates cooperative interaction between the two epithelial progenitors or signals the presence of a third progenitor type capable of producing both ductular and lobular committed daughters. It is, therefore, incorrect that the assumption of clonality based on limiting dilution has been attributed to Gilbert Smith.

Carnosine stimulates vimentin expression in cultured rat fibroblasts

Two-dimensional electrophoretic gel profiles were compared between rat 3Y1 fibroblasts cultured in the presence and absence of 30 mM L-carnosine (beta-alanyl-L-histidine) for one week without any replenishment of medium. While a number of cellular proteins changed their expression levels by the addition of carnosine, we identified one of the most prominently varied proteins as vimentin. Immunoblot analysis with anti-vimentin antibody demonstrated that the vimentin levels increased about 2-fold after one-week culture in the presence of carnosine. We also confirmed that the increase of vimentin expression was dependent on the concentration of carnosine added to the medium. Moreover, when cultured cells were stained with anti-vimentin antibody and observed by light microscopy, most cells grown in the presence of carnosine were found to have markedly developed vimentin filaments. The increase of vimentin expression was also observed by adding with carnosine related dipeptides, N-acetylcarnosine and anserine.

Differentiation of cyst-forming stria vascularis tissues in vitro

The marginal cells of the stria vascularis possess distinctive morphological characteristics associated with their role in endolymph production. Interestingly, when stria-derived epithelial cells are grown in association with the underlying mesenchyme, the final differentiation of these cell types does not occur. Beyond the rudimentary polarity that is established, similar to that shown in epithelial monolayers, cells in culture bear only a slight resemblance to their marginal cell counterparts in vivo. The ultrastructural features that typify these epithelia, extensive cytoplasmic invaginations, with an abundance of mitochondria, and darkly stained cytoplasm, are not evident under standard culture conditions. In order to determine whether fluid transport, a key function of the stria vascularis, has an effect on the ultrastructural morphology, we examined de novo stria vascularis tissues that formed a fluid-filled cyst in vitro. We found that only cells associated with the luminal structure demonstrated dark cytoplasmic staining and amplification of the basolateral membrane of the marginal cells. Additionally, other epithelial features, such as mitochondria-rich and microvilli-rich cells, were observed in cyst-forming tissues. The enhancement of the marginal cell specializations was not as robust as that observed in vivo; however, they were clearly more extensive when compared to cells in the same culture that were not associated with a fluid-filled lumen. Thus it appears that fluid transport may be necessary to maximize differentiation of stria vascularis tissues in vitro.

Contrasting effects of K8 and K18 on stabilizing K19 expression, cell motility and tumorigenicity in the BSp73 adenocarcinoma

The co-expression of vimentin and keratin-type intermediate filaments in the same cell was often reported to correlate with increased invasiveness and a more aggressive tumorigenic phenotype. To address the possible physiological relevance of these observations, we transfected simple keratins (K8 and 18) either individually, or in combination, into a tumorigenic but non-metastatic pancreatic adenocarcinoma that expresses vimentin but no keratins. Expression of K8 resulted in the stabilization of endogenous K19 in these cells, and formation of keratin filaments containing K8 and K19. Transfection of K18 yielded unstable K18 protein, but K18 could be stabilized when K8 was co-expressed in the same cells. Clones expressing K18 alone, or together with K8, displayed a reduced ability to grow in soft agar and decreased motility when compared to control, or K8/19 expressing cells. Moreover, K18 expressing cells were dramatically inhibited in their ability to form tumors when injected into syngeneic animals. The extent of suppression in the tumorigenicity of these cells correlated with the level of K18 expressed by these cells. The results show that K18 expression in cells may result in the suppression of the motile and tumorigenic abilities of this adenocarcinoma.

Expression of the intermediate filament-associated protein related to beta-amyloid precursor protein is developmentally regulated in cultured cells

It was previously reported that a monoclonal antibody to beta-amyloid precursor protein (mab22C11; Boehringer Mannheim, Indianapolis, IN) labels an intermediate filament-associated protein (beta APP-IFAP) in cultured human skin fibroblasts (Dooley et al.: J Neurosci Res 33:60-67, 1992). The time course of its expression and association with different classes of intermediate filaments has been assessed in neurons, Schwann cells, and astrocytes in dissociated cultures of murine brain and spinal cord-dorsal root ganglia; in primary cultures of human muscle; and in the epithelial cell line PtK1. beta APP-IFAP was expressed in all non-neuronal cell types examined. Mab22C11 immunoreactivity was minimal or absent following dissociation or subculture, but gradually increased with time. In fibroblasts, myoblasts, and epithelial cells, the distribution eventually resembled that of vimentin. With the exception of glial fibrillary acidic protein (GFAP), beta APP-IFAP was not associated with the intermediate filament proteins characteristically found in differentiated cells, i.e., desmin, the cytokeratins, and neurofilament proteins. No labeling of neurons by mab22C11 was observed at any stage of in vitro maturation. In sections of Alzheimer's brain, the antibody labeled a subpopulation of reactive astrocytes. It is suggested that beta APP-IFAP may be the product of a member of the beta APP multigene family expressed developmentally in non-neuronal cells.

Paracrine interactions among parathyroid cells: effect of cell density on cell secretion

Cell-cell interactions are important in the regulation of endocrine cell secretion. To investigate the possibility that cell communication may alter the regulation of parathyroid cell secretion, we utilized the reverse hemolytic plaque assay (RHPA) to measure parathyroid hormone (PTH) release from individual cells. Bovine parathyroid cells were dispersed and plated with protein A-conjugated erythrocytes at cell densities ranging from 0.9 to 36 x 10(2) cells/cm2 in 0.2 mM calcium. Cell populations were greater than 98% homogenous as determined by immunocytochemistry and in situ hybridization for PTH mRNA. Plaques were developed and data analyzed for the amount of PTH per cell released (plaque area in microns 2 x 10(4)) and the determination of cell recruitment (% plaques formed). A positive correlation existed between parathyroid cell density and the amount of PTH released. As the distance between cells increased, the plaque area (amount of PTH released per cell) decreased (ranging from 1.0 x 10(4) microns 2 at 0.9 x 10(2) cells/cm2 versus 1.6 x 10(4) microns 2 at 36 x 10(2) cells/cm2). The percentage of cells releasing PTH (recruitment) also decreased (16% at 0.9 x 10(2) cells/cm2 versus 47% at 36 x 10(2) cells/cm2). These data suggest that parathyroid cells in close proximity are stimulated to secrete more hormone than those at lesser densities. In addition, parathyroid cells are recruited to secrete PTH when plated at high density. Factor(s) released by the parathyroid cell may increase cell responsiveness and stimulate secretion in a paracrine fashion.

Cytokeratin reorganization induced by adenosine diphosphate in kidney epithelial cells

Exogenous adenosine diphosphate (ADP), the most potent mitogen for nontransformed African green monkey kidney epithelial cells of the BSC-1 line, rapidly alters the appearance of the cell monolayer. Examination of the cells with indirect immunofluorescence using monoclonal antibodies reveals a considerable reorganization of cytokeratin filaments without a major change in the pattern of microtubules or microfilaments. In untreated confluent cells, cytokeratin filaments are predominantly confined to a star-like spot in the perinuclear area, but these can be seen to begin to spread within 2 min after addition of ADP. The effect is particularly notable using anti-cytokeratin 8 antibodies. At 6 h this process is complete and produces a well-developed filamentous network throughout the cell. By 12 h, the network appears to collapse, so that the filaments again form a spot in the perinuclear area, a process that is complete by 24 h. Immunoblotting of total cellular proteins reveals no apparent alterations in the amounts of several species of cytokeratins, including cytokeratin 8 and 18, at 3 or 24 h after exposure to ADP. Other purine and pyrimidine nucleotides which do not stimulate DNA synthesis in these cells fail to alter cytokeratin organization, and there is no apparent alteration in the distribution of vimentin, another intermediate filament protein. The rapid ADP-induced cytokeratin reorganization appears to coincide with the induction of early growth-response gene transcription in these cells and may be correlated with the capacity of ADP to subsequently initiate DNA synthesis. This dramatic and reversible cytokeratin reorganization immediately after exposure to ADP may be an important step in the mitogenic signal transduction pathway.

Nucleokinesis: distinct pattern of cell translocation in response to an autocrine motility factor-like substance or fibronectin

Human lung adenocarcinoma cells develop bipolar shape with prominent pseudopodia (greater than or equal to 200 microns) when cultured in the presence of autocrine motility factor (AMF)-like substance or on fibronectin-coated substrata. AMF was partially purified from a human lung adenocarcinoma cell line and has a peak biological activity at a molecular mass of 67 kDa. Using time-lapse photography, we observed that during AMF- or fibronectin-induced cell translocation, the nuclei of some bipolar cells are transported to the opposite end of the cell, while gross cell shape and position remain unchanged. Following this nuclear movement, which we call "nucleokinesis," the posterior pseudopodium is retracted behind the nucleus. Thus, extension of a pseudopodium followed by nucleokinesis in the same direction and retraction of the cell body behind the nucleus is a normal motile sequence in translocating bipolar cells. This suggests that nucleokinesis is a distinct step in whole-cell translocation of bipolar cells on biological substrata and that pseudopodia can be used as nuclear transport organs. In contrast, adenocarcinoma cells cultured on artificial substrata and in the absence of AMF display a fibroblast-like motility pattern with the nucleus centrally located within the migrating cell.

Cultivation, characterization and modulation of rat thymic nonlymphoid cells in vitro

Thymic fragments of young adult rats were cultivated in vitro using an explant technique. Two weeks later, non-lymphoid cells were characterized by enzyme-cytochemistry and immuno-cytochemistry. Based on cytomorphological criteria and cell-specific markers approximately 95% of cells were classified into 3 main types: epithelial cells, macrophages and fibroblasts. The effect of dexamethasone and amphotericin B, known modulators of cell growth in culture was also studied. Quantitative analysis showed that amphotericin B inhibited proliferation of macrophages and epithelial cells, while dexamethasone suppressed proliferation of fibroblasts and promoted growth of epithelial cells.

Altered expression of keratin and vimentin in human retinal pigment epithelial cells in vivo and in vitro

Actively proliferating human retinal pigment epithelial (RPE) cells grown in tissue culture possess keratin-containing intermediate filaments that react with a combination of AE1 and AE3 anti-keratin monoclonal antibodies. Antibody reactivity is lost, however, from RPE cells as the cell population ceases to proliferate when it approaches confluence and attains morphological characteristics more similar to those in vivo. In contrast, clone 8.13 anti-keratin antibody stains all cells in the culture at all stages of the growth cycle and cell densities. These findings were reflected in vivo using retinal pigment epithelium taken directly from the eye. Normal non-proliferating RPE cells bound 8.13 antibody to cytoskeletal structures, as judged by indirect immunofluorescence, but did not bind AE1/AE3 antibodies. However, proliferating dedifferentiated RPE cells from the vitreous humor of patients with proliferative vitreoretinopathy possess filaments that bind both AE1/AE3 and 8.13 antibodies. Thus it appears that structures detected by AE1/AE3 antibodies only occur in actively growing RPE cells in vitro and in vivo. Keratins produced by RPE cells were identified using Western blotting. Species with molecular masses of 54 (keratin 7), 52 (keratin 8), 42 (keratin 18), and 40 (keratin 19) kiloDaltons were the most abundant in proliferating cultured cells, but cells isolated directly from the eye were found to lack keratin 7 and 19. Keratin 19 was, however, observed in proliferating RPE cells from some patients with proliferative vitreoretinopathy. The latter findings explain the differential staining observed with AE1/AE3 antibodies in cells in culture and isolated directly from the eye since these antibodies interact primarily with keratin 19 which is absent from non-proliferating RPE cells. In contrast to the presence of keratin-containing intermediate filaments in human RPE cells in vivo, there are apparently no detectable vimentin-containing cytoskeletal structures. However, all RPE cells cultured in vitro develop filaments composed of vimentin which persist in cells that have reached confluence.

Intermediate filaments in the inner ear of normal and experimentally damaged guinea pigs

The hypothesis that proteins known to occur in glial cells in the central nervous system may be present in inner-ear supporting cells was investigated. Immunocytochemical techniques were used to look for the existence of two classes of intermediate filaments, vimentin and glial fibrillary acidic protein (GFAP), in cellular elements of the inner-ear epithelium in normal and experimentally damaged guinea-pig cochleas. Vimentin is present in two types of supporting cells in the normal organ of Corti: Deiters' cells and inner pillar cells. Differences in intensity and distribution of vimentin immunostaining are observed across the three rows of Deiters' cells. GFAP immunoreactivity was not detected in any supporting-cell type in the organ. Cochlear hair cells were not labeled for either GFAP or vimentin. Following hair-cell destruction by exposure to noise or the administration of aminoglycosides, GFAP and vimentin are not present in phalangeal scars replacing lost hair cells.

Application of two-dimensional gel electrophoresis in the study of cytoskeletal protein regulation during growth activation and differentiation

Two-dimensional gel electrophoresis was used to study the regulation of cytoskeletal protein synthesis during growth activation and development of the differentiated phenotype. We demonstrated a correlation between the state of organization and the expression of the respective cytoskeletal protein by showing that depolymerization of microtubules leads to a rapid decrease in new tubulin synthesis. We found that the synthesis of vimentin in both fibroblasts and epithelial cells correlates with extensive cell spreading on the substrate, while cytokeratin synthesis is maximal when cell to cell contacts are abundant. The analysis of cytoskeletal elements, involved directly in the formation of cell contacts, revealed that the level of vinculin synthesis is dependent on the extent of adherent type of cell contacts formed. Moreover, we found that the transient disappearance of vinculin from adhesion plaques of quiescent fibroblasts in response to serum factors was followed by an induction of vinculin mRNA and protein synthesis. The morphological changes associated with establishment of the differentiated phenotype were also found to include changes in the expression of the cytoskeletal-extracellular matrix complex. This was demonstrated in several differentiating systems: in 3T3 preadipocytes which change their shape from a fibroblastic to a spherical shape when stimulated to differentiate with adipogenic medium, we observed a decrease in mRNA levels and in the synthesis of fibronectin, beta-integrin, and the microfilament proteins, vinculin, alpha-actinin, tropomyosin and actin. The culturing of these cells on a certain extracellular matrix prevented the morphological changes occurring in the presence of adipogenic medium and blocked the shifts in cytoskeletal- and differentiation-related gene expression. Similar changes in the organization and expression of cytoskeletal proteins were identified during maturation of primary ovarian granulosa cell cultures, stimulated with gonadotropic hormones to form highly steroidogenic cells. The cell rounding and aggregation occurring during this process were associated with a decreased synthesis of vinculin, alpha-actinin, actin and the nonmuscle tropomyosins. The physiological relevance of these changes was suggested by the observation that the level of tropomyosin mRNA was lower in follicles of animals at late stages of granulosa cell maturation when compared to earlier stages. The expression of tissue-specific and cytoskeletal proteins was also determined in primary cultures of liver hepatocytes, maintained under conditions either favorable for growth or for expression of liver-specific functions. When DNA synthesis was elevated, cytoskeletal protein synthesis was high and that of liver-specific proteins was low.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokeratins and cytokeratin filaments in subpopulations of cultured human and rodent cells of nonepithelial origin: modes and patterns of formation

Using immunofluorescence microscopy, we observed that in several established cell culture lines derived from different nonepithelial tissues and species, cells spontaneously emerge, usually at low frequencies, which contain cytoplasmic structures decorated by antibodies specific for cytokeratins 8 and 18. This phenomenon was further examined at both the protein (gel electrophoreses of cytoskeletal proteins, followed by immunoblotting) and the RNA (Northern blots, "nuclear run-on" analysis, in situ hybridization) level. Positive cell lines included simian virus (SV40)-transformed human fibroblasts (HF-SV80, WI-38 VA13), human astrocytic glioma cells (U333 CG/343MG), rat (RVF-SMC) and hamster (BHK-21/13) cells derived from vascular smooth muscle and murine sarcoma MS-180 cells. In two cell lines (HF-SV80 and BHK-21/13), the frequency of the cytokeratin-containing cells and of the cytokeratin fibril arrays per cell was drastically increased upon treatment with 5-azacytidine. The structural appearance of the cytokeratins was variable in the different cell lines but could also differ among cells of the same culture: While small granular or comma-shaped structures or bizarrely shaped filament arrays prevailed in WI-38, RVF and normally grown BHK-21 cells, most of the other lines revealed extended normal-looking, fibrillar arrays. In one line (MS-180), the appearance of cytokeratins was associated with a morphological change, as it was only found in a subpopulation of cells that had lost their typical elongated and spindle-shaped phenotype and assumed a rounded ("coccoid") shape. Our results show that the expression of the genes encoding cytokeratins 8 and 18 is not necessarily restricted to programs of epithelial differentiation and that factors stochastically effective appear in cultured cell lines that allow the synthesis of these cytoskeletal components. Mechanisms possibly involved in this spontaneous and selective advent of cytokeratins 8 and 18 and implications for tumor diagnosis are discussed.

Plasticity of T-cell function. II. Transient induction of CD8 (Ly-2) expression in cloned EL-4 lymphoma cells depending on cell density

EL-4 lymphoma cells are able to suppress the primary humoral immune response of spleen cells to sheep erythrocytes or 4-hydroxy-3-iodo-5-nitrophenylacetyl-keyhole limpet haemocyanin (NIP-KLH) in vitro. Typically, the cells suppress very efficiently in small numbers, but lose this capacity as the numbers increase. Three clones were analysed and this fluctuation in function was paralleled by a fluctuation in the expression of CD8 (Ly-2). Clones were incubated for 2 days, starting from different seeding concentrations, and analysed with cytofluorography. Neither Thy-1 nor CD5 (Ly-1), H-2 K, H-2 D, LFA-1 (all positive) nor CD4 (L3T4) or MEL-14 (both negative) were influenced by this treatment. In contrast, cells were CD8- at high seeding concentrations, and CD8+ at low seeding concentrations. When cell cultures grew to higher densities, the cells again lost the capacity to express CD8. Experiments testing the suppressive capacity of individual EL-4 clones after preculture at different densities or in the presence of antibodies against CD8 suggest that the efficiency of suppression may well be correlated to the amount of CD8 expressed.

Novel redistribution of myosin-containing filaments in cultured keratinocytes identified by a human monoclonal autoantibody

A time-dependent redistribution of microfilaments was observed in cultured human keratinocytes using a human monoclonal autoantibody specific for myosin. Immunofluorescent staining revealed that 5 days after plating keratinocytes in either 0.1 mM or 2.0 mM Ca++, myosin was distributed uniformly throughout the cytoplasm. At day 6, parallel arrays of myosin-containing microfilaments were prominent in the cell peripheries. At day 7 the microfilaments formed circumferential rings. The distribution of the microfilaments was disrupted by cytochalasin but not by colchicine, indicating that this novel distribution of myosin was not dependent on colchicine-sensitive vimentin intermediate filaments. The time-dependent redistribution of myosin was not influenced by cell population density, cell shape or cell cycle phase, except for mitotic cells in which myosin was distributed diffusely through the cytoplasm. If, as suggested by Kolega (9), microfilaments align parallel to the direction of applied tension, the redistribution of myosin-containing microfilaments in cultured keratinocytes may reflect the increased tension between cells resulting from increasing strength of cell-cell junctions over time. In sectioned human skin, myosin was localized in the peripheral cytoplasm of stratified epidermal cells. Tensions arising from the numerous desmosomal junctions between cells in vivo could account for this distribution of myosin.

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.

The pattern of cytokeratin synthesis is a marker of type 2 cell differentiation in adult and maturing fetal lung alveolar cells

During the last stages of fetal life, the immature epithelial cells of the rat lung alveolus develop the properties of mature type 2 cells. Adult type 2 cells rapidly lose these same properties when isolated and maintained in cell culture. We have examined the synthesis of cytokeratin proteins by adult type 2 cells as they lose their differentiated characteristics during 1 week in culture, and of immature fetal alveolar epithelial cells as they differentiate either in utero or when cultured on an extracellular matrix. Freshly isolated adult type 2 cells synthesize four cytokeratins which by electrophoretic mobilities and Western blot analysis correspond to human cytokeratins Nos. 7, 8, 18, and 19. During 7 days in culture synthesis of cytokeratin No. 19 is dramatically decreased and cytokeratin No. 18 becomes the predominant acidic cytokeratin produced. Fetal lung epithelial cells at 18 days gestation lack most characteristics of mature type 2 cells. When freshly isolated, these cells synthesize cytokeratins Nos. 7, 8, and 18 but make only minimal amounts of cytokeratin No. 19. When these cells are allowed to mature either in utero or in culture on a whole basement membrane extract, they develop both the morphological characteristics and the pattern of cytokeratin synthesis of fully developed type 2 cells, with cytokeratins No. 19 being the major acidic cytokeratin produced.

Distribution of vimentin-type intermediate filaments in Sertoli cells of the human testis, normal and pathologic

The presence, distribution and spatial arrangement of vimentin-type intermediate filaments in Sertoli cells from human testis biopsies, were studied in semithin and ultrathin sections using a polyclonal rabbit antiserum. At the ultrastructural level, vimentin immunoreactivity was seen concentrated around the nuclei, along fibrillary material within the cytoplasm and at the ectoplasmic specializations of the Sertoli cell junctions, as well as throughout the periphery of the Sertoli cell processes. It is therefore well suited as a marker for Sertoli cell configuration. In computer-aided 3D reconstructions of 20 serial sections, Sertoli cells displayed particular configurations of intermediate filaments in the different stages of spermatogenesis. Two basic configurations, named AS (before spermiation, stages V, VI, I and II), and PS (after spermiation, stages III and IV) respectively, could be differentiated. In addition to the reconstruction and morphological analysis of vimentin filaments in Sertoli cells from patients with unaltered spermatogenesis (obstructive azoospermia), pathological specimens (spermatogenetic arrest, Sertoli cells only-syndrome) were studied with respect to vimentin immunohistochemistry. The results indicate that vimentin filaments play an important role in the adaptation of Sertoli cells to the varying configurations of neighbouring cells during spermatogenesis as well as under pathological conditions.

3,3',5-Triiodothyronine-induced differences in water-insoluble protein synthesis in primary epidermal cell cultures from the hind limb of premetamorphic Rana catesbeiana tadpoles

Epidermal cells from the hind limb of premetamorphic tadpoles of the American bullfrog Rana catesbeiana (stages IX-XI) were maintained in primary culture for 120 hr. Cultures, maintained for 36 hr in medium supplemented with L-triiodothyronine (T3; 3 x 10(-10) mol T3/ml medium), synthesize water-insoluble proteins with Mrs of 59, 50, 48, and 43. The 59 and 48 kDa proteins synthesized by T3-supplemented cultures are not detectably synthesized by 36-hr-old cell cultures without added T3, but they are synthesized by both hormone-supplemented and unsupplemented cultures after 120 hr. These two proteins have Mrs and pIs which correspond with keratins detected in stratifying mammalian epidermis and are immunoprecipitated by antibodies prepared against human keratins. These observations indicate that T3 induces epidermal cell cultures from the hind limb of premetamorphic tadpoles to precociously synthesize water-insoluble proteins which (1) have Mrs and pIs similar to keratins from differentiating amphibian epidermal tissue and (2) are biochemically and immunologically similar to keratins associated with the differentiation of mammalian epidermal tissue.

Nucleotide sequence of the human vimentin gene and regulation of its transcription in tissues and cultured cells

We have previously reported the identification and isolation by mRNA selection/translation of a recombinant clone containing 80% of the human vimentin gene sequence [Lilienbaum et al., EMBO J. 5 (1986) 2809-2814]. We present here the nucleotide sequence of this genomic clone including the 3' untranslated region. To complete the coding sequence, we have isolated cDNA recombinant clones (1.1 kb) of vimentin from human libraries constructed in lambda gt11. Comparison of the coding sequence between human and hamster shows 90% homology at the nucleotide level and four differences out of 353 amino acid residues, as deduced from the nucleotide sequences. In addition to the extensive homology previously reported between the coding sequences of hamster and human vimentin genes [Ferrari et al., Mol. Cell. Biol. 6 (1986) 3614-3620], we observed that the positions of the noncoding regions are also conserved and that the 3' nontranslated region includes two canonic poly(A) signals. Hybridization of the clones to mRNA from different mammalian sources revealed a single species of 2 kb and confirmed that the length of the untranslated and coding sequences are conserved. Quantitative estimations of the mRNA levels in mammalian cells and tissues of various origins are consistent with transcriptional regulation.

The thymic microenvironment. Characterization of in vitro differentiation of the IT26R21 rat thymic epithelial cell line

We have previously postulated an in vivo pathway of thymic epithelial (TE) cell maturation in pre- and postnatal thymus, whereby endocrine medullary TE cells terminally differentiate to form Hassall's bodies. Epithelial-cell differentiation has been well documented in vitro using epidermal keratinocytes. Therefore, to characterize TE-cell differentiation in vitro, we observed clones of the rat TE cell line, IT26R21, after 4 and 14 days in culture. We found alterations in cell morphology, the cessation of cell proliferation, and the acquisition of a differentiation antigen defined by monoclonal antibody TE-19 (a marker of terminally differentiated epithelial cells). At light and electron microscopy, we detected progressive TE-cell stratification and squamous-cell formation between 4 and 14 days of culture. Autoradiography on day 14 showed that squamous TE cells in stratified layers did not incorporate tritiated thymidine, while surrounding smaller cells adhering to the substratum continued to synthesize DNA. At indirect immunofluorescence, only 3% of cells reacted with monoclonal antibody TE-19 at day 4, while on day 14, 22% of the TE cells were TE-19 positive (P less than 0.02). Antibody-TE-19 reactivity was limited to stratified, squamous TE cells. Additionally, we isolated a clone of the IT26R21 cell line that did not undergo these changes characteristic of TE cell differentiation. We conclude that IT26R21 TE cells are capable of undergoing programs of both terminal differentiation and cell renewal in vitro.

Cleavage of vimentin in dense cell cultures. Inhibition upon transformation by type 5 adenovirus

The analysis on two-dimensional isoelectric focusing and SDS polyacrylamide gels (2D gels) of the Triton X-100 and high salt-insoluble fraction of fibroblast cell lines, certain epithelial cell lines and granulosa cells revealed various amounts of a vimetin cleavage product, with a more basic pI and with a MW (1,500-2,000) lower than that of intact vimentin. This cleavage product of vimentin which constituted as much as 30% of the total vimentin in an established rat embryo fibroblast cell line (CREF), was detected by a monoclonal antivimentin antibody in whole cell and Triton-insoluble extracts, and it has a phosphorylated variant which can be degraded to form the "staircase pattern" on 2D gels similarly to intact vimentin. This processing of vimentin occurred mainly in dense cell cultures and it could not be induced in sparse cell cultures by inhibiting DNA synthesis with ara C, or by arresting cell growth in medium containing 0.1% serum. Transformation of CREF cells with intact wild-type (H5wt) and host-range cold-sensitive mutants (H5hr1 or H5d1101) of type 5 adenovirus (Ad5), or transformation of CREF cells by Ca2+-mediated DNA transfection with the transforming E1a (0-4.5 map units) or E1a + E1b (0-11.5 map units) region of Ad5 inhibits the cleavage of vimentin in dense cultures only at temperatures which are permissive for expression of the transformed phenotype. The transformation of cells with bovine papilloma virus type 1, with T24 ras oncogene, or with RSV does not interfere with the cleavage of vimentin. The organization of the vimentin network in dense cultures, where the vimentin cleavage occurs, is very different from that of sparse untransformed and sparse or dense Ad5-transformed cells. The possibility that the acidic amino acid-rich C-terminus of vimentin is cleaved in dense cell cultures in conjunction with the reorganization of the vimentin network and the inhibition of this cleavage by transformation with Ad5, are discussed.

Effects of cell density and extracellular matrix on the lateral diffusion of major histocompatibility antigens in cultured fibroblasts

We have studied the effect of cell density on the lateral diffusion of major histocompatibility (MHC) antigens in the plasma membranes of fibroblasts using fluorescence recovery after photobleaching. The percent recovery of fluorescence was decreased in fibroblasts grown in confluent cultures. While recovery of fluorescence was measurable in greater than 90% of the cells from sparse cultures, measurable recovery was detected in only 60-80% of the cells from dense cultures; no mobile antigens were detectable in 20-40% of cells examined. The diffusion coefficient on human skin fibroblast cells that did show recovery was the same for cells grown in sparse or dense conditions. In WI-38, VA-2, and c1 1d cultures the diffusion coefficients of mobile antigens were smaller in cells from dense cultures. Changes in lateral diffusion occurred with increased cell-cell contact and with age of cell culture but were not observed in growth-arrested cells or in sparse cells cultured in medium conditioned by confluent cells. Decreased mobile fractions of MHC antigens were observed when cells were plated on extracellular matrix materials derived from confluent cultures. Treatment of the extracellular matrix materials with a combination of proteolytic enzymes or by enzymes that degrade proteoglycans abolished this effect. Matrices produced by cells from other cell lines were less effective in inducing changes in mobile fractions and purified matrix components alone did not induce changes in lateral diffusion. Finally, there were no differences in the proportion of MHC antigens that were resistant to Triton X-100 extraction in sparse and dense cells. These results suggest that cell-cell interactions mediated through extracellular matrix materials can influence the lateral diffusion of at least part of the population of MHC antigens.

Tumor promoter-induced disruption of junctional complexes in cultured epithelial cells is followed by the inhibition of cytokeratin and desmoplakin synthesis

The organization and synthesis of proteins involved in the formation and stabilization of desmosome-type junctions was investigated in cultured epithelial cells treated with a tumor promoter (12-O-tetradecanoyl-phorbol-13-acetate (TPA]. In Madin-Darby bovine (MDBK) and canine (MDCK) kidney cell colonies, TPA induced a rapid disruption of desmosomes and marked alterations in cell morphology. Within 4-6 h after TPA treatment, cell shape changed from cuboidal to highly irregular, with some very long extensions that contained cytokeratin fibrils, and many flat lamellar protrusions which were devoid of cytokeratin fibrils. These morphological changes in both MDBK and MDCK cells were followed by a dramatic and coordinated inhibition in the synthesis of all cytokeratins, 14-24 h after the addition of TPA, but without a similar effect on the synthesis of vimentin, which is coexpressed in these cells. In contrast, in dense cultures of MDBK and MDCK cells the synthesis of cytokeratins and the organization of desmosomal contacts were not affected by TPA. In an epithelial cell line derived from the bovine mammary gland (BMGE-H) the synthesis of an acidic cytokeratin of 45 kD, which was previously shown to be synthesized at high levels only in dense cultures, was dramatically inhibited by TPA treatment. Cell-free in vitro translation assays with mRNA from control and TPA-treated cells also demonstrated a decrease in the synthesis of cytokeratins in response to TPA. The inhibition of cytokeratin synthesis after TPA treatment was paralleled by a decrease in the synthesis of a high molecular weight (HMW) desmoplakin protein, which was abundant in dense MDBK and BMGE-H cells. The results with TPA-treated cells are suggestive of a coordinated down-regulation in the synthesis of only those cytokeratins and of a desmoplakin which were shown to be regulated by the extent of cell-cell contact. Cytokeratin phosphorylation in TPA-treated cells was low and reflected the decrease in their total mass, suggesting that it was not altered by TPA treatment. The possible linkage between the regulation of synthesis and organization of proteins involved in desmosome formation is discussed.