Effect of anisotonic conditions on the transport of hydrophilic model compounds across monolayers of human colonic cell lines

The effect of anisotonic solutions on the enhancement of the transport of hydrophilic model compounds across monolayers of Caco-2 and HT-29.cl19A intestinal epithelial cells was studied. In filter-grown monolayers of the highly differentiated villus-like Caco-2 cell line, a profound and dose-dependent drop in the transepithelial electrical resistance was found after apical treatment with a 30 or a 50% hypotonic solution (200 and 150 mOsmol, respectively). This drop was not observed after basolateral and two-sided application of a 50% hypotonic solution. During apical hypotonic treatment a 12- and 8-fold increase also was observed in transepithelial transport of two hydrophilic model compounds, i.e., fluorescein-Na and fluorescein-isothiocyanate-labeled dextran, MW 4000, respectively. Through confocal laser scanning microscopy, it was revealed that this enhanced transport was predominantly via the paracellular route. Moreover, morphological changes in the cell layers indicating cell swelling were observed after apical hypotonic, but not after basolateral or bilateral treatment, probably resulting from an incomplete regulatory volume decrease response. This swelling, and slight lateral retraction of the cells, allowed the hydrophilic compounds to pass between the cells. The effects of hypotonic challenge also were studied in monolayers of the more crypt cell-like HT-29.cl19A cell line. After apical hypotonic shock, these cells showed no effect on transepithelial electrical resistance, whereas an increase was observed after basolateral and bilateral treatment. Hypotonic shock failed to increase the transport of the hydrophilic model compounds in this cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

Crowding-induced organization of cytoskeletal elements: II. Dissolution of spontaneously formed filament bundles by capping proteins

Through calculations of molecular packing constraints in crowded solutions, we have previously shown that dispersions of filament forming proteins and soluble proteins can be unstable at physiological concentrations, such that tight bundles of filaments are formed spontaneously, in the absence of any accessory binding proteins. Here we consider the modulation of this phenomenon by capping proteins. The theory predicts that, by shortening the average filament length, capping alleviates the packing problem. As a result, the dispersed isotropic solution is stable over an expanded range of compositions.

Colchicine antagonizes the activity of human smooth muscle cells cultivated from arteriosclerotic lesions after atherectomy

AIM

Proliferative, migratory, and secretory activities of vascular smooth muscle cells are functional determinants of human atherosclerotic plaque and restenosis formation. The present study was designed to examine the effects of interfering with these processes using drugs.

MATERIALS AND METHODS

For in-vitro studies of smooth muscle cell activity, arterial smooth muscle cells were cultivated from human plaque tissue excised from 22 coronary and peripheral lesions and treated with the antitubulin colchicine. Smooth muscle cell migratory activity was analyzed by a standardized semi-automatic video system. Transmission electron microscopy was used to examine cytoplasmic structures.

RESULTS

Colchicine caused a concentration-dependent decrease in smooth muscle cell proliferative activity at a half-maximal inhibitory concentration (IC50) of 5 nmol/l. Smooth muscle cell migratory activity was reduced by colchicine in a concentration-dependent manner (IC50, 3 nmol/l). Concordantly, transmission electron microscopy revealed severe disorganization of cytoplasmic structures, especially of organelles, indicating metabolic activation.

CONCLUSIONS

In-vitro studies with human smooth muscle cells from arteriosclerotic lesions suggest that the antitubulin principle may be useful in producing anti-arteriosclerotic effects, since a pronounced antagonization of smooth muscle cell proliferative, migratory, and secretory processes, indirectly inferred from ultrastructural analysis, was demonstrated with low concentrations of colchicine.

Cytoskeletal organization of the vestibular supporting cells. Saponin perfusion method for observing intracellular structures by scanning electron microscopy

The cytoskeletal organization of the guinea pig vestibular supporting cells was investigated employing the saponin perfusion method using scanning electron microscopy. The skeletal framework of a cell was composed of actin, intermediate filaments and microtubules. The membrane bound organelles such as nucleus mitochondria, endoplasmic reticulum, Golgi apparatus, etc. were also well documented. This made it possible to investigate the three-dimensional organization of cytoskeletons as well as their complex interaction with various membrane bound organelles. The intermediate filaments were usually seen surrounding the nucleus and extending through the cytoplasm which connected the nuclear membrane to the plasma membrane, reticular lamina or other cytoorganelles. The intermediate filaments also closely related to the desmosomes. These findings suggest that the intermediate filaments provide mechanical support to the cell and its nucleus. The microtubules were closely related to the secretory granules, Golgi apparatus and intermediate filaments, which supports the idea that the microtubules may control the distribution of intermediate filaments, and also play an important role for the transport of the secretory granules.

Pseudomalignant spindle cell proliferations of the urinary bladder

Twelve cases of polypoid, nonrecurrent, pseudomalignant spindle cell proliferations of the urinary bladder (eight women and four men) were analyzed. Two patients had a simultaneous urinary bladder carcinoma. The lesions were characterized by proliferating spindle- or strap-shaped cells, which on electron microscopic examination (performed in all 12 cases) revealed characteristics of fibroblasts and myofibroblasts. The cells showed immunoreactivity for vimentin in all cases, for alpha-smooth muscle-specific and muscle-specific actin in six cases, for cytokeratins in five cases, and for CD 34 in one case. No immunoreactivity was observed for desmin, myoglobin, epithelial membrane antigen, S-100 protein, endothelial cell antigen (H and Y), CD 68, or factor VIII RAG. Immunoreactivity for Ki-67 and proliferating cell nuclear antigen was detected in up to 30% of the spindle cell nuclei. The static cytometric DNA analysis revealed a diploid, or in two cases a hyperdiploid, stem cell line. An awareness of this type of spindle cell lesion and its immunophenotypic characteristics and diversity is of importance to avoid an erroneous diagnosis of spindle cell sarcoma (in particular leiomyosarcoma and embryonal rhabdomyosarcoma) or spindle cell carcinoma.

Quantification of mRNA of tyrosine hydroxylase and aromatic L-amino acid decarboxylase in the substantia nigra in Parkinson's disease and schizophrenia

Using the reverse transcription-polymerase chain reaction (RT-PCR), we developed a sensitive and quantitative method to detect all four types of human tyrosine hydroxylase (TH) mRNAs in the human brain (substantia nigra). All four types of TH mRNAs were found in the substantia nigra in the control brains examined, and the ratio of type-1, type-2, type-3, and type-4 mRNAs to the total amount of TH was 45, 52, 1.4, and 2.1%, respectively. The average amount of total TH mRNA in the normal brain (substantia nigra) was 5.5 amol of TH mRNA per microgram of total RNA. The ratios of four TH isoforms were not altered significantly in Parkinson's disease or schizophrenia. Further we measured the relative amount of aromatic L-amino acid decarboxylase (AADC) and beta-actin mRNAs in the brain samples. TH and AADC mRNAs were highly correlated in the control cases. We found that parkinsonian brains had very low levels of all four TH isoforms and AADC mRNAs in the substantia nigra compared with control brains, while no significant differences were found between schizophrenic brains and normal ones. Since the decrease in AADC mRNA was comparable to that in TH mRNA, the alteration of TH in Parkinson's disease would not be a primary event, but it would reflect the degeneration of dopaminergic neurons in the substantia nigra. This is the first reported measurement of mRNA contents of TH isoforms and AADC in Parkinson's disease and schizophrenia.

Enhancement of axial resolution in fluorescence microscopy by standing-wave excitation

The use of fluorescence microscopy for investigating the three-dimensional structure of cells and tissue is of growing importance in cell biology, biophysics and biomedicine. Three-dimensional data are obtained by recording a series of images of the specimen as it is stepped through the focal plane of the microscope. Whether by direct imaging or by confocal scanning, diffraction effects and noise generally limit axial resolution to about 0.5 microns. Here we describe a fluorescence microscope in which axial resolution is increased to better than 0.05 microns by using the principle of standing-wave excitation of fluorescence. Standing waves formed by interference in laser illumination create an excitation field with closely spaced nodes and antinodes, allowing optical sectioning of the specimen at very high resolution. We use this technique to obtain images of actin fibres and filaments in fixed cells, actin single filaments in vitro and myosin II in a living cell.

The structure of crystalline profilin-beta-actin

The three-dimensional structure of bovine profilin-beta-actin has been solved to 2.55 A resolution by X-ray crystallography. There are several significant local changes in the structure of beta-actin compared with alpha-actin as well as an overall 5 degrees rotation between its two major domains. Actin molecules in the crystal are organized into ribbons through intermolecular contacts like those found in oligomeric protein assemblies. Profilin forms two extensive contacts with the actin ribbon, one of which appears to correspond to the solution contact in vitro.

A Drosophila homologue of the Schizosaccharomyces pombe act2 gene

Diverse proteins that are 35% to 55% identical to actins have been discovered recently in yeasts, nematodes, and vertebrates. In order to study these proteins systematically and relate their functions to those of conventional actins, we are isolating the corresponding genes from the genetically tractable eukaryote, Drosophila melanogaster. Here we report the isolation and partial characterization of a Drosophila homologue of the Schizosaccharomyces pombe act2 gene. Degenerate oligonucleotide primers specifying peptides that are highly conserved within the actin protein superfamily were used in conjunction with polymerase chain reaction (PCR) to amplify a portion of the Drosophila gene that we have named actr66B. The corresponding full-length cDNA sequence encodes a protein of 418 residues that is 65% identical to the product of the S. pombe act2 gene, 80% identical to the bovine act2 homologue, but only 48% identical to the principal Drosophila cytoplasmic actin encoded by the Act5C actin gene. Alignment of the yeast, bovine, and Drosophila actin-related proteins shows that they have four peptide insertions, relative to conventional actins, three of which are well placed to modify actin polymerization and one that is likely to perturb the binding of myosin. Locations of two of the five actr66B introns are conserved between Drosophila and yeast genes, further attesting that they evolved from a common ancestor and are likely to encode proteins having similar functions. We demonstrate that the Drosophila gene is located on the left arm of chromosome 3, within subdivision 66B. Finally, we show by RNA blot-hybridization that the gene is expressed at low levels, relative to conventional nonmuscle actin, in all developmental stages. From these and other observations we infer that the actr66B protein is a minor component of all cells, perhaps serving to modify the polymerization, structure, and dynamic behavior of actin filaments.

Fetal bovine serum and other sera used in tissue culture increase epithelial permeability

Fetal bovine serum (FBS) or heat-inactivated FBS (56 degrees C for 30 min, HFBS) caused a dose-dependent decrease in the transepithelial electrical resistance of an epithelial monolayer (MDCK). A saturating concentration of HFBS (30%) caused an average fall of 25 +/- 2% within 60 min. Upon removal of HFBS, the resistance returned to its starting value within 1 h. Flux studies with [3H]mannitol demonstrate that the fall in resistance is due to an increased permeability of the tight junctions. Thirty percent heat inactivated sera from goat, newborn calf, calf, bovine, and horse caused falls ranging from 26 to 47%. In contrast with the basolateral preference of human and bovine adult sera, fetal bovine and newborn calf sera elicit this response primarily by interacting with the apical surface of the epithelium. HFBS-treated monolayers show a significant increase in the condensation of F-actin at points where > or = 3 cells meet. These results demonstrate that FBS and other sera used as nutritional supplements can increase the permeability of the tight junctions of cultured epithelial cells.

Evaluation of the fluorescence actin staining test for detection of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) strains designated on the basis of their serotypes are epidemiologically associated with diarrhea. They adhere to the intestinal mucosa, producing the characteristic attaching and effacing (AE) lesion in an in vitro organ culture system. EPEC manifest localized adherence (LA) in the HEp-2 cell assay, and this is commonly used for clinical diagnosis. Recently, the fluorescence actin staining (FAS) test was proposed for the identification of E. coli causing the AE lesion. We therefore compared the FAS test with the HEp-2 cell assay and the EPEC adherence factor (EAF) probe assay for the detection of EPEC strains. Among 240 stool samples from children with diarrhea examined, 176 yielded E. coli and 14 of these strains showed the LA pattern in the HEp-2 cell assay; 11 of these were positive by both the EAF and the FAS tests. By using the HEp-2 cell assay as the "gold standard," the FAS test gave a sensitivity of 78.5% and a specificity of 100%. The three localized adherent FAS-negative strains tested subsequently were positive by the enteroaggregative E. coli DNA Probe and failed to produce the AE lesions characteristic of EPEC. When these strains were not considered, the sensitivity of the FAS test for detecting isolates that manifest LA was 100%. Against the EAF probe, the sensitivity and specificity of the FAS test were 91.6 and 100%, respectively. The FAS test avoids infrequent but nevertheless important phenotypic misclassifications in the HEp-2 cell assay, and it may therefore serve as a confirmatory test for EPEC.

Fibroblastic cell cycling in collagen gels

Quiescent C3H10T1/2 mouse fibroblasts resume DNA synthesis and proliferation following incubation in medium containing fresh serum both when grown in monolayer and when grown in a collagen matrix. We observed that the rate of DNA synthesis is reduced at high initial cell densities and low initial collagen concentrations. In a collagen matrix, fibroblasts contract the matrix causing an increase in cell density and collagen concentration. We studied the chronological relationship between the kinetics of DNA synthesis and the collagen matrix contraction. The rate of collagen collection per cell changes in time, dependent on initial cell and collagen concentration. The kinetics of the collagen collection showed a positive correlation with the kinetics of DNA synthesis, 16 h later.

Centrifugation causes adaptation of microfilaments: studies on the transport of statoliths in gravity sensing Chara rhizoids

The actin cytoskeleton is involved in the positioning of statoliths in tip growing Chara rhizoids. The balance between the acropetally acting gravity force and the basipetally acting net outcome of cytoskeletal force results in the dynamically stable position of the statoliths 10-30 micrometers above the cell tip. A change of the direction and/or the amount of one of these forces in a vertically growing rhizoid results in a dislocation of statoliths. Centrifugation was used as a tool to study the characteristics of the interaction between statoliths and microfilaments (MFs). Acropetal and basipetal accelerations up to 6.5 g were applied with the newly constructed slow-rotating-centrifuge-microscope (NIZEMI). Higher accelerations were applied by means of a conventional centrifuge, namely acropetally 10-200 g and basipetally 10-70 g. During acropetal accelerations (1.4-6g), statoliths were displaced to a new stable position nearer to the cell vertex (12-6.5 micrometers distance to the apical cell wall, respectively), but they did not sediment on the apical cell wall. The original position of the statoliths was reestablished within 30 s after centrifugation. Sedimentation of statoliths and reduction of the growth rates of the rhizoids were observed during acropetal accelerations higher than 50 g. When not only the amount but also the direction of the acceleration were changed in comparison to the natural condition, i.e., during basipetal accelerations (1.0-6.5 g), statoliths were displaced into the subapical zone (up to 90 micrometers distance to the apical cell wall); after 15-20 min the retransport of statoliths to the apex against the direction of acceleration started. Finally, the natural position in the tip was reestablished against the direction of continuous centrifugation. Retransport was observed during accelerations up to 70 g. Under the 1 g condition that followed the retransported statoliths showed an up to 5-fold increase in sedimentation time onto the lateral cell wall when placed horizontally. During basipetal centrifugations > or = 70 g all statoliths entered the basal vacuolar part of the rhizoid where they were cotransported in the streaming cytoplasm. It is concluded that the MF system is able to adapt to higher mass accelerations and that the MF system of the polarly growing rhizoid is polarly organized.

[Cryopreservation of spermatozoa of a transgenic mouse]

Spermatozoa of a homozygous transgenic mouse, in which the firefly luciferase gene was expressed under the control of beta-actin promoter, were frozen at -196 degrees C. One fourth of the frozen sperm was later thawed and used for in vitro fertilization. Thirty-six of 65 oocytes (55.4%) developed to the 2-cell stage. All the 2-cell embryos were transferred to the oviducts of pseudopregnant recipients and 23 young (63.9%, 23/36) were born. All of young analyzed carried the transgene and showed the luciferase gene expression.

[Suppression of myeloperoxidase gene expression by gamma-interferon]

The gene expression of myeloperoxidase (MPO) in HL60 cells, as tested by Northern blot analysis with a MPO gene probe, was markedly suppressed by treatment with gamma interferon (IFN-gamma)(200U/ml) for 9hr, whereas cytochemically detected MPO activity, cell surface antigen expression, and cell morphology remained unchanged even at 48hr after the treatment. IFN-gamma of 50U/ml was sufficient for the suppression at 24hr. When the HL60 cells treated with IFN-gamma (200U/ml) for 24hr were cultured in the absence of IFN-gamma for another 24hr, the transcript of MPO gene reverted to a level comparable to that of the HL60 cells cultured thoroughly in the absence of IFN-gamma, indicating the reversibility of the suppression. The suppression of MPO expression at RNA level, possibly independent of differentiation, is one of the biological activities exerted by IFN-gamma, which has not been previously reported.

Cell shape changes during transition of basal keratinocytes to mature enucleate-cornified envelopes: modulation of terminal differentiation by fibronectin

Normal human keratinocytes (NHK) in submerged culture were used to assess mechanisms associated with in vitro exposure to known stimulators (sodium butyrate; NaB) and inhibitors (fibronectin; FN) of NHK maturation. A multiparameter approach was used to define cell types generated under a range of growth conditions. Differentiation induced in response to NaB occurred through a series of morphologically distinct phenotypes and culminated in the formation of enucleate-cornified envelopes. Two-dimensional electrophoresis provided a limited database to evaluate global changes in cellular protein composition as a function of induced differentiation. Proteins were identified that characterized predominantly basal cell cultures, NaB-treated cells, and fully differentiated NHKs. Growth of NHKs on FN suppressed both spontaneous and NaB-directed maturation and inhibited maximal expression of protein changes associated with the differentiated state. Thus, the composition of the extracellular matrix can modulate (at both the morphologic and protein levels) the response of basal NHKs to a potent differentiation-inducing agent. Abrogation of NHK maturation by FN was not due to adverse effects on cellular metabolism, abortive differentiation, or altered timing of induced differentiation. FN appears to exert its suppressive effect by either maintaining an early stem cell phenotype which is poorly competent for terminal maturation or attenuating an as yet unknown aspect of the NaB-initiated differentiation cascade.

Computer-assisted tracking of actin filament motility

In vitro motility assays, in which fluorescently labeled actin filaments are propelled by myosin molecules adhered to a glass coverslip, require that actin filament velocity be determined. We have developed a computer-assisted filament tracking system that reduced the analysis time, minimized investigator bias, and provided greater accuracy in locating actin filaments in video images. The tracking routine successfully tracked filaments under experimental conditions where filament density, size, and extent of photobleaching varied dramatically. Videotaped images of actin filament motility were digitized and processed to enhance filament image contrast relative to background. Once processed, filament images were cross correlated between frames and a filament path was determined. The changes in filament centroid or center position between video frames were then used to calculate filament velocity. The tracking routine performance was evaluated and the sources of noise that contributed to errors in velocity were identified and quantified. Errors originated in algorithms for filament centroid determination and in the choice of sampling interval between video frames. With knowledge of these error sources, the investigator can maximize the accuracy of the velocity calculation through access to user-definable computer program parameters.

Fc receptor endocytosis is controlled by a cytoplasmic domain determinant that actively prevents coated pit localization

Macrophages and B-lymphocytes express two major isoforms of Fc receptor (FcRII-B2 and FcRII-B1) that exhibit distinct capacities for endocytosis. This difference in function reflects the presence of an in-frame insertion of 47 amino acids in the cytoplasmic domain of the lymphocyte isoform (FcRII-B1) due to alternative mRNA splicing. By expressing wild type and mutant FcRII cDNAs in fibroblasts, we have now examined the mechanism by which the insertion acts to prevent coated pit localization and endocytosis. We first identified the region of the FcRII-B2 cytoplasmic domain that is required for rapid internalization. Using a biochemical assay for endocytosis and an immuno-EM assay to determine coated pit localization directly, we found that the distal half of the cytoplasmic domain, particularly a region including residues 18-31, as needed for coated pit-mediated endocytosis. Elimination of the tyrosine residues at position 26 and 43, separately or together, had little effect on coated pit localization and a partial effect on endocytosis of ligand. Since the FcRII-B1 insertion occurs in the membrane-proximal region of the cytoplasmic domain (residue 6) not required for internalization, it is unlikely to act by physically disrupting the coated pit localization determinant. In fact, the insertion was found to prevent endocytosis irrespective of its position in the cytoplasmic tail and appeared to selectively exclude the receptor from coated regions. Moreover, receptors bearing the insertion exhibited a temperature- and ligand-dependent association with a detergent-insoluble fraction and with actin filaments, perhaps in part explaining the inability of FcRII-B1 to enter coated pits.

Organelle motility within mitotic asters of the fungus Nectria haematococca

The mitotic asters of the fungus, Nectria haematococca, pull on the spindle pole bodies during anaphase B and help to elongate the central spindle. Because these asters are invisible in vivo, studies of their functions during mitosis have been limited. Invisible asters in other organisms can be studied in vivo because of visible, membranous organelles that are held or transported within them. This is the first report of intra-astral motility of organelles in a fungus, and it lays the foundation for additional studies of aster function in vivo. Using phase-contrast, video-enhanced microscopy, we observed directed motility of mitochondria, small vesicles of various kinds, lipid bodies and, rarely, small vacuoles within the astral region during anaphase B. Both bidirectional motility--toward and away from the spindle pole body--and reversal of direction by an individual organelle were common. Organelles usually did not tend to accumulate either within the aster or near the spindle pole. They were drawn toward the spindle pole body from up to 5.0 microns away. Average velocities were 2.3 to 3.2 microns/s, depending on the organelle and its direction of movement. Transmission electron microscopy revealed apparent cross bridging between astral microtubules and mitochondria, vesicles, endoplasmic reticulum, microbodies, and vacuoles. The antimicrotubule drug, methylbenzimidazole-2-ylcarbamate (MBC), destroyed astral microtubules and virtually eliminated intra-astral motility in vivo, whereas the antiactin drug, cytochalasin E, did not greatly affect the frequency of intra-astral motility episodes. The results suggest a role for astral microtubules in intra-astral motility in this fungus.

Myxoid leiomyosarcoma of the ovary: analysis of three cases

The first three cases of myxoid leiomyosarcoma occurring in the ovary are reported. Two cases in stage III were found in postmenopausal patients and a further case was found in stage I in a 32-year-old. All masses were large and gelatinous with cystic change, necrosis, and hemorrhage, but both uteri and ligaments and contralateral adnexa appeared normal. Microscopically, the tumors showed a predominantly reticular meshwork of elongated cells surrounded by abundant basophilic material. While electron microscopy proved inconclusive due to nondifferentiation, the use of monoclonal antibodies against smooth muscle actin demonstrated a smooth muscle type of differentiation. The differential diagnosis of this rare ovarian condition includes other myxoid ovarian lesions, such as ovarian edema, myxoma, endodermal sinus tumors, and the sarcomatous component of malignant mixed müllerian tumor and carcinosarcoma, as well as lymphovascular tumors. Since mitotic count due to decreased cellular density is unusually low in myxoid leiomyosarcoma, capsular rupture and clinical stage seem to be more reliable prognostic markers. The highly aggressive behavior of myxoid leiomyosarcoma parallels that of typical ovarian leiomyosarcoma. Two of the three patients in this series died of tumor at 13 and 24 months after diagnosis; the other patient is free of disease at 3 years after diagnosis.

Toward a more complete 3-D structure of the nuclear pore complex

The nuclear pore complex (NPC) is a large supramolecular assembly embedded in the double-membraned nuclear envelope (NE) that plays a pivotal role in the exchange of macromolecules and particles between the nucleus and the cytoplasm. Applying various methods of sample preparation to Xenopus laevis whole nuclei and isolated NEs in combination with conventional transmission electron microscopy and digital image processing, we have characterized several distinct components of the NPC, including massive cytoplasmic and more tenuous nuclear rings, NPCs devoid of their cytoplasmic or both rings, and prominent "knobs" that protrude from the periphery of the NPC proper into the lumen of the NE. Moreover, by quick freezing/freeze drying/rotary metal shadowing isolated NEs, we have visualized two distinct types of NPC-associated filaments: (1) eight short, highly twisted filaments that project from the cytoplasmic ring and sometimes collapse into short cylinders; and (2) eight long, thin filaments that protrude from the nuclear ring and whose ends join to form a distal ring centered above the NPC such that the assembly resembles a "fishtrap." These nuclear fishtraps are sensitive to divalent cations: removal unfolds them and addition reforms them. The significance of these various structural components in terms of current NPC models is discussed, and the emerging asymmetry of the NPC relative to its nuclear and cytoplasmic face is stressed.

Analysis of actin microfilaments and cell-to-substrate adhesive structures in human fibroblasts from individuals genetically predisposed to colonic carcinoma

Skin fibroblasts from patients with inherited adenomatosis of the large bowel (ACR-SF) possess alterations in actin microfilament (MF) organization which serve to distinguish "predisposed" cells from fibroblasts derived from normal individuals (NSF). MF bundle frequency and diameter were considerably reduced in ACR-SF compared to NSF. This deficit in MF density correlated with a 60% decline in cytoskeletal-associated actin half-life. Absence of a well-structured MF network in ACR-SF was reflected in relatively poor cell-to-substrate adhesion (as indicated by increased sensitivity to trypsin release) and extensive membrane ruffling. Unlike NSF, ACR-SF failed to develop well-defined vinculin-containing focal contacts although the cellular content of vinculin was approximately the same in both cell types. The relatively low substrate adhesivity and reduced incidence of adhesive structures (i.e., MF and associated focal contacts) which typify ACR-SF correlated with a sixfold increase in cellular plasminogen activator (PA) activity. This increased protease activity corresponded with a 50-70% reduction in the content of the PA inhibitor-like protein p50 in both the saponin-resistant undersurface matrix and the culture medium. Increased motility and reduced cell-to-substrate adhesion, involving several cellular structural elements, appear to be significant correlates of the "predisposed" phenotype in cultured fibroblasts.

Chromatin organization in Entamoeba histolytica

The chromatin structure of Entamoeba histolytica was investigated. It was found that this protozoan organizes its chromatin in nucleosome-like particles 10 nm in diameter, but digestion of the chromatin with micrococcal nuclease did not render a regularly spaced DNA ladder in agarose gels. Southern blot analysis of the products of Entamoeba chromatin digestion using total amebic DNA and a non-transcribed repetitive sequence produced a banding pattern characteristic of eukaryotic chromatin with a repetitive size of approximately 130 bp. Conversely, hybridization with two active gene probes, actin and ribosomal RNA, showed that these sequences are not part of the chromatin organized in nucleosomes. It was also found that the basic nuclear proteins differ from histones of higher eukaryotes in electrophoretic mobility. Screening of an E. histolytica HM1-IMSS genomic library with Saccharomyces cerevisiae H3 and H4 genes and attempts to amplify E. histolytica sequences, homologous to these yeast histone genes, gave negative results suggesting that the Entamoeba proteins involved in chromatin organization are not typical histones.