Aggregation of normal and transformed cells attached to a substrate]

On the surface of the nirtocellulose membrane filter (pore size 0.3--0.5 mem), normal mouse or hamster embryo fibroblasts formed discrete cell aggregates. Behaviour of transformed fibroblast-like cells of 9 different lines was compared with that of normal cells. Cells of 3 transformed lines grew on this substratum as a uniform monolayer displaying no tendency to aggregation. The following 3 cell lines exposed a slightly "patchy" cell distribution on the 3rd--4th day of cultivation but were unable to form discrete aggregates. The remaining 3 lines did form aggregates but the dynamics of aggregation and the final aggregation pattern for two of them were abnormal. Only one of the 9 investigated transformed lines had the normal aggregation behaviour. Hence, in the course of the neoplastic evolution, cells lose their ability fo form aggregates on the filter surface. Mechanisms of cell aggregation and possible reasons of differencies in the aggregation behaviour between normal and transformed cells, are discussed.     

Cytoskeletal Control of Cell Length Regulation

It was shown that mouse embryo fibroblasts and human foreskin diploid fibroblasts of AGO 1523 line cultivated on specially prepared substrates with narrow (15 ± 3 m) linear adhesive strips were elongated and oriented along the strips, but the mean lengths of the fibroblasts of each type on the strips differed from those on the standard culture substrates. In contrast to the normal fibroblasts, the length of mouse embryonic fibroblasts with inactivated gene-suppressor Rb responsible for negative control of cell proliferation (MEF Rb-/-), ras-transformed mouse embryonic fibroblasts (MEF Rb-/-ras), or normal rat epitheliocytes of IAR2 line significantly exceeded those of the same cells on the standard culture substrates. The results of experiments with the drugs specifically affecting the cytoskeleton (colcemid and cytochalasin D) suggest that the constant mean length of normal fibroblasts is controlled by a dynamic equilibrium between two forces: centripetal tension of contractile actin-myosin microfilaments and centrifugal force generated by growing microtubules. This cytoskeletal mechanism is disturbed in MEF Rb-/- or MEF Rb-/-ras, probably, because of an impaired actin cytoskeleton and also in IAR2 epitheliocytes due to the different organization of the actin-myosin system in these cells, as compared to that in the fibroblasts.     

Serum-free growth of normal and transformed fibroblasts in milk: differential requirements for fibronectin

Bovine milk may be used as a supplement for the serum-free growth of certain fibroblastic cells in culture. The growth properties of three representative cell types in milk-supplemented medium were examined; fibroblastic cell strains, fibroblastic cell lines, and transformed fibroblasts. Transformed fibroblasts, which included RNA and DNA tumor virus-transformed cells and carcinogen-transformed cells, grew in milk. Instead of growing attached to the culture dishes, as they normally do in serum, transformed fibroblasts grew in milk as large clusters in suspension. In contrast, nontransformed fibroblastic cell strains and cell lines did not grow in milk-supplemented medium. Fibroblasts transformed by a temperature-sensitive transformation mutant of Rous sarcoma virus were temperature-sensitive for growth in milk. The failure of cells to adhere to the substratum in milk-supplemented medium suggested that milk might be deficient in attachment factors for fibroblasts. When the attachment of fibroblastic cells in milk- supplemented medium was facilitated by pretreating culture dishes with fibronectin, (a) transformed cells grew attached rather than in suspension, (b) normal cell lines attached and grew to confluence, and (c) normal cell strains adhered and survived but did not exhibit appreciable cell proliferation.     

Cytoskeletal control of cell length regulation

It was shown that mouse embryo fibroblasts and human foreskin diploid fibroblasts of AGO 1523 line cultivated on specially prepared substrates with narrow (15 +/- 3 microns) linear adhesive strips were elongated and oriented along the strips, but the mean lengths of the fibroblasts of each type on the strips differed from those on the standard culture substrates. In contrast to the normal fibroblasts, the length of mouse embryonic fibroblasts with inactivated gene-suppresser Rb responsible for negative control of cell proliferation (MEF Rb-/-), ras-transformed mouse embryonic fibroblasts (MEF Rb-/-ras), or normal rat epitheliocytes of IAR2 line significantly exceeded those of the same cells on the standard culture substrates. The results of experiments with the drugs specifically affecting the cytoskeleton (colcemid and cytochalasin D) suggest that the constant mean length of normal fibroblasts is controlled by a dynamic equilibrium between two forces: centripetal tension of contractile actin-myosin microfilaments and centrifugal force generated by growing microtubules. This cytoskeletal mechanism is disturbed in MEF Rb-/- or MEF Rb-/-ras, probably, because of an impaired actin cytoskeleton and also in IAR2 epitheliocytes due to the different organization of the actin-myosin system in these cells, as compared to that in the fibroblasts.     

Effect of colchamine on the morphology of transformed fibroblast-like cells in culture]

Colcemid-induced changes in the morphology of cultured transformed fibroblast-like mouse cells were studied using scanning electron microscope. Colcemid interferes with the normal cell polarization so that all the cell edges became active. Colcemid-treated normal cells remained well spread over the substrate. Transformed cells lost their polarization after colcemid treatment--the long, narrow, poorly attached processes of different form appeared along all the cell periphery. As in the case of the absence of colcemid, transformed cells remained less spread and worse attached to the substrate than normal ones. It is suggests that a) the same colcemid-sensitive structures are responsible for the polarization of transformed and normal cells; b) morphological differences between transformed and normal cells are determined mainly by structures different from colcemide-sensitive ones.     

Substrate-induced polarisation of cultured epitheliocytes and fibroblasts: non-reactivity of Ras-transformed cells

Non-transformed epitheliocytes and fibroblasts undergo modulations between the less polarised and more polarised phenotypes depending on the nature of the substrate. In contrast, transformed cells express polarised phenotype regardless of the substrate.     

In vivo development of adipose tissue following implantation of lipid-depleted cultured adipocyte

The monolayer culture of isolated and disaggregated adipocytes from rat omental and perirenal sites, gave rise to a population of fibroblast-like cells, usually devoid of lipid inclusion. Similar fibroblast-like cells have been obtained in cultures of adipose tissue stromal cells and are thought to be undifferentiated adipocyte stem cells. Although the adipocyte-derived fibroblasts were morphologically indistinguishable from culture-derived fibroblasts of other origins, upon autoimplantation into the splenic bed they regained the lipid inclusion and developed again into adipose tissue. The findings suggest that the transformation of adipose cells into fibroblast-like cells is reversible modulation and not a dedifferentiation into the adipose tissue stem cell. This work also substantiates the increasingly recognized heterogeneity of fibroblasts.     

gamma-Glutamyltransferase in human diploid fibroblasts and other mammalian cells.

gamma-Glutamyltransferase was determined in WI-38 human diploid fibroblasts and compared to enzyme levels determined in several other mammalian cell lines including: fibroblast-like cells from human skin, tibia and foreskin; epithelial-like cells from human, bovine and monkey kidney; and transformed cells (Chinese hamster ovary, HeLa S3 and SV-40 transformed WI-38). Transformed cells had the lowest activity found followed in increasing order by fibroblasts, human and bovine epithelial cells and monkey kidney epithelial cells. The enzyme isolated from the plasma membrane of WI-38 cells, like the enzyme from kidney and brain, was found to be irreversibly inhibited by iodoacetamide, reversibly by serine-borate, and had a strong specificity for certain amino acids. The possibility exists that gamma-glutamyltransferase could be involved in transport of amino acids into cells in culture; and glutamine, used in media, is an excellent substrate for the enzyme.     

Mechanical stretch-induced changes in cell morphology and mRNA expression of tendon/ligament-associated genes in rat bone-marrow mesenchymal stem cells

It has been demonstrated that mechanical stimulation plays a vital role in regulating the proliferation and differentiation of stem cells. However, little is known about the effects of mechanical stress on tendon/ligament development from mesenchymal stem cells (MSCs). Here, using a custom-made cell-stretching device, we studied the effects of mechanical stretching on the cell morphology and mRNA expression of several key genes modulating tendon/ligament genesis. We demonstrate that bone-marrow-derived rat MSCs (rMSCs), when subjected to cyclic uniaxial stretching, express obvious detectable mRNAs for tenascin C and scleraxis, a unique maker of tendon/ligament formation, and significantly increased levels of type I collagen and type III collagen mRNAs. The stretched cells also orient at approximately 65 degrees with respect to the stretching direction and exhibit a more fibroblast-like morphology. Collectively, these results indicate that mechanical stretching facilitates the directed differentiation of rMSCs into tendon/ligament fibroblasts, which has potential implications for the tissue engineering of bioartificial tendons and ligaments.     

Bending of z-lines by mechanical stimuli: an input signal for integrin dependent modulation of ion channels?

We studied which components of mechanical cell deformation are involved in "stretch modulated ion currents" (SMIC). Murine ventricular myocytes were attached to glass coverslips and deformed in x, y and z with a 16 microm thin glass stylus (S) of calibrated stiffness. Three-dimensional confocal microscopy characterized cell deformation (T-tubular membranes, mitochondria) and bending of S (indicative of the applied force). Axial (x-) displacement of S sheared the upper cell part versus the attached bottom, close to S, it changed sarcomere length and bent z-lines ("z-line displacement"). Vertical (z-press) or transversal (y-shear) displacement of S bulged cytoplasm and mitochondria transversally without detectable z-line displacement. Axial stiffness increased with the extent of stress ("stress stiffening"). Depolymerization of F-actin or block of integrin receptors reduced stiffness. SMIC served as a proxy readout of deformation-induced signaling. Axial deformation activated a non-selective cation conductance (Gns) and deactivated an inwardly rectifying K+ conductance (GK1), z-press or y-shear did not induce SMIC. Depolymerization of F-actin or block of integrin receptors reduced SMIC. SMIC did not depend on changes in sarcomere length but correlated with the extent of z-line bending. We discuss that both shear stress at the attached cell bottom and z-line bending could activate mechanosensors. Since SMIC was absent during deformations without z-line bending we postulate that z-line bending is a necessary component for SMIC signaling.     

Unphosphorylated gelsolin is localized in regions of cell-substratum contact or attachment in Rous sarcoma virus-transformed rat cells

Regions associated with cell-substratum contact or attachment in Rous sarcoma virus (RSV)-transformed rat fibroblasts (RR1022 cells) were identified by reflection-interference microscopy. Electron microscopy of such regions revealed the presence of discrete membrane-associated structures composed of a paracrystalline lattice of hexagons and pentagons to which actin filaments appear to be attached. Staining of actin by biotin-labeled heavy meromyosin showed that transformed cells, unlike normal fibroblasts, lack prominent actin fibers, and that, instead, much of the fluorescence is concentrated in loci corresponding to locations of transient association between the cell and the substratum. In stationary cells, such loci were found in rosette formation, predominantly in the region beneath the nucleus. In cells engaged in active movement, such as during migration into a wound, the actin-containing spots were concentrated in the region of the leading edge. A similar pattern of staining was observed with antibody to gelsolin, a 91,000-dalton Ca2+-dependent actin filament-shortening protein. Since the action of gelsolin on actin is reversible and dependent on physiologically relevant changes in calcium concentration, the localization of gelsolin, together with actin-bundling proteins such as alpha-actinin, in the regions containing many small microfilament bundles on the ventral side of cytoplasm suggests that gelsolin may be a component of the mechanism for the disassembly and assembly of actin during the dissolution and reformation of structures for cell-substratum contact during cell locomotion. Regulation of gelsolin activity was not dependent on protein phosphorylation, as shown by lack of 32P-incorporation into gelsolin in either transformed or normal fibroblasts.     

Mechanics of fibroblast locomotion: quantitative analysis of forces and motions at the leading lamellas of fibroblasts

Shapes, motions, and forces developed in lamellipodia and ruffles at the leading edges of primary chick embryo heart fibroblasts were characterized by differential interference contrast microscopy and digital video enhancement techniques. The initial extension of the cell edge to form a thin, planar lamellipodium parallel to the substrate surface was analyzed in two dimensions with temporal and spatial resolution of 3 s and 0.2 micron, respectively. An extension begins and ends with brief, rapid acceleration and deceleration separated by a long period of nearly constant velocity in the range of 4-7 microns/min. Extensions and retractions were initiated randomly over time. As demonstrated by optical sectioning microscopy, the extended lamellipodia formed ruffles by sharply bending upward at hinge points 2- 4 microns behind their tips. Surprisingly, ruffles continued to grow in length at the same average rate after bending upward. They maintained a straight shape in vertical cross section, suggesting the ruffles were mechanically stiff. The forces required to bend ruffles of these cells and of BC3H1 cells were measured by pushing a thin quartz fishpole probe against the tip of a ruffle 7-10 microns from its base either toward or away from the center of the cell. Force was determined by measuring the bending of the probe monitored by video microscopy. Typically the probe forced the ruffle to swing rigidly in an arc about an apparent hinge at is base, and ruffles rapidly, and almost completely, recovered their shape when the probe was removed. Hence, ruffles appeared to be relatively stiff and to resist bending with forces more elastic than viscous, unlike the cell body. Ruffles on both types of cells resisted bending with forces of 15-30 mudyn/microns of displacement at their tips when pushed toward or away from the cell center. The significance of the observations for mechanisms of cell locomotion is discussed.     

Biochemical and morphological differences between fibroblasts and myoblasts from embryonic chicken skeletal muscle

Summary Non-myogenic cells were isolated from the breast muscle of 10-day-old chicken embryos employing Percoll density centrifugation. In culture, these cells exhibited the spread out, stellate morphology of fibroblast-like cells. They also exhibited receptor-mediated binding of plateletderived growth factor (PDGF). Such binding was not detected in cultures of predominantly myogenic cells isolated by the Percoll density centrifugation from the same muscle. Percoll-isolated myogenic and fibrogenic cell populations were also analyzed by two-dimensional polyacrylamide gel electrophoresis immediately after removal from the muscle. This analysis revealed at least six polypeptides specific to the fibroblasts but not detected in the myogenic cell population. In addition, at least eight polypeptides found in the myogenic population were barely detectable, or lacking altogether from the fibroblast-like cells. Ultrastructural analysis of the freshly isolated cells demonstrated that the fibroblasts were larger than the myoblasts and that their cytoplasm contained many vesicles. We conclude that the fibrogenic and myogenic cells isolated by Percoll from embryonic muscle express cell type-specific characteristics. Moreover, based on the PDGF binding studies, the fibrogenic cells can be categorized as true fibroblasts.     

The fate and role of openings formed in the mesentery of bullfrog tadpoles,with reference to the contour of mesothelial cells

Using morphological techniques, histological changes of the mesentery were observed during the development of the bullfrog, Rana catesbeiana. The tadpoles of this species had many openings all over the mesentery from the duodenum through the large intestine. Most of the openings were elliptical and less than 3 × 2 mm in size. The openings became remarkably decreased in size and number with rapid narrowing of the mesentery occurring during the period of metamorphic climax, and had almost completely disappeared by the end of metamorphosis. Appearance and disappearance of the openings were closely correlated with the changes in the dimensions of the mesentery. Furthermore, in parallel with these changes in the openings, a noticeable alteration occurred in the shape of the mesothelial cells of the mesentery. In tadpoles having no mesenteric openings, the mesothelial cells had a polygonal contour, which became transformed once the openings were formed in the mesentery. The shapes of the transformed cells were classified into two types, one having many radiating cell processes and the other a very slender and spindle-shaped contour. Both types of cells eventually became transformed into a definitive type of cell exhibiting a roundish polygonal contour by the end of metamorphosis. From these findings it was concluded that the growing mesentery might, of necessity, give rise to the openings and transformation of the mesothelial cells to enable rapid lengthening and shortining of the intestinal tract to occur during the postembryonic development of anuran amphibians.     

Paracrine control of myoblast proliferation and differentiation by fibroblasts

Double-muscling (DM) is a hereditary (apparently single-gene) skeletal muscle hyperplasia which occurs in beef cattle. In order to investigate the cellular basis of this phenotype, cell cultures from developing muscle tissue of normal and DM fetal calves were studied. In cultures composed of both myogenic cells and nonmyogenic, fibroblast-like cells, DM myoblasts exhibited a prolonged proliferative phase. This resulted in delayed, but increased production of fused myotubes in the DM cultures. "Conditioned" media experiments indicated that the fibroblast-like cells in the cultures produced soluble myoblast growth factor activity. Both normal and DM fibroblast-like cells produced the growth factor activity, but the mutant fibroblast-like cells produced a greater level of such activity. The conditioned media failed to increase proliferation of bovine muscle fibroblasts and did not stimulate quiescent Swiss 3T3 cells to divide, indicating that the myoblast trophic activity is distinct from bFGF or PDGF. Also, the myotrophic activity present in the conditioned media acted in an additive fashion with saturating doses of bFGF and of IGF-1, suggesting that the activity is not due to either of these known myogenic growth factors. Both normal and DM fibroblast-like cells produced myoblast trophic activity when the cells were proliferating, but did not produce myotrophic activity when the fibroblasts were mitotically quiescent. These findings indicate that the proliferative state of the connective tissue cells in muscle may have a controlling influence on myoblast proliferation and differentiation during development.     

Comparison of the mechanical properties of normal and transformed fibroblasts

In order to achieve coordinated migration through extracellular matrix and endothelial barriers during metastasis, cancer cells must be endowed with specific structural and adhesive properties. In this context, comparison of the mechanical properties of transformed versus normal cells, on which little quantitative information is available, was the focus of this study. Normal human dermal fibroblasts and their SV40-transformed counterparts were analyzed using various manipulations. First, micropipet aspiration of suspended cells allowed calculation of a cortical tension (similar for normal and transformed cells), and an apparent viscosity (30% lower for transformed than for normal fibroblasts); in addition, transformed fibroblasts exhibited a more fragile surface than their normal counterparts. Second, tangential ultracentrifugation of adherent cells demonstrated cellular elongation in the direction of the centrifugal field and the existence of critical forces for cell detachment, around 10⁻⁷ N: these were 1.6-fold greater for normal than for transformed cells. Finally, examination of the wrinkle patterns formed by cells plated on a deformable polydimethylsiloxane substrate, plus analysis of cell retraction caused by ATP treatment following detergent permeabilization showed that normal fibroblasts exhibited much more contractility than their transformed counterparts, which we characterized by a cell contraction rate. Such quantitative parameters which reveal differences in the mechanical behavior of normal and transformed cells may be used in the future as new markers; of oncogenic transformation.     

Displacement of soil aggregates by elongating roots and emerging shoots of crop plants

Summary Models are presented in this paper for prediction of the extent to which soil aggregates in a loose seed bed can be displaced by extending roots and shoots. For roots, the maximum applied force is considered to be limited by either elastic bending, when the angle of contact with an aggregate surface is oblique, or buckling, when the root meets an aggregate perpendicularly. For emerging shoots, only the maximum forces are known. These forces are related to the known force displacement behaviour of artificially prepared beds of graded soil aggregates.It is concluded that displacement of soil aggregates which lie between 20 and 100 mm from the surface of the aggregate bed is only likely to be important for roots with diameters of 0.5 mm or less when the diameter of the aggregates in the bed is less than 1 mm. However, for plant species which have relatively large root diameters, such as pea, significant displacement of aggregates of up to 4 mm diameter may be possible. In contrast, emerging shoots are able to displace very much larger aggregates from their paths.     

Cell coupling modulates the contraction of fibroblast-populated collagen lattices

Cultured dermal fibroblasts become notably elongated when incorporated into a fibroblast-populated collagen lattice (FPCL). With time these fibroblasts reorganize the collagen responsible for reduction in lattice size. In monolayer the microinjection of Lucifer Yellow (LY) into cultured human fibroblasts shows cell coupling through gap junctions. Human fibroblasts residing on the periphery of a FPCL are at high density and the microinjection of LY into one of those fibroblasts demonstrates cell coupling. Cells within the center of an FPCL are at low density and appear to be independent of one another; however, the microinjection of LY into selected fibroblasts again demonstrates cell coupling. Hence the microinjection of cells in both the center and the edge of a FPCL pass dye to numerous neighbors. Does cell coupling influence FPCL contraction? FPCL incubated with heptanol and octanol, aliphatic alcohols that uncouple cells, inhibits lattice contraction, whereas hexanol, an aliphatic alcohol that does not uncouple cells, did not alter lattice contraction. Fibroblasts derived from connexin 43 (a transmembrane protein responsible for gap junction structures) knockout mice were demonstrated to lack gap junctional communications. When incorporated into a FPCL these cells failed to elongate and demonstrated retarded lattice contraction. Hence, gap junctional communications between fibroblasts incorporated into collagen lattices appear to optimize FPCL contraction and suggest a role for gap junctions in the organization of collagen fibers.     

Effect of microinjected amine and diamine oxidases on the ultrastructure of eukaryotic cultured cells

Diamine oxide and serum amine oxidase, which catalyse the oxidation of diamines and polyamines, respectively, were trapped within reconstituted Sendai virus envelopes. These loaded envelopes were incubated with cultured normal chick fibroblasts or with fibroblasts transformed by Rous sarcoma viruses. The binding of the reconstituted envelopes to the cultured cells was confirmed by scanning electron microscopy. It has been shown that the reconstituted envelopes (1-3 microns diameter) were attached to the eukaryotic cells. No significant changes in the morphology of the normal chick embryo fibroblasts were noted upon treatment with enzyme-loaded envelopes. On the other hand, chick embryo fibroblasts transformed by Rous sarcoma virus were affected by the microinjected amine oxidases. Scanning electron microscopy demonstrated the formation of holes in the microinjected cells. Similar morphological changes were also observed when diamine oxidase was microinjected into cultured glioma cells. These holes may be the result of the ejection of the nucleus. These findings are in line with the observed effect of the injected amine oxidases on macromolecular synthesis in normal and transformed chick embryo fibroblasts.     

γ-glutamyltransferase in human diploid fibroblasts and other mammalian cells

Summary γ-Glutamyltransferase was determined in WI-38 human diploid fibroblasts and compared to enzyme levels determined in several other mammalian cell lines including: fibroblast-like cells from human skin, tibia and foreskin; epithelial-like cells from human, bovine and monkey kidney; and transformed cells (Chinese hamster ovary, HeLa S₃ and SV-40 transformed WI-38). Transformed cells had the lowest activity found followed in increasing order by fibroblasts, human and bovine epithelial cells and monkey kidney epithelial cells. The enzyme isolated from the plasma membrane of WI-38 cells, like the enzyme from kidney and brain, was found to be irreversibly inhibited by iodoacetamide, reversibly by serine-borate, and had a strong specificity for certain amino acids. The possibility exists that γ-glutamyltransferase could be involved in transport of amino acids into cells in culture; and glutamine, used in media, is an excellent substrate for the enzyme. Preliminary reports of some of this work were presented at meetings of The American Society of Biological Chemists in Minneapolis (Abstracts Fed. Proc. 33: 957, 1974) and at Atlantic City (Abstracts Fed. Proc. 34: 2243, 1975). This work was supported by Grant NIH 1 P01 HD 07173. The WI-38 starter cultures and cell pack used in these studies were obtained through Contract M01 HD 42828 to Stanford University from the National Institute of Aging.