Wet cleaving of cells: a method to introduce macromolecules into the cytoplasm. Application for immunolocalization of cytosol-exposed antigens

Imaging Cytoskeleton Components by Electron Microscopy

The cytoskeleton is a complex of detergent-insoluble components of the cytoplasm playing critical roles in cell motility, shape generation, and mechanical properties of a cell. Fibrillar polymers-actin filaments, microtubules, and intermediate filaments-are major constituents of the cytoskeleton, which constantly change their organization during cellular activities. The actin cytoskeleton is especially polymorphic, as actin filaments can form multiple higher-order assemblies performing different functions. Structural information about cytoskeleton organization is critical for understanding its functions and mechanisms underlying various forms of cellular activity. Because of the nanometer-scale thickness of cytoskeletal fibers, electron microscopy (EM) is a key tool to determine the structure of the cytoskeleton.This article describes application of rotary shadowing (or platinum replica ) EM (PREM) for visualization of the cytoskeleton . The procedure is applicable to thin cultured cells growing on glass coverslips and consists of detergent extraction (or mechanical "unroofing") of cells to expose their cytoskeleton , chemical fixation to provide stability, ethanol dehydration and critical point drying to preserve three-dimensionality, rotary shadowing with platinum to create contrast, and carbon coating to stabilize replicas. This technique provides easily interpretable three-dimensional images, in which individual cytoskeletal fibers are clearly resolved and individual proteins can be identified by immunogold labeling. More importantly, PREM is easily compatible with live cell imaging, so that one can correlate the dynamics of a cell or its components, e.g., expressed fluorescent proteins, with high-resolution structural organization of the cytoskeleton in the same cell.

Cell Adhesion Strengthening: Measurement and Analysis

Cell adhesion to the extracellular matrix is a dynamic process involving numerous focal adhesion components, which act in coordination to strengthen and optimize the mechanical anchorage of cells over time. A method for systematically analyzing the cell adhesion strengthening process and the components involved in this process is described here. The method combines an adhesion strength assay based on applying fluid shearing to a population of cells and quantitative biochemical analyses.

Analyzing focal adhesion structure by atomic force microscopy

Atomic force microscopy (AFM) can produce high-resolution topographic images of biological samples in physiologically relevant environments and is therefore well suited for the imaging of cellular surfaces. In this work we have investigated focal adhesion complexes by combined fluorescence microscopy and AFM. To generate high-resolution AFM topographs of focal adhesions, REF52 (rat embryo fibroblast) cells expressing YFP-paxillin as a marker for focal adhesions were de-roofed and paxillin-positive focal adhesions subsequently imaged by AFM. The improved resolution of the AFM topographs complemented the optical images and offered ultrastructural insight into the architecture of focal adhesions. Focal adhesions had a corrugated dorsal surface formed by microfilament bundles spaced 127+/-50 nm (mean+/-s.d.) apart and protruding 118+/-26 nm over the substratum. Within focal adhesions microfilaments were sometimes branched and arranged in horizontal layers separated by 10 to 20 nm. From the AFM topographs focal adhesion volumes could be estimated and were found to range from 0.05 to 0.50 microm(3). Furthermore, the AFM topographs show that focal adhesion height increases towards the stress-fiber-associated end at an angle of about 3 degrees . Finally, by correlating AFM height information with fluorescence intensities of YFP-paxillin and F-actin staining, we show that the localization of paxillin is restricted to the ventral half of focal adhesions, whereas F-actin-containing microfilaments reside predominantly in the membrane-distal half.

Surface chemistry modulates focal adhesion composition and signaling through changes in integrin binding

Biomaterial surface properties influence protein adsorption and elicit diverse cellular responses in biomedical and biotechnological applications. However, the molecular mechanisms directing cellular activities remain poorly understood. Using a model system with well-defined chemistries (CH3, OH, COOH, NH2) and a fixed density of the single adhesive ligand fibronectin, we investigated the effects of surface chemistry on focal adhesion assembly and signaling. Surface chemistry strongly modulated integrin binding and specificity--alpha5beta1 integrin binding affinity followed the pattern OH>NH2=COOH>CH3, while integrin alphaVbeta3 displayed the relationship COOH>NH2>>OH=CH3. Immunostaining and biochemical analyses revealed that surface chemistry modulates the structure and molecular composition of cell-matrix adhesions as well as focal adhesion kinase (FAK) signaling. The neutral hydrophilic OH functionality supported the highest levels of recruitment of talin, alpha-actinin, paxillin, and tyrosine-phosphorylated proteins to adhesive structures. The positively charged NH2 and negatively charged COOH surfaces exhibited intermediate levels of recruitment of focal adhesion components, while the hydrophobic CH3 substrate displayed the lowest levels. These patterns in focal adhesion assembly correlated well with integrin alpha5beta1 binding. Phosphorylation of specific tyrosine residues in FAK also showed differential sensitivity to surface chemistry. Finally, surface chemistry-dependent differences in adhesive interactions modulated osteoblastic differentiation. These differences in focal adhesion assembly and signaling provide a potential mechanism for the diverse cellular responses elicited by different material properties.

Targeting of cytoskeletal linker proteins to focal adhesion complexes is reduced in fibroblasts adhering to laminin-1 when compared to fibronectin

Cellular interactions with the extracellular matrix determine to a large extent cell behavior, including cell migration. These interactions take place at specialized cellular structures, the focal adhesions, which have a substrate-specific morphology. To determine the molecular and functional relevance of this observation, the composition of isolated focal adhesions developed by fibroblasts adhering to fibronectin or laminin-1 was analyzed by indirect immunofluorescence and immunoblotting with or without stabilization of the structures by cross-linking. In the absence of cross-linking, integrins, talin, vinculin and, to a lower extent, paxillin remained associated with the focal adhesions formed on both substrates, indicating a tight association of these proteins with the extracellular matrix support. By contrast, alpha-actinin, FAK, and actin were apparently loosely maintained within focal adhesions and were found associated to these structures only after stabilization by cross-linking. Interestingly, although both substrates induced clustering and aggregation of all these proteins, their relative concentration, with the exception of alpha-actinin, was lower within the focal adhesions formed on laminin-1 than in those formed on fibronectin. Moreover, as assessed in migration assays, the locomotory speed of fibroblasts was higher on laminin-1 than on fibronectin. Altogether these results indicate that integrins involved in cellular interactions with fibronectin or laminin-1 trigger the formation of focal adhesion structures which differ by molecular organization, concentration in several adhesion plaque components, and function.

ARF1 mediates paxillin recruitment to focal adhesions and potentiates Rho-stimulated stress fiber formation in intact and permeabilized Swiss 3T3 fibroblasts

Focal adhesion assembly and actin stress fiber formation were studied in serum-starved Swiss 3T3 fibroblasts permeabilized with streptolysin-O. Permeabilization in the presence of GTPgammaS stimulated rho-dependent formation of stress fibers, and the redistribution of vinculin and paxillin from a perinuclear location to focal adhesions. Addition of GTPgammaS at 8 min after permeabilization still induced paxillin recruitment to focal adhesion-like structures at the ends of stress fibers, but vinculin remained in the perinuclear region, indicating that the distributions of these two proteins are regulated by different mechanisms. Paxillin recruitment was largely rho-independent, but could be evoked using constitutively active Q71L ADP-ribosylation factor (ARF1), and blocked by NH2-terminally truncated Delta17ARF1. Moreover, leakage of endogenous ARF from cells was coincident with loss of GTPgammaS- induced redistribution of paxillin to focal adhesions, and the response was recovered by addition of ARF1. The ability of ARF1 to regulate paxillin recruitment to focal adhesions was confirmed by microinjection of Q71LARF1 and Delta17ARF1 into intact cells. Interestingly, these experiments showed that V14RhoA- induced assembly of actin stress fibers was potentiated by Q71LARF1. We conclude that rho and ARF1 activate complimentary pathways that together lead to the formation of paxillin-rich focal adhesions at the ends of prominent actin stress fibers.

Isolation and contraction of the stress fiber

Stress fibers were isolated from cultured human foreskin fibroblasts and bovine endothelial cells, and their contraction was demonstrated in vitro. Cells in culture dishes were first treated with a low-ionic-strength extraction solution and then further extracted using detergents. With gentle washes by pipetting, the nucleus and the apical part of cells were removed. The material on the culture dish was scraped, and the freed material was forced through a hypodermic needle and fractionated by sucrose gradient centrifugation. Isolated, free-floating stress fibers stained brightly with fluorescently labeled phalloidin. When stained with anti-alpha-actinin or anti-myosin, isolated stress fibers showed banded staining patterns. By electron microscopy, they consisted of bundles of microfilaments, and electron-dense areas were associated with them in a semiperiodic manner. By negative staining, isolated stress fibers often exhibited gentle twisting of microfilament bundles. Focal adhesion-associated proteins were also detected in the isolated stress fiber by both immunocytochemical and biochemical means. In the presence of Mg-ATP, isolated stress fibers shortened, on the average, to 23% of the initial length. The maximum velocity of shortening was several micrometers per second. Polystyrene beads on shortening isolated stress fibers rotated, indicating spiral contraction of stress fibers. Myosin regulatory light chain phosphorylation was detected in contracting stress fibers, and a myosin light chain kinase inhibitor, KT5926, inhibited isolated stress fiber contraction. Our study demonstrates that stress fibers can be isolated with no apparent loss of morphological features and that they are truly contractile organelle.

Analysis of the actin-myosin II system in fish epidermal keratocytes: mechanism of cell body translocation

While the protrusive event of cell locomotion is thought to be driven by actin polymerization, the mechanism of forward translocation of the cell body is unclear. To elucidate the mechanism of cell body translocation, we analyzed the supramolecular organization of the actin-myosin II system and the dynamics of myosin II in fish epidermal keratocytes. In lamellipodia, long actin filaments formed dense networks with numerous free ends in a brushlike manner near the leading edge. Shorter actin filaments often formed T junctions with longer filaments in the brushlike area, suggesting that new filaments could be nucleated at sides of preexisting filaments or linked to them immediately after nucleation. The polarity of actin filaments was almost uniform, with barbed ends forward throughout most of the lamellipodia but mixed in arc-shaped filament bundles at the lamellipodial/cell body boundary. Myosin II formed discrete clusters of bipolar minifilaments in lamellipodia that increased in size and density towards the cell body boundary and colocalized with actin in boundary bundles. Time-lapse observation demonstrated that myosin clusters appeared in the lamellipodia and remained stationary with respect to the substratum in locomoting cells, but they exhibited retrograde flow in cells tethered in epithelioid colonies. Consequently, both in locomoting and stationary cells, myosin clusters approached the cell body boundary, where they became compressed and aligned, resulting in the formation of boundary bundles. In locomoting cells, the compression was associated with forward displacement of myosin features. These data are not consistent with either sarcomeric or polarized transport mechanisms of cell body translocation. We propose that the forward translocation of the cell body and retrograde flow in the lamellipodia are both driven by contraction of an actin-myosin network in the lamellipodial/cell body transition zone.

Convergence of integrin and growth factor receptor signaling pathways within the focal adhesion complex

Extracellular matrix controls capillary endothelial cell sensitivity to soluble mitogens by binding integrin receptors and thereby activating a chemical signaling response that rapidly integrates with growth factor-induced signaling mechanisms. Here we report that in addition to integrins, growth factor receptors and multiple molecules that transduce signals conveyed by both types of receptors are immobilized on the cytoskeleton (CSK) and spatially integrated within the focal adhesion complex (FAC) at the site of integrin binding. FACs were rapidly induced in round cells and physically isolated from the remainder of the CSK after detergent-extraction using magnetic microbeads coated with fibronectin or a synthetic RGD-containing peptide. Immunofluorescence microscopy revealed that multiple signaling molecules (e.g., pp60c-src, pp125FAK, phosphatidylinositol-3-kinase, phospholipase C-gamma, and Na+/H+ antiporter) involved in both integrin and growth factor receptor signaling pathways became associated with the CSK framework of the FAC within 15 min after binding to beads coated with integrin ligands. Recruitment of tyrosine kinases to the FAC was also accompanied by a local increase in tyrosine phosphorylation, as indicated by enhanced phosphotyrosine staining at the site of integrin binding. In contrast, neither recruitment of signaling molecules nor increased phosphotyrosine staining was observed when cells bound to beads coated with a control ligand (acetylated low density lipoprotein) that ligates transmembrane scavenger receptors, but does not induce FAC formation. Western blot analysis confirmed that FACs isolated using RGD-beads were enriched for pp60c-src, pp125FAK, phospholipase C-gamma, and the Na+/H+ antiporter when compared with intact CSK or basal cell surface preparations that retained lipid bilayer. Isolated FACs were also greatly enriched for the high affinity fibroblast growth factor receptor flg. Most importantly, isolated FACs continued to exhibit multiple chemical signaling activities in vitro, including protein tyrosine kinase activities (pp60c-src and pp125FAK) as well as the ability to undergo multiple sequential steps in the inositol lipid synthesis cascade. These data suggest that many of the chemical signaling events that are induced by integrins and growth factor receptors in capillary cells may effectively function in a "solid-state" on insoluble CSK scaffolds within the FAC and that the FAC may represent a major site for signal integration between these two regulatory pathways. Future investigations into the biochemical and biophysical basis of signal transduction may be facilitated by this method, which results in isolation of FACs that retain the CSK framework as well as multiple associated chemical signaling activities.

Focal adhesion proteins associated with apical stress fibers of human fibroblasts

Human fibroblasts stained with fluorescently labeled phalloidin revealed many stress fibers within the apical cytoplasm in addition to those located along the basal plasma membrane and associated with focal adhesions. The staining patterns of these apical stress fibers with fluorescent phalloidin, anti-alpha-actinin, and antimyosin were identical to those of the basal stress fibers, suggesting the same macromolecular organization for both types of stress fibers. There were two types of apical stress fibers that clearly interacted with the apical plasma membrane, those extending between the basal and the apical plasma membrane and those having both ends on the basal membrane forming arches whose top interacted with the apical plasma membrane. By electron microscopy, we observed that apical stress fibers were associated with the apical plasma membrane via electron-dense plaques reminiscent of the focal adhesion. Since several proteins have been specifically localized to the focal adhesion site, we examined whether they were also present at the apical stress fiber-membrane association site by using immunocytochemical methods and image reconstruction techniques. We found that vinculin, talin, paxillin, a fibronectin receptor protein, several integrin subunits including beta 1, fibronectin, and proteins with phosphorylated tyrosine were also components of the apical plaque. These observations indicate that apical stress fibers are attached to the plasma membrane by using principally the same molecular assembly as the focal adhesion associated with the basal stress fiber. We suggest that the complex molecular organization of the focal adhesion is not demanded by cell adhesion, but rather it is needed for anchoring stress fibers to the plasma membrane. Apical plaques did not stain with the anti-integrin alpha v subunit or anti-focal adhesion associated kinase (FAK), although these antibodies stained focal adhesions. These results suggest that the apical stress fiber-membrane contact has some important functions different from those of the focal adhesion.

LFA-1 integrin redistribution during T-cell hybridoma invasion of hepatocyte cultures and manganese-induced adhesion to ICAM-1

We have reported previously that the integrin LFA-1 is essential for metastasis of T-cell hybridomas to the liver. We show here that hepatocytes isolated from normal non-inflamed rat liver express intercellular adhesion molecule-1 (ICAM-1) at the dorsal surface and more prominently at the lateral and substratum-adherent surfaces. Anti-rat ICAM-1 mAb inhibited adhesion of TAM8C4 T-cell hybridoma cells to hepatocytes. Invasion between hepatocytes was not affected, but this is probably due to lack of penetration of the mAb between the hepatocytes. In all hepatocyte-adherent TAM8C4 cells, LFA-1 was concentrated at the adhesion site. Redistribution of ICAM-1 to the interacting hepatocyte membrane was also seen, but only for part of the adherent TAM8C4 cells. LFA-1 was highly concentrated on pseudopods of invading TAM8C4 cells inserted between hepatocytes, and on the upper surface of invaded TAM8C4 cells located under the hepatocytes. ICAM-1 was concentrated in the hepatocyte membrane overlying TAM8C4 cells located underneath the monolayer. These results suggests that ICAM-1 is of major importance for liver invasion by these lymphoma cells. For optimal adhesion to ICAM-1, LFA-1 on T-cell hybridomas requires activation, which apparently occurs upon contact with cell layers that are invaded (G. La Riviere et al., J. Cell Sci. 107, 551–559, 1994). LFA-1 can be activated artificially by Mn2+. To study LFA-1 redistribution upon ICAM-1 interaction with higher resolution, we performed immuno-EM on cells before and after Mn(2+)-induced adhesion and spreading on immobilized ICAM-1. By immune fluorescence, LFA-1 was observed to redistribute to the ICAM-1-adherent surface, and to be concentrated in lamellipodia of spreading TAM8C4 cells. By immuno-EM, LFA-1 was localized in microclusters of approximately 10 gold particles. This was seen in cells fixed in suspension, and the size of these clusters did not change upon adhesion to ICAM-1. LFA-1 was present at high density in thin filopodia, but again in microclusters of similar size. Comparable results were obtained with a cytotoxic T-cell clone. We conclude that Mn(2+)-induced activation of LFA-1 is not associated with the formation or enlargement of LFA-1 clusters.

Immuno-EM localization of the beta 1 integrin subunit in wet-cleaved fibronectin-adherent fibroblasts

Using immuno-EM, we have studied the distribution of the beta 1 integrin subunit in chicken embryo fibroblasts allowed to adhere and spread for 3 hours on a fibronectin-coated surface in serum-free medium. The cells were wet-cleaved, which removed most of the cell body, yielding ventral plasma membranes with little, and sometimes virtually no, associated cytoskeleton. The beta 1 integrin subunit was detected with antibodies against the cytoplasmic domain. In immune fluorescence, it colocalized with adhesion plaques, in a punctate staining pattern, and often seemed to be at the periphery of the plaque. By immuno-EM, beta 1 was in fact found in discrete clusters, not throughout the plaque. In deep-cleaved cells from which virtually all cytoskeleton was removed, clusters could often be seen to be located on fibronectin fibrils. Furthermore, beta 1 was present in clusters at the cell margins, and isolated or in small groups at the very edge of the cell. When fibronectin synthesis, and consequently fibril formation, was inhibited by cycloheximide, large adhesion plaque-like structures were formed at the cell margin. This phenotype was reversed by addition of soluble fibronectin, which was incorporated into fibrils. As in normal plaques, talin and vinculin were present, the plasma membrane was very close (10-20 nm) to the substratum and the fibronectin layer underneath was removed. These plaques did contain beta 1 integrins but they were not in clusters. These observations indicate that the talin-vinculin network of an adhesion plaque is normally anchored to the substratum at discrete beta 1 integrin clusters that may be located on fibronectin fibrils, and that elsewhere the plaque is not necessarily attached to the substratum by interaction of integrins with matrix proteins. In the absence of fibronectin fibrils, adhesion plaque-like structures can be formed, but these are aberrant in size, location and fine structure.

Calmodulin and wound healing in the coenocytic green alga Ernodesmis verticillata (Kützing) Børgesen: Ultrastructure of the cortical cytoskeleton and immunogold labeling

Ultrastructural changes in the cortical cytoskeleton during wound-induced cytoplasmic contraction were examined in the coenocytic green alga Ernodesmis verticillata. Both calmodulin (CaM) and actin were localized in intact and contracting cells by immunogold labeling. Within 5 min after wounding, compact microfilament (MF) bundles were observed which increase in diameter as cytoplasmic contraction proceeds. Calmodulin labeling is associated with amorphous material studding the MF bundles, whereas actin labeling occurs along the individual MFs. No MF bundles were ever observed during contraction that were not also labeled with anti-CaM antibodies. In cells treated with the CaM antagonist W-7 (N-[6-aminohexyl]-5-chloro-1-naphtha-lenesulfonamide), MF bundles do not form, and the formation of loosely arranged MFs (similar to nascent bundles in untreated cells) is greatly retarded. We propose that CaM binds indirectly to actin by activating an actin-binding regulatory protein which functions in early stages of the transduction sequence leading to functional MF bundles. Additionally, ultrastructural evidence is presented for a plasma-membrane skeleton or undercoating in this alga.

Negative staining-carbon film technique: new cellular and molecular applications

Two techniques are presented which extend the original negative staining-carbon film technique into new areas of cellular and molecular application. These relate (1) to the production of negatively stained specimens of single-layer plasma membrane split from intact cells during the overall procedure that are negatively stained from the cytoplasmic face and (2) to the production of negatively stained specimens directly from glycerol-containing protein solutions, membrane or viral suspensions. In both cases in vacuo drying onto mica from glycerol is performed, prior to deposition of a carbon film. (For the cellular technique, freshly cleaved mica is firstly rendered positively charged by immersion in Alcian blue.) This is followed by release of the carbon film plus adsorbed membrane or protein by floating onto water, with subsequent negative staining. Selected preliminary applications using human erythrocyte membrane and the high molecular weight (native) human erythrocyte tripeptidyl peptidase-II complex are given and considered speculation as to the future application of the techniques is provided.

PtK1 cells contain a nondiffusible, dominant factor that makes the Golgi apparatus resistant to brefeldin A

Brefeldin A (BFA) was shown in earlier studies of numerous cell types to inhibit secretion, induce enzymes of the Golgi stacks to redistribute into the ER, and to cause the Golgi cisternae to disappear. Here, we demonstrate that the PtK1 line of rat kangaroo kidney cells is resistant to BFA. The drug did not disrupt the morphology of the Golgi complex in PtK1 cells, as judged by immunofluorescence using antibodies to 58- (58K) and 110-kD (beta-COP) Golgi proteins, and by fluorescence microscopy of live cells labeled with C6-NBD-ceramide. In addition, BFA did not inhibit protein secretion, not alter the kinetics or extent of glycosylation of the vesicular stomatitis virus (VSV) glycoprotein (G-protein) in VSV-infected PtK1 cells. To explore the mechanism of resistance to BFA, PtK1 cells were fused with BFA-sensitive CV-1 cells that had been infected with a recombinant SV-40 strain containing the gene for VSV G-protein and, at various times following fusion, the cultures were exposed to BFA. Shortly after cell fusion, heterokaryons contained one Golgi complex associated with each nucleus. Golgi membranes derived from CV-1 cells were sensitive to BFA, whereas those of PtK1 origin were BFA resistant. A few hours after fusion, most heterokaryons contained a single, large Golgi apparatus that was resistant to BFA and contained CV-1 galactosyltransferase. In unfused cells that had been perforated using nitrocellulose filters, retention of beta-COP on the Golgi was optimal in the presence of cytosol, ATP, and GTP. In perforated cell models of the BFA-sensitive MA104 line, BFA caused beta-COP to be released from the Golgi complex in the presence of nucleotides, and either MA104 or PtK1 cytosol. In contrast, when perforated PtK1 cells were incubated with BFA, nucleotides, and cytosol from either cell type, beta-COP remained bound to the Golgi complex. We conclude that PtK1 cells contain a nondiffusible factor, which is located on or very close to the Golgi complex, and confers a dominant resistance to BFA. It is possible that this factor is homologous to the target of BFA in cells that are sensitive to the drug.

Disintegration of adhesion plaques in chicken embryo fibroblasts upon Rous sarcoma virus-induced transformation: different dissociation rates for talin and vinculin

The localization of talin and vinculin in chicken embryo fibroblasts (CEF) during transformation was studied by immunoelectron microscopy. CEF cells were infected with a temperature-sensitive mutant of Rous sarcoma virus. After 16 h at 42 degrees C, transformation was induced by incubation at 37 degrees C for different intervals up to 3 h. Cells were cleaved by "wet cleaving" as reported previously by us (R. Brands and C.A. Feltkamp, 1988, Exp. Cell Res. 176, 309) and labeled with affinity-purified polyclonal antibodies to talin or vinculin, or monoclonal anti-vinculin. We observed a rapid reduction of vinculin in adhesion plaques within 15 min and a much slower dissociation of talin. This was found using single-labeling procedures and also within the same cell using double labeling. Seemingly intact microfilament bundles were observed associated with adhesion plaques that contained relatively little vinculin. These observations show that an early event in src-induced transformation is the release of vinculin from adhesion plaques. Furthermore, since adhesion plaques with attached filament bundles can exist at least transiently with very little or no vinculin present, it seems likely that vinculin is not, or not the only protein, linking actin filaments to adhesion plaques.

Strategy and tactics in electron microscopy of cell surfaces

Over the past decade new methods have been developed to visualize both the external and the protoplasmic surfaces of cultured cells in the electron microscope. In this review the emphasis is on cell monolayers, though some of the techniques are also applicable to cells in suspension. There is no universal method which would satisfy all our requirements i.e. the preservation of native structure and antigenicity and the visualization of the whole cell surface at high resolution. While surface replicas of freeze-dried or critical point-dried cells are eminently suited for high resolution studies including gold immunolabelling, scanning electron microscopy provides a view of the whole cell and a large sample for 'statistical' evaluation. Whole mount preparations of cleaved cells prove useful in studies of plasma membrane associated structures such as the cytoskeleton. A series of new procedures have been developed for studies of cytoskeleton/membrane interactions, identification of intramembrane particles and their contacts with the glycocalyx, to mention some of the biological problems. Although the lysis-squirting technique appears most suitable for the visualization and immunolabelling of protoplasmic surfaces of ventral membranes, dry- or wet-cleaving represent a useful alternative for studies of the protoplasmic surfaces of dorsal membranes and of the ventral membrane associated cytoplasmic domains. An assessment of the methods is given though this should only serve as guidance and it is up to the experimentor to choose the most useful technique for the project under study. Briefly the aim of the project determines the choice of the method. A multi-methodical approach is recommended when one method does not provide satisfactory results.