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Author(s): Anja K. Büscher [sup.1] , Nora Celebi [sup.2] , Peter F. Hoyer [sup.1] , Hanns-Georg Klein [sup.3] , Stefanie Weber [sup.4] , Julia Hoefele [sup.5] Author Affiliations: (1) Pediatric [...], Background In 2010, INF2 mutations were associated with autosomal-dominant focal segmental glomerulosclerosis (FSGS), clinically presenting with moderate proteinuria in adolescence. However, in the meantime, cases with more severe clinical courses have been described, including progression to end-stage renal disease (ESRD) during childhood. INF2 mutations in patients with isolated FSGS are clustered in exons 2 to 4, encoding the diaphanous inhibitory domain, involved in the regulation of the podocyte actin cytoskeleton. Methods We report a family with 14 affected individuals (autosomal-dominant mode of inheritance), most of whom presented with nephrotic-range proteinuria, hypertension, and progressive renal failure. Four members received a kidney transplant without disease recurrence. Two patients underwent renal biopsy with the result of minimal-change glomerulopathy and IgA nephropathy respectively. We performed mutational analysis of ACTN4, CD2AP, COQ6, INF2, LAMB2, NPHS1, NPHS2, PLCE1, TRPC6, and WT1 in the index patient by next-generation sequencing. Additionally, in 6 affected and 2 unaffected family members target diagnostics were performed. Results We identified a novel heterozygous mutation c.490G>C (p.(Ala164Pro) in exon 3 of the INF2 gene in the index patient and 6 additionally examined affected family members. In silico analysis predicted it as "probably damaging". Additionally, three patients and 2 unaffected relatives harbored a novel heterozygous variant in ACTN4 (c.1149C>G, p.(Ile383Met)) with uncertain pathogenicity. Conclusion Mutations in INF2 are associated with familial proteinuric diseases - irrespective of the presence of FSGS and in the case of rapid disease progression. Therefore, mutational analysis should be considered in patients with renal histology other than FSGS and severe renal phenotype.

Introduction The ability of cells to sense and respond to mechanical loads is fundamental to the maintenance of tissue structure. Although the exact types of loads cells experience in vivo [...], Culture of human osteoblast-like MG-63 cells within collagen gels results in the generation of intrinsic stress. Release of such collagen gels from attachment results in gel contraction and enhanced MMP-1, MMP-3, and α2 integrin mRNA levels. To understand the potential role of microtubules and signaling pathways involved in MG-63 cell-mediated contraction and gene expression, cells were cultured in collagen gels. After 24 h collagen gels were released, then immediately treated with nocodazole or specific protein kinase inhibitors. Contraction was assessed, RNA isolated, and real-time PCR analysis performed. Treatment with high concentrations of a microtubule depolymerization agent, nocodazole, enhanced early contraction and led to elevated mRNA levels for MMP-3, whereas low concentrations inhibited contraction at later time points and did not affect mRNA levels. ROCK inhibitor treatment (Y27632) inhibited collagen gel contraction and led to depressed mRNA levels. The ERK1/2 inhibitor U0126 did not affect contraction, but treatment led to depressed MMP-1, MMP-3, and α2 mRNA levels. The p38MAPK inhibitor SB203580 modestly affected contraction, but did not affect mRNA levels. These results suggest the potential role of cytoskeletal integrity and multiple kinase signaling pathways in specific bone-remodeling events. Key words: mechanical loading, collagen gel contraction, osteoblast, mechanotransduction. La culture des cellules osteoblastoides humaines MG-63 a l'interieur de gels de collagene genere un stress intrinse que. Le detachement de ces gels de collagene produit une contraction du gel et une augmentation des niveaux d'ARNm de MMP-1, MMP-3 et des integrines α2. Afin de comprendre le role potentiel des microtubules et des voies signaletiques impliquees dans la contraction produite par les cellules et dans la regulation genique des cellules MG-63, les cellules ont ete cultivees dans des gels de collagene. Apres 24 heures, les gels de collagenes ont ete detaches et traites immediatement avec du nocodazole ou des inhibiteurs specifiques de proteine kinases. La contraction a ete evaluee, l'ARN isole et une analyse en RT-PCR realisee. Un traitement avec de fortes concentrations d'un agent de depolymerisation de microtubules, le nocodazole, augmentait la contraction precoce et augmentait les niveaux d'ARNm de MMP-3, alors que de faibles concentrations inhibaient la contraction a des temps plus tardifs et n'affectaient pas les niveaux d'ARNm de MMP-3. Un traitement avec un inhibiteur de ROCK (Y27632) inhibait la contraction du gel de collagene et reprimait l'expression des ARNm. Un inhibiteur de ERK1/2, le U0126, n'affectait pas la contraction mais reprimait les ARNm de MMP-1, MMP-3 et α2. Un inhibiteur de p38MAPK, le SB203580, affectait modestement la contraction mais n'affectait pas les niveaux d'ARNm. Ces resultats suggerent l'existence d'un role potentiel de l'integrite du cytosquelette et des voies signaletiques de differentes kinases dans certains evenements specifiques du remodelage osseux. Mots-cles : charge mecanique, contraction du gel de collagene, osteoblaste, mecanotransduction. [Traduit par la Redaction]

The article explores possibility to obtain a taxonomy based on the interactions between hyperstructures on trajectory-based classification. The taxonomy based on interactions proves to be informative.

Study of impact of cytokinesis on cytoskeleton of cell plate, based on role of endosomes in vesicle trafficking through plasma membrane during mitosis, is presented.

It has been speculated that heart valve interstitial cells (VICs) maintain valvular tissue homeostasis through regulated extracellular matrix (primarily collagen) biosynthesis. VICs appear to be phenotypically plastic, inasmuch as they transdifferentiate into myofibroblasts during valve development, disease, and remodeling. Under normal physiological conditions, transvalvular pressures (TVPs) on the right and left side of the heart are vastly different. Hence, we hypothesize that higher left-side TVPs impose larger local tissue stress on VICs, which increases their stiffness through cytoskeletal composition, and that this relation affects collagen biosynthesis. To evaluate this hypothesis, isolated ovine VICs from the four heart valves were subjected to micropipette aspiration to assess cellular stiffness, and cytoskeletal composition and collagen biosynthesis were quantified by using the surrogates smooth muscle [alpha]-actin (SMA) and heat shock protein 47 (HSP47), respectively. VICs from the aortic and mitral valves were significantly stiffer (P < 0.001) than those from the pulmonary and tricuspid valves. Left-side isolated VICs contained significantly more (P < 0.001) SMA and HSP47 than right-side VICs. Mean VIC stiffness correlated well (r = 0.973) with TVP; SMA and HSP47 also correlated well (r = 0.996) with one another. Assays were repeated for VICs in situ, and, as with in vitro results, left-side VIC protein levels were significantly greater (P < 0.05). These findings suggest that VICs respond to local tissue stress by altering cellular stiffness (through SMA content) and collagen biosynthesis. This functional VIC stress-dependent biosynthetic relation may be crucial in maintaining valvular tissue homeostasis and also prove useful in understanding valvular pathologies. valve remodeling; cytoskeleton; cell mechanics; micropipette aspiration

Actin, one of the most highly conserved and abundant eukaryotic proteins, is constantly being polymerized and depolymerized within cells as part of cellular motility, tissue formation and repair, and embryonic development. Many proteins exist that bind to monomeric or filamentous (F) forms of actin to regulate the polymerization state. It has become increasingly apparent that the ability of different proteins to bind to and regulate actin filament dynamics depends on the ability of the filament to exist in altered conformations. Yet, little is known about how these conformational changes occur at the molecular level. We have destabilized F-actin filaments by forming a disulfide that locks the 'hydrophobic plug' to the body of the actin subunit or by altering the C terminus of actin with a tetramethylrhodamine label. We also examined F-actin filaments at short times after the initiation of polymerization. In all three cases, a substantial fraction of protomers can be found in a 'tilted' state that also is induced by actin depolymerizing factor/cofilin proteins. These observations suggest that F-actin filaments are annealed over time into a stable filament and that actin-depolymerizing proteins can effect a time reversal of polymerization. cytoskeleton | EM | image analysis

The cytoskeleton is a dynamic scaffold in living cells even in the absence of externally imposed forces. In this study on cytoskeletal deformation, the applicability of hierarchical feature vector matching (HFVM), a new matching method, currently applied in space research and three-dimensional surface reconstruction, was investigated. Stably transfected CHO-K1 cells expressing green fluorescent protein (GFP) coupled to vimentin were used to visualize spontaneous movement of the vimentin cytoskeleton of individual cells using a confocal laser scanning system. We showed that, with proper parameter and configuration settings, HFVM could recognize and trace 60-70% of all image points in artificially translated, rotated, or deformed images. If only points belonging to the cytoskeleton were selected for matching purposes, the percentage of matched points increased to 98%. This high percentage of recognition also could be reached in a time series of images, in which a certain degree of bleaching of the fluorescence over the recording time of 30 min was inevitable. In these images, HFVM allowed the detection as well as the quantification of spontaneous cytoskeletal movements of up to 10% of the cell width. Therefore, HFVM appears to be a reliable method of quantifying dynamic cytoskeletal behavior in living cells. vimentin; fibroblast; green fluorescent protein; confocal laser scanning

The Epithelial Cell Cytoskeleton and Intracellular Trafficking. I. Shiga toxin B-subunit system: retrograde transport, intracellular vectorization, and more. Am J Physiol Gastrointest Liver Physiol 283: G1-G7, 2002; 10.1152/ajpgi.00088.2002.--Many intracellular transport routes are still little explored. This is particularly true for retrograde transport between the plasma membrane and the endoplasmic reticulum. Shiga toxin B subunit has become a powerful tool to study this pathway, and recent advances on the molecular mechanisms of transport in the retrograde route and on its physiological function(s) are summarized. Furthermore, it is discussed how the study of retrograde transport of Shiga toxin B subunit allows one to design new methods for the intracellular delivery of therapeutic compounds. Shigella dysenteriae; endocytosis; endosomes; Golgi apparatus; signaling; vaccination

Cadherin receptors are key morphoregulatory molecules during development. To dissect their mode of action, we developed an approach based on the use of myogenic C2 cells and beads coated with an Ncad-Fc ligand, allowing us to mimic cadherin-mediated adhesion. We used optical tweezers and video microscopy to investigate the dynamics of N-cadherin anchoring within the very first seconds of bead-cell contact. The analysis of the bead movement by single-particle tracking indicated that N-cadherin molecules were freely diffusive in the first few seconds after bead binding. The beads rapidly became diffusion-restricted and underwent an oriented rearward movement as a result of N-cadherin anchoring to the actin cytoskeleton. The kinetics of anchoring were dependent on ligand density, suggesting that it was an inducible process triggered by active cadherin recruitment. This anchoring was inhibited by the dominant negative form of Rac1, but not that of Cdc42. The Rac1 mutant had no effect on cell contact formation or cadherin-catenin complex recruitment, but did inhibit actin recruitment. Our results suggest that cadherin anchoring to the actin cytoskeleton is an adhesion-triggered, Rac1 -regulated process enabling the transduction of mechanical forces across the cell membrane; they uncover novel aspects of the action of cadherins in cell sorting, cell migration, and growth cone navigation.

The cytoskeletal changes that alter cellular morphogenesis and motility depend upon a complex interplay among molecules that regulate actin, myosin, and other cytoskeletal components. The Rho family of GTP binding proteins are important upstream mediators of cytoskeletal organization. Gem and Rad are members of another family of small GTP binding proteins (the Rad, Gem, and Kir family) for which biochemical functions have been mostly unknown. Here we show that Gem and Rad interface with the Rho pathway through association with the Rho effectors, Rho kinase (ROK) [alpha] and [beta]. Gem binds ROK[beta] independently of RhoA in the ROK[beta] coiled-coil region adjacent to the Rho binding domain. Expression of Gem inhibited ROK[beta]-mediated phosphorylation of myosin light chain and myosin phosphatase, but not LIM kinase, suggesting that Gem acts by modifying the substrate specificity of ROK[beta]. Gem or Rad expression led to cell flattening and neurite extension in N1E-115 neuroblastoma cells. In interference assays, Gem opposed ROK[beta]- and Rad opposed ROK[alpha]-mediated cell rounding and neurite retraction. Gem did not oppose cell rounding initiated by ROK[beta] containing a deletion of the Gem binding region, demonstrating that Gem binding to ROK[beta] is required for the effects observed. In epithelial or fibroblastic cells, Gem or Rad expression resulted in stress fiber and focal adhesion disassembly. In addition, Gem reverted the anchorage-independent growth and invasiveness of Dbl-transformed fibroblasts. These results identify physiological roles for Gem and Rad in cytoskeletal regulation mediated by ROK.

The mechanisms by which Rho family GTPases (Rho, Rac and Cdc42) regulate coordinated changes to the actin cytoskeleton are being elucidated. This review will focus on the current evidence that the p21-activated kinases (PAKs) are involved in regulating some of the diverse cytoskeletal changes induced by Rac and Cdc42. PAKs have been shown to be required for processes including neurite formation and axonal guidance, development of cell polarity and motile responses. Signaling molecules interacting with PAKs that might contribute to the regulation of such processes have recently been identified.

Research was conducted to study the function of the cytoskeleton in surfactant protein gene expression. Alveolar type II cells were determined from the lungs of specific pathogen-free adult Sprague-Dawley rats while cultured cells were lysed in guanidinium isothiocyanate, laurylsarcosine and mercapto-ethanol. Results indicated the need for an intact cytoskeleton to maintain an aspect of type II cell differentiation even when the cells are characterized by their normal cuboidal shape.

Research was conducted to study the remodeling of the apical membrane-cytoskeleton during the stimulation of gastric parietal cells to secrete HCl. Actin assays were utilized to quantitate actin while the deoxyribonuclease I binding assay was used to determine G-actin and F-actin contents. Results showed that the treatment of gastric glands with cytochalasin D led to an inhibition of acid secretion, a decrease in F-actin and an increase in G-actin.

The domain interaction between PDZ and spectrin-like repeat motifs was identified through cloning of a novel cDNA encoding protein, actinin-associated LIM protein (ALP), occuring at the Z lines in association with alpha-actinin-2. Analyses indicated that the PDZ domain of ALP interacted with the spectrin-like repeats of alpha-actinin-2. This established the novel mode of interaction for PDZ domains.

The organization of myosin II and its influence on the cell body translocation were investigated through time-lapsed observation of the lamellipodia of fish epidermal keratocytes. Results have shown that new filaments were nucleated at the sides of preexisting filaments. According to the dynamic network model, the contraction of an actin-myosin network in the lamellipodia-cell body transition zone was coupled to effect translocation.

Spindle orientation is one of the main functions of cytoskeleton in all eukaryotic cells. Two general classes of cell division show the relevance of this process. These are the asymmetric division, in which some aspect of the cell is differentially apportioned between the two products of division, and the symmetric division within the asymmetric cell, in which a cellular component, such as the nucleus, must be segregated equally to two cells that are unequal in size and/or shape.

An examination of actin filaments in Drosophila ovarian nurse cells found that each nurse cell actin bundle is composed of modules that laterally associated and overlap like an extension ladder during cable assembly. Data show that the actin bundles overlap and thicken during compression and evenutally removes any trace of striation. Results indicate that the design of the actin modules keeps the nucleus away from the ring canals during dumping.

The role of Drosophila myoblast city (mbc) locus in mediating myoblast fusion, dorsal closure, and cytoskeletal organization was investigated through whole mount embryo analysis. Results have shown that mbc had a striking homology to DOCK180, a human gene involved in binding of the small adapter protein Crk. Mbc was implicated in signal transduction from focal adhesions and functions as Drac1 in the epidermis leading ot myoblast fusion.

The actin filament polymerization, structure, and dynamics were evaluated through the utilization of various analytical methods. Results revealed that actin polymerization involved a facultative, lower dimer-based pathway which could be responsible for the production of an actin meshwork. The lower dimer constitution in the growing actin filaments suggested the additional level of regulation of actin cytoskeleton dynamics.

The cytoskeleton of Saccharomyces cerevisiae is essentially invisible using conventional microscopy techniques. A similar problem was solved for the mammalian cell cytoskeleton using resinless section electron microscopy, a technique applied here to yeast. In the resinless image, soluble proteins are no longer cloaked by embedding medium and must be removed by selective detergent extraction. In yeast, this requires breaching the cell wall by digesting with Zymolyase sufficiently to allow detergent extraction of the plasma membrane lipids. Gel electropherograms show that the extracted or 'soluble' proteins are distinct from the retained or 'structural' proteins that presumably comprise the cytoskeleton. These putative cytoskeleton proteins include the major portions of a 43-kda protein, which is presumably actin, and of proteins in a band appearing at 55 kda, as well as numerous less abundant, nonactin proteins. Resinless section electron micrographs show a dense, three-dimensional web of anastomosing, polymorphic filaments bounded by the remnant cell wall. Although the filament network is very heterogenous, there appear to be two principal classes of filament diameters - 5 nm and 15-20 nm - which may correspond to actin and intermediate filaments, respectively. A large oval region of lower filament density probably corresponds to the vacuole, and an electron dense spheroidal body, 300-500 nm in diameter, is likely the nucleus. The techniques detailed in this report afford new approaches to the study of yeast cytoarchitecture.

The length of individual actin filaments in the F-actin bundles was analyzed in the macrochaetes or large bristles of Drosophila. The actin bundles in the large bristles of Drosophila is 400 micrometers in length while the actin bundles in the small bristles range from 65-70 micrometers in length. The actin filaments are cross-linked together to form the hexagonally packed actin bundles. Furthermore, the actin bundles are also composed of individual filaments that are three micrometers in length with modules that are attached from end-to-end.

The Ras-related GTPase controls the cytoskeleton. GTPase cascades regulate movement, morphogenesis and potential for choreographing cellular behavior. A GTPase cascade has one GTPase regulate the action of another GTPase. GTP-bound form and GDP-bound form are the two conformations of GTPase. The GTP-bound form is active and sends a signal but the GDP form is inactive and sends no signal. Functions like vesicular transport, translation, growth control, apoptosis and nuclear import are controlled by GTPases.

Light and electron microscopical study of a temperature-sensitive mutant of Saccharomyces cerevisiae, DBY 1693, find that the disruption of the actin cytoskeleton in budding yeast results in the formation of an aberrant cell wall. This aberrant cell wall is of loose texture with bulging glucan microfibrils incompletely masked with amorphous matrix. The localization of wall synthesis is in accordance with an even distribution of submembranous actin in the form of patches.

A novel assay for the polarized assembly of cortical actin cytoskeleton in yeast involves the permeabilization of the yeast cells, without altering the polarity of cellular constituents. Fluorescently labeled actin monomers that are added exogenously form specific patches, which resemble actin distribution in vivo. The actin nucleation activity that facilitates actin assembly is eliminated when the SLA1 or SLA2 gene is mutagenized. Actin assembly is also regulated by Cdc42, a Rho-like GTP-binding protein.

An analysis of the morphogenesis of Xenopus embryo reveals that functional cytoskeletal components of the cells are the major mediators of the morphogenesis from oocyte to embryo in Xenopus. Cytoskeletal components regulate cellular asymmetries and the integration of forces and signals essential for morphogenesis, helped by several embryonic proteins that regulate gastrulation. The morphogenetic pattern in Xenopus enables its use as a model system for examining 'body language' of embryonic growth.

Germination studies of the dimorphic yeast Candida albicans indicates that the actin and microtubule (MT) constituted cytoskeleton controls hyphal growth polarity in the species. The actin and MT interrelationship is involved in establishing the polarity. Actin cables may not be necessary for retaining the polarized location of actin while MTS may be crucial for the asymmetrical actin distribution.

Early transportation of Ca2+ agonists induces raising of neural folds at the median hinge point and joining of folds by bending at the lateral furrows, suggesting that neural tube formation is a calcium dependent process. Anti-calcium transportation factors prevent neural folding, confirming calcium's role in the process. Anti-calmodulin factors also inhibit neural folding. The size of fluorescently labeled phalliciding rings also reduces during the early transportation, which is a characteristic of calcium-dependent processes.

The interresponse of ion transport proteins and the actin-based cytoskeleton affects the short-term regulation of water and intestinal salt. This was revealed in an analysis of the phalloidin influence on the Cl-secretory response stimulated by the enterotoxin of Escherichia coli. The functional activity of the Na+-K+-2Cl was restricted by phalloidin.

An analysis of the isotonic shortening velocity of canine tracheal smooth muscle as a function of contraction history demonstrates a higher shortening velocity, affected by the initiation of muscle activity at a shorter muscle length. This confers a plasticity to the force-velocity relationship associated with the canine tracheal smooth muscle, which may be attributed to the cytostructural reassembling of the cell during contractile activation. The experiment involves isometric contraction of muscles for 20 seconds at initial (Lo) lengths of maximal active force, 85% of Lo affected by electrical field stimuli, which is subsequented by isotonic shortening of muscles at different afterloads. Measurements taken during isotonic shortening are used to plot a graph between instantaneous velocities against instantaneous muscle lengths. The isotonic shortening velocity is found to decrease linearly as a function of instantaneous muscle lengths.

The remarkable decline in stress fibers during shear-stress exposure is consistent with the doxorubicin-stimulated decrease in endothelial adhesiveness, which is attributed to the side effect of doxorubicin on action polymerization. There is no prominent decrease of stress fibers occurring during the exposure of drug-treated relaxed monolayers to shear-stress. The discrepancies in the response of relaxed and shear stress-subjected cultured cells is a consequence of the enhanced production of action monomers during the shear stress-induced realignment of the action filament structure.

The cytoskeletal patterns of actin, vinculin, talin and integrin distribution in human platelets were examined. It was suggested that vinculin self-organizes at the plasma membrane by competitive aggregation. Some of the actin and vinculin patterns exhibit handedness, implying that asymmetry in biological systems is generated at the interface between the plasma membrane and the cytosol.

Author Affiliations: A skin-cancer cell. Cells might rely on cues from their internal skeletons to expand without becoming cancerous. [see PDF for image] Credit: Steve Gschmeissner/SPL Credit: Steve Gschmeissner/SPL How [...], A protein called YAP might help to convey messages from a cell&apos;s internal framework. A protein called YAP might help to convey messages from a cell&apos;s internal framework. A protein called YAP might help to convey messages from a cell&apos;s internal framework.

The role of F-actin in cellular morphogenesis was investigated. F-actin is a filamentous polymer of globular G-actin involved in cellular functions such as microspike extension, contraction of the contractile ring in mitosis, structural support and pseudopod extension/retraction in amoeboid movement. G-actin was incorporated into liposomes and the transformation processes of liposomes due to actin polymerization were observed. The results showed that liposomes changed from initial spherical to two regular geometric shapes, which was correlated with G-actin polymerization into filaments. These filaments aligned themselves into bundles along the liposome periphery.

A study was done to obtain a molecular characterization of the Euglena gracilis cytoskeletal proteins called articulins. Two sets of cDNAs obtained after an expression library constructed from E. gracilis mRNAs were screened with articulin antibodies. The deduced amino acid sequences of the articulins were found to have no significant similarities with other proteins, leading to the conclusion that the E. gracilis articulins are a new class of membrane cytoskeletal proteins.

Previous investigations have suggested that glycolytic metabolism is closely associated with cell motility and cytoskeletal organization. This apparent relationship was tested by examining the effects of 2-deoxyglucose (2-DG), a glycolytic inhibitor, and cytochalasin D (CD), an actin cytoskeletal modulator, on the mobility of aldolase in living cells. The results showed that both inhibitors could release the bound fraction of aldolase to the solid phase of the cytoplasm. This indicates that glycolytic enzymes are not exclusively soluble proteins, but may associate with the actin-based cytoskeleton.

The consequences arising from internal deletions and point mutations in the beta1c cytoplasmic region on focal adhesion localization of integrin were investigated. Complementary DNA from wild type and mutant chicken beta1c subunits were expressed and their focal adhesion localizations were examined by immunofluorescent staining using specific anti-beta1 antibodies. Beta1c cytoplasmic region was observed to contain three sites that are active in integrin localization. These activities of the three regions were greatly decreased upon single amino acid substitution.

The effect of zinc deficiency on the membrane skeleton of red blood cells from rats was examined through composition analysis and extractability evaluation of spectrin from rats kept on a zinc-deficient diet. Results showed that zinc deficiency did not modify spectrin oligomeric form and extractability. It did, however, reduce protein R5 composition of spectrin. This alteration in the composition of the membrane skeleton suggests a structural or compositional modification not indicated by spectrin extractability and oligomeric analysis.

Study analyzing the role of the Rho family members, Cdc42/G25K, Rac1, Rac2, RhoA, RhoB and RhoC in various biological processes finds a link from these GTPases to the nucleus and, for Cdc42 and Rac, to a mitogen activating protein kinase (MAPK) cascade. Rho family members also play vital roles in the regulation of the actin cytoskeleton. The observation that chronic activation of Cdc42, Rac and Rho by deregulated exchange factors induces malignant transformation as well as morphological changes suggests that these GTPases may regulate nuclear as well as cytoplasmic effects.

The article investigates the association of the dopamine transporter (DAT) with lipid microdomains in the plasma membrane and the cytoskeleton. The findings propose that the association serves to regulate both the lateral mobility of the transporter and its transport capacity.

Tropomyosin has regulated filament dynamics at the barbed end and is bound to constructs of FRL1 and mDia2. It is shown that tropomyosin functions as an activator of formin and its various features has established it as a universal regulator of the multifaceted chain cytoskeleton.

The tau filament formation forms the basis of cytoskeletal disorganization, which is characteristic of degenerating neurons, and its effect is studied in detail. The tests done on the basis of morphology and protomer stoichiometry and the seemingly common protomer among the morphologies implies that 3-(2-hydroxyethyl)-2-[2-[[3-(2-hydroxyethyl)-5-methoxy-2-benzothiazolylidene]methyl]-1-butenyl]-5-methoxybenzothiazolium (N744) could be useful in modulating tau fibrillization in different cells and animal models of tauopathic neurofibriallry degeneration.

Chen, Jing, and Mark C. Wagner. Altered membrane/cytoskeleton linkage and membrane blebbing in energy-depleted renal proximal tubular cells. Am J Physiol Renal Physiol 280: F619-F627, 2001.--The effects of energy depletion on two membrane-cytoskeletal linker proteins (ezrin and myosin-1[Beta]) and membrane bleb formation were studied in isolated rabbit proximal tubule cells. Measurements of cytoskeletal-membrane interactions by using the laser optic trap method revealed a stronger association of control tubule membrane with the apical cytoskeleton compared with the basal cytoskeleton. Energy depletion weakened the apical membrane-cytoskeleton interactions to a greater degree. Biochemical studies demonstrated that energy depletion altered both ezrin and myosin-1[Beta]. The salt-insensitive ezrin fraction dissociated from the cytoskeleton; myosin-1[Beta] redistributed from the peripheral cytoskeleton to a perinuclear/nuclear complex. These changes in ezrin and myosin-1[Beta] and the weakening of the membrane-cytoskeleton interactions correlated with the release of brush-border membrane blebs observed by differential interference contrast microscopy. Permeability of membrane blebs was also evaluated during energy depletion and indicated an increased permeabilization of basal blebs to 3-kDa dextrans. These results support the hypothesis that alterations in membrane-cytoskeleton linkers facilitate the formation and detachment of blebs by weakening membrane-cytoskeleton interactions. ezrin; myosin-1; microvilli; adenosine 5'-triphosphate depletion; ischemia

Bicaudal-D (Bic-D) is required for the transport of determinant mRNAs and proteins to the presumptive oocyte, an essential step in the differentiation of the oocyte. Bic-D protein contains four well-defined heptad repeat domains characteristic of intermediate filament proteins. We characterized the ovarian phenotypes of females expressing mutant Bic-D proteins (Bic-[D.sup.h]) deleted for each of the heptad repeat domains. The altered migration of follicle cells we observe in mutant ovaries suggests that Bic-D functions in the germline and directs the inward migration of somatic follicle cells. In the germarium Bic-D is required for the organization of the egg chamber and the structural integrity of the oocyte and nurse cells. Examination of the polarized microtubule network in Bic-[D.sup.h] ovaries shows that Bic-D function is required for both the establishment of the polarized microtubule network and its maintenance throughout oogenesis. To explain the multiple functions suggested by the pleiotropic Bic-D phenotype, we propose that Bic-D protein could form itself a filamentous structure and represent an integral, essential part of the cytoskeleton. [C] 2001 Academic Press Key Words: Drosophila; oogenesis; follicle cells; oocyte; cytoskeleton; MTOC.

The specialized point of contact that forms between the membrane of a T cell and that of an antigen presenting cell (APC) has been dubbed the 'immunological synapse,' because of [...]