Effect of Focal Adhesion Proteins on Endothelial Cell Adhesion,Motility and Orientation Response to Cyclic Strain

Focal adhesion proteins link cell surface integrins and intracellular actin stress fibers and therefore play an important role in mechanotransduction and cell motility. When endothelial cells are subjected to cyclic mechanical strain, time-lapse imaging revealed that cells underwent significant morphological changes with their resultant long axes aligned away from the strain direction. To explore how this response is regulated by focal adhesion-associated proteins the expression levels of paxillin, focal adhesion kinase (FAK), and zyxin were knocked down using gene silencing techniques. In addition, rescue of endogenous and two mutant zyxins were used to investigate the specific role of zyxin interactions. Cells with decreased zyxin expression levels and rescue with the mutant lacking zyxin/α-actinin binding exhibited lower orientation angles after comparable times of stretching as compared to normal and control cells. However, knockdown of the expression levels of paxillin and FAK and rescue with the mutant lacking zyxin/VASP (vasodilator-stimulated phosphoprotein) binding did not significantly affect the degree of cell orientation. In addition, wound closure speed and cell–substratum adhesive strength were observed to be significantly reduced only for cells with zyxin depletion and the mutation lacking zyxin/α-actinin binding. These results suggest that zyxin and its interaction with α-actinin are important in the regulation of endothelial cell adhesive strength, motility and orientation response to mechanical stretching.     

The effect of noisy flow on endothelial cell mechanotransduction: a computational study

Flow in the arterial system is mostly laminar, but turbulence occurs in vivo under both normal and pathological conditions. Turbulent and laminar flow elicit significantly different responses in endothelial cells (ECs), but the mechanisms allowing ECs to distinguish between these different flow regimes remain unknown. The authors present a computational model that describes the effect of turbulence on mechanical force transmission within ECs. Because turbulent flow is inherently “noisy” with random fluctuations in pressure and velocity, our model focuses on the effect of signal noise (a stochastically changing force) on the deformation of intracellular transduction sites including the nucleus, cell–cell adhesion proteins (CCAPs), and focal adhesion sites (FAS). The authors represent these components of the mechanical signaling pathway as linear viscoelastic structures (Kelvin bodies) connected to the cell surface via cytoskeletal elements. The authors demonstrate that FAS are more sensitive to signal noise than the nucleus or CCAP. The relative sensitivity of these various structures to noise is affected by the nature of the cytoskeletal connections within the cell. Finally, changes in the compliance of the nucleus dramatically affect nuclear sensitivity to noise, suggesting that pathologies that alter nuclear mechanical properties will be associated with abnormal EC responsiveness to turbulent flow.     

Micropit surfaces designed for accelerating osteogenic differentiation of murine mesenchymal stem cells via enhancing focal adhesion and actin polymerization

Recent reports demonstrate that enhanced focal adhesion (FA) between cells and the extracellular matrix (ECM) and intracellular actin polymerization (AP) upregulates cellular functions such as proliferation, stem-cell fate and differentiation. Purposed to accelerate osteogenic differentiation, enhancement of FAs and AP of cells was induced by adding a tailor-made micropit (tMP, 3 × 3 μm²) with different heights (2 or 4 μm). The tMP surface was examined for its differentiation efficiency using mouse mesenchymal stem cells, C3H10T1/2. Though the cell spreading area was not affected by the surface topography, cells on the tMP substrates had enhanced FAs which were significantly confined inside the micropits, increased actin polymerization and traction forces, and osteogenic differentiation. Further experiments with Y-27632 and Blebbistatin, which specifically regulate FA or AP functions, demonstrated that the tMP-induced acceleration of osteogenic differentiation was caused by the rho-associated, coiled-coil containing protein kinase (ROCK) and nonmuscle myosin II (NM II), which are key molecules of the RhoA/ROCK signaling pathway. The tMP is applicable as an osteo-active substrate for the instructive bone cell differentiation and population.     

Shear stress-mediated changes in the expression of leukocyte adhesion receptors on human umbilical vein endothelial cellsin vitro

Extensive monocyte recruitment is an early phenomenon associated with the development of atherosclerotic lesions, suggesting an active role for the involvement of adhesion receptors expressed by endothelial cells. In this study we describe the contribution of hemodynamic shear forces in regulating the expression of a few of the monocyte adhesion receptors, including intercellular adhesion molecule (ICAM-1), vascular cell adhesion molecule (VCAM-1), and E-selectin on endothelial cells. A parallel plate flow chamber and recirculating flow loop device was used to expose human umbilical vein endothelial cells (HUVECs) to different levels of shear (2–25 dyn/cm²). Subsequently the cells were analyzed either for shear induced changes in the mRNA levels of adhesion receptors by Northern blot analyses or for changes in the surface expression of ICAM-1 using flow cytometry. Results from the fluorescence analysis showed a transient increase in the surface expression of ICAM-1, 12 hr after exposure to 25 dyn/cm² shear, returning to basal levels within 24 hr. This was quite different from the time dependent response of ICAM-1 to lipopolysaccharide (LPS), where ICAM-1 expression was maximally induced 18–24 hr poststimulus. ICAM-1 mRNA level appeared slightly elevated after exposure to shear for 1 hr, compared to basal values, but dropped below basal levels within 6 hr. This biphasic response was seen irrespective of the magnitude of applied shear stress. VCAM-1 mRNA expression, in contrast, decreased below the baseline expression within an hour after onset of flow, and appeared to be considerably down-regulated within 6 hr. After exposure to shear for 24 hr no increase in mRNA levels could be detected for either molecule, at any shear magnitude. E-selectin mRNA was less responsive to shear stress, especially at the lower magnitudes of shear. After an hour of exposure to flow E-selectin mRNA level appeared slightly reduced compared with control levels, but it remained at this level even after 6 hr of flow. These results indicate that the expression of adhesion receptors is sensitive to local shear stresses in a manner that is molecule specific in the short term even though prolonged exposure to flow results in similar down-regulation for both ICAM-1 and VCAM-1.     

Ultrastructure of the spermatozoon of Taeniarhynchus saginatus (syn. Taenia saginata) (Goeze, 1782) Weinland, 1858 (Cestoda, Taeniidae) an intestinal parasite of human

The mature Taeniarhynchus saginatus spermatozoon exhibits an apical cone of electron-dense material and one helicoidal crest-like body roughly 50 nm thick. The axoneme is of the 9 + “1” Trepaxonemata pattern. It is surrounded by a periaxonemal sheath of electron-dense material. The cytoplasm is electron lucent and divided into compartments by intracytoplasmic walls of electron-dense material in regions III and IV. The nucleus is an electron-dense cord 60–90 nm thick coiled in a spiral around the axoneme. It reaches the posterior extremity of the gamete where the axoneme is disorganized and is accompanied on all its posterior length by the nucleus. To our knowledge, such a posterior extremity has never been described before in a cyclophyllidean cestode.     

Cellular uptake and localization of liposomal-methylphosphonate oligodeoxynucleotides

 Nuclease digestion and intracellular delivery are major factors limiting the potential use of oligodeoxynucleotides as antisense molecules. Structural analogues of phosphodiester oligodeoxynucleotides, such as phosphorothioates and methylphosphonates, are resistant to nuclease degradation and can still bind to their mRNA targets. However, their limited ability to escape from the endosomal/lysosomal compartments and reach the intracellular sites of action have dampened their potential clinical application. To circumvent this problem we have incorporated methylphosphonate oligodeoxynucleotides into liposomes. We found that the level of uptake of liposome-incorporated methylphosphonate oligodeoxynucleotides is time and concentration dependent. Maximal uptake occurred at 8 h when 4–8 μM liposome-incorporated methylphosphonate oligodeoxynucleotides was added. Approximately 50% of liposome-incorporated methylphosphonate oligodeoxynucleotides were retained in cells after 24 h of incubation. Using fluorescent microscopy, intracellular fluorescence could be seen within 2.5 h of incubation. Diffused fluorescence was found throughout the cytoplasm, suggesting that the liposome-incorporated methylphosphonate oligodeoxynucleotides were not confined within the endosomal/lysosomal structures. We conclude that liposomes can effectively deliver methylphosphonate oligodeoxynucleotides to the cytoplasm, which is the major intracellular site of action for translational arrest. Received: 12 December 1995 / Accepted: 7 June 1996     

Endothelial paxillin and focal adhesion kinase (FAK) play a critical role in neutrophil transmigration

During an inflammatory response, endothelial cells undergo morphological changes to allow for the passage of neutrophils from the blood vessel to the site of injury or infection. Although endothelial cell junctions and the cytoskeleton undergo reorganization during inflammation, little is known about another class of cellular structures, the focal adhesions. In this study, we examined several focal adhesion proteins during an inflammatory response. We found that there was selective loss of paxillin and focal adhesion kinase (FAK) from focal adhesions in proximity to transmigrating neutrophils; in contrast the levels of the focal adhesion proteins β1-integrin and vinculin were unaffected. Paxillin was lost from focal adhesions during neutrophil transmigration both under static and flow conditions. Down-regulating endothelial paxillin with siRNA blocked neutrophil transmigration while having no effect on rolling or adhesion. As paxillin dynamics are regulated partly by FAK, the role of FAK in neutrophil transmigration was examined using two complementary methods. siRNA was used to down-regulate total FAK protein while dominant-negative, kinase-deficient FAK was expressed to block FAK signaling. Disruption of the FAK protein or FAK signaling decreased neutrophil transmigration. Collectively, these findings reveal a novel role for endothelial focal adhesion proteins paxillin and FAK in regulating neutrophil transmigration.     

Adhesion of HT-29 colon carcinoma cells to endothelial cells requires sequential events involving E-selectin and integrin β4

HT-29 colon carcinoma cells attach to TNFα-activated human umbilical vein endothelial cells (HUVECs) by their specific binding to E-selectin. This interaction activates, in the cancer cells, the MAPK SAPK2/p38, which leads to their transendothelial migration (Laferrière et al., J Biol Chem 2001; 276: 33762). In this study, we investigated the role of E-selectin in activating integrins to modulate adhesion and regulate integrin-mediated events. Blocking the integrins from HT-29 cells (α2, α3, α6, αvβ5, β1 and β4) with specific antibodies revealed a role for β4 integrin in their adhesion to TNFα-treated HUVEC. The β4 integrin-dependent adhesion was maximal after 30 min, whereas the-E-selectin-dependent adhesion was maximal after 15 min. Integrin β4 became quickly phosphorylated upon addition of HT-29 cells to endothelial cells and the effect was independent of the expression of E-selectin. Moreover, a recombinant E-selectin/Fc chimera did not induce the phosphorylation of β4. The phosphorylation of β4 is not required for adhesion since adhesion was not affected in HT-29 cells that express a truncated form of β4 that is deleted from its cytoplasmic phosphorylatable domain. However, the expression of the non-phosphorylatable deletant of β4 was associated with decreased transendothelial cell migration underscoring the key role for the cytoplasmic domain of β4 in cell migration. We suggest: 1) that the adhesion of HT-29 cells to activated endothelial cells follows at least two essential sequential steps involving the binding of E-selectin to its receptor on carcinoma cells and then the binding of β4 to its own receptor on endothelial cells; 2) that the phosphorylation of integrin β4 contributes to enhance the motile potential of cancer cells and increase their trans-endothelial migration. Overall, our results indicate that the interaction of metastatic cancer cells with endothelial cells implies a specific sequence of signaling events that ultimately leads to an increase in their efficient transendothelial migration. Abbreviations: ERK – extracellular signal-regulated kinase; GFP – green fluorescent protein; ICAM – intercellular adhesion molecules: JNK – c-Jun NH₂-terminal kinase; MAPK – mitogen-activated protein kinase; MAPKAP K2, MAP kinase-activated protein kinase 2; PI3K – phosphatidyl inositol 3-kinase; SAPK – stress-activated protein kinase; TNFα– tumor necrosis factor-α. This revised version was published online in July 2006 with corrections to the Cover Date.     

CNTO 95, a fully human anti αv integrin antibody, inhibits cell signaling, migration, invasion, and spontaneous metastasis of human breast cancer cells

CNTO 95 is a fully human monoclonal antibody that recognizes αv integrins. Previous studies have shown that CNTO 95 exhibits both anti-tumor and anti-angiogenic activities (Trikha M et al., Int J Cancer 110:326–335, 2004). In this study we investigated the biological activities of CNTO 95 on breast tumor cells both in vitro and in vivo. In vitro treatment with CNTO 95 decreased the viability of breast tumor cells adhering to vitronectin. CNTO 95 inhibited tumor cell adhesion, migration, and invasion in vitro. CNTO 95 treatment also induced tyrosine dephosphorylation of focal adhesion kinase (FAK), and the docking protein paxillin that recruits both structural and signaling molecules to focal adhesions (Turner CE, Int J Biochem Cell Biol 30:955–959, 1998; O’Neil GM et al., Trends Cell Biol 10:111–119, 2000). These results suggest that CNTO 95 inhibits breast tumor cell growth, migration and invasion by interruption of αv integrin mediated focal adhesions and cell motility signals. In vivo studies of CNTO 95 were conducted in an orthotopic breast tumor xenograft model. Treatment with CNTO 95 resulted in significant inhibition of both tumor growth and spontaneous metastasis of MDA-MB-231 cells to the lungs. CNTO 95 also inhibited lung metastasis in a separate experimental (tail vein injection) model of metastasis. The results presented here demonstrate the anti-tumor and anti-metastatic activities of CNTO 95 in breast cancer models and provide insight into the cellular and molecular mechanisms mediating its inhibitory effects on metastasis.     

Potential roles for focal adhesion kinase in development

 Focal adhesion kinase (pp125^FAK or FAK) is a protein tyrosine kinase which is associated with intracellular signalling cascades which are initiated when the integrin family of cell adhesion molecules engage extracellular matrix molecules. In cultured cells, this molecule is physically associated with focal adhesions, which are well-defined regions of intimate cell-to-substratum adhesion. In this location, it interacts with other proteins of the focal adhesion to activate intracellular signalling events associated with cell adhesion. The in vitro expression of FAK and its level of phosphorylation appear to be related to several physiological phenomena, including cell spreading, cell differentiation, cell locomotion and cell death. Because these phenomena are all of critical importance during morphogenesis, and because FAK is expressed in embryonic cells, evidence has been accumulating to indicate that FAK may be an important modulator of developmental processes. In this review, this evidence is surveyed together with evidence from analogous situations, such as tumour cell migration and invasiveness. Although evidence suggesting a role for FAK in morphogenesis is accumulating, current uncertainties regarding its cytoplasmic location and its molecular interactions in vivo make it difficult to reach definitive conclusions regarding the significance of its contributions to developmental processes. Accepted: 14 September 1998     

Hydrodynamic shear-stress-dependent retention of endothelial and endothelial progenitor cells adhered to vascular endothelial growth factor-fixed surfaces

The luminal surfaces of small-diameter artificial vascular grafts must be fully endothelialized to be nonthrombogenic following implantation. To achieve this goal, we have attempted to capture circulating endothelial progenitor cells (EPCs) in situ on the luminal surfaces of implanted grafts. We examined potential receptor-ligand pairs that promote selective and tight adhesion of EPCs using a radial flow chamber comprising three regions, each containing a specific protein-bound substrate: fibronectin (FN) for integrin, and vascular endothelial growth factor (VEGF) and anti-Flk-1 antibody for VEGF receptor. In the presence of shear stress, the greatest retention of endothelial cells and EPCs was observed with FN followed by VEGF and then anti-Flk-1 antibody. Regardless of the bound protein, cell adhesion increased with larger areas of cell adhesion and enhanced cell spreading; the latter was also greatest with FN followed by VEGF and then anti-Flk-1 antibody. The distribution of vinculin-a key protein in focal adhesion plaques-in adherent endothelial cells was examined using total internal reflection fluorescence microscopy; FN-bound surfaces resulted in larger areas of adhesion and more focal adhesion plaques compared with surfaces bound with VEGF. On the other hand, examining these parameters relative to the area of cell adhesion revealed that VEGF-bound surfaces resulted in larger focal adhesion areas and greater fluorescence signals, both of which indicate increased resistance to shear stress. We also discuss in situ capturing of EPCs on surfaces bound with VEGF or anti-Flk-1 antibody, with the goal of creating endothelialized small-diameter vascular grafts.     

Endonuclease G expression in thalamic reticular nucleus after global cerebral ischemia

Endonuclease G is a mitochondrial enzyme, known to be translocated to the nucleus after transient focal cerebral ischemia and contribute to DNA degradation. After global cerebral ischemia, delayed cell death is observed in the thalamic reticular nucleus but the mechanisms involved are not well described. The purpose of this study was to identify if Endonuclease G was expressed in the cell nucleus of parvalbumin⁺ GABA’ergic neurons in relation to cell death after global cerebral ischemia in the thalamic reticular nucleus. The cell death in male Wister rats were studied from 6 h until 4 days after global cerebral ischemia induced by transient 2-vessel carotid occlusion with hypotension for 15 min. Hematoxylin–eosin staining and immunohistochemistry for Endonuclease G, Parvalbumin and Glial fibrillary acidic protein was performed after the ischemic insult. Eosinophilic neurons and vacuolization of the cytoplasm in parvalbumin⁺ neurons were observed 2 days after ischemia. Endonuclease G immunoreactivity increased in the cytoplasm 12 h after ischemia and was translocated to the nucleus of parvalbumin⁺ neurons after 24 h. In the nucleus of astroglia, Endonuclease G was expressed after 2 days with an apoptotic-like morphology and the number of Endonuclease G-expressing astroglia increased during the later time points. During the same period the number of parvalbumin⁺ neurons decreased. In conclusion, this study has identified that Endonuclease G is translocated from the cytoplasm to the nucleus of neurons and expressed with apoptotic-like morphology in the nucleus of astroglia in the thalamic reticular nucleus after global cerebral ischemia.     

Cocksfoot mottle sobemovirus coat protein contains two nuclear localization signals

Cocksfoot mottle virus (CfMV) coat protein (CP) localization was studied in plant and mammalian cells. Fusion of the full-length CP with enhanced green fluorescent protein (EGFP) localized to the cell nucleus whereas similar constructs lacking the first 33 N-terminal amino acids of CP localized to the cytoplasm. CP and EGFP fusions containing mutations in the arginine-rich motif of CP localized to the cytoplasm and to the nucleus in plant cells indicating the involvement of the motif in nuclear localization. In mammalian cells, mutations in the arginine-rich region were sufficient to completely abolish nuclear transport. The analysis of deletions of amino acid residues 1–11, 1–22, and 22–33 of CP demonstrated that there were two separate nuclear localization signals (NLS) within the N-terminus—a strong NLS1 in the arginine-rich region (residues 22–33) and a weaker NLS2 within residues 1–22. Analysis of point mutants revealed that the basic amino acid residues in the region of the two NLSs were individually not sufficient to direct CP to the nucleus. Additional microinjection studies with fluorescently labeled RNA and CP purified from CfMV particles demonstrated that the wild-type CP was capable of transporting the RNA to the nucleus. This feature was not sequence-specific in transient assays since both CfMV and GFP mRNA were transported to the cell nucleus by CfMV CP. Together the results suggest that the nucleus may be involved in CfMV infection.     

A fiber matrix model for fluid flow and streaming potentials in the canaliculi of an osteon

A theoretical model is developed to predict the fluid shear stress and streaming potential at the surface of osteocytic processes in the lacunar-canalicular porosity of an osteon when the osteon is subject to mechanical loads that are parallel or perpendicular to its axis. The theory developed in Weinbaumet al. (31) for the flow through a proteoglycan matrix in a canaliculus is employed in a poroelastic model for the osteon. Our formulation is a generalization of that of Petrovet al. (17). Our model predicts that, in order to satisfy the measured frequency dependence of the phase and magnitude of the SGP in macroscopic bone samples, the fiber spacing in the fluid annulus must lie in the narrow range 6–7 nm typical of the spacing of GAG sidechains along a protein monomer. The model predictions for the local SGP profiles in the osteon agree with the experimental observations of Starkebaumet al. (24). The theory predicts that the pore pressure relaxation time, τ_d, for a 150–300 μm diameter osteon with the foregoing matrix structure is approximately 0.03–0.13 sec, and that the amplitude of the mean fluid shear stress on the membrane of the osteocytic process at the mean areal radius of the osteon has a maximum at 28 Hz if τ_d = 0.06 sec. This maximum, which is independent of the magnitude of the loading, could be importantin vivo since the recent experiments of Turneret al. (28) and McLeodet al. (15) have a peak in the strain frequency spectrum between 20 and 30 Hz that also appears to be independent of the type (magnitude) of loading. Numerical predictions for the amplitude of the average fluid shear stress on the osteocytic membrane at the mean areal radius of the osteon show that the fluid shear stress associated with the low amplitude 20–30 Hz spectral strain component is at least as large as the average fluid shear stress associated with the high amplitude 1 Hz stride component, although the latter loading is an order of magnitude larger, and has a magnitude that lies within the middle of the range, 6–30 dynes/cm², where fluid shear stresses in tissue culture studies with osteoblast monolayers have elicited an intracellular Ca⁺⁺ response (31). The implications of these results for intracellular electrical communication are discussed.     

The regulation of dynamic mechanical coupling between actin cytoskeleton and nucleus by matrix geometry

Cells sense their physical microenvironment and transduce these signals through actin-nuclear links to regulate nuclear functions including gene expression. However, the spatio-temporal coupling between perinuclear actin and nucleus and their functional importance are still unclear. Using micropatterned substrates to control cell geometry, we show that perinuclear actin organization at the apical plane remodels from mesh-like structure to stress fibers. The formation of these apical stress fibers (ASFs) correlated with significant reduction in nuclear height and was found to exert an active compressive load on the nucleus via direct contact with mature focal adhesion sites. Interestingly, the dynamic nature of ASFs was found to transduce forces to chromatin assembly. In addition, geometric perturbations or using pharmacological drugs to inhibit actomyosin contractility of ASFs resulted in nuclear instability. Taken together, our work provides direct evidence of physical links between the nucleus and focal adhesion sites via ASFs, which modulate nuclear homeostatic balance and internal chromatin structure. We suggest that such direct links may underlie nuclear mechanotransduction to regulate genomic programs.     

Morphofunctional characteristics of neurons in the spinal ganglia of the dog in the post-distraction period

The aims of the present work were to study the morphofunctional state of neurons in the spinal ganglia and to perform a comparative analysis of changes in neuron-glial relationships after lengthening of the hindlimb of mongrel dogs by 14–16% of initial at different rates. Longitudinal serial sections of thickness 5 μm of the L6, L7, and S1 ganglia (n = 36) stained with thionine and cresyl violet by the Nissl method and hallocyanine and chromic alum by the Einarson method were examined. Reversible transformations of the structure of some neurons were seen at 45–48 days, these consisting of hyperchromia of the cytoplasm and nucleus, peripheral chromatolysis, displacement of the nucleolus, and increases in the quantities of perineuronal and interneuronal gliocytes. Changes were most marked in the ganglia on the side of limb lengthening at a rate of 3 mm/day, while the smallest changes were seen on the side contralateral to limb lengthening at a rate of 1 mm/day. __________ Translated from Morfologiya, Vol. 127, No. 2, pp. 44–47, March–April, 2005.     

Morphometric characteristics of epitheliocytes in the choroid plexus of the cerebral ventricles in humans during aging

Morphometric studies of villous epitheliocytes of the choroid plexus of the lateral (glomus) and third and fourth (lateral zone) ventricles of the brain were undertaken in humans aged from 22 to 89 years. Cell height, width, and cross-sectional area were measured, along with the cross-sectional areas of nuclei and cytoplasm for calculation of the nucleus:cytoplasm ratio. These studies showed that epitheliocytes were of variable shape depending on their locations on the surfaces of villi. Epitheliocyte height and the cross-sectional areas of the cytoplasm and cells were greatest in the choroid plexus of the lateral ventricle, while the cross-sectional area of the nucleus and the nucleus:cytoplasm ratio were greatest in the choroid plexus of the fourth ventricle; these features correlate with their functional characteristics. Aging is associated with decreases in the sizes of epitheliocytes and their nuclei and a reduction in the nucleus:cytoplasm ratio, with the development of adaptive rearrangements. Director: Professor V. V. Turygin __________ Translated from Morfologiya, Vol. 129, No. 1, pp. 39–41, January–February, 2006.     

Ultrastructure of the spermatozoon of the bank vole tapeworm, Paranoplocephala omphalodes (Cestoda, Cyclophyllidea, Anoplocephalidae)

The mature Paranoplocephala omphalodes spermatozoon is filiform, tapered at both ends and lacks mitochondria. Its anterior extremity exhibits an apical cone of electron-dense material measuring about 900 nm in length and 200 nm in width, and two crested-like bodies. The cortical microtubules follow a 25–35° helicoidal path along their whole length, except at the posterior extremity where they become parallel to the spermatozoon axis. They are arranged in a single or two fields which may cover each other partially. The axoneme, of the 9+“1” pattern of the Trepaxonemata, lacks a peri-axonemal sheath and does not reach the extremity of the spermatozoon. The nucleus is a compact and irregular cord coiled in a spiral around the axoneme. Moreover, we report for the first time a nucleus in the spermatozoon of a Cyclophyllidea species which reaches beyond the axonemal posterior extremity. The cytoplasm, depending on the level where the section is cut, is slightly electron dense or electron lucent and contains numerous small electron-dense granules in regions III–V. In the posterior spermatozoon extremity, granular material is replaced by a terminal and compact electron-dense material. Received: 1 June 1997 / Accepted: 20 September 1997     

Pathomorphological signs of damage to capillary endothelium in skeletal muscle after traumatic injury to or replantation of a limb

Several months after an extensive crush injury to or replantation of a limb in rats, capillary endotheliocytes of its skeletal muscle are seen to undergo ultrastructural changes of both “dark” and “light” types. Destructive/degenerative changes of the “light” type are accompanied by intracellular edema and cytoplasmic homogenization and can eventually result in monocellular colliquative necrosis. Changes of the “dark” type are characterized by signs of functional overstrain in the endotheliocytes, succeeded by destructive/degenerative cytoplasmic changes, increased electron density of intracellular organelles, loss of distinct boundaries by the nucleus and intracellular structures, rupture of cell membranes, endothelial desquamation, and some other changes, which eventually lead to coagulation necrosis, followed by breakdown of the cell into small fragments. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N^no 10, pp. 378–383, October, 1994