Haemostatic role of intermediate filaments in adhered platelets: importance of the membranous system stability

The role of platelets in coagulation and the haemostatic process was initially suggested two centuries ago, and under appropriate physiological stimuli, these undergo abrupt morphological changes, attaching and spreading on damaged endothelium, preventing bleeding. During the adhesion process, platelet cytoskeleton reorganizes generating compartments in which actin filaments, microtubules, and associated proteins are arranged in characteristic patterns mediating crucial events, such as centralization of their organelles, secretion of granule contents, aggregation with one another to form a haemostatic plug, and retraction of these aggregates. However, the role of Intermediate filaments during the platelet adhesion process has not been explored. J. Cell. Biochem. 114: 2050-2060, 2013. © 2013 Wiley Periodicals, Inc.

A role for β-dystroglycan in the organization and structure of the nucleus in myoblasts

We recently characterized a nuclear import pathway for β-dystroglycan; however, its nuclear role remains unknown. In this study, we demonstrate for the first time, the interaction of β-dystroglycan with distinct proteins from different nuclear compartments, including the nuclear envelope (NE) (emerin and lamins A/C and B1), splicing speckles (SC35), Cajal bodies (p80-coilin), and nucleoli (Nopp140). Electron microscopy analysis revealed that β-dystroglycan localized in the inner nuclear membrane, nucleoplasm, and nucleoli. Interestingly, downregulation of β-dystroglycan resulted in both mislocalization and decreased expression of emerin and lamin B1, but not lamin A/C, as well in disorganization of nucleoli, Cajal bodies, and splicing speckles with the concomitant decrease in the levels of Nopp140, and p80-coilin, but not SC35. Quantitative reverse transcription PCR and cycloheximide-mediated protein arrest assays revealed that β-dystroglycan deficiency did not change mRNA expression of NE proteins emerin and lamin B1 bud did alter their stability, accelerating protein turnover. Furthermore, knockdown of β-dystroglycan disrupted NE-mediated processes including nuclear morphology and centrosome-nucleus linkage, which provides evidence that β-dystroglycan association with NE proteins is biologically relevant. Unexpectedly, β-dystroglycan-depleted cells exhibited multiple centrosomes, a characteristic of cancerous cells. Overall, these findings imply that β-dystroglycan is a nuclear scaffolding protein involved in nuclear organization and NE structure and function, and that might be a contributor to the biogenesis of nuclear envelopathies.

Neuronal differentiation modulates the dystrophin Dp71d binding to the nuclear matrix

The function of dystrophin Dp71 in neuronal cells remains unknown. To approach this issue, we have selected the PC12 neuronal cell line. These cells express both a Dp71f cytoplasmic variant and a Dp71d nuclear isoform. In this study, we demonstrated by electron and confocal microscopy analyses of in situ nuclear matrices and Western blotting evaluation of cell extracts that Dp71d associates with the nuclear matrix. Interestingly, this binding is modulated during NGF-induced neuronal differentiation of PC12 cells with a twofold increment in the differentiated cells, compared to control cells. Also, distribution of Dp71d along the periphery of the nuclear matrix observed in the undifferentiated cells is replaced by intense fluorescent foci localized in the center of the nucleoskeletal structure. In summary, we revealed that Dp71d is a dynamic component of nuclear matrix that might participate in the nuclear modeling occurring during neuronal differentiation.

Subcellular localization and dynamics of a digalactolipid-like epitope in Toxoplasma gondii

Toxoplasma gondii is a unicellular parasite characterized by unique extracellular and intracellular membrane compartments. The lipid composition of subcellular membranes has not been determined, limiting our understanding of lipid homeostasis, control, and trafficking, a series of processes involved in pathogenesis. In addition to a mitochondrion, Toxoplasma contains a plastid called the apicoplast. The occurrence of a plastid raised the question of the presence of chloroplast galactolipids. Using three independent rabbit and rat antibodies against digalactosyldiacylglycerol (DGDG) from plant chloroplasts, we detected a class of Toxoplasma lipids harboring a digalactolipid-like epitope (DGLE). Immunolabeling characterization supports the notion that the DGLE polar head is similar to that of DGDG. Mass spectrometry analyses indicated that dihexosyl lipids having various hydrophobic moieties (ceramide, diacylglycerol, and acylalkylglycerol) might react with anti-DGDG, but we cannot exclude the possibility that more complex dihexosyl-terminated lipids might also be immunolabeled. DGLE localization was analyzed by immunofluorescence and immunoelectron microscopy and confirmed by subcellular fractionation. No immunolabeling of the apicoplast could be observed. DGLE was scattered in pellicle membrane domains in extracellular tachyzoites and was relocalized to the anterior tip of the cell upon invasion in an actin-dependent manner, providing insights on a possible role in pathogenetic processes. DGLE was detected in other Apicomplexa (i.e., Neospora, Plasmodium, Babesia, and Cryptosporidium).

In-vitro model for the ultrastructural study of the formation of thrombi in human platelets

Platelets are cell fragments with dynamic properties involved in clot formation after tissue damage. Platelet activation causes a change in shape, secretion of intracellular granules and aggregation with each other through the cytoskeleton components and biochemical changes. Platelet adhesion, considered as the major event in haemostasis, has been studied in several in-vitro and in-vivo models to evaluate the feasible thrombogenicity of some materials, the dynamics of specific receptors, as well as the effect of different buffers and inhibitors in this process. In spite of the numerous reports about platelet activation, to date there is no information available about the fine structure of the platelet-platelet and platelet-substrate interactions. In the present report we describe an in-vitro system that allows the visualization of these interactions: platelets are adhered to an inert substrate, and interactions with suspended platelets as a process to initiate the formation of thrombi was followed by ultramicrotomy and transmission electron microscopy.

Identification and purification of actin from the subpellicular network of Toxoplasma gondii tachyzoites

Toxoplasma gondii infects cells through dynamic events dependent on actin. Although the presence of cortical actin has been widely suggested, visualisation and localisation of actin filaments has not been reported. The subpellicular cytoskeleton network is a recently described structure possibly involved in the dynamic events. Using non-ionic detergent extractions, the cortical cytoskeleton network was enriched and used for the isolation and identification of actin. Actin was detected by Western blots in extracts of cytoskeleton networks, and it was localised by gold staining in the network and in both the apical end and the posterior polar ring. Actin was isolated from subpellicular cytoskeleton extracts by binding to DNase I, and it polymerised in vitro as filaments that were gold-decorated by a monoclonal anti-actin antibody. Filaments bound the subfragment 1 of heavy meromyosin, although with atypical arrangements in comparison with the arrowheads observed in muscle actin filaments. Treatment with cytochalasin D and colchicine altered the structural organisation of the subpellicular network indicating the participation of actin filaments and microtubules in the maintenance of its structure. Actin filaments and microtubules, in the subpellicular network, participate reciprocally in the maintaining of the parasite's shape and the gliding motility.

Interaction of the 530 ribosomal site with regions of mRNA

We evaluated the energetic stability of all possible 10-base fragments of the small subunit (SS) rRNA with a large ensemble of mRNAs. Results show that the 530 loop is the only conserved region that interacts favorably around the start codon as well as the elongation region of messengers. The interaction profile of the 530 loop around the stop codon showed that base pairing was energetically unfavorable in that region. With these results we constructed a simple scheme for the role of rRNA-mRNA interactions in the protein translation mechanism.

[Corrected transposition of the great arteries. Study of 14 cases (author's transl)]

We have studied 14 patients of corrected transposition, 12 with situs solitus and 2 with situs inversus. In all the patients, excepting one, a clinical, radiological and angiocardiographical study was performed. The associated anomalies were determining elements of the clinical situation; the patients with pulmonary obstruction and interventricular communication had cianosis, while the 4 patients with aortic obstruction or anomalies type left Ebstein show cardiac insufficiency. The simple radiological study helped us to determinate the ascendent aorta in the left side of the heart, in 9 cases. It was unusual to see the droped hilium in the right hemitorax. The more significants electrical signs were: The presence of complete A-V block, Q-waves in D2, D3 and aVF, absence of right waves in precordial leads in most of the patients and a negative T wave in a VL. Summarizing, authors believe that in this type of defects selective injection of contrast in both ventricles is the best method to establish the difference between corrected transposition and other cardiopathies with the aorta situated at the left side of the pulmonary artery.