Interventional ultrasound in pregnant macaques: embryonic/fetal applications

Similarities in developmental biology between human and nonhuman primates have resulted in the use of macaque species as models in perinatal research. Studies have frequently included invasive surgical procedures or may have required "blind" injections. Several techniques have been established in human subjects using ultrasound as a guide such as cordocentesis and fetal therapy. These techniques have been applied to the nonhuman primate laboratory setting, which significantly decreases the risk of pregnancy loss due to experimental intervention.     

乙型肝炎病毒胎内及围产期传播的研究

对78名HBsAg携带者母亲的新生儿系列血清,用ELISA检测抗-HBc·IgM,有5名出生后48小时血清阳性滴度在1:1,000以上,占6％。有3名母血HBeAg阳性的新生儿,其脐血、出生后48小时足跟血及以后的连续血清标本HBsAg均阳性,且滴度趋于升高。母血抗-HBc·IgM均阴性。认为前者可能为HBV眙内感染,后者为母血通过胎盘溃面直接进入胎儿血循环所致。     

Unveiling the polarity of actin filaments by cryo-electron tomography

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Correlation between the interaction of the vinculin tail domain with lipid membranes,its phosphorylation and cell mechanical behaviour

Cell adhesion and cell–cell contacts are a pre‐requisite for proper metabolism, protein synthesis and cell survival. Integrins are the transmembrane receptors that link the extracellular matrix via the FAC (focal adhesion complex) with the cytoskeleton. Vinculin is a pivotal FAC protein that has not only been implicated in regulating FAC formation and transmitting mechanical forces, but also in associating with membranous lipids in biological systems.     

Microtubules mediate changes in membrane cortical elasticity during contractile activation

The mechanical properties of living cells are highly regulated by remodeling dynamics of the cytoarchitecture, and are linked to a wide variety of physiological and pathological processes. Microtubules (MT) and actomyosin contractility are both involved in regulating focal adhesion (FA) size and cortical elasticity in living cells. Although several studies have examined the effects of MT depolymerization or actomyosin activation on biological processes, very few have investigated the influence of both on the mechanical properties, FA assembly, and spreading of fibroblast cells. Here, we examine how activation of both processes modulates cortical elasticity as a function of time. Enhancement of contractility (calyculin A treatment) or the depolymerization of MTs (nocodazole treatment) individually caused a time-dependent increase in FA size, decrease in cell height and an increase in cortical elasticity. Surprisingly, sequentially stimulating both processes led to a decrease in cortical elasticity, loss of intact FAs and a concomitant increase in cell height. Our results demonstrate that loss of MTs disables the ability of fibroblast cells to maintain increased contractility and cortical elasticity upon activation of myosin-II. We speculate that in the absence of an intact MT network, a large amount of contractile tension is transmitted directly to FA sites resulting in their disassembly. This implies that tension-mediated FA growth may have an upper bound, beyond which disassembly takes place. The interplay between cytoskeletal remodeling and actomyosin contractility modulates FA size and cell height, leading to dynamic time-dependent changes in the cortical elasticity of fibroblast cells.     

Contact guidance of smooth muscle cells is associated with tension-mediated adhesion maturation

Contact guidance is a cellular phenomenon observed during wound healing and developmental patterning, in which adherent cells align in the same direction due to physical cues. Despite numerous studies, the molecular mechanism underlying the consistent cell orientation is poorly understood. Here we fabricated microgrooves with a pitch of submicrons to study contact guidance of smooth muscle cells. We show that both integrin-based cell–substrate adhesions and cellular tension are necessary to achieve contact guidance along microgrooves. We further show through analyses on paxillin that cell–substrate adhesions are more prone to become mature when they run along microgrooves than align at an angle to the direction of microgrooves. Because cellular tension promotes the maturation of cell–substrate adhesions, we propose that the adhesions aligning across microgrooves are not physically efficient for bearing cellular tension compared to those aligning along microgrooves. Thus, the proposed model describes a mechanism of contact guidance that cells would finally align preferentially along microgrooves because cellular tensions are more easily borne within the direction, and the direction of resulting mature adhesions determines the direction of the whole cells.     

The Role of Vinculin in the Regulation of the Mechanical Properties of Cells

Vinculin couples as a focal adhesion protein the extracellular matrix (ECM) through integrins to the actomyosin cytoskeleton. During the last years vinculin has become the focus of cell mechanical measurements and a key protein regulating the transmission of contractile forces. In earlier reports vinculin has been described as an inhibitor of cell migration on planar substrates, because knock-out of vinculin in F9 mouse embryonic carcinoma cells and mouse embryonic fibroblasts showed increased cell motility on 2D substrates. The role of vinculin in cell invasion through a 3D extracellular matrix is still fragmentarily investigated. This review presents vinculin in its role as a regulator of cellular mechanical functions. Contractile force generation is reduced when vinculin is absent, or enhanced when vinculin is present. Moreover, the generation of contractile forces is a prerequisite for cell invasion through a dense 3D ECM, where the pore-size is smaller than the diameter of the cell nucleus (<2 μm). Measurements of cell’s biophysical properties will be presented. In summary, vinculin’s leading role among focal adhesion proteins in regulating the mechanical properties of cells will be discussed.     

The influence of Pyk2 on the mechanical properties in fibroblasts

The cell surface receptor integrin is involved in signaling mechanical stresses via the focal adhesion complex (FAC) into the cell. Within FAC, the focal adhesion kinase (FAK) and Pyk2 are believed to act as important scaffolding proteins. Based on the knowledge that many signal transducing molecules are transiently immobilized within FAC connecting the cytoskeleton with integrins, we applied magnetic tweezer and atomic force microscopic measurements to determine the influence of FAK and Pyk2 in cells mechanically. Using mouse embryonic fibroblasts (MEF; FAK^+/+, FAK^−/−, and siRNA-Pyk2 treated FAK^−/− cells) provided a unique opportunity to describe the function of FAK and Pyk2 in more detail and to define their influence on FAC and actin distribution.     

Vitronectin and collagen I differentially regulate osteogenesis in mesenchymal stem cells

The roles of various soluble factors in promoting the osteogenic differentiation of adult mesenchymal stem cells (MSCs) have been widely studied, but little is known about how the extracellular matrix (ECM) instructs the phenotypic transition between growth and differentiation. To investigate this question, we cultured MSCs on purified vitronectin or type-I collagen, motivated by our earlier tissue engineering work demonstrating that MSC adhesion to polymer scaffolds is primarily mediated by the passive adsorption of these two ECM ligands from serum. Using alkaline phosphatase activity and matrix mineralization as indicators of the early and late stages of osteogenesis, respectively, we report here that both substrates supported differentiation, but the mechanism was substrate dependent. Specifically, osteogenesis on vitronectin correlated with enhanced focal adhesion formation, the activation of focal adhesion kinase (FAK) and paxillin, and the diminished activation of extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3 kinase (PI3K) pathways. By contrast, MSCs on type-I collagen exhibited reduced focal adhesion formation, reduced activation of FAK and paxillin, and increased activation of ERK and PI3K. Inhibition of ERK and FAK blocked mineral deposition on both substrates, suggesting that the observed differences in signaling pathways ultimately converge to the same cell fate. Understanding these mechanistic differences is essential to predictably control the osteogenic differentiation of MSCs and widen their use in regenerative medicine.