Netrin-1 Confines Rhombic Lip-Derived Neurons to the CNS

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Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal‐Retzius cells

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long‐range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal‐Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell‐autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact‐redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847–881, 2016     

陕西省南郑县户用沼气池经济效益分析

南郑县农村生活用能严重短缺，农民每年不得不大量消耗柴草秸秆等生物质能源资源，导致南郑县山地退化、水土流失及农田有机质含量减少，影响了农业生产的发展。南郑县的气候特点，适宜于沼气池的建设，常温下全年可产沼气，当地农村养殖业较发达，有充分的沼气发酵原料。...     

Wide-surface pore microfiltration membrane drastically improves sieving decay in TFF-based perfusion cell culture and streamline chromatography integration for continuous bioprocessing

Although several compelling benefits for bioprocess intensification have been reported, the need for a streamlined integration of perfusion cultures with capture chromatography still remains unmet. Here, a robust solution is established by conducting tangential flow filtration-based perfusion with a wide-surface pore microfiltration membrane. The resulting integrated continuous bioprocess demonstrated negligible retention of antibody, DNA, and host cell proteins in the bioreactor with average sieving coefficients of 98 ± 1%, 124 ± 28%, and 109 ± 27%, respectively. Further discussion regarding the potential membrane fouling mechanisms is also provided by comparing two membranes with different surface pore structures and the same hollow fiber length, total membrane area, and chemistry. A cake-growth profile is reported for the narrower surface pore, 0.65-µm nominal retention perfusion membrane with final antibody sieving coefficients ≤70%. Whereas the sieving coefficient remained ≥85% during 40 culture days for the wide-surface pore, 0.2-µm nominal retention rating membrane. The wide-surface pore structure, confirmed by scanning electron microscopy imaging, minimizes the formation of biomass deposits on the membrane surface and drastically improves product sieving. This study not only offers a robust alternative for integrated continuous bioprocess by eliminating additional filtration steps while overcoming sieving decay, but also provides insight into membranes' fouling mechanism.     

Oligomerized Tie2 localizes to clathrin-coated pits in response to angiopoietin-1

The tyrosine kinase receptor Tie2 is expressed on endothelial cells, and together with its ligand angiopoietin-1 (Ang1), is important for angiogenesis and vascular stability. Upon activation by Ang1, Tie2 is rapidly internalized and degraded, a mechanism most likely necessary to attenuate receptor activity. Using immunogold electron microscopy, we show that on the surface of endothelial cells, Tie2 is arranged in variably sized clusters containing dimers and higher order oligomers. Clusters of Tie2 were expressed on the apical and basolateral plasma membranes, and on the tips of microvilli. Upon activation by Ang1, Tie2 co-localized with the clathrin heavy chain at the apical and basolateral plasma membranes and within endothelial cells indicating that Tie2 internalizes through clathrin-coated pits. Inhibiting cellular endocytosis by depleting cellular potassium or by acidifying the cytosol blocked the internalization of Tie2 in response to Ang1. Our results suggest that one pathway mediating the internalization of Tie2 in response to Ang1 is through clathrin-coated pits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The preprophase band is a localized center of clathrin-mediated endocytosis in late prophase cells of the onion cotyledon epidermis

The preprophase band (PPB) marks the site on the plant cell cortex where the cell plate will fuse during the final stage of cytokinesis. Recent studies have shown that several cytoskeletal proteins are depleted at the PPB site, but the processes that bring about these changes are still unknown. We have investigated the membrane systems associated with the PPB regions of epidermal cells of onion cotyledons by means of serial thin sections and electron tomograms. In contrast with specimens preserved by chemical fixatives, our high-pressure frozen cells demonstrated the presence of large numbers of clathrin-coated pits and vesicles in the PPB regions. The vesicles were of two types: clathrin-coated and structurally related, non-coated vesicles. Quantitative analysis of the data revealed that the number of clathrin-coated pits and vesicles is higher in the PPB regions than outside of these regions. Immunofluorescent microscopy using anti-plant clathrin-antibody confirmed this result. In contrast, no differences in secretory activities were observed. We postulate that the removal of membrane proteins by endocytosis plays a role in the formation of PPB 'memory' structures.     

Distinct clathrin-coated pits sort different G protein-coupled receptor cargo

Upon activation, many G protein-coupled receptors (GPCRs) internalize by clathrin-mediated endocytosis and are subsequently sorted to undergo recycling or lysosomal degradation. Here we observe that sorting can take place much earlier than previously thought, by entry of different GPCRs into distinct populations of clathrin-coated pit (CCP). These distinct populations were revealed by analysis of two purinergic GPCRs, P2Y(1) and P2Y(12), which enter two populations of CCPs in a mutually exclusive manner. The mechanisms underlying early GPCR sorting involve differential kinase-dependent processes because internalization of P2Y(12) is mediated by GPCR kinases (GRKs) and arrestin, whereas P2Y(1) internalization is GRK- and arrestin-independent but requires protein kinase C. Importantly, the beta(2) adrenoceptor which also internalizes in a GRK-dependent manner also traffics exclusively to P2Y(12)-containing CCPs. Our data therefore reveal distinct populations of CCPs that sort GPCR cargo at the plasma membrane using different kinase-dependent mechanisms.     

浓香型白酒窖泥中兼性厌氧细菌的分离鉴定

为探讨浓香型白酒窖泥中微生物区系的构成,采用传统微生物分类鉴定法,对泸州老窖不同窖龄窖底和窖壁泥样的可培养兼性厌氧细菌进行了分类计数,并初步鉴定到属。平板涂布法计数得出,老窖底样的菌落总数最多,达3.98×103cfu/g泥,新窖壁样菌落数最少,只有0.24×103cfu/g泥;经生理生化鉴定,参照伯杰氏细菌鉴定手册等将划线单离后的菌株归为8个属,其大部分属于芽孢杆菌属(Bacillus)和芽孢乳杆菌属(Sporolac-tobacillus),也存在假单胞菌属(Pseudomonas)、梭菌属(Clostridium)等。     

Identification of Caveolae-like Structures on the Surface of Intact Cells Using Scanning Force Microscopy

Caveolae are small, functionally important membrane invaginations found on the surface of many different cell types. Using electron microscopy, caveolae can be unequivocally identified in cell membranes by virtue of their size and the presence of caveolin/VIP22 proteins in the caveolar coat. In this study we have applied for the first time scanning force microscopy (SFM), to visualize caveolae on the surface of living and fixed cells. By scanning the membranes of Chinese hamster ovary cells (CHO), using the tapping mode of the SFM in fluid, we could visualize small membrane pits on the cell membranes of living and fixed cells. Two populations of pits with mean diameters of around 100 nm and 200 nm were present. In addition, the location of many pits visualized with the SFM was coincident with membrane spots fluorescently labeled with a green fluorescent protein-caveolin-1 fusion protein. Scanning force microscopy on cells treated with methyl--cyclodextrin, an agent that sequesters cholesterol and disrupts caveolae, abolished pits with a measured diameter of 100 nm but left pits of around 200 nm diameter intact. Thus, the smallest membrane pits measured with the SFM in CHO cells were indeed very likely to be identical to caveolae. These experiments show for the first time that SFM can be used to visualize caveolae in intact cells.     

Beyond leopards: tooth marks and the contribution of multiple carnivore taxa to the accumulation of the Swartkrans Member 3 fossil assemblage

The ca. 1.0 myr old fauna from Swartkrans Member 3 (South Africa) preserves abundant indication of carnivore activity in the form of tooth marks (including pits) on many bone surfaces. This direct paleontological evidence is used to test a recent suggestion that leopards, regardless of prey body size, may have been almost solely responsible for the accumulation of the majority of bones in multiple deposits (including Swartkrans Member 3) from various Sterkfontein Valley cave sites. Our results falsify that hypothesis and corroborate an earlier hypothesis that, while the carcasses of smaller animals may have been deposited in Swartkrans by leopards, other kinds of carnivores (and hominids) were mostly responsible for the deposition of large animal remains. These results demonstrate the importance of choosing appropriate classes of actualistic data for constructing taphonomic inferences of assemblage formation. In addition, they stress that an all-encompassing model of assemblage formation for the hominid-bearing deposits of the Sterkfontein Valley is inadequate and that each must be evaluated individually using not just analogical reasoning but also incorporating empirical data generated in the preserved fossil samples.