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Molecular Biology of the Cell

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https://www.readbyqxmd.com/read/28209733/dual-function-of-tgf%C3%AE-in-lens-epithelial-cell-fate-implications-for-secondary-cataract
#1
Bruce A Boswell, Anna Korol, Judith A West-Mays, Linda S Musil
The most common vision-disrupting complication of cataract surgery is posterior capsule opacification (PCO; secondary cataract). PCO is caused by residual lens cells undergoing one of two very different cell fates: either transdifferentiating into myofibroblasts, or maturing into lens fiber cells. Although TGFβ has been strongly implicated in lens cell fibrosis, the factors responsible for the latter process have not been identified. We show here for the first time that TGFβ can induce purified primary lens epithelial cells within the same culture to undergo differentiation into either lens fiber cells or myofibroblasts...
February 16, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28209732/direct-measurement-of-cortical-force-generation-and-polarization-in-a-living-parasite
#2
Rachel V Stadler, Lauren A White, Ke Hu, Brian P Helmke, William H Guilford
Apicomplexa is a large phylum of intracellular parasites that are notable for the diseases they cause, including toxoplasmosis, malaria and cryptosporidiosis. A conserved motile system is critical to their lifecycles as it drives directional gliding motility between cells, as well as invasion of and egress from host cells. However, our understanding of this system is limited by a lack of measurements of the forces driving parasite motion. We used a laser trap to measure the function of the motility apparatus of living Toxoplasma gondii by adhering a microsphere to the surface of an immobilized parasite...
February 16, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28209731/transport-of-fungal-rab11-secretory-vesicles-involves-myosin-5-dynein-dynactin-p25-and-kinesin-1-and-is-independent-of-kinesin-3
#3
Miguel A Peñalva, Jun Zhang, Xin Xiang, Areti Pantazopoulou
Hyphal tip cells of the fungus Aspergillus nidulans are useful to study long-range intracellular traffic. Post-Golgi secretory vesicles (SVs) containing the RAB11 orthologue RabE engage myosin-5 as well as plus-end- and minus-end-directed microtubule motors, providing an experimental system to investigate the interplay between microtubule and actin motors acting on the same cargo. By exploiting the fact that depolymerization of F-actin 'unleashes' SVs focused at the apex by myosin-5 to microtubule-dependent motors, we establish that the minus-end directed transport of SVs requires the dynein/dynactin supercomplex...
February 16, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28209730/role-of-stard4-in-sterol-transport-between-the-endocytic-recycling-compartment-and-the-plasma-membrane
#4
David B Iaea, Shu Mao, Frederik W Lund, Frederick R Maxfield
Cholesterol is an essential constituent of membranes in mammalian cells. The plasma membrane and the endocytic recycling compartment (ERC) are both highly enriched in cholesterol. The abundance and distribution of cholesterol among organelles are tightly controlled by a combination of mechanisms involving vesicular and non-vesicular sterol transport processes. Using the fluorescent cholesterol analog, dehydroergosterol, we examined sterol transport between the plasma membrane and the ERC using fluorescence recovery after photobleaching and a novel sterol efflux assay...
February 16, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28179460/vamp-7-dependent-secretion-at-the-immune-synapse-regulates-antigen-extraction-and-presentation-in-b-lymphocytes
#5
Dorian Obino, Jheimmy Diaz, Juan José Sáez, Jorge Ibañez-Vega, Pablo J Sáez, Martina Alamo, Danielle Lankar, Maria-Isabel Yuseff
Recognition of surface-tethered antigens (Ag) by B cells leads to the formation of an immune synapse that promotes Ag uptake for presentation onto MHC-II molecules. Extraction of immobilized antigens at the immune synapse of B cells relies on the local secretion of lysosomes, which are recruited to the antigen contact site by polarization of their microtubule network. Although conserved polarity proteins have been implicated in coordinating cytoskeleton remodeling with lysosome trafficking, the cellular machinery associated with lysosomal vesicles that regulates their docking and secretion at the synaptic interface has not been defined...
February 8, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28179459/practical-method-for-targeted-disruption-of-cilia-related-genes-by-using-crispr-cas9-mediated-homology-independent-knock-in-system
#6
Yohei Katoh, Saki Michisaka, Shohei Nozaki, Teruki Funabashi, Tomoaki Hirano, Ryota Takei, Kazuhisa Nakayama
The CRISPR/Cas9 system has revolutionized genome editing in virtually all organisms. Although the CRISPR/Cas9 system enables the targeted cleavage of genomic DNA, its use for gene knock-in remains challenging because levels of homologous recombination activity vary among various cells. In contrast, the efficiency of homology-independent DNA repair is relatively high in most cell types. Therefore, the utilization of a homology-independent repair mechanism is a possible alternative for efficient genome editing...
February 8, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28179458/individual-s-acylated-cysteines-differentially-contribute-to-h-ras-endomembrane-trafficking-and-acylation-deacylation-cycles
#7
Maria P Pedro, Aldo A Vilcaes, Guillermo A Gomez, Jose L Daniotti
S-acylation/deacylation cycles and vesicular transport are critical for an adequate subcellular distribution of S-acylated Ras proteins. H-Ras is dually acylated on cysteines 181 and 184, but it is unknown how these residues individually contribute to H-Ras trafficking. In this study, we characterized the acylation and deacylation rates and membrane trafficking of mono-acylated H-Ras mutants to analyze their contributions to H-Ras plasma membrane and endomembrane distribution. We demonstrated that dually acylated H-Ras interacts with acyl-protein thioesterases (APT) 1 and 2 at the plasma membrane...
February 8, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28179457/microtubule-motors-involved-in-nuclear-movement-during-skeletal-muscle-differentiation
#8
V Gache, E R Gomes, B Cadot
Nuclear positioning is a determining event in several cellular processes such as fertilization, cell migration and cell differentiation. The structure and function of muscle cells, which contain hundreds of nuclei, have been described to rely, in part, on proper nuclear positioning. Remarkably, in the course of muscle differentiation, nuclear movements along the myotube axis might represent the event required for the evenly positioning of nuclei in the mature myofiber. Here we report the analysis of nuclear behavior, time in motion, speed and alignment, during myotube differentiation and temporal interference of cytoskeletal microtubule related motors...
February 8, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28179456/kinetics-of-milk-lipid-droplet-ld-transport-growth-and-secretion-revealed-by-intravital-imaging-ld-release-is-intermittently-stimulated-by-oxytocin
#9
Andrius Masedunskas, Yun Chen, Rebecca Stussman, Roberto Weigert, Ian H Mather
The lipid droplet (LD) fraction of milk has attracted special attention because it supplies preformed lipids for neonatal development and the assembled LDs are secreted by a unique apocrine mechanism. Because many aspects of this key process remain uncharacterized we developed a facile method for the intravital imaging of mammary cells in transgenic mice, which express fluorescently-tagged marker proteins. Using these techniques, we describe the first kinetic analysis of LD growth and secretion at peak lactation in real time...
February 8, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148652/calcium-signals-drive-cell-shape-changes-during-zebrafish-midbrain-hindbrain-boundary-formation
#10
Srishti U Sahu, Mike R Visetsouk, Ryan J Garde, Leah Hennes, Constance Kwas, Jennifer H Gutzman
One of the first morphogenetic events in the vertebrate brain is the formation of the highly conserved midbrain-hindbrain boundary (MHB). Specific cell shape changes occur at the point of deepest constriction of the MHB, the midbrain-hindbrain boundary constriction (MHBC), and are critical for proper MHB formation. These cell shape changes are controlled by non-muscle myosin II (NMII) motor proteins which are tightly regulated via the phosphorylation of their associated myosin regulatory light chains (MRLC)...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148651/an-intramolecular-interaction-within-the-lipid-kinase-fab1-regulates-cellular-phosphatidylinositol-3-5-bisphosphate-lipid-levels
#11
Michael J Lang, Bethany S Strunk, Nadia Azad, Jason L Petersen, Lois S Weisman
Phosphorylated phosphoinositide lipids (PPIs) are low-abundance signaling molecules that control signal transduction pathways and are necessary for cellular homeostasis. The PPI phosphatidylinositol (3,5)-bisphosphate (PI(3,5)P2) is essential in multiple organ systems. PI(3,5)P2 is generated from PI3P by the conserved lipid kinase Fab1/PIKfyve. Defects in the dynamic regulation of PI(3,5)P2 are linked to human diseases. However, few mechanisms that regulate PI(3,5)P2 have been identified. Here we report an intramolecular interaction between the yeast Fab1 kinase region and an upstream conserved cysteine-rich (CCR) domain...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148650/the-septin-associated-kinase-gin4-recruits-gps1-to-the-site-of-cell-division
#12
Franz Meitinger, Gislene Pereira
Cell cycle dependent morphogenesis of unicellular organisms depends on the spatio-temporal control of cell polarity. Rho GTPases are the major players that guide cells through structural reorganizations such as cytokinesis (Rho1-dependent) and polarity establishment (Cdc42-dependent). In budding yeast, the protein Gps1 plays a pivotal role in both processes. Gps1 resides at the bud-neck to maintain Rho1 localization and restrict Cdc42 activity during cytokinesis. Here, we analyzed how Gps1 is recruited to the bud-neck during the cell cycle...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148649/c3g-shows-regulated-nucleo-cytoplasmic-exchange-and-represses-histone-modifications-associated-with-euchromatin
#13
Dhruv Kumar Shakyawar, Kunal Dayma, Anesh Ramadhas, Chavvakula Varalakshmi, Vegesna Radha
C3G (RapGEF1) is a ubiquitously expressed guanine nucleotide exchange factor that functions in signaling pathways regulating cell proliferation, apoptosis, and actin reorganization. It is essential for differentiation, and early embryonic development in mice. Over-expressed C3G shows predominant cytoplasmic localization, but endogenous C3G is a component of nuclear fractions in a variety of cell types. Co-expression of Importin-α and inhibition of nuclear export by Leptomycin B resulted in predominant nuclear localization of C3G...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148648/coupled-excitable-ras-and-f-actin-activation-mediate-spontaneous-pseudopod-formation-and-directed-cell-movement
#14
Peter J M van Haastert, Ineke Keizer-Gunnink, Arjan Kortholt
Many eukaryotic cells regulate their mobility by external cues. Genetic studies have identified more than hundred components that participate in chemotaxis, which hinders to identify the conceptual framework how cells sense and respond to shallow chemical gradients. The activation of Ras occurs during basal locomotion, and is an essential connector between receptor and the cytoskeleton during chemotaxis. Using a sensitive assay for activated Ras we show here that activation of Ras and F-actin form two excitable systems that are coupled through mutual positive feedback and memory...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28148647/hops-catalyzes-the-interdependent-assembly-of-each-vacuolar-snare-into-a-snare-complex
#15
Amy Orr, Hongki Song, Scott F Rusin, Arminja N Kettenbach, William Wickner
Rab GTPases, their effectors, SNAREs of the R, Qa, Qb, and Qc families, and SM SNARE-binding proteins catalyze intracellular membrane fusion. At the vacuole/lysosome, they are integrated by the HOPS (homotypic fusion and vacuole protein sorting) complex. Two HOPS subunits bind vacuolar Rabs for tethering, another binds the Qc SNARE, and a fourth HOPS subunit, an SM protein, has conserved grooves which bind R- and Qa-SNARE domains. Spontaneous quaternary SNARE complex assembly is very slow. We now report an assay of SNARE complex assembly which does not rely on fusion and where tethering doesn't co-enrich the 4 SNAREs...
February 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28122820/sequestration-of-cholesterol-within-the-host-late-endocytic-pathway-restricts-liver-stage-plasmodium-development
#16
Wiebke Petersen, Werner Stenzel, Olivier Silvie, Judith Blanz, Paul Saftig, Kai Matuschewski, Alyssa Ingmundson
While lysosomes are degradative compartments and one of the defenses against invading pathogens, they are also hubs of metabolic activity. Late endocytic compartments accumulate around Plasmodium berghei liver-stage parasites during development, and whether this is a host defense strategy or active recruitment by the parasites is unknown. In support of the latter hypothesis, we observed that the recruitment of host late endosomes (LE) and lysosomes is reduced in uis4- parasites, which lack a parasitophorous vacuole membrane protein and arrest during liver-stage development...
January 25, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28122819/method-to-study-cell-migration-under-uniaxial-compression
#17
Nishit Srivastava, Robert R Kay, Alexandre J Kabla
The chemical, physical and mechanical properties of the extra-cellular environment have a strong effect on cell migration. Aspects such as pore-size or stiffness of the matrix influence the selection of the mechanism used by cells to propel themselves, including pseudopod or blebbing. How a cell perceives its environment, and how such a cue triggers a change in behaviour are largely unknown, but mechanics is likely to be involved. Because mechanical conditions are often controlled by modifying the composition of the environment, separating chemical and physical contributions is difficult and requires multiple controls...
January 25, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28100639/munc13-4-functions-as-a-ca2-sensor-for-homotypic-secretory-granule-fusion-to-generate-endosomal-exocytic-vacuoles
#18
Sang Su Woo, Declan J James, Thomas F J Martin
Munc13-4 is a Ca(2+)-dependent SNARE- and phospholipid-binding protein that localizes to and primes secretory granules (SGs) for Ca(2+)-evoked secretion in various secretory cells. Studies in mast cell-like RBL-2H3 cells provides direct evidence that Munc13-4 with its two Ca(2+)-binding C2 domains functions as a Ca(2+) sensor for SG exocytosis. Unexpectedly, Ca(2+) stimulation also generated large (>2.4 μm diameter) Munc13-4(+)/Rab7(+)/Rab11(+) endosomal vacuoles. Vacuole generation involved the homotypic fusion of Munc13-4(+)/Rab7(+) SGs followed by a merge with Rab11(+) endosomes, and depended on Ca(2+) binding to Munc13-4...
January 18, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28100638/retromer-driven-membrane-tubulation-separates-endosomal-recycling-from-rab7-ypt7-dependent-fusion
#19
Latha Kallur Purushothaman, Henning Arlt, Anne Kuhlee, Stefan Raunser, Christian Ungermann
Endosomes are the major protein sorting hubs of the endocytic pathway. They sort proteins destined for degradation into internal vesicles, while in parallel recycling receptors via tubular carriers back to the Golgi. Tubule formation depends on the Rab7/Ypt7-interacting retromer complex, consisting of the sorting nexin dimer (SNX-BAR) and the trimeric cargo selection complex (CSC). Fusion of mature endosomes with the lysosome-like vacuole also requires Rab7/Ypt7. Here, we now solved a major problem in understanding this dual function of endosomal Rab7/Ypt7 using a fully reconstituted system, including purified, full-length yeast SNX-BAR and CSC, whose overall structure we present...
January 18, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28100637/a-zip3-like-protein-plays-a-role-in-crossover-formation-in-the-sc-less-meiosis-of-the-protist-tetrahymena
#20
Anura Shodhan, Kensuke Kataoka, Kazufumi Mochizuki, Maria Novatchkova, Josef Loidl
When programmed meiotic DNA double-strand breaks (DSBs) undergo recombinational repair, genetic crossovers (COs) may be formed. A certain level of these are required for the faithful segregation of chromosomes, but the majority of DSBs are processed toward a safer alternative, namely non-crossovers (NCOs), via non-reciprocal DNA exchange. At the crossroads between these two DSB fates are the Msh4-Msh5 (MutSγ) complex, which stabilizes CO-destined recombination intermediates, and members of the Zip3/RNF212 family of RING finger proteins, which in turn stabilize MutSγ...
January 18, 2017: Molecular Biology of the Cell
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