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Molecular Biology of the Cell

Valentin Dunsing, Magnus Mayer, Filip Liebsch, Gerhard Multhaup, Salvatore Chiantia
The Amyloid-precursor-like protein 1 (APLP1) is a type I transmembrane protein which plays a role in synaptic adhesion and synaptogenesis. Past investigations indicated that APLP1 is involved in the formation of protein-protein complexes that bridge the junctions between neighboring cells. Nevertheless, APLP1-APLP1 trans interactions have never been directly observed in higher eukaryotic cells. Here, we investigated APLP1 interactions and dynamics directly in living human embryonic kidney (HEK) cells, using fluorescence fluctuation spectroscopy techniques, namely cross-correlation scanning fluorescence correlation spectroscopy (sFCS) and Number&Brightness (N&B)...
October 11, 2017: Molecular Biology of the Cell
Masashi Yukawa, Tomoki Kawakami, Masaki Okazaki, Kazunori Kume, Ngang Heok Tang, Takashi Toda
Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end directed motor Kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end directed motor Kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of Kinesin-5/Cut7 and Kinesin-14/Pkl1...
October 11, 2017: Molecular Biology of the Cell
Annapurna Vemu, Joseph Atherton, Jeffrey O Spector, Carolyn A Moores, Antonina Roll-Mecak
Microtubules polymerize and depolymerize stochastically, a behavior essential for cell division, motility and differentiation. While many studies advanced our understanding of how microtubule-associated proteins tune microtubule dynamics in trans, we have yet to understand how tubulin genetic diversity regulates microtubule functions. The majority of in vitro dynamics studies are performed with tubulin purified from brain tissue. This preparation is not representative of tubulin found in many cell types. Here we report the 4...
October 11, 2017: Molecular Biology of the Cell
Shaista Hussain, Xavier Le Guezennec, Wang Yi, Huang Dong, Joanne Chia, Ke Yiping, Lee Kee Khoon, Frédéric Bard
The synthesis of glycans and sorting of proteins are critical functions of the Golgi apparatus and depend on its highly complex and compartmentalized architecture. High-content image analysis coupled to RNAi screening offers opportunities to explore this organelle organisation and the gene network underlying it. To date, image-based Golgi screens were based on a single parameter or supervised analysis with pre-defined Golgi structural classes. Here, we report the use of multi-parametric data extracted from a single marker and a computational unsupervised analysis framework to explore Golgi phenotypic diversity more extensively...
October 11, 2017: Molecular Biology of the Cell
Barclay J Lee, Emily M Mace
Human natural killer (NK) cells are generated from CD34(+) precursors and can be differentiated in vitro by co-culture with developmentally supportive stromal cells. We have previously described the acquisition of cell migration as a feature of NK cell terminal maturation in this system. Here, we perform continuous long-term imaging and tracking of NK cell progenitors undergoing in vitro differentiation. We demonstrate that NK cell precursors can be tracked over long time periods on the order of weeks by utilizing phase-contrast microscopy, and show that these cells acquire increasing motility as they mature...
October 11, 2017: Molecular Biology of the Cell
Mohamad Rima, Marwa Daghsni, Anaïs Lopez, Ziad Fajloun, Lydie Lefrancois, Mireia Dunach, Yasuo Mori, Philippe Merle, Juan L Brusés, Michel de Waard, Michel Ronjat
The β4 isoform of the β-subunits of Voltage-Gated Calcium Channel regulates cell proliferation and cell cycle progression. Herein we show that co-expression of the β4-subunit with actors of the canonical Wnt/β-catenin signaling pathway in a hepatoma cell line inhibits Wnt responsive gene transcription and decreases cell division, in agreement with the role of the Wnt pathway in cell proliferation. β4-subunit-mediated inhibition of Wnt signaling is observed in the presence of LiCl, an inhibitor of GSK3 that promotes β-catenin translocation to the nucleus...
October 11, 2017: Molecular Biology of the Cell
Anastasia F Thévenin, Rachel A Margraf, Charles G Fisher, Rachael M Kells-Andrews, Matthias M Falk
To investigate whether connexin phosphorylation regulates ZO-1's known role in gap junction (GJ) function, we generated and analyzed a series of phosphomimetic and phosphorylation-dead mutants by exchanging known conserved regulatory serine (S) residues 255, 279/282, 365, 368, and 373 located in the C-terminal domain of connexin43 (Cx43) into glutamic acid (E) or alanine (A) residues. All connexin mutants were translated into stable, full-length proteins and assembled into GJs when expressed in HeLa or MDCK cells...
October 11, 2017: Molecular Biology of the Cell
Nicolas Aznar, Nina Sun, Ying Dunkel, Jason Ear, Matthew D Buschman, Pradipta Ghosh
Cellular proliferation is antagonistically regulated by canonical and non-canonical Wnt signals; their dysbalance triggers cancers. We previously showed that a multimodular signal transducer, Daple, enhances PI3-K→Akt signals within the non-canonical Wnt signaling pathway and antagonistically inhibits canonical Wnt responses. Here we demonstrate that the PI3-K→Akt pathway serves as a positive feedback loop that further enhances non-canonical Wnt signals by compartmentalizing β-catenin. By phosphorylating the phosphoinositide(PI)-binding domain of Daple, Akt abolishes Daple's ability to bind PI3-P-enriched endosomes that engage dynein motor complex for long-distance trafficking of β-catenin/E-cadherin complexes to pericentriolar recycling endosomes (PCREs)...
October 11, 2017: Molecular Biology of the Cell
Carlos Anton, Bettina Zanolari, Irene Arcones, Congwei Wang, Jose Miguel Mulet, Anne Spang, Cesar Roncero
Exomer is an adaptor complex required for the direct transport of a selected number of cargoes from the TGN to the plasma membrane in S. cerevisiae However, exomer mutants are highly sensitive to increased concentrations of alkali metal cations, a situation which remains unexplained by the lack of transport of any known cargoes. Here, we identify several HAL genes that act as multicopy suppressors of this sensitivity and are connected to the reduced function of the sodium ATPase Ena1. Furthermore, we find that Ena1 is dependent on exomer function...
October 11, 2017: Molecular Biology of the Cell
Margaret A Gustafson, J Christopher Fromme
At the Golgi complex, the biosynthetic sorting center of the cell, the Arf GTPases are responsible for coordinating vesicle formation. The Arf-GEFs activate Arf GTPases and are therefore the key molecular decision-makers for trafficking from the Golgi.  In Saccharomyces cerevisiae, three conserved Arf-GEFs function at the Golgi: Sec7, Gea1, and Gea2.  Our group has described the regulation of Sec7, the trans-Golgi Arf-GEF, through autoinhibition, positive feedback, dimerization, and interactions with a suite of small GTPases...
October 4, 2017: Molecular Biology of the Cell
Erin M Craig, Howard T Yeung, Anand N Rao, Peter W Baas
We present a computational model to test a "polarity sorting" mechanism for microtubule (MT) organization in developing axons. We simulate the motor-based axonal transport of short MTs to test the hypothesis that immobilized cytoplasmic dynein motors transport short MTs with their plus ends leading, so that "mal-oriented" MTs with minus-end-out are transported toward the cell body while "correctly" oriented MTs are transported in the anterograde direction away from the soma. We find that dynein-based transport of short MTs can explain the predominately plus-end-out polarity pattern of axonal MTs, but that transient attachments of plus-end-directed motor proteins and non-motile cross-linker proteins are needed to explain the frequent pauses and occasional reversals observed in live-cell imaging of MT transport...
October 4, 2017: Molecular Biology of the Cell
Timothy Loveless, Hiroshi Qadota, Guy M Benian, Jeff Hardin
We have identified and characterized sorb-1, the only Sorbin and SH3 domain-containing protein family member in C. elegans SORB-1 is strongly localized to integrin adhesion complexes in larvae and adults, including adhesion plaques and dense bodies (Z-disks) of striated muscles and attachment plaques of smooth muscles. SORB-1 is recruited to the actin-binding, membrane-distal regions of dense bodies via its C-terminal SH3 domains in an ATN-1(α-actinin)- and ALP-1(ALP/Enigma)-dependent manner, where it contributes to the organization of sarcomeres...
October 4, 2017: Molecular Biology of the Cell
Jean-Francois Rupprecht, Kok Haur Ong, Jianmin Yin, Anqi Huang, Huy-Hong-Quan Dinh, Anand P Singh, Shaobo Zhang, Weimiao Yu, Timothy E Saunders
Organ and tissue formation are complex three-dimensional processes involving cell division, growth, migration, and rearrangement, all of which occur within physically constrained regions. However, analyzing such processes in three-dimensions in vivo is challenging. Here, we focus on the process of cellularization in the anterior pole of the early Drosophila embryo to explore how cells compete for space under geometric constraints. Using microfluidics combined with fluorescence microscopy, we extract quantitative information on the three-dimensional epithelial cell morphology...
October 4, 2017: Molecular Biology of the Cell
Jennifer Landino, Stephen R Norris, Muyi Li, Edward R Ballister, Michael A Lampson, Ryoma Ohi
During cytokinesis, the chromosomal passenger complex (CPC) promotes midzone organization, specifies the cleavage plane, and regulates furrow contractility. The localizations of the CPC are coupled to its cytokinetic functions. At the metaphase-to-anaphase transition, the CPC dissociates from centromeres and localizes to midzone microtubules and the equatorial cortex. CPC relocalization to the cell middle is thought to depend on MKlp2-driven plus-end directed transport. In support of this idea, MKlp2 depletion impairs cytokinesis; however, cytokinesis failure stems from furrow regression rather than failed initiation of furrowing...
September 27, 2017: Molecular Biology of the Cell
Carlos Nogueras-Ortiz, Cristina Roman-Vendrell, Gabriel E Mateo-Semidey, Yu-Hsien Liao, Debra A Kendall, Guillermo A Yudowski
G protein-coupled receptors (GPCRs) mediate their complex functions through activation of signaling cascades from receptors localized at the cell surface and endosomal compartments. These signaling pathways are modulated by heterotrimeric G proteins and the scaffold proteins beta-arrestin 1 and 2. However, in contrast to the events occurring at the cell surface, our knowledge of the mechanisms controlling signaling from receptors localized at intracellular compartments is still very limited. Here, we sought to investigate the intracellular signaling from cannabinoid 2 receptor (CB2R)...
September 27, 2017: Molecular Biology of the Cell
Ting-Sung Hsieh, Yu-Ju Chen, Chi-Lun Chang, Wan-Ru Lee, Jen Liou
ER-plasma membrane (PM) junctions mediate crucial activities ranging from Ca(2+) signaling to lipid metabolism. Spatial organization of ER-PM junctions may modulate the extent and location of these cellular activities. However, the morphology and distribution of ER-PM junctions are not well characterized. Using photoactivated localization microscopy (PALM), we reveal that the contact area of single ER-PM junctions is mainly oblong with the dimensions of ∼120 nm × ∼80 nm in HeLa cells. Using total internal reflection fluorescence microscopy (TIRFM) and structure illumination microscopy (SIM), we show that cortical actin contributes to spatial distribution and stability of ER-PM junctions...
September 27, 2017: Molecular Biology of the Cell
Christoph Sommer, Rudolf Hoefler, Matthias Samwer, Daniel W Gerlich
Supervised machine learning is a powerful and widely used method to analyze high-content screening data. Despite its accuracy, efficiency, and versatility, supervised machine learning has drawbacks, most notably its dependence on a priori knowledge of expected phenotypes and time-consuming classifier training. We provide a solution to these limitations with CellCognition Explorer, a generic novelty detection and deep learning framework. Application to several large-scale screening data sets on nuclear and mitotic cell morphologies demonstrates that CellCognition Explorer enables discovery of rare phenotypes without user training, which has broad implications for improved assay development in high-content screening...
September 27, 2017: Molecular Biology of the Cell
David C Morris, Julia L Popp, Leung K Tang, Holly C Gibbs, Emily Schmitt, Sankar P Chaki, Briana C Bywaters, Alvin T Yeh, Weston W Porter, Robert C Burghardt, Rola Barhoumi, Gonzalo M Rivera
Although it is known that Nck regulates cell adhesion and migration by bridging tyrosine phosphorylation with cytoskeletal remodeling, the role of Nck in tumorigenesis and metastasis has remained undetermined. Here, we report that Nck is required for the growth and vascularization of primary tumors and lung metastases in a breast cancer xenograft model as well as extravasation following injection of carcinoma cells into the tail vein. We provide evidence that Nck directs the polarization of cell-matrix interactions for efficient migration in three-dimensional microenvironments...
September 27, 2017: Molecular Biology of the Cell
Nathalie R Reinhard, Marieke Mastop, Taofei Yin, Yi Wu, Esmeralda K Bosma, Theodorus W J Gadella, Joachim Goedhart, Peter L Hordijk
The bioactive sphingolipid S1P is present in plasma, bound to carrier proteins, and is involved in many physiological processes, including angiogenesis, inflammatory responses and vascular stabilization. S1P can bind to several G-protein-coupled receptors (GPCRs) activating a number of different signalling networks. At present, the dynamics and relative importance of signalling events activated immediately downstream of GPCR activation are unclear. To examine this, we used a set of FRET-based biosensors for different RhoGTPases (Rac1, RhoA/B/C, Cdc42) as well as for heterotrimeric G-proteins in a series of live-cell imaging experiments in primary human endothelial cells...
September 27, 2017: Molecular Biology of the Cell
Yunfeng Chen, Lining Ju, Muaz Rushdi, Chenghao Ge, Cheng Zhu
Mechanosensing describes the ability of a cell to sense mechanical cues of its micro-environment, including not only all components of force, stress and strain but also substrate rigidity, topology and adhesiveness. This ability is crucial for the cell to respond to the surrounding mechanical cues and adapt to the changing environment. Examples of responses and adaptation include (de)activation, proliferation/apoptosis, and (de)differentiation. Receptor-mediated cell mechanosensing is a multi-step process that is initiated by binding of cell surface receptors to their ligands on the extracellular matrix or the surface of adjacent cells...
September 27, 2017: Molecular Biology of the Cell
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