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Molecular Biology of the Cell

David Pincus, Jayamani Anandhakumar, Prathapan Thiru, Michael J Guertin, Alexander M Erkine, David S Gross
Heat Shock Factor 1 is the master transcriptional regulator of molecular chaperones and binds to the same cis-acting Heat Shock Element (HSE) across the eukaryotic lineage. In budding yeast, Hsf1 drives the transcription of ∼20 genes essential to maintain proteostasis under basal conditions, yet its specific targets and extent of inducible binding during heat shock remain unclear. Here, we combine Hsf1 ChIP-seq, nascent RNA-seq and Hsf1 nuclear depletion to quantify Hsf1 binding and transcription across the yeast genome...
October 17, 2018: Molecular Biology of the Cell
Ruddi Rodriguez-Garcia, Laurent Chesneau, Sylvain Pastezeur, Julien Roul, Marc Tramier, Jacques Pécréaux
During asymmetric cell division, the molecular motor dynein generates cortical pulling forces which position the spindle to reflect polarity and adequately distribute cell fate determinants. In Caenorhabditis elegans embryos, despite a measured anteroposterior force imbalance, antibody staining failed to reveal dynein enrichment at the posterior cortex, suggesting a transient localization there. Dynein accumulates at the microtubule plus ends, indirectly binding to EBP-2EB . This accumulation, although not transporting dynein, contributes modestly to cortical forces...
October 17, 2018: Molecular Biology of the Cell
Matthew R Dilsaver, Pan Chen, Trey A Thompson, Traci Reusser, Richik N Mukherjee, John Oakey, Daniel L Levy
Emerin is an inner nuclear membrane protein often mutated in Emery-Dreifuss muscular dystrophy. Because emerin has diverse roles in nuclear mechanics, cytoskeletal organization, and gene expression, it has been difficult to elucidate emerin's contribution to nuclear structure and disease pathology. In this study, we investigated emerin's impact on nuclei assembled in Xenopus laevis egg extract, a simplified biochemical system that lacks potentially confounding cellular factors and activities. Notably, these extracts are transcriptionally inert and lack endogenous emerin and filamentous actin...
October 17, 2018: Molecular Biology of the Cell
Yi Liao, Hung-Chi Chang, Feng-Xia Liang, Pei-Jung Chung, Yuan Wei, Tuan-Phi Nguyen, Ge Zhou, Sheeva Talebian, Lewis C Krey, Fang-Ming Deng, Tak-Wah Wong, Javier U Chicote, James A Grifo, David L Keefe, Ellen Shapiro, Herbert Lepor, Xue-Ru Wu, Robert DeSalle, Antonio Garcia-España, Sang Yong Kim, Tung-Tien Sun
Uroplakin (UP) tetraspanins and their associated proteins are major mammalian urothelial differentiation products that form unique 2D-crystals of 16-nm particles ("urothelial plaques") covering the apical urothelial surface. Although uroplakins are highly expressed only in mouse urothelium and are often referred to as being urothelium-specific, they are also expressed in several nonurothelial cell types in stomach, kidney, prostate, epididymis, testis/sperms and ovary/oocytes. In oocytes, uroplakins co-localize with CD9 on cell surface and multivesicular body-derived exosomes, and the cytoplasmic tail of UPIIIa undergoes a conserved fertilization-dependent, Fyn-mediated tyrosine-phosphorylation that also occurs in Xenopus laevis eggs...
October 10, 2018: Molecular Biology of the Cell
Ralitza Staneva, Federica Burla, Gijsje H Koenderink, Stéphanie Descroix, Danijela Matic Vignjevic, Youmna Attieh, Marine Verhulsel
Tumor initiation and growth is associated with significant changes in the surrounding tissue. During carcinoma progression, a global stiffening of the extracellular matrix is observed and is interpreted as a signature of aggressive invasive tumors. However, it is still unknown if this increase in matrix rigidity promotes invasion and whether this effect is constant along the course of invasion. Here, we have developed a biomimetic in vitro assay that enabled us to address the question of the importance of tissue rigidity in the chronology of tumor invasion...
October 10, 2018: Molecular Biology of the Cell
G Hwang, D E Verver, M A Handel, G Hamer, P W Jordan
The structural maintenance of chromosomes complex, SMC5/6, is thought to be essential for DNA repair and chromosome segregation during mitosis and meiosis. To determine the requirements of the SMC5/6 complex during mouse spermatogenesis we combined a conditional knockout allele for Smc5, with four germ cell specific Cre recombinase transgenes, Ddx4-Cre, Stra8-Cre, Spo11-Cre and Hspa2-Cre, to mutate Smc5 in spermatogonia, in spermatocytes prior to meiotic entry, during early meiotic stages, and during mid-meiotic stages, respectively...
October 3, 2018: Molecular Biology of the Cell
Kumiko Hayashi, Yuta Tsuchizawa, Mitsuhiro Iwaki, Yasushi Okada
Although its importance is recently widely accepted, force measurement has been difficult in living biological systems, mainly due to the lack of the versatile non-invasive force measurement methods. The fluctuation theorem, which represents the thermodynamic properties of small fluctuating non-equilibrium systems, has been applied to the analysis of the thermodynamic properties of motor proteins in vitro. Here, we extend it to the axonal transport (displacement) of endosomes. The distribution of the displacement fluctuation had three or four distinct peaks around multiples of a unit value, which the fluctuation theorem can convert into the drag force exerted on the endosomes...
October 3, 2018: Molecular Biology of the Cell
David S Booth, Heather Szmidt-Middleton, Nicole King
As the closest living relatives of animals, choanoflagellates offer unique insights into animal origins and core mechanisms underlying animal cell biology. However, unlike traditional model organisms, such as yeast, flies and worms, choanoflagellates have been refractory to DNA delivery methods for expressing foreign genes. Here we report the establishment of a robust method for expressing transgenes in the choanoflagellate Salpingoeca rosetta, overcoming barriers that have previously hampered DNA delivery and expression...
October 3, 2018: Molecular Biology of the Cell
Pedro N Pozo, Jacob P Matson, Yasemin Cole, Katarzyna M Kedziora, Gavin D Grant, Brenda Temple, Jeanette Gowen Cook
The earliest step in DNA replication is origin licensing which is the DNA loading of MCM helicase complexes. The Cdt1 protein is essential for MCM loading during G1 phase of the cell cycle, yet the mechanism of Cdt1 function is still incompletely understood. We examined a collection of rare Cdt1 variants that cause a form of primordial dwarfism (Meier-Gorlin syndrome) plus one hypomorphic Drosophila allele to shed light on Cdt1 function. Three hypomorphic variants load MCM less efficiently than WT Cdt1, and their lower activity correlates with impaired MCM binding...
October 3, 2018: Molecular Biology of the Cell
Karthik Damodaran, Saradha Venkatachalapathy, Farid Alisafaei, A V Radhakrishnan, Doorgesh Sharma Jokhun, Vivek B Shenoy, G V Shivashankar
Fibroblasts exhibit heterogeneous cell geometries in tissues and integrate both mechanical and biochemical signals in their local microenvironment to regulate genomic programs via chromatin remodelling. While in connective tissues fibroblasts experience tensile and compressive forces (CFs), the role of compressive forces in regulating cell behaviour and in particular, the impact of cell geometry in modulating transcriptional response to such extrinsic mechanical forces is unclear. Here, we show that CF on geometrically well-defined mouse fibroblast cells reduces actomyosin contractility and shuttles Histone Deacetylase 3 (HDAC3), into the nucleus...
September 26, 2018: Molecular Biology of the Cell
Kaibo Lin, Shikun Zhang, Qinghua Shi, Mengyi Zhu, Liuze Gao, Wenjuan Xia, Baobao Geng, Zimeng Zheng, Eugene Yujun Xu
Mouse PUMILIO1 (PUM1) and PUMILIO2 (PUM2) belong to the PUF (Pumilio/FBF) family, a highly conserved RNA binding protein family whose homologs play critical roles in embryonic development and germ line stem cell maintenance in invertebrates. However, their roles in mammalian embryonic development and stem cell maintenance remained largely uncharacterized. Here, we report an essential requirement of the Pum gene family in early embryonic development. A loss of both Pum1 and Pum2 genes led to gastrulation failure, resulting in embryo lethality at E8...
September 26, 2018: Molecular Biology of the Cell
Claudia Lin-Kar Hung, Tamara Maiuri, Laura Erin Bowie, Ryan Gotesman, Susie Son, Mina Falcone, James Victor Giordano, Tammy Gillis, Virginia Mattis, Trevor Lau, Vickie Kwan, Vanessa Wheeler, Jonathan Schertzer, Karun Singh, Ray Truant
The huntingtin protein participates in several cellular processes that are disrupted when the polyglutamine tract is expanded beyond a threshold of 37 CAG DNA repeats in Huntington's disease (HD). Cellular biology approaches to understand these functional disruptions in HD have primarily focused on cell lines with synthetically long CAG length alleles that clinically represent outliers in this disease and a more severe form of HD that lacks age-onset. Patient-derived fibroblasts are limited to a finite number of passages before succumbing to cellular senescence...
September 26, 2018: Molecular Biology of the Cell
Cody J Boese, Jonathan Nye, Daniel W Buster, Tiffany A McLamarrah, Amy E Byrnes, Kevin C Slep, Nasser M Rusan, Gregory C Rogers
Centriole assembly initiates when Polo-like kinase 4 (Plk4) interacts with a centriole 'targeting-factor'. In Drosophila, Asterless/Asl (Cep152 in humans) fulfills the targeting role. Interestingly, Asl also regulates Plk4 levels. The N-terminus of Asl (Asl-A; amino acids 1-374) binds Plk4 and promotes Plk4 self-destruction, although it is unclear how this is achieved. Moreover, Plk4 phosphorylates the Cep152 N-terminus, but the functional consequence is unknown. Here, we show that Plk4 phosphorylates Asl and mapped 13 phospho-residues in Asl-A...
September 26, 2018: Molecular Biology of the Cell
Anneliese C Striz, Anna P Stephan, Alfonso López-Coral, Pamela L Tuma
A major focus for our laboratory is identifying the molecules and mechanisms that regulate basolateral-to-apical transcytosis in polarized hepatocytes. Our most recent studies have focused on characterizing the biochemical and functional properties of the small rab17 GTPase. We determined that rab17 is a mono-sumoylated protein and that this modification likely mediates selective interactions with the apically-located syntaxin 2. Using polarized hepatic WIF-B cells exogenously expressing wild type, dominant active/GTP-bound, dominant negative/GDP-bound or sumoylation-deficient/K68R rab17 proteins, we confirmed that rab17 regulates basolateral-to-apical transcytotic vesicle docking and fusion with the apical surface...
September 26, 2018: Molecular Biology of the Cell
Ke Zhang, Wanqing Lyu, Ji Yu, Anthony J Koleske
Abl family non-receptor tyrosine kinases regulate changes in cell shape and migration. Abl2 localizes to dynamic actin-rich protrusions, such as lamellipodia in fibroblasts and dendritic spines in neurons. Abl2 interactions with cortactin, an actin filament stabilizer are crucial for the formation and stability of actin-rich structures, but Abl2:cortactin-positive structures have not been characterized with high spatiotemporal resolution in cells. Using TIRF microscopy, we demonstrate that Abl2 colocalizes with cortactin at wave-like structures within lamellum and lamellipodium tips...
September 26, 2018: Molecular Biology of the Cell
Wylie Stroberg, Hadar Aktin, Yonatan Savir, Santiago Schnell
Cellular protein homeostasis requires continuous monitoring of stress in the endoplasmic reticulum (ER). Stress detection networks control protein homeostasis by mitigating the deleterious effects of protein accumulation, such as aggregation and misfolding, with precise modulation of chaperone production. Here, we develop a coarse model of the unfolded protein response in yeast, and use multi-objective optimization to determine which sensing and activation strategies optimally balance the trade-off between unfolded protein accumulation and chaperone production...
September 26, 2018: Molecular Biology of the Cell
Vera Pfanzagl, Wolfram Görner, Martin Radolf, Alexandra Parich, Rainer Schuhmacher, Joseph Strauss, Wolfgang Reiter, Christoph Schüller
In yeast, protein kinase A (PKA) adjusts transcriptional profiles, metabolic rates and cell growth in concordance with carbon source availability. PKA affects gene expression mostly via the transcription factors Msn2 and Msn4, two key regulators of the environmental stress response. Here we analyzed the role of the PKA-Msn2 signaling module by using an Msn2 allele that harbors serine to alanine substitutions at six functionally important PKA motifs (Msn2A6). Expression of Msn2A6 mimics low PKA activity, entails a transcription profile similar to respiring cells and prevents formation of colonies on glucose containing medium...
September 26, 2018: Molecular Biology of the Cell
Alicia McCarthy, Aron Deiulio, Elliot Todd Martin, Maitreyi Upadhyay, Prashanth Rangan
Germline stem cells (GSCs) self-renew and differentiate to sustain a continuous production of gametes. In the female Drosophila germ line, two differentiation factors, bag of marbles ( bam) and benign gonial cell neoplasm ( bgcn), work in concert in the stem cell daughter to promote the generation. In GSCs, bam transcription is repressed by signaling from the niche and is activated in stem cell daughters. In contrast, bgcn is transcribed in both the GSCs and stem cell daughters, but little is known about how bgcn is transcriptionally modulated...
September 19, 2018: Molecular Biology of the Cell
Li Liu, David E Levin
Stress-activated MAP kinases (SAPKs) respond to a wide variety of stressors. In most cases, the pathways through which specific stress signals are transmitted to the SAPKs are not known. The S. cerevisiae SAPK Mpk1 (Slt2) is a well-characterized component of the cell wall integrity (CWI) signaling pathway, which responds to physical and chemical challenges to the cell wall. However, Mpk1 is also activated in response to genotoxic stress through an unknown pathway. We show that, in contrast to cell wall stress, the pathway for Mpk1 activation by genotoxic stress does not involve the stimulation of the MAP kinase kinases (MEKs) that function immediately upstream of Mpk1...
September 19, 2018: Molecular Biology of the Cell
Chii Shyang Fong, Kanako Ozaki, Meng-Fu Bryan Tsou
Centriole to centrosome conversion (CCC) safeguards centriole homeostasis by coupling centriole duplication with segregation, and is essential for stabilization of mature vertebrate centrioles naturally devoid of the geometric scaffold or the cartwheel. Here we identified PPP1R35, a putative regulator of the protein phosphatase PP1, as a novel centriolar protein required for CCC. We found that PPP1R35 is enriched at newborn daughter centrioles in S or G2 phase. In the absence of PPP1R35, centriole assembly initiates normally in S phase, but none of the nascent centrioles can form active centrosomes or recruit CEP295, an essential factor for CCC...
September 19, 2018: Molecular Biology of the Cell
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