CDK1-CCNB1 creates a spindle checkpoint-permissive state by enabling MPS1 kinetochore localization
Spindle checkpoint signaling is initiated by recruitment of the kinase MPS1 to unattached kinetochores during mitosis. We show that CDK1-CCNB1 and a counteracting phosphatase PP2A-B55 regulate the engagement of human MPS1 with unattached kinetochores by controlling the phosphorylation status of S281 in the kinetochore-binding domain. This regulation is essential for checkpoint signaling, since MPS1S281A is not recruited to unattached kinetochores and fails to support the recruitment of other checkpoint proteins. Directly tethering MPS1S281A to the kinetochore protein Mis12 bypasses this regulation and hence the requirement...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Hayward, D., Alfonso-Perez, T., Cundell, M. J., Hopkins, M., Holder, J., Bancroft, J., Hutter, L. H., Novak, B., Barr, F. A., Gruneberg, U. Tags: Cell Cycle and Division, Biochemistry, Systems and Computational Biology Articles Source Type: research
CDK1-mediated phosphorylation at H2B serine 6 is required for mitotic chromosome segregation
Faithful mitotic chromosome segregation is required for the maintenance of genomic stability. We discovered the phosphorylation of histone H2B at serine 6 (H2B S6ph) as a new chromatin modification site and found that this modification occurs during the early mitotic phases at inner centromeres and pericentromeric heterochromatin. This modification is directly mediated by cyclin B1–associated CDK1, and indirectly by Aurora B, and is antagonized by PP1-mediated dephosphorylation. H2B S6ph impairs chromatin binding of the histone chaperone SET (I2PP2A), which is important for mitotic fidelity. Injection of phosphorylat...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Seibert, M., Krüger, M., Watson, N. A., Sen, O., Daum, J. R., Slotman, J. A., Braun, T., Houtsmuller, A. B., Gorbsky, G. J., Jacob, R., Kracht, M., Higgins, J. M. G., Schmitz, M. L. Tags: Cell Cycle and Division, Biochemistry, Cancer Articles Source Type: research
Mitotic chromosome alignment ensures mitotic fidelity by promoting interchromosomal compaction during anaphase
Chromosome alignment at the equator of the mitotic spindle is a highly conserved step during cell division; however, its importance to genomic stability and cellular fitness is not understood. Normal mammalian somatic cells lacking KIF18A function complete cell division without aligning chromosomes. These alignment-deficient cells display normal chromosome copy numbers in vitro and in vivo, suggesting that chromosome alignment is largely dispensable for maintenance of euploidy. However, we find that loss of chromosome alignment leads to interchromosomal compaction defects during anaphase, abnormal organization of chromosom...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Fonseca, C. L., Malaby, H. L. H., Sepaniac, L. A., Martin, W., Byers, C., Czechanski, A., Messinger, D., Tang, M., Ohi, R., Reinholdt, L. G., Stumpff, J. Tags: Cell Cycle and Division, Genetics Articles Source Type: research
Type I myosins anchor actin assembly to the plasma membrane during clathrin-mediated endocytosis
The actin cytoskeleton generates forces on membranes for a wide range of cellular and subcellular morphogenic events, from cell migration to cytokinesis and membrane trafficking. For each of these processes, filamentous actin (F-actin) interacts with membranes and exerts force through its assembly, its associated myosin motors, or both. These two modes of force generation are well studied in isolation, but how they are coordinated in cells is mysterious. During clathrin-mediated endocytosis, F-actin assembly initiated by the Arp2/3 complex and several proteins that compose the WASP/myosin complex generates the force necess...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Pedersen, R. T. A., Drubin, D. G. Tags: Cytoskeleton, Biophysics, Genetics Reports Source Type: research
An amphipathic helix enables septins to sense micrometer-scale membrane curvature
Cell shape is well described by membrane curvature. Septins are filament-forming, GTP-binding proteins that assemble on positive, micrometer-scale curvatures. Here, we examine the molecular basis of curvature sensing by septins. We show that differences in affinity and the number of binding sites drive curvature-specific adsorption of septins. Moreover, we find septin assembly onto curved membranes is cooperative and show that geometry influences higher-order arrangement of septin filaments. Although septins must form polymers to stay associated with membranes, septin filaments do not have to span micrometers in length to ...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Cannon, K. S., Woods, B. L., Crutchley, J. M., Gladfelter, A. S. Tags: Cytoskeleton, Biochemistry Reports Source Type: research
Degradation of Blos1 mRNA by IRE1 repositions lysosomes and protects cells from stress
Cells respond to stress in the ER by initiating the widely conserved unfolded protein response. Activation of the ER transmembrane nuclease IRE1 leads to the degradation of specific mRNAs, but how this pathway affects the ability of cells to recover from stress is not known. Here, we show that degradation of the mRNA encoding biogenesis of lysosome-related organelles 1 subunit 1 (Blos1) leads to the repositioning of late endosomes (LEs)/lysosomes to the microtubule-organizing center in response to stress in mouse cells. Overriding Blos1 degradation led to ER stress sensitivity and the accumulation of ubiquitinated protein ...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Bae, D., Moore, K. A., Mella, J. M., Hayashi, S. Y., Hollien, J. Tags: Organelles, Protein Homeostasis Reports Source Type: research
MAD1-dependent recruitment of CDK1-CCNB1 to kinetochores promotes spindle checkpoint signaling
Cyclin B–dependent kinase (CDK1-CCNB1) promotes entry into mitosis. Additionally, it inhibits mitotic exit by activating the spindle checkpoint. This latter role is mediated through phosphorylation of the checkpoint kinase MPS1 and other spindle checkpoint proteins. We find that CDK1-CCNB1 localizes to unattached kinetochores and like MPS1 is lost from these structures upon microtubule attachment. This suggests that CDK1-CCNB1 is an integral component and not only an upstream regulator of the spindle checkpoint pathway. Complementary proteomic and cell biological analysis demonstrate that the spindle checkpoint prote...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Alfonso-Perez, T., Hayward, D., Holder, J., Gruneberg, U., Barr, F. A. Tags: Cell Cycle and Division, Biochemistry Reports Source Type: research
Advances in understanding DNA processing and protection at stalled replication forks
The replisome, the molecular machine dedicated to copying DNA, encounters a variety of obstacles during S phase. Without a proper response to this replication stress, the genome becomes unstable, leading to disease, including cancer. The immediate response is localized to the stalled replisome and includes protection of the nascent DNA. A number of recent studies have provided insight into the factors recruited to and responsible for protecting stalled replication forks. In response to replication stress, the SNF2 family of DNA translocases has emerged as being responsible for remodeling replication forks in vivo. The prot...
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Rickman, K., Smogorzewska, A. Tags: Review Source Type: research
Enabling migration by moderation: YAP/TAZ are essential for persistent migration
Persistent cell migration plays a crucial role in physiological processes, but its underlying mechanisms of regulation remain unclear. Mason et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201806065) show that YAP/TAZ limit cytoskeletal tension, which is essential for persistent (but not initiation of) cell migration. Potential implications of this study range from embryonic development to metastasis. (Source: Journal of Cell Biology)
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Nair, P. R., Wirtz, D. Tags: Cytoskeleton, Migration, Motility, Biophysics Spotlight Source Type: research
Getting a handle on lipid droplets: Insights into ER-lipid droplet tethering
Lipid droplets (LDs) are hubs for lipid metabolism that form membrane contact sites with multiple organelles. In this issue, Hariri et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808119) reveal the functions of Mdm1-mediated endoplasmic reticulum (ER)–LD tethering in yeast and Datta et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808133) identify a role for the Mdm1 orthologue, Snx14, as an ER–LD tether that regulates lipid metabolism in human cells. (Source: Journal of Cell Biology)
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Nguyen, T. B., Olzmann, J. A. Tags: Organelles, Biochemistry, Metabolism Spotlight Source Type: research
No chromosome left behind: The importance of metaphase alignment for mitotic fidelity
Chromosome alignment is a hallmark of mitosis in metazoans, but the physiological relevance of this orderly behavior has remained unclear. In this issue, Fonseca et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201807228) show that chromosome alignment ensures mitotic fidelity by promoting interchromosomal compaction during anaphase. (Source: Journal of Cell Biology)
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: Orr, B., Maiato, H. Tags: Cell Cycle and Division, Cancer Spotlight Source Type: research
The long and short of membrane curvature sensing by septins
Septin proteins form hetero-oligomers that associate with membranes of specific curvatures, but the mechanism is unknown. In this issue, Cannon et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201807211) identify a single amphipathic helix that is necessary and sufficient for membrane curvature sensing by septins. (Source: Journal of Cell Biology)
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: McMurray, M. A. Tags: Spotlight Source Type: research
Lillian Fritz-Laylin: Keeping up to speed with evolutionary cell biology
Fritz-Laylin studies the evolution of complex protein networks associated with cell movement. (Source: Journal of Cell Biology)
Source: Journal of Cell Biology - March 31, 2019 Category: Cytology Authors: ODonnell, M. A. Tags: People & amp;amp; Ideas Source Type: research
A high-avidity biosensor reveals plasma membrane PI(3,4)P2 is predominantly a class I PI3K signaling product
Class I phosphoinositide 3-OH kinase (PI3K) signaling is central to animal growth and metabolism, and pathological disruption of this pathway affects cancer and diabetes. However, the specific spatial/temporal dynamics and signaling roles of its minor lipid messenger, phosphatidylinositol (3,4)-bisphosphate (PI(3,4)P2), are not well understood. This owes principally to a lack of tools to study this scarce lipid. Here we developed a high-sensitivity genetically encoded biosensor for PI(3,4)P2, demonstrating high selectivity and specificity of the sensor for the lipid. We show that despite clear evidence for class II PI3K in...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Goulden, B. D., Pacheco, J., Dull, A., Zewe, J. P., Deiters, A., Hammond, G. R. V. Tags: Cell Signaling, Membrane and Lipid Biology, Biochemistry Tools Source Type: research
Molecular determinants of ER-Golgi contacts identified through a new FRET-FLIM system
ER–TGN contact sites (ERTGoCS) have been visualized by electron microscopy, but their location in the crowded perinuclear area has hampered their analysis via optical microscopy as well as their mechanistic study. To overcome these limits we developed a FRET-based approach and screened several candidates to search for molecular determinants of the ERTGoCS. These included the ER membrane proteins VAPA and VAPB and lipid transfer proteins possessing dual (ER and TGN) targeting motifs that have been hypothesized to contribute to the maintenance of ERTGoCS, such as the ceramide transfer protein CERT and several members o...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Venditti, R., Rega, L. R., Masone, M. C., Santoro, M., Polishchuk, E., Sarnataro, D., Paladino, S., DAuria, S., Varriale, A., Olkkonen, V. M., Di Tullio, G., Polishchuk, R., De Matteis, M. A. Tags: Organelles, Metabolism Tools Source Type: research
