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Latest Articles Include:
- Building consensus
- Nature Cell Biology 12(1):1 (2010)
A group of Golgi researchers tackle controversies in the field head-on and emerge with a blueprint for future research. - Advising the government
- Nature Cell Biology 12(1):1 (2010)
The dismissal of a senior science advisor in the UK has lead to a debate on the role of expert advice in crafting public policy. - Accidental encounters: the chance to solve a mystery
- Nature Cell Biology 12(1):2 (2010)
Cells organize into tissues by adhering to one another. Such intercellular associations can be disrupted artificially and, under the right culture conditions, the dissociated cells can re-aggregate and reconstitute their original tissue-like structures, as demonstrated by early pioneering studies. - Two Rabs for exosome release
- Nature Cell Biology 12(1):3-4 (2010)
Exosomes are endosome-derived membrane vesicles that are key for intercellular communication in the immune system and elsewhere. Rab27A and Rab27B GTPases and two of their cognate effector proteins seem to be needed to drive the physiologically important exosome-release process in certain cell types. - Tensions divide
- Nature Cell Biology 12(1):5-7 (2010)
During development, proliferating cells are organized into compartments with boundaries across which cells fail to intermix. Compartment boundaries are often attributed to differential cell–cell adhesion between separate compartments. However, tension generated by actomyosin cables at boundaries can also function as a barrier that prevents cell mixing. - Myc and a Cdk2 senescence switch
- Nature Cell Biology 12(1):7-9 (2010)
Cdk2 has been shown to have an unanticipated role in suppressing Myc-induced senescence. This has implications for how c-Myc overcomes failsafe mechanisms to induce tumorigenesis and suggests that the inhibition of Cdk2 may have therapeutic efficacy in the treatment of cancer. - Research highlights
- Nature Cell Biology 12(1):10 (2010)
MicroRNAs (miRNAs) can act either as oncogenes or tumour suppressors when regulating mRNAs in cancer. The miRNA-processing factor, Dicer, is required for miRNA maturation and is essential for mouse development. - GM1 structure determines SV40-induced membrane invagination and infection
Ewers H Römer W Smith AE Bacia K Dmitrieff S Chai W Mancini R Kartenbeck J Chambon V Berland L Oppenheim A Schwarzmann G Feizi T Schwille P Sens P Helenius A Johannes L - Nature Cell Biology 12(1):11-18 (2010)
Incoming simian virus 40 (SV40) particles enter tight-fitting plasma membrane invaginations after binding to the carbohydrate moiety of GM1 gangliosides in the host cell plasma membrane through pentameric VP1 capsid proteins. This is followed by activation of cellular signalling pathways, endocytic internalization and transport of the virus via the endoplasmic reticulum to the nucleus. Here we show that the association of SV40 (as well as isolated pentameric VP1) with GM1 is itself sufficient to induce dramatic membrane curvature that leads to the formation of deep invaginations and tubules not only in the plasma membrane of cells, but also in giant unilamellar vesicles (GUVs). Unlike native GM1 molecules with long acyl chains, GM1 molecular species with short hydrocarbon chains failed to support such invagination, and endocytosis and infection did not occur. To conceptualize the experimental data, a physical model was derived based on energetic considerations. Taken t! ogether, our analysis indicates that SV40, other polyoma viruses and some bacterial toxins (Shiga and cholera) use glycosphingolipids and a common pentameric protein scaffold to induce plasma membrane curvature, thus directly promoting their endocytic uptake into cells. - Rab27a and Rab27b control different steps of the exosome secretion pathway
Ostrowski M Carmo NB Krumeich S Fanget I Raposo G Savina A Moita CF Schauer K Hume AN Freitas RP Goud B Benaroch P Hacohen N Fukuda M Desnos C Seabra MC Darchen F Amigorena S Moita LF Thery C - Nature Cell Biology 12(1):19-30 (2010)
Exosomes are secreted membrane vesicles that share structural and biochemical characteristics with intraluminal vesicles of multivesicular endosomes (MVEs). Exosomes could be involved in intercellular communication and in the pathogenesis of infectious and degenerative diseases. The molecular mechanisms of exosome biogenesis and secretion are, however, poorly understood. Using an RNA interference (RNAi) screen, we identified five Rab GTPases that promote exosome secretion in HeLa cells. Among these, Rab27a and Rab27b were found to function in MVE docking at the plasma membrane. The size of MVEs was strongly increased by Rab27a silencing, whereas MVEs were redistributed towards the perinuclear region upon Rab27b silencing. Thus, the two Rab27 isoforms have different roles in the exosomal pathway. In addition, silencing two known Rab27 effectors, Slp4 (also known as SYTL4, synaptotagmin-like 4) and Slac2b (also known as EXPH5, exophilin 5), inhibited exosome secretion an! d phenocopied silencing of Rab27a and Rab27b, respectively. Our results therefore strengthen the link between MVEs and exosomes, and introduce ways of manipulating exosome secretion in vivo. - Orphan nuclear receptor TLX activates Wnt/β-catenin signalling to stimulate neural stem cell proliferation and self-renewal
Qu Q Sun G Li W Yang S Ye P Zhao C Yu RT Gage FH Evans RM Shi Y - Nature Cell Biology 12(1):31-40 (2010)
The nuclear receptor TLX (also known as NR2E1) is essential for adult neural stem cell self-renewal; however, the molecular mechanisms involved remain elusive. Here we show that TLX activates the canonical Wnt/β-catenin pathway in adult mouse neural stem cells. Furthermore, we demonstrate that Wnt/β-catenin signalling is important in the proliferation and self-renewal of adult neural stem cells in the presence of epidermal growth factor and fibroblast growth factor. Wnt7a and active β-catenin promote neural stem cell self-renewal, whereas the deletion of Wnt7a or the lentiviral transduction of axin, a β-catenin inhibitor, led to decreased cell proliferation in adult neurogenic areas. Lentiviral transduction of active β-catenin led to increased numbers of type B neural stem cells in the subventricular zone of adult brains, whereas deletion of Wnt7a or TLX resulted in decreased numbers of neural stem cells retaining bromodeoxyuridine label in the adult brain. Both W! nt7a and active β-catenin significantly rescued a TLX (also known as Nr2e1) short interfering RNA-induced deficiency in neural stem cell proliferation. Lentiviral transduction of an active β-catenin increased cell proliferation in neurogenic areas of TLX-null adult brains markedly. These results strongly support the hypothesis that TLX acts through the Wnt/β-catenin pathway to regulate neural stem cell proliferation and self-renewal. Moreover, this study suggests that neural stem cells can promote their own self-renewal by secreting signalling molecules that act in an autocrine/paracrine mode. - Sec24b selectively sorts Vangl2 to regulate planar cell polarity during neural tube closure
Merte J Jensen D Wright K Sarsfield S Wang Y Schekman R Ginty DD - Nature Cell Biology 12(1):41-46 (2010)
Craniorachischisis is a rare but severe birth defect that results in a completely open neural tube. Mouse mutants in planar cell polarity (PCP) signalling components have deficits in the morphological movements of convergent extension that result in craniorachischisis. Using a forward genetic screen in mice, we identified Sec24b, a cargo-sorting member of the core complex of the endoplasmic reticulum (ER)-to-Golgi transport vesicle COPII, as critical for neural tube closure. Sec24bY613 mutant mice exhibit craniorachischisis, deficiencies in convergent extension and other PCP-related phenotypes. Vangl2, a key component of the PCP-signalling pathway critical for convergent extension, is selectively sorted into COPII vesicles by Sec24b. Moreover, Sec24bY613 genetically interacts with a loss-of-function Vangl2 allele (Vangl2LP), causing a marked increase in the prevalence of spina bifida. Interestingly, the Vangl2 looptail point mutants Vangl2D255E and Vangl2S464N, known t! o cause defects in convergent extension, fail to sort into COPII vesicles and are trapped in the ER. Thus, during COPII vesicle formation, Sec24b shows cargo specificity for a core PCP component, Vangl2, of which proper ER-to-Golgi transport is essential for the establishment of PCP, convergent extension and closure of the neural tube. - A role for Rho GTPases and cell–cell adhesion in single-cell motility in vivo
Kardash E Reichman-Fried M Maître JL Boldajipour B Papusheva E Messerschmidt EM Heisenberg CP Raz E - Nature Cell Biology 12(1):47-53 (2010)
Cell migration is central to embryonic development, homeostasis and disease1, processes in which cells move as part of a group or individually. Whereas the mechanisms controlling single-cell migration in vitro are relatively well understood2, 3, 4, less is known about the mechanisms promoting the motility of individual cells in vivo. In particular, it is not clear how cells that form blebs in their migration use those protrusions to bring about movement in the context of the three-dimensional cellular environment5, 6. Here we show that the motility of chemokine-guided germ cells within the zebrafish embryo requires the function of the small Rho GTPases Rac1 and RhoA, as well as E-cadherin-mediated cell–cell adhesion. Using fluorescence resonance energy transfer we demonstrate that Rac1 and RhoA are activated in the cell front. At this location, Rac1 is responsible for the formation of actin-rich structures, and RhoA promotes retrograde actin flow. We propose that the! se actin-rich structures undergoing retrograde flow are essential for the generation of E-cadherin-mediated traction forces between the germ cells and the surrounding tissue and are therefore crucial for cell motility in vivo. - Cdk2 suppresses cellular senescence induced by the c-myc oncogene
Campaner S Doni M Hydbring P Verrecchia A Bianchi L Sardella D Schleker T Perna D Tronnersjö S Murga M Fernandez-Capetillo O Barbacid M Larsson LG Amati B - Nature Cell Biology 12(1):54-59 (2010)
Activated oncogenes induce compensatory tumour-suppressive responses, such as cellular senescence or apoptosis, but the signals determining the main outcome remain to be fully understood1, 2. Here, we uncover a role for Cdk2 (cyclin-dependent kinase 2) in suppressing Myc-induced senescence. Short-term activation of Myc promoted cell-cycle progression3 in either wild-type or Cdk2 knockout4, 5 mouse embryo fibroblasts (MEFs). In the knockout MEFs, however, the initial hyper-proliferative response was followed by cellular senescence. Loss of Cdk2 also caused sensitization to Myc-induced senescence in pancreatic β-cells or splenic B-cells in vivo, correlating with delayed lymphoma onset in the latter. Cdk2−/− MEFs also senesced upon ectopic Wnt signalling or, without an oncogene, upon oxygen-induced culture shock6. Myc also causes senescence in cells lacking the DNA repair protein Wrn7. However, unlike loss of Wrn8, loss of Cdk2 did not enhance Myc-induced replication! stress, implying that these proteins suppress senescence through different routes. In MEFs, Myc-induced senescence was genetically dependent on the ARF–p53–p21Cip1 and p16INK4a–pRb pathways, p21Cip1 and p16INK4a being selectively induced in Cdk2−/− cells. Thus, although redundant for cell-cycle progression and development4, 5, 9, 10, 11, 12, Cdk2 has a unique role in suppressing oncogene- and/or stress-induced senescence1. Pharmacological inhibition of Cdk2 induced Myc-dependent senescence in various cell types, including a p53-null human cancer cell line. Our data warrant re-assessment of Cdk2 as a therapeutic target in Myc- or Wnt-driven tumours. - An actomyosin-based barrier inhibits cell mixing at compartmental boundaries in Drosophila embryos
Monier B Pélissier-Monier A Brand AH Sanson B - Nature Cell Biology 12(1):60-65 (2010)
Partitioning tissues into compartments that do not intermix is essential for the correct morphogenesis of animal embryos and organs1, 2, 3. Several hypotheses have been proposed to explain compartmental cell sorting, mainly differential adhesion1, 2, 3, 4, 5, 6, 7, 8, 9, but also regulation of the cytoskeleton10, 11 or of cell proliferation10, 12. Nevertheless, the molecular and cellular mechanisms that keep cells apart at boundaries remain unclear. Here we demonstrate, in early Drosophila melanogaster embryos, that actomyosin-based barriers stop cells from invading neighbouring compartments. Our analysis shows that cells can transiently invade neighbouring compartments, especially when they divide, but are then pushed back into their compartment of origin. Actomyosin cytoskeletal components are enriched at compartmental boundaries, forming cable-like structures when the epidermis is mitotically active. When MyoII (non-muscle myosin II) function is inhibited, including! locally at the cable by chromophore-assisted laser inactivation (CALI)13, 14, in live embryos, dividing cells are no longer pushed back, leading to compartmental cell mixing. We propose that local regulation of actomyosin contractibility, rather than differential adhesion, is the primary mechanism sorting cells at compartmental boundaries. - A bacterial E3 ubiquitin ligase IpaH9.8 targets NEMO/IKKγ to dampen the host NF-κB-mediated inflammatory response
Ashida H Kim M Schmidt-Supprian M Ma A Ogawa M Sasakawa C - Nature Cell Biology 12(1):66-73 (2010)
NF-κB (nuclear factor κB) has a pivotal role in many cellular processes, including the inflammatory and immune responses and, therefore, its activation is tightly regulated by the IKK (IκB kinase) complex and by IκBα degradation. When Shigella bacteria multiply within epithelial cells they release peptidoglycans, which are recognized by Nod1 and stimulate the NF-κB pathway, thus leading to a severe inflammatory response. Here, we show that IpaH9.8, a Shigella effector possessing E3 ligase activity, dampens the NF-κB-mediated inflammatory response to the bacterial infection in a unique way. IpaH9.8 interacts with NEMO/IKKγ and ABIN-1, a ubiquitin-binding adaptor protein, promoting ABIN-1-dependent polyubiquitylation of NEMO. Consequently, polyubiquitylated NEMO undergoes proteasome-dependent degradation, which perturbs NF-κB activation. As NEMO is essential for NF-κB activation, we propose that the polyubiquitylation and degradation of NEMO during Shigella inf! ection is a new bacterial strategy to modulate host inflammatory responses. - Defects in DNA ligase I trigger PCNA ubiquitylation at Lys 107
Das-Bradoo S Nguyen HD Wood JL Ricke RM Haworth JC Bielinsky AK - Nature Cell Biology 12(1):74-79 (2010)
In all eukaryotes, the ligation of newly synthesized DNA, also known as Okazaki fragments, is catalysed by DNA ligase I (ref. 1). An individual with a DNA ligase I deficiency exhibits growth retardation, sunlight sensitivity and severe immunosuppression2, probably due to accumulation of DNA damage. Surprisingly, not much is known about the DNA damage response (DDR) in DNA ligase I-deficient cells. As DNA replication and DDR pathways are highly conserved in eukaryotes, we used Saccharomyces cerevisiae as a model system to address this issue. We uncovered a new pathway, which facilitates ubiquitylation at Lys 107 of proliferating cell nuclear antigen (PCNA). Unlike ubiquitylation at Lys 164 of PCNA in response to UV irradiation, which triggers translesion synthesis3, modification of Lys 107 is not dependent on the ubiquitin conjugating enzyme (E2) Rad6 (ref. 4) nor the ubiquitin ligase (E3) Rad18 (ref. 5), but requires the E2 variant Mms2 (ref. 6) in conjunction with Ubc! 4 (ref. 7) and the E3 Rad5 (Refs 8, 9). Surprisingly, DNA ligase I-deficient S. cerevisiae cdc9-1 cells that carry a PCNAK107R mutation are inviable, because they cannot activate a robust DDR. Furthermore, we show that ubiquitylation of PCNA in response to DNA ligase I deficiency is conserved in humans, yet the lysine residue that is modified remains to be determined. We propose that PCNA ubiquitylation provides a 'DNA damage code' that allows cells to categorize different types of defects that arise during DNA replication. - HERC2 coordinates ubiquitin-dependent assembly of DNA repair factors on damaged chromosomes
Bekker-Jensen S Danielsen JR Fugger K Gromova I Nerstedt A Bartek J Lukas J Mailand N - Nature Cell Biology 12(1):80-86 (2010)
Regulatory ubiquitylation is emerging as an important mechanism to protect genome integrity in cells exposed to DNA damage1, 2, 3, 4, 5, 6, 7, 8, 9. However, the spectrum of known ubiquitin regulators of the DNA damage response (DDR) is limited and their functional interplay is poorly understood. Here, we identify HERC2 as a factor that regulates ubiquitin-dependent retention of repair proteins on damaged chromosomes. In response to ionising radiation (IR), HERC2 forms a complex with RNF8, a ubiquitin ligase involved in the DDR3, 4, 5, 6. The HERC2–RNF8 interaction requires IR-inducible phosphorylation of HERC2 at Thr 4827, which in turn binds to the forkhead-associated (FHA) domain of RNF8. Mechanistically, we provide evidence that HERC2 facilitates assembly of the ubiquitin-conjugating enzyme Ubc13 with RNF8, thereby promoting DNA damage-induced formation of Lys 63-linked ubiquitin chains. We also show that HERC2 interacts with, and maintains the levels of, RNF168,! another ubiquitin ligase operating downstream of RNF8 (Refs 7, 8). Consequently, knockdown of HERC2 abrogates ubiquitin-dependent retention of repair factors such as 53BP1, RAP80 and BRCA1. Together with the increased radiosensitivity of HERC2-depleted cells, these results uncover a regulatory layer in the orchestration of protein interactions on damaged chromosomes and they underscore the role of ubiquitin-mediated signalling in genome maintenance. - Carbonic anhydrases are upstream regulators of CO2-controlled stomatal movements in guard cells
Hu H Boisson-Dernier A Israelsson-Nordström M Böhmer M Xue S Ries A Godoski J Kuhn JM Schroeder JI - Nature Cell Biology 12(1):87-93 (2010)
The continuing rise in atmospheric CO2 causes stomatal pores in leaves to close and thus globally affects CO2 influx into plants, water use efficiency and leaf heat stress1, 2, 3, 4. However, the CO2-binding proteins that control this response remain unknown. Moreover, which cell type responds to CO2, mesophyll or guard cells, and whether photosynthesis mediates this response are matters of debate5, 6, 7, 8. We demonstrate that Arabidopsis thaliana double-mutant plants in the β-carbonic anhydrases βCA1 and βCA4 show impaired CO2-regulation of stomatal movements and increased stomatal density, but retain functional abscisic-acid and blue-light responses. βCA-mediated CO2-triggered stomatal movements are not, in first-order, linked to whole leaf photosynthesis and can function in guard cells. Furthermore, guard cell βca-overexpressing plants exhibit instantaneous enhanced water use efficiency. Guard cell expression of mammalian αCAII complements the reduced sensiti! vity of ca1 ca4 plants, showing that carbonic anhydrase-mediated catalysis is an important mechanism for βCA-mediated CO2-induced stomatal closure and patch clamp analyses indicate that CO2/HCO3− transfers the signal to anion channel regulation. These findings, together with ht1-2 (ref. 9) epistasis analysis demonstrate that carbonic anhydrases function early in the CO2 signalling pathway, which controls gas-exchange between plants and the atmosphere. - Maintenance of a constitutive heterochromatin domain in vertebrates by a Dicer-dependent mechanism
Giles KE Ghirlando R Felsenfeld G - Nature Cell Biology 12(1):94-99 (2010)
The 16 kilobase (kb) heterochromatin domain between the chicken β-globin locus and the folate receptor gene is used here to study the roles of RNA-dependent mechanisms and histone modifications in the maintenance of a constitutive heterochromatic structure. Inhibition of histone deacetylase (HDAC) activity is shown to both increase intergenic transcription and render the heterochromatin more accessible to MspI digestion. We show that short interfering RNA (siRNA)-mediated downregulation of the enzyme Dicer has similar effects: histone acetylation is increased, transcript levels rise and the compact chromatin structure becomes more accessible to restriction endonucleases. We also show that the chicken Argonaute 2 homologue binds the 16 kb region in a Dicer-dependent manner and is necessary for a condensed chromatin structure. Heterochromatic domains of this kind, which are widely distributed in vertebrate genomes, thus seem to be maintained in their condensed form by h! ighly conserved mechanisms.
