Hot off the presses! Jun 01 njobs

The Jun 01 issue of the njobs is now up on Pubget (About njobs): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• Don't hang UK science
  - njobs 12(6):521 (2010)
  The formation of a coalition government led by David Cameron has ended the uncertainty following the general election in the United Kingdom. Although the challenges facing a coalition government are immense, securing the future of UK science must remain a priority.
• α-catenin mechanosensing for adherens junctions
  - njobs 12(6):522-524 (2010)
  The balance of cohesion and remodelling is essential for the integrity and morphogenesis of epithelia. This requires adhesion and transmission of actomyosin tension, both of which are mediated by E-cadherin. The finding that actomyosin tension reinforces mechanical coupling of actin to E-cadherin through α-catenin reveals similarities with integrin regulation.
• Nuclear mRNA on the move
  - njobs 12(6):525-527 (2010)
  Innovations in live-cell microscopy and single-molecule analysis have allowed a new direct view of nuclear messenger RNA dynamics. A new study extends previous analyses of mRNA-protein intranuclear transport and links this critical step to the kinetics of moving through nuclear pore complexes. Seeing nuclear mRNA on the move will impact future work on pore translocation and nuclear organization.
• A new chisel for sculpting Darwin's endless forms
  - njobs 12(6):528-529 (2010)
  The distribution of secreted morphogens in a developing organ determines its form by instructing size, shape and pattern. Pentagone has been identified as a secreted factor that controls the distribution of the morphogen Decapentaplegic (Dpp) in the Drosophila melanogaster wing.
• Research highlights
  - njobs 12(6):530 (2010)
  A fragile link between ES and iPS cells 'Ragulating' mTORC1 activation An EMAP for mechanosensing Cancer cell invasion: breaking down the wall
• α-Catenin as a tension transducer that induces adherens junction development
  - njobs 12(6):533-542 (2010)
  Adherens junctions (AJs), which are organized by adhesion proteins and the underlying actin cytoskeleton, probably sense pulling forces from adjacent cells and modulate opposing forces to maintain tissue integrity, but the regulatory mechanism remains unknown at the molecular level. Although the possibility that α-catenin acts as a direct linker between the membrane and the actin cytoskeleton for AJ formation and function has been minimized, here we show that α-catenin recruits vinculin, another main actin-binding protein of AJs, through force-dependent changes in α-catenin conformation. We identified regions in the α-catenin molecule that are required for its force-dependent binding of vinculin by introducing mutant α-catenin into cells and using in vitro binding assays. Fluorescence recovery after photobleaching analysis for α-catenin mobility and the existence of an antibody recognizing α-catenin in a force-dependent manner further supported the notion that �! �-catenin is a tension transducer that translates mechanical stimuli into a chemical response, resulting in AJ development.
• Dynamics of single mRNP nucleocytoplasmic transport and export through the nuclear pore in living cells
  - njobs 12(6):543-552 (2010)
  The flow of genetic information in eukaryotic cells occurs through the nucleocytoplasmic translocation of mRNAs. Knowledge of in vivo messenger RNA export kinetics remains poor in comparison with that of protein transport. We have established a mammalian system that allowed the real-time visualization and quantification of large single mRNA–protein complexes (mRNPs) during export. The in vivo dynamics of bulk mRNP transport and export, from transcription to the nuclear pore complex (NPC), occurred within a 5–40 minute time frame, with no NPC pile-up. mRNP export was rapid (about 0.5 s) and kinetically faster than nucleoplasmic diffusion. Export inhibition demonstrated that mRNA–NPC interactions were independent of ongoing export. Nucleoplasmic transport dynamics of intron-containing and intronless mRNAs were similar, yet an intron did increase export efficiency. Here we provide visualization and analysis at the single mRNP level of the various steps in nuclear ge! ne expression and the inter-chromatin tracks through which mRNPs diffuse, and demonstrate the kinetics of mRNP–NPC interactions and translocation.
• MTCH2/MIMP is a major facilitator of tBID recruitment to mitochondria
  Zaltsman Y Shachnai L Yivgi-Ohana N Schwarz M Maryanovich M Houtkooper RH Vaz FM De Leonardis F Fiermonte G Palmieri F Gillissen B Daniel PT Jimenez E Walsh S Koehler CM Roy SS Walter L Hajnóczky G Gross A - njobs 12(6):553-562 (2010)
  The BH3-only BID protein (BH3-interacting domain death agonist) has a critical function in the death-receptor pathway in the liver by triggering mitochondrial outer membrane permeabilization (MOMP). Here we show that MTCH2/MIMP (mitochondrial carrier homologue 2/Met-induced mitochondrial protein), a novel truncated BID (tBID)-interacting protein, is a surface-exposed outer mitochondrial membrane protein that facilitates the recruitment of tBID to mitochondria. Knockout of MTCH2/MIMP in embryonic stem cells and in mouse embryonic fibroblasts hinders the recruitment of tBID to mitochondria, the activation of Bax/Bak, MOMP, and apoptosis. Moreover, conditional knockout of MTCH2/MIMP in the liver decreases the sensitivity of mice to Fas-induced hepatocellular apoptosis and prevents the recruitment of tBID to liver mitochondria both in vivo and in vitro. In contrast, MTCH2/MIMP deletion had no effect on apoptosis induced by other pro-apoptotic Bcl-2 family members and no de! tectable effect on the outer membrane lipid composition. These loss-of-function models indicate that MTCH2/MIMP has a critical function in liver apoptosis by regulating the recruitment of tBID to mitochondria.
• The role of Cdk5-mediated apurinic/apyrimidinic endonuclease 1 phosphorylation in neuronal death
  - njobs 12(6):563-571 (2010)
  Accumulating evidence suggests that deregulated cyclin-dependent kinase 5 (Cdk5) plays a critical part in neuronal death. However, the pathogenic targets of Cdk5 are not fully defined. Here we demonstrate that the Cdk5 activator p35 interacts directly with apurinic/apyrimidinic endonuclease 1 (Ape1), a protein crucial for base excision repair (BER) following DNA damage. Cdk5 complexes phosphorylate Ape1 at Thr 232 and thereby reduces its apurinic/apyrimidinic (AP) endonuclease activity. Ape1 phosphorylation is dependent on Cdk5 in in vitro and in vivo. The reduced endonuclease activity of phosphorylated Ape1 results in accumulation of DNA damage and contributes to neuronal death. Overexpression of Ape1WT and Ape1T232A, but not the phosphorylation mimic Ape1T232E, protects neurons against MPP+/MPTP. Loss of Ape1 sensitizes neurons to death. Importantly, increased phosphorylated Ape1 was also observed in post-mortem brain tissue from patients with Parkinson's and Alzheim! er's diseases, suggesting a potential link between Ape1 phosphorylation and the pathogenesis of neurodegenerative diseases.
• Bcl-2 and accelerated DNA repair mediates resistance of hair follicle bulge stem cells to DNA-damage-induced cell death
  - njobs 12(6):572-582 (2010)
  Adult stem cells (SCs) are at high risk of accumulating deleterious mutations because they reside and self-renew in adult tissues for extended periods. Little is known about how adult SCs sense and respond to DNA damage within their natural niche. Here, using mouse epidermis as a model, we define the functional consequences and the molecular mechanisms by which adult SCs respond to DNA damage. We show that multipotent hair-follicle-bulge SCs have two important mechanisms for increasing their resistance to DNA-damage-induced cell death: higher expression of the anti-apoptotic gene Bcl-2 and transient stabilization of p53 after DNA damage in bulge SCs. The attenuated p53 activation is the consequence of a faster DNA repair activity, mediated by a higher non-homologous end joining (NHEJ) activity, induced by the key protein DNA-PK. Because NHEJ is an error-prone mechanism, this novel characteristic of adult SCs may have important implications in cancer development and age! ing.
• AMPK controls the speed of microtubule polymerization and directional cell migration through CLIP-170 phosphorylation
  - njobs 12(6):583-590 (2010)
  AMP-activated protein kinase (AMPK) is an energy-sensing Ser/Thr protein kinase originally shown to be regulated by AMP1. AMPK is activated by various cellular stresses that inhibit ATP production or stimulate ATP consumption2. In addition to its role in metabolism, AMPK has recently been reported to reshape cells by regulating cell polarity and division3, 4, 5, 6. However, the downstream targets of AMPK that participate in these functions have not been fully identified. Here, we show that phosphorylation of the microtubule plus end protein CLIP-170 by AMPK is required for microtubule dynamics and the regulation of directional cell migration. Both inhibition of AMPK and expression of a non-phosphorylatable CLIP-170 mutant resulted in prolonged and enhanced accumulation of CLIP-170 at microtubule tips, and slower tubulin polymerization. Furthermore, inhibition of AMPK impaired microtubule stabilization and perturbed directional cell migration. All of these phenotypes we! re rescued by expression of a phosphomimetic CLIP-170 mutant. Our results demonstrate, therefore, that AMPK controls basic cellular functions by regulating microtubule dynamics through CLIP-170 phosphorylation.
• Light-mediated activation reveals a key role for Rac in collective guidance of cell movement in vivo
  - njobs 12(6):591-597 (2010)
  The small GTPase Rac induces actin polymerization, membrane ruffling and focal contact formation in cultured single cells1 but can either repress or stimulate motility in epithelial cells depending on the conditions2, 3. The role of Rac in collective epithelial cell movements in vivo, which are important for both morphogenesis and metastasis4, 5, 6, 7, is therefore difficult to predict. Recently, photoactivatable analogues of Rac (PA-Rac) have been developed, allowing rapid and reversible activation or inactivation of Rac using light8. In cultured single cells, light-activated Rac leads to focal membrane ruffling, protrusion and migration. Here we show that focal activation of Rac is also sufficient to polarize an entire group of cells in vivo, specifically the border cells of the Drosophila ovary. Moreover, activation or inactivation of Rac in one cell of the cluster caused a dramatic response in the other cells, suggesting that the cells sense direction as a group ac! cording to relative levels of Rac activity. Communication between cells of the cluster required Jun amino-terminal kinase (JNK) but not guidance receptor signalling. These studies further show that photoactivatable proteins are effective tools in vivo.
• A distinctive role for focal adhesion proteins in three-dimensional cell motility
  - njobs 12(6):598-604 (2010)
  Focal adhesions are large multi-protein assemblies that form at the basal surface of cells on planar dishes, and that mediate cell signalling, force transduction and adhesion to the substratum. Although much is known about focal adhesion components in two-dimensional (2D) systems, their role in migrating cells in a more physiological three-dimensional (3D) matrix is largely unknown. Live-cell microscopy shows that for cells fully embedded in a 3D matrix, focal adhesion proteins, including vinculin, paxillin, talin, α-actinin, zyxin, VASP, FAK and p130Cas, do not form aggregates but are diffusely distributed throughout the cytoplasm. Despite the absence of detectable focal adhesions, focal adhesion proteins still modulate cell motility, but in a manner distinct from cells on planar substrates. Rather, focal adhesion proteins in matrix-embedded cells regulate cell speed and persistence by affecting protrusion activity and matrix deformation, two processes that have no d! irect role in controlling 2D cell speed. This study shows that membrane protrusions constitute a critical motility/matrix-traction module that drives cell motility in a 3D matrix.
• RhoL controls invasion and Rap1 localization during immune cell transmigration in Drosophila
  - njobs 12(6):605-610 (2010)
  Human immune cells have to penetrate an endothelial barrier during their beneficial pursuit of infection and their destructive infiltration of tissues in autoimmune diseases. This transmigration requires Rap1 GTPase to activate integrin affinity1. We define a new model system for this process by demonstrating, with live imaging and genetics, that during embryonic development Drosophila melanogaster immune cells penetrate an epithelial, Drosophila E-cadherin (DE-cadherin)-based tissue barrier. A mutant in RhoL, a GTPase homologue that is specifically expressed in haemocytes, blocks this invasive step but not other aspects of guided migration. RhoL mediates integrin adhesion caused by Drosophila Rap1 overexpression and moves Rap1 away from a concentration in the cytoplasm to the leading edge during invasive migration. These findings indicate that a programmed migratory step during Drosophila development bears striking molecular similarities to vertebrate immune cell tran! smigration during inflammation, and identify RhoL as a new regulator of invasion, adhesion and Rap1 localization. Our work establishes the utility of Drosophila for identifying novel components of immune cell transmigration and for understanding the in vivo interplay of immune cells with the barriers they penetrate.
• Control of Dpp morphogen signalling by a secreted feedback regulator
  - njobs 12(6):611-617 (2010)
  In many instances during development, morphogens specify cell fates by forming concentration gradients. In the Drosophila melanogaster wing imaginal disc, Decapentaplegic (Dpp), a bone morphogenetic protein (BMP), functions as a long-range morphogen to control patterning and growth1. Dpp is secreted from a stripe of cells at the anterior-posterior compartment boundary and spreads into both compartments to generate a characteristic BMP activity gradient2, 3, 4, 5, 6. Ever since the identification of the morphogen activity of Dpp in the developing wing, the system has served as a paradigm to understand how long-range gradients are established and how cells respond to such gradients. Here we reveal the tight and direct connection of these two processes with the identification and characterization of pentagone (pent), a transcriptional target of BMP signalling encoding a secreted regulator of the pathway. Absence of pent in the wing disc causes a severe contraction of the ! BMP activity gradient resulting in patterning and growth defects. We show that Pent interacts with the glypican Dally to control Dpp distribution and provide evidence that proper establishment of the BMP morphogen gradient requires the inbuilt feedback loop embodied by Pent.
• Jarid2 is a PRC2 component in embryonic stem cells required for multi-lineage differentiation and recruitment of PRC1 and RNA Polymerase II to developmental regulators
  - njobs 12(6):618-624 (2010)
  Polycomb Repressor Complexes (PRCs) are important regulators of embryogenesis. In embryonic stem (ES) cells many genes that regulate subsequent stages in development are enriched at their promoters for PRC1, PRC2 and Ser 5-phosphorylated RNA Polymerase II (RNAP), and contain domains of 'bivalent' chromatin (enriched for H3K4me3; histone H3 di- or trimethylated at Lys 4 and H3K27me3; histone H3 trimethylated at Lys 27). Loss of individual PRC components in ES cells can lead to gene de-repression and to unscheduled differentiation. Here we show that Jarid2 is a novel subunit of PRC2 that is required for the co-recruitment of PRC1 and RNAP to genes that regulate development in ES cells. Jarid2-deficient ES cells showed reduced H3K4me2/me3 and H3K27me3 marking and PRC1/PRC2 recruitment, and did not efficiently establish Ser 5-phosporylated RNAP at target genes. ES cells lacking Jarid2, in contrast to previously characterized PRC1 and PRC2 mutants, did not inappropriately e! xpress PRC2 target genes. Instead, they show a severely compromised capacity for successful differentiation towards neural or mesodermal fates and failed to correctly initiate lineage-specific gene expression in vitro. Collectively, these data indicate that transcriptional priming of bivalent genes in pluripotent ES cells is Jarid2-dependent, and suggests that priming is critical for subsequent multi-lineage differentiation.
• Targeting WW domains linker of HECT-type ubiquitin ligase Smurf1 for activation by CKIP-1
  - njobs 12(6):625 (2010)
  Introduction ; published online 20 July 2009; corrected after print, 27 April 2010 In the version of this letter initially published online, Fig. 1c (middle panel), Fig. 3a (bottom panels) and Fig. 3c (bottom panel) were incorrectly labelled. The corrected labelling is shown below. These errors have been corrected in both the HTML and PDF versions of the letter.
• Regulation of NF-κB inhibitor IκBα and viral replication by a KSHV microRNA
  - njobs 12(6):625 (2010)
  Introduction ; published online 17 January 2010; corrected after print, 29 April 2010 In the version of the article originally published, the lanes corresponding to WT and ΔmiRs_rt were duplicated in Figure S1b. New data from an independent experiment are presented below. The conclusions remain unaltered.