Prime movers : mechanochemistry of mitotic kinesins

Mitotic spindles are self-organizing protein machines that harness teams of multiple force generators to drive chromosome segregation. Kinesins are key members of these force-generating teams. Different kinesins walk directionally along dynamic microtubules, anchor, crosslink, align and sort microtubules into polarized bundles, and influence microtubule dynamics by interacting with microtubule tips. The mechanochemical mechanisms of these kinesins are specialized to enable each type to make a specific contribution to spindle self-organization and chromosome segregation

Developmentally regulated GTP binding protein 1 (DRG1) controls microtubule dynamics

The mitotic spindle, essential for segregating the sister chromatids into the two evolving daughter cells, is composed of highly dynamic cytoskeletal filaments, the microtubules. The dynamics of microtubules are regulated by numerous microtubule associated proteins. We identify here Developmentally regulated GTP binding protein 1 (DRG1) as a microtubule binding protein with diverse microtubule-associated functions. In vitro, DRG1 can diffuse on microtubules, promote their polymerization, drive microtubule formation into bundles, and stabilize microtubules. HeLa cells with reduced DRG1 levels show delayed progression from prophase to anaphase because spindle formation is slowed down. To perform its microtubule-associated functions, DRG1, although being a GTPase, does not require GTP hydrolysis. However, all domains are required as truncated versions show none of the mentioned activities besides microtubule binding

Diffusion of Myosin V on Microtubules: A Fine-Tuned Interaction for Which E-Hooks Are Dispensable

Organelle transport in eukaryotes employs both microtubule and actin tracks to deliver cargo effectively to their destinations, but the question of how the two systems cooperate is still largely unanswered. Recently, in vitro studies revealed that the actin-based processive motor myosin V also binds to, and diffuses along microtubules. This biophysical trick enables cells to exploit both tracks for the same transport process without switching motors. The detailed mechanisms underlying this behavior remain to be solved. By means of single molecule Total Internal Reflection Microscopy (TIRFM), we show here that electrostatic tethering between the positively charged loop 2 and the negatively charged C-terminal E-hooks of microtubules is dispensable. Furthermore, our data indicate that in addition to charge-charge interactions, other interaction forces such as non-ionic attraction might account for myosin V diffusion. These findings provide evidence for a novel way of myosin tethering to microtubules that does not interfere with other E-hook-dependent processes

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Long-term monitoring of the ANTARES optical module efficiencies using K-40 decays in sea water

[EN] Cherenkov light induced by radioactive decay products is one of the major sources of background light for deep-sea neutrino telescopes such as ANTARES. These decays are at the same time a powerful calibration source. Using data collected by the ANTARES neutrino telescope from mid 2008 to 2017, the time evolution of the photon detection ef¿ciency of optical modules is studied. A modest loss of only 20% in 9 years is observed. The relative time calibration between adjacent modules is derived as well.Albert, A.; Andre, M.; Anghinolfi, M.; Anton, G.; Ardid Ramírez, M.; Aubert, J.; Aublin, J.... (2018). Long-term monitoring of the ANTARES optical module efficiencies using K-40 decays in sea water. The European Physical Journal C. 78(8):1-8. https://doi.org/10.1140/epjc/s10052-018-6132-2S18788M. Ageron et al., ANTARES: The first undersea neutrino telescope. Nuclear Instruments and Methods in Physics Research A 656, 11–38 (2011)A. Albert et al., First all-flavor neutrino pointlike source search with the ANTARES neutrino telescope. Physical Review D 96, 082001 (2017)A. Albert et al., All-flavor Search for a Diffuse Flux of Cosmic Neutrinos with Nine Years of ANTARES Data. The Astrophysical Journal Letters 853, L7 (2018)B.P. Abbott et al., Multi-messenger Observations of a Binary Neutron Star Merger. The Astrophysical Journal Letters 848, L12 (2017)S. Adrián-Martínez et al., Measurement of atmospheric neutrino oscillations with the ANTARES neutrino telescope. Physics Letters B 714, 224–230 (2012)A. Albert et al., Search for relativistic magnetic monopoles with five years of the ANTARES detector data. Journal of High Energy Physics 7, 54 (2017)S. Adrián-Martínez et al., Limits on dark matter annihilation in the sun using the ANTARES neutrino telescope. Physics Letters B 759, 69–74 (2016)A. Albert et al., Results from the search for dark matter in the Milky Way with 9 years of data of the ANTARES neutrino telescope. Physics Letters B 769, 249–254 (2017)M.G. Aartsen et al., The IceCube Neutrino Observatory: instrumentation and online systems. Journal of Instrumentation 12, P03012 (2017)K. Abe et al., Calibration of the Super-Kamiokande detector. Nuclear Instruments and Methods in Physics Research A 737, 253–272 (2014)P. Amram et al., The ANTARES optical module. Nuclear Instruments and Methods in Physics Research A 484, 369–383 (2002)S. Adrián-Martínez et al., The positioning system of the ANTARES Neutrino Telescope. Journal of Instrumentation 7, T08002 (2012)J.A. Aguilar et al., Performance of the front-end electronics of the ANTARES neutrino telescope. Nuclear Instruments and Methods in Physics Research A 622, 59–73 (2010)J.A. Aguilar et al., The data acquisition system for the ANTARES neutrino telescope. Nuclear Instruments and Methods in Physics Research A 570, 107–116 (2007)J.A. Aguilar et al., Measurement of the atmospheric muon flux with a 4 GeV threshold in the ANTARES neutrino telescope. Astroparticle Physics 33, 86–90 (2010)J.A. Aguilar et al., Transmission of light in deep sea water at the site of the ANTARES neutrino telescope. Astroparticle Physics 23, 131–155 (2005)S. Kim et al., PubChem Substance and Compound databases. Nucleic Acids Research 44, 1202–13 (2016)G. Audi et al., The NUBASE evaluation of nuclear and decay properties. Nuclear Physics A 729, 3–128 (2003)J. Floor Anthoni. The chemical composition of seawater. http://www.seafriends.org.nz/oceano/seawater.htmJ.R. De Laeter et al., Atomic Weights of the Elements: Review 2000 (IUPAC Technical Report). Pure Applied Chemistry 75, 683–800 (2003)P. Amram et al., Background light in potential sites for the ANTARES undersea neutrino telescope. Astroparticle Physics 13, 127–136 (2000)C. Tamburini et al., Deep-sea bioluminescence blooms after dense water formation at the ocean surface. PLOS ONE, 8(7), (2013)J.A. Aguilar et al., Time calibration of the ANTARES neutrino telescope. Astroparticle Physics 34, 539–549 (2011)M. Ageron et al., The ANTARES optical beacon system. Nuclear Instruments and Methods in Physics Research A 578, 498–509 (2007)S. Adrián-Martínez et al., Time calibration with atmospheric muon tracks in the ANTARES neutrino telescope. Astroparticle Physics 78, 43–51 (2016)S. Adrián-Martínez et al., Letter of Intent for KM3NeT 2.0. Journal of Physics G. Nuclear Physics 43(8), 084001 (2016

Multi-messenger Observations of a Binary Neutron Star Merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of {40}-8+8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 {M}ȯ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.</p