ORCID Profile
0000-0002-4159-6934
Current Organisation
University of Helsinki
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Publisher: IOP Publishing
Date: 15-06-2021
Publisher: MDPI AG
Date: 09-03-2022
Abstract: Injecting optical squeezed states of light, a technique known as squeezing, is now a tool for gravitational wave detection. Its ability to reduce quantum noise is helping to reveal more gravitational wave transients, expanding the catalog of observations in the last observing run. This review introduces squeezing and its history in the context of gravitational-wave detectors. It overviews the benefits, limitations and methods of incorporating squeezing into advanced interferometers, emphasizing the most relevant details for astrophysics instrumentation.
Publisher: Rockefeller University Press
Date: 03-12-2007
Abstract: The endoplasmic reticulum (ER) is a multifaceted cellular organelle both structurally and functionally, and its cell cycle–dependent morphological changes are poorly understood. Our quantitative confocal and EM analyses show that the ER undergoes dramatic reorganization during cell ision in cultured mammalian cells as mitotic ER profiles become shorter and more branched. 3D modeling by electron tomography reveals that the abundant interphase structures, sheets, are lost and subsequently transform into a branched tubular network that remains continuous. This is confirmed by observing the most prominent ER subdomain, the nuclear envelope (NE). A NE marker protein spreads to the mitotic ER tubules, although it does not show a homogenous distribution within the network. We mimicked the mitotic ER reorganization using puromycin to strip the membrane-bound ribosomes from the interphase ER corresponding to the observed loss of ribosomes normally occurring during mitosis. We propose that the structural changes in mitotic ER are linked to ribosomal action on the ER membranes.
Publisher: Springer Science and Business Media LLC
Date: 11-09-2011
DOI: 10.1038/NPHYS2083
Publisher: Springer Science and Business Media LLC
Date: 27-10-2016
DOI: 10.1038/SREP35969
Abstract: Reticulons (RTNs) are a large family of membrane associated proteins with various functions. NOGO-A/RTN4A has a well-known function in limiting neurite outgrowth and restricting the plasticity of the mammalian central nervous system. On the other hand, Reticulon 4 proteins were shown to be involved in forming and maintaining endoplasmic reticulum (ER) tubules. Using comparative transcriptome analysis and qPCR, we show here that NOGO-B/RTN4B and NOGO-A/RTN4A are simultaneously expressed in cultured epithelial, fibroblast and neuronal cells. Electron tomography combined with immunolabelling reveal that both isoforms localize preferably to curved membranes on ER tubules and sheet edges. Morphological analysis of cells with manipulated levels of NOGO-B/RTN4B revealed that it is required for maintenance of normal ER shape over-expression changes the sheet/tubule balance strongly towards tubules and causes the deformation of the cell shape while depletion of the protein induces formation of large peripheral ER sheets.
Publisher: Wiley
Date: 23-11-2018
Publisher: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.YMETH.2014.11.013
Abstract: Both light microscopy (LM) and electron microscopy (EM) are able to reveal important information about the formation and function of various autophagic compartments. In this article we will outline the various techniques that are emerging in EM, focusing on analyzing three-dimensional morphology, collectively known as volume electron microscopy (volume EM), as well as on methods that can be used to localize proteins and antigenic epitopes. Large cell volumes can now be visualized at the EM level by using one of the two complementary imaging techniques, namely Serial Block-face Scanning Electron Microscopy (SB-SEM) or Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). These two block-face imaging methods reveal ultrastructural information from all membrane-bound organelles such as autophagic compartments to be visualized in a three-dimensional space, in association with their surrounding organelles. Another method which falls into the volume EM category is dual-axis electron tomography (ET). This method is more suited to reconstructing smaller volumes from areas of interest that require nano-structural detail to be confirmed such as membrane contact sites (MCSs) between autophagic compartments and various organelles. Further to this, to complement the morphological identification of autophagic compartments, immunolabeling can be carried out at the EM level to confirm the nature of various autophagic compartments depending on the localization of various antigens at a sub-cellular level. To determine this, various immunolabeling techniques can be carried out, namely the pre-embedding or the post-embedding immunolabeling methods. Ex les of both of these methods will be described in this chapter. Correlative light-electron microscopy (CLEM) can be used to visualize the same autophagic organelles under the LM, followed by high-resolution imaging under the EM. Finally, cryofixation has revolutionized the EM field by allowing rapid immobilization of cells and tissue in the near native state, so s les are no longer prone to artefacts induced by chemical fixation. Collectively, this chapter will discuss the aforementioned capabilities of the EM in more detail, with a particular focus on autophagy, namely the impact of EM in the study of the morphology and biogenesis of the phagophore/isolation membrane (referred to as the phagophore hereafter).
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-06-2021
Abstract: Cooling objects to low temperature can increase the sensitivity of sensors and the operational performance of most devices. Removing most of the thermal vibrations—or phonons—such that the object reaches its motional quantum ground state has been achieved but typically with tiny, nanoscale objects. Using the suspended mirrors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) that form a 10-kg optomechanical oscillator, Whittle et al. demonstrate the ability to cool such a large-scale object to nearly the motional ground state. An upgrade to LIGO with such a modification could increase its sensitivity and range to gravitational waves but also extend studies of quantum mechanics to large-scale objects. Science , abh2634, this issue p. 1333
Publisher: Elsevier BV
Date: 10-2015
Publisher: Informa UK Limited
Date: 25-02-2015
Publisher: American Astronomical Society
Date: 29-06-2021
Abstract: We report the observation of gravitational waves from two compact binary coalescences in LIGO’s and Virgo’s third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115 the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors. The source of GW200105 has component masses 8 . 9 − 1 . 5 + 1. 2 and 1. 9 − 0. 2 + 0. 3 M ⊙ , whereas the source of GW200115 has component masses 5. 7 − 2 . 1 + 1. 8 and 1. 5 − 0. 3 + 0. 7 M ⊙ (all measurements quoted at the 90% credible level). The probability that the secondary’s mass is below the maximal mass of a neutron star is 89%–96% and 87%–98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are 280 − 110 + 110 and 300 − 100 + 150 Mpc , respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45 − 33 + 75 Gpc − 3 yr − 1 when assuming that GW200105 and GW200115 are representative of the NSBH population or 130 − 69 + 112 Gpc − 3 yr − 1 under the assumption of a broader distribution of component masses.
Publisher: Optica Publishing Group
Date: 30-04-2021
DOI: 10.1364/AO.419689
Abstract: Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.
Publisher: Elsevier
Date: 2015
Publisher: The Company of Biologists
Date: 07-2015
DOI: 10.1242/JCS.169441
Abstract: Nuclear actin plays an important role in many processes that regulate gene expression. Cytoplasmic actin dynamics are tightly controlled by numerous actin-binding proteins, but regulation of nuclear actin has remained unclear. Here, we performed a genome-wide RNA interference (RNAi) screen in Drosophila cells to identify proteins that influence either nuclear polymerization or import of actin. We validate 19 factors as specific hits, and show that Chinmo (known as Bach2 in mammals), SNF4Aγ (Prkag1 in mammals) and Rab18 play a role in nuclear localization of actin in both fly and mammalian cells. We identify several new regulators of cofilin activity, and characterize modulators of both cofilin kinases and phosphatase. For ex le, Chinmo/Bach2, which regulates nuclear actin levels also in vivo, maintains active cofilin by repressing the expression of the kinase Cdi (Tesk in mammals). Finally, we show that Nup98 and lamin are candidates for regulating nuclear actin polymerization. Our screen therefore reveals new aspects of actin regulation and links nuclear actin to many cellular processes.
Publisher: Wiley
Date: 07-2019
DOI: 10.1002/GLIA.23675
Publisher: IOP Publishing
Date: 20-08-2020
Publisher: American Society for Cell Biology (ASCB)
Date: 04-2014
Abstract: The endoplasmic reticulum (ER) comprises a dynamic three-dimensional (3D) network with erse structural and functional domains. Proper ER operation requires an intricate balance within and between dynamics, morphology, and functions, but how these processes are coupled in cells has been unclear. Using live-cell imaging and 3D electron microscopy, we identify a specific subset of actin filaments localizing to polygons defined by ER sheets and tubules and describe a role for these actin arrays in ER sheet persistence and, thereby, in maintenance of the characteristic network architecture by showing that actin depolymerization leads to increased sheet fluctuation and transformations and results in small and less abundant sheet remnants and a defective ER network distribution. Furthermore, we identify myosin 1c localizing to the ER-associated actin filament arrays and reveal a novel role for myosin 1c in regulating these actin structures, as myosin 1c manipulations lead to loss of the actin filaments and to similar ER phenotype as observed after actin depolymerization. We propose that ER-associated actin filaments have a role in ER sheet persistence regulation and thus support the maintenance of sheets as a stationary subdomain of the dynamic ER network.
Publisher: Public Library of Science (PLoS)
Date: 04-01-2016
Publisher: American Society for Cell Biology (ASCB)
Date: 07-2012
Abstract: The endoplasmic reticulum (ER) is both structurally and functionally complex, consisting of a dynamic network of interconnected sheets and tubules. To achieve a more comprehensive view of ER organization in interphase and mitotic cells and to address a discrepancy in the field (i.e., whether ER sheets persist, or are transformed to tubules, during mitosis), we analyzed the ER in four different mammalian cell lines using live-cell imaging, high-resolution electron microscopy, and three dimensional electron microscopy. In interphase cells, we found great variation in network organization and sheet structures among different cell lines. In mitotic cells, we show that the ER undergoes both spatial reorganization and structural transformation of sheets toward more fenestrated and tubular forms. However, the extent of spatial reorganization and sheet-to-tubule transformation varies among cell lines. Fenestration and tubulation of the ER correlates with a reduced number of membrane-bound ribosomes.
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Publisher: IOP Publishing
Date: 26-11-2014
Publisher: IOP Publishing
Date: 05-11-2020
Abstract: Teleseismic, or distant, earthquakes regularly disrupt the operation of ground–based gravitational wave detectors such as Advanced LIGO. Here, we present EQ mode , a new global control scheme, consisting of an automated sequence of optimized control filters that reduces and coordinates the motion of the seismic isolation platforms during earthquakes. This, in turn, suppresses the differential motion of the interferometer arms with respect to one another, resulting in a reduction of DARM signal at frequencies below 100 mHz. Our method greatly improved the interferometers’ capability to remain operational during earthquakes, with ground velocities up to 3.9 μ m s −1 rms in the beam direction, setting a new record for both detectors. This sets a milestone in seismic controls of the Advanced LIGO detectors’ ability to manage high ground motion induced by earthquakes, opening a path for further robust operation in other extreme environmental conditions.
Publisher: American Physical Society (APS)
Date: 05-12-2019
Publisher: American Physical Society (APS)
Date: 11-09-2020
Publisher: Public Library of Science (PLoS)
Date: 08-01-2014
Publisher: American Physical Society (APS)
Date: 13-09-2021
Publisher: IOP Publishing
Date: 19-10-2020
Abstract: The raw outputs of the detectors within the Advanced Laser Interferometer Gravitational-Wave Observatory need to be calibrated in order to produce the estimate of the dimensionless strain used for astrophysical analyses. The two detectors have been upgraded since the second observing run and finished the year-long third observing run. Understanding, accounting, and/or compensating for the complex-valued response of each part of the upgraded detectors improves the overall accuracy of the estimated detector response to gravitational waves. We describe improved understanding and methods used to quantify the response of each detector, with a dedicated effort to define all places where systematic error plays a role. We use the detectors as they stand in the first half (six months) of the third observing run to demonstrate how each identified systematic error impacts the estimated strain and constrain the statistical uncertainty therein. For this time period, we estimate the upper limit on systematic error and associated uncertainty to be % in magnitude and deg in phase (68% confidence interval) in the most sensitive frequency band 20–2000 Hz. The systematic error alone is estimated at levels of % in magnitude and deg in phase.
Publisher: Elsevier
Date: 2017
DOI: 10.1016/BS.MIE.2016.09.063
Abstract: Electron tomography has significantly contributed to recent findings regarding the biogenesis of the phagophore, an organelle which initiates autophagic sequestration. The information obtained from 1.9nm slices through the tomograms have revealed that during biogenesis the phagophore is in contact with the membranes of apposing organelles to form tubular connections and membrane contact sites (MCSs). The most reported and established tubular connections occur between the phagophore and the endoplasmic reticulum. However, as the phagophore continues to grow and expand, connections and MCSs have also been reported to occur between the phagophore and several other organelles in a possible attempt to utilize lipids for membrane expansion from alternative sources. Since the lifespan of the phagophore is only a few minutes and membrane connections and MCSs are very dynamic, capturing these two events requires precision during fixation. Up to date there is no quicker alternative for s le preservation in transmission electron microscopy than cryoimmobilization. In this report, we describe our protocol for cryoimmobilization using high-pressure freezing and freeze substitution, and report our first findings on phagophore morphology using this approach.
Publisher: The Optical Society
Date: 12-2011
DOI: 10.1364/OL.36.004680
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Eija Jokitalo.