The Experts below are selected from a list of 25866 Experts worldwide ranked by ideXlab platform
Hiroyuki Ohkura - One of the best experts on this subject based on the ideXlab platform.
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the conserved kinase srpk regulates karyosome formation and spindle microtubule assembly in drosophila oocytes
Journal of Cell Science, 2012Co-Authors: Fiona C Cullen, Nina Vogt, Hiroyuki OhkuraAbstract:In Drosophila oocytes, after the completion of recombination, meiotic chromosomes form a Compact Cluster called the karyosome within the nucleus, and later assemble spindle microtubules without centrosomes. Although these oocyte-specific phenomena are also observed in humans, their molecular basis is not well understood. Here, we report essential roles for the conserved kinase SRPK in both karyosome formation and spindle microtubule assembly in oocytes. We have identified a female-sterile srpk mutant through a cytological screen for karyosome defects. Unlike most karyosome mutants, the karyosome defect is independent of the meiotic recombination checkpoint. Heterochromatin Clustering found within the wild-type karyosome is disrupted in the mutant. Strikingly, a loss of SRPK severely prevents microtubule assembly for acentrosomal spindles in mature oocytes. Subsequently, bi-orientation and segregation of meiotic chromosomes are also defective. Therefore, this study demonstrates new roles of this conserved kinase in two independent meiotic steps specific to oocytes.
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nhk 1 phosphorylates baf to allow karyosome formation in the drosophila oocyte nucleus
Journal of Cell Biology, 2007Co-Authors: Oscar M Lancaster, Fiona C Cullen, Hiroyuki OhkuraAbstract:Accurate chromosome segregation in meiosis requires dynamic changes in chromatin organization. In Drosophila melanogaster, upon completion of recombination, meiotic chromosomes form a single, Compact Cluster called the karyosome in an enlarged oocyte nucleus. This Clustering is also found in humans; however, the mechanisms underlying karyosome formation are not understood. In this study, we report that phosphorylation of barrier to autointegration factor (BAF) by the conserved kinase nucleosomal histone kinase-1 (NHK-1; Drosophila Vrk1) has a critical function in karyosome formation. We find that the noncatalytic domain of NHK-1 is crucial for its kinase activity toward BAF, a protein that acts as a linker between chromatin and the nuclear envelope. A reduction of NHK-1 or expression of nonphosphorylatable BAF results in ectopic association of chromosomes with the nuclear envelope in oocytes. We propose that BAF phosphorylation by NHK-1 disrupts anchorage of chromosomes to the nuclear envelope, allowing karyosome formation in oocytes. These data provide the first mechanistic insight into how the karyosome forms.
S Savaglio - One of the best experts on this subject based on the ideXlab platform.
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a Compact Cluster of massive red galaxies at a redshift of 1 5
The Astrophysical Journal, 2007Co-Authors: P J Mccarthy, Haojing Yan, Roberto Abraham, Erin Mentuch, Karl Glazebrook, Lin Yan, Hsiaowen Chen, Eric S Persson, Preethi Nair, S SavaglioAbstract:We describe a Compact Cluster or group of massive red galaxies at z = 1.5 discovered in one of the Gemini Deep Deep Survey (GDDS) fields. Deep H-band imaging from the Hubble Space Telescope (HST) reveals a high density of red galaxies associated with a galaxy with a spectroscopic redshift of 1.51. These galaxies have spectral energy distributions (SEDs) that peak between 3.6 and 4.5 μm, and fits to 12-band photometry reveal 12 or more galaxies with spectral shapes consistent with z = 1.5. Most are within ~170 comoving kpc of the GDDS galaxy, and the enclosed stellar mass is >6 × 10^(11) M_☉. The colors of the most massive galaxies are close to those expected from passive evolution of simple stellar populations (SSPs) formed at much higher redshifts. We suggest that several of these galaxies will merge to form a single, very massive galaxy by the present day. This system may represent an example of a short-lived dense group or Cluster core typical of the progenitors of massive Clusters in the present day and suggests that the red sequence was in place in overdense regions at early times.
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a Compact Cluster of massive red galaxies at a redshift of 1 51
arXiv: Astrophysics, 2007Co-Authors: P J Mccarthy, Haojing Yan, Roberto Abraham, Erin Mentuch, Karl Glazebrook, Lin Yan, Preethi Nair, Heidi Chen, S E Persson, S SavaglioAbstract:We describe a Compact Cluster of massive red galaxies at z=1.51 discovered in one of the Gemini Deep Deep Survey (GDDS) fields. Deep imaging with the Near Infrared Camera and Multi Object Spectrometer (NICMOS) on the Hubble Space Telescope reveals a high density of galaxies with red optical to near-IR colors surrounding a galaxy with a spectroscopic redshift of 1.51. Mid-IR imaging with Infrared Array Camera (IRAC) on the Spitzer Space telescope shows that these galaxies have spectral energy distributions that peak between 3.6 and 4.5 microns. Fits to 12-band photometry reveal 12 or more galaxies with spectral shapes consistent with z = 1.51. Most are within ~170 co-moving kpc of the GDDS galaxy. Deep F814W images with the Advanced Camera for Surveys (ACS) on HST reveal that these galaxies are a mix of early-type galaxies, disk galaxies and close pairs. The total stellar mass enclosed within a sphere of 170 kpc in radius is > 8E+11 solar masses. The colors of the most massive galaxies are close to those expected from passive evolution of simple stellar populations (SSP) formed at much higher redshifts. We suggest that several of these galaxies will merge to form a single, very massive galaxy by the present day. This system may represent an example of a short-lived dense group or Cluster core typical of the progenitors of massive Clusters in the present day and suggests the red sequence was in place in over-dense regions at early times.
C Hieret - One of the best experts on this subject based on the ideXlab platform.
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unveiling a Compact Cluster of massive and young stars in iras 17233 3606
The Astronomical Journal, 2008Co-Authors: Luis A Zapata, S Leurini, K M Menten, P Schilke, R Rolffs, C HieretAbstract:We have analyzed sensitive high spatial resolution archival radio continuum data at 1.3, 2.0, 3.6, and 6.0 cm as well as the H2O maser molecular line data obtained using the Very Large Array (VLA) in its hybrid AB configuration toward the high-mass star-forming region IRAS 17233-3606 (G351.78-0.54). We find nine Compact radio sources associated with this region, six of them are new radio detections. We discuss the characteristics of these sources based mostly on their spectral indices and find that most of them appear to be optically thin or thick ultra- and hyper-Compact H II regions ionized by B zero-age main-sequence stars. Furthermore, in a few cases the radio emission may arise from optically thick dusty disks and/or cores; however more observations at different wavelengths are necessary to firmly confirm their true nature. In addition, we compared our centimeter maps with the mid-infrared images from the Spitzer Space Observatory GLIMPSE survey revealing a Cluster of young protostars in the region together with multiple collimated outflows, some of which might be related to the Compact centimeter objects. Finally, we find that one of these centimeter objects, VLA2d, is well centered in an apparent strong and Compact north-south bipolar outflow traced by OH masers and we therefore suggest that this object is energizing the latter.
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unveiling a Compact Cluster of massive and young stars in iras 17233 3606
arXiv: Astrophysics, 2008Co-Authors: Luis A Zapata, S Leurini, K M Menten, P Schilke, R Rolffs, C HieretAbstract:We have analyzed sensitive high spatial resolution archival radio continuum data at 1.3, 2.0, 3.6 and 6.0 cm as well as the H2O maser molecular line data obtained using the Very Large Array (VLA) in its hybrid AB configuration toward the high-mass star-forming region IRAS 17233-3606 (G351.78-0.54). We find nine Compact radio sources associated with this region, six of them are new radio detections. We discuss the characteristics of these sources based mostly on their spectral indices and find that most of them appear to be optically thin or thick ultra- and hyper-Compact HII regions ionized by B ZAMS stars. Furthermore, in a few cases the radio emission may arise from optically thick dusty disks and/or cores, however more observations at different wavelengths are necessity to firmly confirm their true nature. In addition, we compared our centimeter maps with the mid-infrared images fromthe Spitzer Space Observatory GLIMPSE survey revealing a Cluster of young protostars in the region together with multiple collimated outflows some of whom might be related with the Compact centimeter objects.
Fiona C Cullen - One of the best experts on this subject based on the ideXlab platform.
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the conserved kinase srpk regulates karyosome formation and spindle microtubule assembly in drosophila oocytes
Journal of Cell Science, 2012Co-Authors: Fiona C Cullen, Nina Vogt, Hiroyuki OhkuraAbstract:In Drosophila oocytes, after the completion of recombination, meiotic chromosomes form a Compact Cluster called the karyosome within the nucleus, and later assemble spindle microtubules without centrosomes. Although these oocyte-specific phenomena are also observed in humans, their molecular basis is not well understood. Here, we report essential roles for the conserved kinase SRPK in both karyosome formation and spindle microtubule assembly in oocytes. We have identified a female-sterile srpk mutant through a cytological screen for karyosome defects. Unlike most karyosome mutants, the karyosome defect is independent of the meiotic recombination checkpoint. Heterochromatin Clustering found within the wild-type karyosome is disrupted in the mutant. Strikingly, a loss of SRPK severely prevents microtubule assembly for acentrosomal spindles in mature oocytes. Subsequently, bi-orientation and segregation of meiotic chromosomes are also defective. Therefore, this study demonstrates new roles of this conserved kinase in two independent meiotic steps specific to oocytes.
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nhk 1 phosphorylates baf to allow karyosome formation in the drosophila oocyte nucleus
Journal of Cell Biology, 2007Co-Authors: Oscar M Lancaster, Fiona C Cullen, Hiroyuki OhkuraAbstract:Accurate chromosome segregation in meiosis requires dynamic changes in chromatin organization. In Drosophila melanogaster, upon completion of recombination, meiotic chromosomes form a single, Compact Cluster called the karyosome in an enlarged oocyte nucleus. This Clustering is also found in humans; however, the mechanisms underlying karyosome formation are not understood. In this study, we report that phosphorylation of barrier to autointegration factor (BAF) by the conserved kinase nucleosomal histone kinase-1 (NHK-1; Drosophila Vrk1) has a critical function in karyosome formation. We find that the noncatalytic domain of NHK-1 is crucial for its kinase activity toward BAF, a protein that acts as a linker between chromatin and the nuclear envelope. A reduction of NHK-1 or expression of nonphosphorylatable BAF results in ectopic association of chromosomes with the nuclear envelope in oocytes. We propose that BAF phosphorylation by NHK-1 disrupts anchorage of chromosomes to the nuclear envelope, allowing karyosome formation in oocytes. These data provide the first mechanistic insight into how the karyosome forms.
S Ichimura - One of the best experts on this subject based on the ideXlab platform.
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development of Compact Cluster ion sources using metal Cluster complexes ionization properties of metal Cluster complexes
Applied Surface Science, 2004Co-Authors: T Mizota, Hidehiko Nonaka, T Fujimoto, A Kurokawa, S IchimuraAbstract:Abstract In order to develop a new Compact Cluster ion source as a low damage sputtering source for SIMS to analyze ultra-shallow dopant state we have studied the possibility of using a metal Cluster complex as an ion beam source. Metal Cluster complexes such as Os 3 (CO) 12 and Ir 4 (CO) 12 have been studied from the view point of their stability in high vacuum and how to ionize them by using the electron ionization QMS and the XeCl laser ionization TOF. In the case of electron ionization QMS, peaks of Os 3 (CO) n + ( n =0–12) and Ir 4 (CO) n + ( n =0–12) were observed without the fragment ions such as a monomer, a dimer, etc. In the case of laser ionization TOF, peaks of the fragment and the parent ions without a carbonyl ligand were observed from Os 3 (CO) 12 , and Ir 4 (CO) 12 . The temperature dependence of fragmentation has also been discussed.