98 research outputs found
Charge ordering of magnetic monopoles in triangular spin ice patterns
Artificial spin ice offers the possibility to investigate a variety of
dipolar orderings, spin frustrations and ground states. However, the most
fascinating aspect is the realization that magnetic charge order can be
established without spin order. We have investigated magnetic dipoles arranged
on a honeycomb lattice as a function of applied field, using magnetic force
microscopy. For the easy direction with the field parallel to one of the three
dipole sublattices we observe at coercivity a maximum of spin frustration and
simultaneously a maximum of charge order of magnetic monopoles with alternating
charges 3.Comment: 7 pages, 4 figure
Multifrequency behaviour of the anomalous events of PSR J0922+0638
PSR J0922+0638 (B0919+06) shows unexplained anomalous variations in the
on-pulse phase, where the pulse appears to episodically move to an earlier
longitude for a few tens of rotations before reverting to the usual phase for
approximately several hundred to more than a thousand rotations. These events,
where the pulse moves in phase by up to 5, have been previously
detected in observations from 300 to 2000 MHz. We present simultaneous
observations from the Effelsberg 100-m radio telescope at 1350 MHz and the
Bornim (Potsdam) station of the LOw Frequency ARray at 150 MHz. Our
observations present the first evidence for an absence of the anomalous
phase-shifting behaviour at 150 MHz. Instead, the observed intensity at the
usual pulse-phase typically decreases, often showing a pseudo-nulling feature
corresponding to the times when phase shifts are observed at 1350 MHz. The
presence of weak emission at the usual pulse-phase supports the theory that
these shifts may result from processes similar to the 'profile-absorption'
expected to operate for PSR J0814+7429 (B0809+74). A possible mechanism for
this could be intrinsic variations of the emission within the pulsar's beam
combined with absorption by expanding shells of electrons in the line of sight.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
CTCF binds to sites in the major histocompatibility complex that are rapidly reconfigured in response to interferon-gamma
Activation of the major histocompatibility complex (MHC) by interferon-gamma (IFN−γ) is a fundamental step in the adaptive immune response to pathogens. Here, we show that reorganization of chromatin loop domains in the MHC is evident within the first 30 min of IFN−γ treatment of fibroblasts, and that further dynamic alterations occur up to 6 h. These very rapid changes occur at genomic sites which are occupied by CTCF and are close to IFN−γ-inducible MHC genes. Early responses to IFN−γ are thus initiated independently of CIITA, the master regulator of MHC class II genes and prepare the MHC for subsequent induction of transcription
Widespread Expression of BORIS/CTCFL in Normal and Cancer Cells
BORIS (CTCFL) is the paralog of CTCF (CCCTC-binding factor; NM_006565), a ubiquitously expressed DNA-binding protein with diverse roles in gene expression and chromatin organisation. BORIS and CTCF have virtually identical zinc finger domains, yet display major differences in their respective C- and N-terminal regions. Unlike CTCF, BORIS expression has been reported only in the testis and certain malignancies, leading to its classification as a “cancer-testis” antigen. However, the expression pattern of BORIS is both a significant and unresolved question in the field of DNA binding proteins. Here, we identify BORIS in the cytoplasm and nucleus of a wide range of normal and cancer cells. We compare the localization of CTCF and BORIS in the nucleus and demonstrate enrichment of BORIS within the nucleolus, inside the nucleolin core structure and adjacent to fibrillarin in the dense fibrillar component. In contrast, CTCF is not enriched in the nucleolus. Live imaging of cells transiently transfected with GFP tagged BORIS confirmed the nucleolar accumulation of BORIS. While BORIS transcript levels are low compared to CTCF, its protein levels are readily detectable. These findings show that BORIS expression is more widespread than previously believed, and suggest a role for BORIS in nucleolar function
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