The Low Energy X-ray telescope (LE) is one of the three main instruments of the
Insight-Hard
X-ray Modulation Telescope (
Insight-
HXMT)
.
It is equipped with Swept Charge Device (SCD) sensor arrays ...with a total geometrical area of 384 cm and an energy band from 0.7 to 13 keV. In order to evaluate the particle induced X-ray background and the cosmic X-ray background simultaneously, LE adopts collimators to define four types of Field Of Views (FOVs), i.e., 1.6°×6°, 4°×6°, 50°-60°×2°-6° and the blocked ones which block the X-ray by an aluminum cover. LE is constituted of three detector boxes (LEDs) and an electric control box (LEB) and achieves a good energy resolution of 140 eV@5.9 keV, an excellent time resolution of 0.98 ms, as well as an extremely low pileup (<1%@18000 cts/s). Detailed performance tests and calibration on the ground have been performed, including energy-channel relation, energy response, detection efficiency and time response.
The
Insight
-Hard X-ray Modulation Telescope (
Insight
-HXMT) is a broadband X-ray and γ-ray (1-3000 keV) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope ...(HE). The main detector plane of HE comprises 18 NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) is used as the primary detector to measure ~ 20–250 keV photons incident from the field of view (FOV) defined by collimators, and CsI(Na) is used as the active shielding detector to NaI(Tl) by pulse shape discrimination. Additionally, CsI(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV, i.e. 1.1°×5.7° (15 units), 5.7°×5.7° (2 units), and blocked (1 unit). Therefore, the combined FOV of HE is approximately 5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm
2
, and the energy resolution is ~15% at 60 keV. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the dead-time is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20–250 keV band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 MeV band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments.
Shank and GKAP are scaffold proteins and binding partners at the postsynaptic density (PSD). The distribution and dynamics of Shank and GKAP were studied in dissociated hippocampal cultures by ...pre-embedding immunogold electron microscopy. Antibodies against epitopes containing their respective mutual binding sites were used to verify the expected juxtapositioning of Shank and GKAP. If all Shank and GKAP molecules at the PSD were bound to each other, the distribution of label for the two proteins should coincide. However, labels for the mutual binding sites showed significant differences in distribution, with a narrow distribution for GKAP located close to the postsynaptic membrane, and a wider distribution for Shank extending deeper into the cytoplasm. Upon depolarization with high K+, neither the intensity nor distribution of label for GKAP changed, but labeling intensity for Shank at the PSD increased to ~150% of controls while the median distance of label from postsynaptic membrane increased by 7.5 nm. These results indicate a preferential recruitment of Shank to more distal parts of the PSD complex. Conversely, upon incubation in Ca2+-free medium containing EGTA, the labeling intensity of Shank at the PSD decreased to ~70% of controls and the median distance of label from postsynaptic membrane decreased by 9 nm, indicating a preferential loss of Shank molecules in more distal parts of the PSD complex. These observations identify two pools of Shank at the PSD complex, one relatively stable pool, closer to the postsynaptic membrane that can bind to GKAP, and another more dynamic pool at a location too far away to bind to GKAP.
► CYLD is a deubiquitinase specific for lysine63-linked polyubiquitins. ► Presence of CYLD in PSDs is established by biochemistry and immunoEM. ► CYLD accumulates on PSDs upon depolarization of ...neurons. ► Accumulation of CYLD at PSDs may regulate trafficking/degradation of synaptic proteins.
Polyubiquitin chains on proteins flag them for distinct fates depending on the type of polyubiquitin linkage. While lysine48-linked polyubiquitination directs proteins to proteasomal degradation, lysine63-linked polyubiquitination promotes different protein trafficking and is involved in autophagy. Here we show that postsynaptic density (PSD) fractions from adult rat brain contain deubiquitinase activity that targets both lysine48 and lysine63-linked polyubiquitins. Comparison of PSD fractions with parent subcellular fractions by Western immunoblotting reveals that CYLD, a deubiquitinase specific for lysine63-linked polyubiquitins, is highly enriched in the PSD fraction. Electron microscopic examination of hippocampal neurons in culture under basal conditions shows immunogold label for CYLD at the PSD complex in approximately one in four synapses. Following depolarization by exposure to high K+, the proportion of CYLD-labeled PSDs as well as the labeling intensity of CYLD at the PSD increased by more than eighty percent, indicating that neuronal activity promotes accumulation of CYLD at the PSD. An increase in postsynaptic CYLD following activity would promote removal of lysine63-polyubiquitins from PSD proteins and thus could regulate their trafficking and prevent their autophagic degradation.
SynGAP, a protein abundant at the postsynaptic density (PSD) of glutamatergic neurons, is known to modulate synaptic strength by regulating the incorporation of AMPA receptors at the synapse. Two ...isoforms of SynGAP, α1 and α2, which differ in their C-termini, have opposing effects on synaptic strength. In the present study, antibodies specific for SynGAP-α1 and SynGAP-α2 are used to compare the distribution patterns of the two isoforms at the postsynaptic density (PSD) under basal and excitatory conditions. Western immunoblotting shows enrichment of both isoforms in PSD fractions isolated from adult rat brain. Immunogold electron microscopy of rat hippocampal neuronal cultures shows similar distribution of both isoforms at the PSD, with a high density of immunolabel within the PSD core under basal conditions. Application of NMDA promotes movement of SynGAP-α1 as well as SynGAP-α2 out of the PSD core. In isolated PSDs both isoforms of SynGAP can be phosphorylated upon activation of the endogenous CaMKII. Application of tatCN21, a cell-penetrating inhibitor of CaMKII, to hippocampal neuronal cultures blocks NMDA-induced redistribution of SynGAP-α1 and SynGAP-α2. Thus CaMKII activation promotes the removal of two distinct C-terminal SynGAP variants from the PSD.
The Medium Energy X-ray telescope (ME) is one of the three main telescopes on board the
Insight
hard X-ray modulation telescope (
Insight-
HXMT) astronomy satellite. ME contains 1728 pixels of Si-PIN ...detectors sensitive in 5–30 keV with a total geometrical area of 952 cm
2
. The application specific integrated circuit (ASIC) chip, VA32TA6, is used to achieve low power consumption and low readout noise. The collimators define three kinds of field of views (FOVs) for the telescope, 1°×4°, 4°×4°, and blocked ones. Combination of such FOVs can be used to estimate the in-orbit X-ray and particle background components. The energy resolution of ME is ~3 keV at 17.8 keV (FWHM) and the time resolution is 255 μs. In this paper, we introduce the design and performance of ME.
Highlights • Long forms of Homer 1, 2, and 3 are concentrated at the PSD. • Homer occupies domains in synapses different from those of type I mGluRs. • Homer and Shank are co-localized at the PSD, ...~30-100 nm from the postsynaptic membrane. • Homer at the PSD does not redistribute upon acute (2 min) stimulation. • Homer distribution at the PSD is not dependent on calcium concentration.
•NMDA-induces accumulation of Shank at the postsynaptic density.•Shank accumulation is preferential to the distal region of the postsynaptic density.•Shank accumulation is mediated by CaMKII.
Shank ...is a specialized scaffold protein present in high abundance at the postsynaptic density (PSD). Using pre-embedding immunogold electron microscopy on cultured hippocampal neurons, we had previously demonstrated further accumulation of Shank at the PSD under excitatory conditions. Here, using the same experimental protocol, we demonstrate that a cell permeable CaMKII inhibitor, tatCN21, blocks NMDA-induced accumulation of Shank at the PSD. Furthermore we show that NMDA application changes the distribution pattern of Shank at the PSD, promoting a 7–10nm shift in the median distance of Shank labels away from the postsynaptic membrane. Inhibition of CaMKII with tatCN21 also blocks this shift in the distribution of Shank. Altogether these results imply that upon activation of NMDA receptors, CaMKII mediates accumulation of Shank, preferentially at the distal regions of the PSD complex extending toward the cytoplasm.
SynGAP, a protein abundant at the postsynaptic density (PSD) of glutamatergic neurons, is known to modulate synaptic strength by regulating the incorporation of AMPA receptors at the synapse. Two ...isoforms of SynGAP, alpha1 and alpha2, which differ in their C-termini, have opposing effects on synaptic strength. In the present study, antibodies specific for SynGAP-alpha1 and SynGAP-alpha2 are used to compare the distribution patterns of the two isoforms at the postsynaptic density (PSD) under basal and excitatory conditions. Western immunoblotting shows enrichment of both isoforms in PSD fractions isolated from adult rat brain. Immunogold electron microscopy of rat hippocampal neuronal cultures shows similar distribution of both isoforms at the PSD, with a high density of immunolabel within the PSD core under basal conditions. Application of NMDA promotes movement of SynGAP-alpha1 as well as SynGAP-alpha2 out of the PSD core. In isolated PSDs both isoforms of SynGAP can be phosphorylated upon activation of the endogenous CaMKII. Application of tatCN21, a cell-penetrating inhibitor of CaMKII, to hippocampal neuronal cultures blocks NMDA-induced redistribution of SynGAP-alpha1 and SynGAP-alpha2. Thus CaMKII activation promotes the removal of two distinct C-terminal SynGAP variants from the PSD.
Abstract SynGAP is a Ras GTPase activating protein present at the postsynaptic density (PSD) in quantities matching those of the core scaffold protein PSD-95. SynGAP is reported to inhibit synaptic ...accumulation of AMPA receptors. Here, we characterize by immunogold electron microscopy the distribution of SynGAP at the PSD under basal and depolarizing conditions in rat hippocampal neuronal cultures. The PSD core, extending up to 40 nm from the postsynaptic membrane, typically shows label for SynGAP, while half of the synapses exhibit additional labeling in a zone 40–120 nm from the postsynaptic membrane. Upon depolarization with high K+ , labeling for SynGAP significantly decreases at the core of the PSD and concomitantly increases at the 40–120 nm zone. Under the same depolarization conditions, label for PSD-95, the presumed binding partner of SynGAP, does not change its localization at the PSD. Depolarization-induced redistribution of SynGAP is reversible and also occurs upon application of N-methyl- d -aspartic acid (NMDA). Activity-induced movement of SynGAP could vacate sites in the PSD core allowing other elements to bind to these sites, such as transmembrane AMPA receptor regulatory proteins (TARPs), and simultaneously facilitate access of SynGAP to CaMKII and Ras, elements of a regulatory cascade.
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