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PubMedDate not supplied

Proteomic snapshot analyses of preribosomal ribonucleoprotein complexes formed at various stages of ribosome biogenesis in yeast and mammalian cells.

Proteomic technologies powered by advancements in mass spectrometry and bioinformatics and coupled with accumulated genome sequence data allow a comprehensive study of cell function through large-scale and systematic protein identifications of protein constituents of the cell and tissues, as well as of multi-protein complexes that carry out many cellular function in a higher-order network in the cell. One of the most extensively analyzed cellular functions by proteomics is the production of ribosome, the protein-synthesis machinery, in the nucle(ol)us--the main site of ribosome biogenesis. The use of tagged proteins as affinity bait, coupled with mass spectrometric identification, enabled us to isolate synthetic intermediates of ribosomes that might represent snapshots of nascent ribosomes at particular stages of ribosome biogenesis and to identify their constituents--some of which showed dynamic changes for association with the intermediates at various stages of ribosome biogenesis. In this review, in conjunction with the results from yeast cells, our proteomic approach to analyze ribosome biogenesis in mammalian cells is described.

Animals↗

PubMed1988

Snapshot head imaging at 0.5 T using the echo planar technique.

The echo planar imaging (EPI) method and related variants of this technique can produce complete two-dimensional images from the data collected in a single experiment lasting a fraction of a second. EPI methods are used at 0.5 T to produce snapshot images of the human head with a spatial resolution of less than 2 mm.

Head↗

PubMed1990

Snapshot FLASH MRI. Applications to T1, T2, and chemical-shift imaging.

Snapshot FLASH magnetic resonance imaging techniques have been developed to enable real-time imaging of MR parameters. The first realization of the method is based on a 64 X 128 FLASH tomogram acquired within 200 ms, using improved MR system hardware conditions. The soft tissue contrast obtained in FLASH MRI almost disappears by using flip angles of less than 5 degrees and repetition times of 3 ms. This work describes extensions of FLASH MRI placing conventional MR experiments before the whole imaging sequence. This creates images of any desired contrast without changing the measuring time. Examples of inversion-recovery T1, spin-echo T2, chemical-shift-selective, and spectroscopic FLASH MRI are presented. Further extensions to real-time MRI of blood vessels, diffusion coefficients, combination with two-dimensional MR spectroscopy experiments, and other nuclei are discussed.

Humans↗

PubMed1990

The importance of phase-encoding order in ultra-short TR snapshot MR imaging.

We show the importance of phase-encoding order in ultra-short TR (less than 10 ms) snapshot MR imaging. Contrast is more heavily dictated by the contrast preparation phase early in the measurement phase than later. When the low spatial frequencies are measured first, the resultant image contrast more closely resembles that established by the preparation phase. The transient nature of the data acquisition causes a kappa-space filter to be applied to the data. The effects of this filter can be minimized by appropriate choice of scan parameters.

Filtration↗

PubMed1991

Snapshot imaging using a FLARE sequence.

We have implemented a snapshot FLARE sequence using a scan time of 320 ms for a 64 x 128 image. As in the conventional FLARE sequence the T2 weighting of the image can be altered by manipulating the phase encoding scheme with the position of the zeroth phase encoding effectively determining the amount of T2 weighting. Reducing the flip angle of the refocusing pulse reduces both the RF power deposition and the blurring in images of short T2 samples, at the expense of reduced signal and contrast.

Humans↗

PubMed1997

Real time monitoring of laser-induced thermal changes in cartilage in vitro by using snapshot FLASH.

Snapshot FLASH imaging has been applied to study the spatial and temporal spreading of thermal changes caused by a Holmium:YAG laser in patella cartilage in vitro at 7 T. The temperature dependence of the proton resonance frequency was used to demonstrate the thermal energy deposition. A series of cartilage images, with a time resolution of 512 ms and a spatial resolution of 400 x 200 microm, showed dynamic changes of the temperature-related image phase in the regions irradiated by the laser.

Cartilage, Articular↗

PubMed2002

High-schoolers' peer orientation priorities: a snapshot.

This short paper reports a set of qualitative research findings which reveal something of the peer orientation priorities of 462 British high-schoolers (14-year olds)-who they hang out with and why. Offering a snapshot of young people's current social and relational priorities, these data point to their over-riding concern for mutuality and "hanging" itself (e.g. "having a laugh"); boys' single-minded preference for sport (and computers); girls' consistent attunement to pleasant, caring interactions; and the relative unimportance of ethnically based affiliation.

Adolescent↗

PubMed1997

Dynamic T1 measurement using snapshot-FLASH MRI.

The application of an inversion-recovery snapshot FLASH (fast low-angled shot) imaging sequence to the dynamic measurement of monoexponential T1 relaxation was investigated. The effect of (a) a reduction in the overall sequence repetition time, and (b) an increase of the read-pulse flip angle, on the measurement of T1 was analyzed. The error in T1 introduced by these factors is calculated, and a fuller analysis that takes them into account is presented. Data from a phantom are used to confirm this analysis. The magnitude of the errors is illustrated by measuring myocardial T1 in patients with acute ischaemic heart disease during the injection of a bolus of the contrast medium gadobenate dimeglumine. Overall, there was a 10% difference between the T1 values when the approximate and exact solutions were used; this was statistically significant. However, the difference was on average 25% for patients with a high heart rate (because of the shorter sequence-repetition time) in areas of infarcted myocardium (because of the longer T1).

Contrast Media↗

PubMed1996

Dynamic snapshot gradient-echo imaging of head and neck malignancies: time dependency and quality of contrast-to-noise ratio.

The purpose of this study was to evaluate the time dependency of the contrast-to-noise ratio (CNR) of head and neck malignancies during contrast-enhanced MR imaging. Then we would compare the CNR of dynamic snapshot gradient-echo (SGE) images with conventional spin-echo (SE) and fast spin-echo (FSE) sequences. Fifteen patients with squamous cell carcinomas were examined with T1W-SE, T2W-FSE, contrast-enhanced Gd-T1W-SE, and T1W-SGE sequences, the latter statically and contrast-enhanced dynamically. The CNR for all sequences and adjacent tissues was computed and the time to reach maximal CNR (Tmax) was determined for dynamic studies. The CNR was time dependent with two distinct Tmax at 6-18 and 60-160 s which corresponded to two different tumor enhancement patterns. Neither enhancement pattern correlated with distinct histologic findings or tumor grading. The CNR improved for the Gd-T1W-SE images. The improvement was statistically significant in relation to T1W-SE and Gd-T1W-SE images at the floor of the mouth and at the tongue base. The good CNR of the dynamic Gd-T1W-SGE measurements justifies further investigations of this method in order to improve tumor delineation.

Adult↗

PubMed2005

Subtyping mtDNA haplogroup H by SNaPshot minisequencing and its application in forensic individual identification.

Sequence variation of the hypervariable segments (HVS) I/II of mitochondrial DNA (mtDNA) and the haplogroup affiliation were determined in a sample of 271 Italian subjects. This analysis showed that 42% of the individuals could be ascribed to H, the most frequent haplogroup in European Caucasian populations. This fraction was then screened for specific single nucleotide polymorphisms located in the coding region to identify H subclades H1-H15. We set up two multiplex polymerase chain reactions and specific SNaPshot assays to investigate the frequency distribution of these subgroups in our population sample and to examine their usefulness in discriminating among commonly shared HVS I/II sequences. This allowed the assignment of a large portion of the mtDNAs ( approximately 70%) to specific subhaplogroups, with H1 and H5 being the most represented. About two-thirds of the individuals sharing common HVS I/II sequences were subdivided and ascribed to specific H subhaplogroups with a significant reduction of the frequencies of the most common mtDNA haplotypes. Haplogroup H subtyping could thus be extremely useful in forensic identification when many samples have to be analysed and compared, avoiding excessive time-consuming and labor-intensive sequencing analysis.

Complementarity Determining Regions↗

PubMed1990

Approach to equilibrium in snapshot imaging.

The snapshot FLASH sequence uses a subsecond scan time and a small flip angle in conjunction with nonsteady-state acquisition to produce high-contrast images with minimum motion artifacts. The magnetisation evolves towards an equilibrium state in the course of a scan and it is the form of this approach to equilibrium which determines the contrast and signal-to-noise ratio (SNR) obtained. The contrast obtained is strongly dependent on the phase encoding scheme used. If the flip angle is increased, and the resulting transverse coherences refocused, then the SNR is improved while the contrast is little changed.

Magnetic Resonance Imaging↗

PubMed1990

3D-snapshot flash NMR imaging of the human heart.

SNAPSHOT-FLASH is a recently developed, ultrafast imaging technique, based on conventional FLASH imaging. The application of this new variant to 3D imaging allows the acquisition of a 128 x 128 x 32 data set in 12.5 seconds without triggering, or for cardiac imaging with gating within 32 heartbeats. Compared to standard 3D-FLASH this is 128 times faster, because triggering is only required when the 3D phase-encoding gradient is incremented. The method depicts for the first time fast three-dimensional views of the human heart without motional artifacts. The images are spin-density weighted. Using suitable prepulses any desired T1- or T2-contrast may be achieved. The generation of 3D movies is possible without an increase of the total scan time.

Heart↗

PubMed1992

Fast inversion recovery T1 contrast and chemical shift contrast in high-resolution snapshot FLASH MR images.

Fast MR imaging attracts the interest of both clinicians and physicists because new diagnostic information arises with reduced artifacts due to short investigational times. With the acceleration of the Snapshot FLASH MR sequence, the measurement of high-resolution images with 256 x 256 matrix is reported, together with contrasting prepulses that are applied to attain contrast in combination with higher in-plane resolution. Measuring times are in the range of a second. For whole-body imaging, a TR = 5.2 msec and a TE = 2.6 msec could be attained measuring omit 256 x 256 matrix images. Artifact-free images demonstrating T1 contrast and contrast from chemical shift are performed on moving organs (heart, intestine) in different experiments. These applications can easily be performed in a couple of minutes for clinical use. Especially in the lung, short TE and high resolution result in a new imaging quality of pulmonary and mediastinal vessels.

Abdomen↗

PubMed1992

Partial angle inversion recovery (PAIR) MR imaging: spin-echo and snapshot implementation.

The effects of varying the inversion or excitation RF pulse flip angles on image contrast and imaging time have been investigated in IR imaging theoretically, with phantoms and with normal volunteers. Signal intensity in an IR pulse sequence as a function of excitation, inversion and refocusing pulse flip angles was calculated from the solution to the Bloch equations and was utilized to determine the contrast behavior of a lesion/liver model. Theoretical and experimental results were consistent with each other. With the TI chosen to suppress the fat signal, optimization of the excitation pulse flip angle results in an increase in lesion/liver contrast or allows reduction in imaging time which, in turn, can be traded for an increased number of averages. This, in normal volunteers, improved spleen/liver contrast-to-noise ratio (9.0 vs. 5.7, n = 8, p less than 0.01) and suppressed respiratory ghosts by 33% (p less than 0.01). Reducing or increasing the inversion pulse from 180 degrees results in shorter TI needed to null the signal from the tissue of interest. Although this decreases the contrast-to-noise ratio, it can substantially increase the number of sections which can be imaged per given TR in conventional IR imaging or during breathold in the snapshot IR (turboFLASH) technique. Thus, the optimization of RF pulses is useful in obtaining faster IR images, increasing the contrast and/or increasing the number of imaging planes.

Abdomen↗

PubMed1995

Fast T2-mapping with snapshot flash imaging.

It has been shown recently that quantitative T2-maps may be measured by acquisition of a series of at least eight T2-weighted SNAPSHOT FLASH images. These measurements require a relaxation delay of 10-15 s after each T2-weighted image for the complete relaxation of the spin system. This results in long measuring times. The method presented in this paper allows a considerable reduction of the measuring time by combining the T2-sequence with a fast T1-measurement. Quantitative T1- and T2-maps may be acquired simultaneously in less than 30 s. The method was tested in a phantom experiment. In an in vivo application, relaxation times of different tissues in the abdomen of a rat were measured.

Abdomen↗

PubMed1992

Rapid, accurate and simultaneous noninvasive assessment of right and left ventricular mass with nuclear magnetic resonance imaging using the snapshot gradient method.

Left ventricular, and possibly also right ventricular, mass is an important determinant of prognosis in cardiovascular disease. Consequently, noninvasive estimation of ventricular mass may be an important clinical investigation. The ideal technique for this purpose would be widely available and accurate, employ short study times and avoid exposure to contrast agents and radiation. Conventional nuclear magnetic resonance (NMR) imaging fulfills most of these criteria, but it is time-consuming and expensive. Moreover, its accuracy in estimating right ventricular mass has yet to be assessed. Accordingly, high speed NMR imaging using the snapshot gradient echo technique was used to assess right and left ventricular mass in 10 dogs and the results were compared with values obtained at autopsy, which ranged from 26.1 to 52.9 and 61 to 119.8 g, respectively. The mean absolute difference between the NMR imaging estimates and autopsy findings was 2 +/- 1.2 g (range 0.4 to 4.2) for right ventricular mass and 4.4 +/- 1.7 g (range 1.8 to 6.6) for left ventricular mass. Total NMR imaging time was less than or equal to 5 min. These data demonstrate that high speed NMR imaging can be used to accurately estimate right as well as left ventricular mass.

Animals↗

PubMed2026

Four-dimensional molecular mapping from a spatial snapshot reveals the dynamics of hair follicle organogenesis.

Understanding organ formation requires capturing molecular information simultaneously in three-dimensional (3D) space and across developmental time. To this end, we developed 3D DNase-Enhanced Expression Profiling (3DEEP), a tissue-clearing approach that removes genomic DNA to extend spatial transcriptomic profiling hundreds of microns into intact tissues. We applied 3DEEP to neonatal mouse skin, capturing hundreds of developing hair follicles across their organogenesis trajectory. Ordering follicles by molecularly inferred developmental age transformed this single spatial snapshot into a four-dimensional (3D + time) molecular map of organogenesis. This map revealed developmental dynamics spanning stem cell compartment stratification, emergence of new cell subtypes within the follicle, and cascading structural transformations leading to hair canal formation. Comparative analysis of Foxn1-deficient nude mice, a hairlessness model, revealed organ-wide changes in developmental dynamics, including delayed molecular progression, reduced coordination, and increased developmental instability, preceding overt structural defects. This work demonstrates how deep-tissue spatial transcriptomics can uncover hidden dynamics of organ formation.

Animals↗

PubMed2004

Structural snapshots of the KMSKS loop rearrangement for amino acid activation by bacterial tyrosyl-tRNA synthetase.

Tyrosyl-tRNA synthetase (TyrRS) has been studied extensively by mutational and structural analyses to elucidate its catalytic mechanism. TyrRS has the HIGH and KMSKS motifs that catalyze the amino acid activation with ATP. In the present study, the crystal structures of the Escherichia coli TyrRS catalytic domain, in complexes with l-tyrosine and a l-tyrosyladenylate analogue, Tyr-AMS, were solved at 2.0A and 2.7A resolution, respectively. In the Tyr-AMS-bound structure, the 2'-OH group and adenine ring of the Tyr-AMS are strictly recognized by hydrogen bonds. This manner of hydrogen-bond recognition is conserved among the class I synthetases. Moreover, a comparison between the two structures revealed that the KMSKS loop is rearranged in response to adenine moiety binding and hydrogen-bond formation, and the KMSKS loop adopts the more compact ("semi-open") form, rather than the flexible, open form. The HIGH motif initially recognizes the gamma-phosphate, and then the alpha and gamma-phosphates of ATP, with a slight rearrangement of the residues. The other residues around the substrate also accommodate the Tyr-AMS. This induced-fit form presents a novel "snapshot" of the amino acid activation step in the aminoacylation reaction by TyrRS. The present structures and the T.thermophilus TyrRS ATP-free and bound structures revealed that the extensive induced-fit conformational changes of the KMSKS loop and the local conformational changes within the substrate binding site form the basis for driving the amino acid activation step: the KMSKS loop adopts the open form, transiently shifts to the semi-open conformation according to the adenosyl moiety binding, and finally assumes the rigid ATP-bound, closed form. After the amino acid activation, the KMSKS loop adopts the semi-open form again to accept the CCA end of tRNA for the aminoacyl transfer reaction.

Adenosine↗