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PubMed1998

The detection of K-ras mutations in colorectal cancer using the amplification-refractory mutation system.

A total of 301 colorectal carcinoma (CRC) archival samples were analysed using the amplification-refractory mutation system (ARMS). Each sample was examined to determine the mutation status of codons 12 and 13 of the K-ras oncogene. The results from direct DNA sequence analysis carried out on 30 of the samples differed from the ARMS result in almost 50% of the cases as a result of the relative excess of wild-type to mutated DNA sequences. To assess the validity of the ARMS data, the polymerase chain reaction (PCR) was used to generate an amplicon from K-ras exon 1 from 23 of the samples. The PCR amplicons were cloned and sequenced, and the DNA sequence analysis of the cloned material was in agreement with the ARMS results in all but one case. This case represented a tumour that exhibited a five-nucleotide reversed inversion. The cloned sequence data confirm the sensitivity and specificity of the individual ARMS reactions and that it is possible in certain cases to detect additional, more complex, sequence variations.

Adenoma↗
PubMed1994

A transcriptionally controlled trans-processing assay: putative identification of a vaccinia virus-encoded proteinase which cleaves precursor protein P25K.

Vaccinia virus maturation into infectious particles appears to be dependent on the proteolytic processing of at least five viral proteins, each containing a conserved AG*X cleavage motif and each requiring proper association with the previrion particle. To identify the responsible proteinase, a transcriptionally controlled trans-processing assay was developed to monitor cleavage at the permissive AG*S site of the P25K core protein precursor. This assay led to the putative identification of a VV proteinase encoded by open reading frame G1L. The predicted protein contains an HXXEH sequence which is a direct inversion of the active site consensus sequence present in thermolysin and other metalloendopeptidases. Site-directed mutation of this consensus sequence suggests that the G1L protein may be a novel, virus-encoded metalloendoproteinase, although confirmation of this activity must await the development of a suitable cell-free processing assay.

Amino Acid Sequence↗
PubMed1998

Role of the human rostral supplementary motor area and the basal ganglia in motor sequence control: investigations with H2 15O PET.

The aim of this study was to investigate the functional anatomy of distributed cortical and subcortical motor areas in the human brain that participate in the central control of overlearned complex sequential unimanual finger movements. On the basis of previous research in nonhuman primates, a principal involvement of basal ganglia medial premotor loops [corrected] was predicted for central control of finger sequences performed automatically. In pertinent areas, a correlation of activation levels with the complexity of a motor sequence was hypothesized. H2 15O positron emission tomography (PET) was used in a group of seven healthy male volunteers [mean age 32.0 +/- 10.4 yr] to determine brain regions where levels of regional cerebral blood flow (rCBF) correlated with graded complexity levels of five different key-press sequences. All sequences were overlearned before PET and involved key-presses of fingers II-V of the right hand. Movements of individual fingers were kept constant throughout all five conditions by external pacing at 1-Hz intervals. Positive correlations of rCBF with increasing sequence complexity were identified in the contralateral rostral supplementary motor area (pre-SMA) and the associated pallido-thalamic loop, as well as in right parietal area 7 and ipsilateral primary motor cortex (M1). In contrast, while rCBF in contralateral M1 and [corrected] extensive parts of caudal SMA was increased compared with rest during task performance, significant correlated increases of rCBF with sequence complexity were not observed. Inverse correlations of rCBF with increasing sequence complexity were identified in mesial prefrontal-, medial temporal-, and anterior cingulate areas. The findings provide further evidence in humans supporting the notion of a segregation of SMA into functionally distinct subcomponents: although pre-SMA was differentially activated depending on the complexity of a sequence of learned finger movements, such modulation was not detectable in caudal SMA (except the most antero-superior part), implicating a motor executive role. Our observations of complexity-correlated rCBF increases in anterior globus pallidus suggest a specific role for the basal ganglia in the process of sequence facilitation and control. They may act to filter and focus input from motor cortical areas as patterns of action become increasingly complex.

Adult↗
PubMed1994

Requirement for double-strand breaks but not for specific DNA sequences in herpes simplex virus type 1 genome isomerization events.

Herpes simplex virus type 1 (HSV-1) genome isomerization occurs as a result of DNA replication-mediated homologous recombination between several sets of inverted repeat sequences present in the viral DNA. The frequency with which this recombination occurs has been demonstrated to be dependent upon DNA homology length rather than specific sequences. However, the smallest of the viral inverted repeats, the alpha sequence, has been shown to function as a recombinational hot spot, leading to speculation that this sequence may represent a specific element through which genome isomerization is mediated. To investigate this apparent paradox, a quantitative transient recombination assay system was developed and used to examine the recombinogenic properties of a panel of alpha sequence mutants. This analysis revealed that the presence of both the pac1 and pac2 elements was both necessary and sufficient for the induction of high-frequency recombination events by the alpha sequence. However, it was the double-strand break promoted by pac1 and pac2 during cleavage and packaging at the alpha sequence, and not the DNA sequences of the elements themselves, which appeared to be critical for recombination. This was illustrated (i) by the inability of the same pac1 and pac2 sequences to mediate inversion events in cells infected with an HSV-1 mutant which was competent for DNA replication-dependent recombination but defective for the cleavage and packaging process and (ii) by the ability of double-strand breaks generated in non-HSV-1 DNA by an in vivo-expressed restriction endonuclease to significantly stimulate the initiation of recombination events in virus-infected cells. Thus, the alpha sequence appears to act as a hot spot for homologous recombination simply because it happens to coincide with the site of the double-strand break which is generated during the cleavage and packaging process, not because it contains discrete sequences which are required for this activity. However, it was found that this enhanced recombinogenicity disappeared when the element was flanked by regions of extensive sequence homology, particularly that of the large inverted repeats which flank the alpha sequence at its natural site in the HSV-1 genome. These findings are consistent with a model for HSV-1 genome isomerization in which recombination is initiated primarily by multiple random double-strand breaks which arise during DNA replication across the inverted repeats of the genome, rather than by a single specific break which occurs at the alpha sequence during the cleavage and packaging process.

Animals↗
PubMed1987

The breakpoint of an inversion of chromosome 14 in a T-cell leukemia: sequences downstream of the immunoglobulin heavy chain locus are implicated in tumorigenesis.

T-cell tumors are characterized by inversions or translocations of chromosome 14. The breakpoints of these karyotypic abnormalities occur in chromosome bands 14q11 and 14q32--the same bands in which the T-cell receptor (TCR) alpha-chain and immunoglobulin heavy chain genes have been mapped, respectively. Patients with ataxia-telangiectasia are particularly prone to development of T-cell chronic lymphocytic leukemia with such chromosomal abnormalities. We now describe DNA rearrangements of the TCR alpha-chain gene in an ataxia-telangiectasia-associated leukemia containing both a normal and an inverted chromosome 14. The normal chromosome 14 has undergone a productive join of TCR alpha-chain variable (V alpha) and joining (J alpha) gene segments. The other allele of the TCR alpha-chain gene features a DNA rearrangement, about 50 kilobases from the TCR alpha-chain constant (C alpha) gene, that represents the breakpoint of the chromosome 14 inversion; this breakpoint is comprised of a TCR J alpha segment (from 14q11) fused to sequences derived from 14q32 but on the centromeric side of C mu. These results imply that 14q32 sequences located at an undetermined distance downstream of the immunoglobulin C mu locus can contribute to the development of T-cell tumors.

Ataxia Telangiectasia↗
PubMed1999

Wobble board (ankle disc) training effects on the discrimination of inversion movements.

To assess the effect of a five-week training program using a wobble board on discrimination of discrete movements at the ankle, 40 ankles were tested from 20 subjects in a group of elite athletes. Players in a first grade rugby league squad were randomly allocated to either a wobble board training or no-training group. Pre-tests to assess discrimination of inversion movements made while standing were carried out on both ankles of all subjects using an automated device that enabled a normal share of weightbearing on the tested ankle. From a sequence of 160 inversion movements, a discrimination index was determined. This measure represents the relative difference in angular extent needed for an inversion movement to be differentiated 75 per cent of the time from the standard movement of 12.5 degrees below horizontal. Subjects were re-tested after either undertaking a five-week wobble board training program, or after having had no training. Discrimination of movements into inversion improved from the pre-test (Weber fraction 8.8 per cent) to the post training test (6.4 per cent) in the wobble board trained group. This discrimination improvement was significantly greater than the change in the untrained group (pre-test: 8.4 per cent and post-test: 8.1 per cent). These data demonstrate that wobble board training can improve discrimination of discrete ankle inversion movements, and support the Weber fraction as a measure of movement sensitivity.

Journal Article↗
PubMed1975

Occurrence of insertion sequence (IS) regions on plasmid deoxyribonucleic acid as direct and inverted nucleotide sequence duplications.

Insertion sequence (IS) regions have been identified previously as a cause of strongly polar mutations in Escherichia coli and several bacteriophages. The present experiments indicate that genetically characterized IS regions occur on bacterial plasmid deoxyribonucleic acid (DNA) as both direct and inverted DNA sequence duplications. The DNA insertion which has been shown previously (Sharp et al., 1973) to control expression of tetracycline resistance in the R6-5 plasmid, and which occurs as directly and inversely repeated DNA sequences adjacent to the region believed to contain the tetracycline resistance gene, has been identified as IS3. A second genetically characterized insertion sequence (IS1) has been identified as a direct DNA duplication occurring at both junctions of the resistance transfer factor and R-determinant components of R6-5 and related plasmids. A model is presented for the reversible dissociation of resistance transfer factor and R-determinant components of co-integrate R plasmids at the sites of DNA sequence homology provided by the repeated IS regions.

Base Sequence↗
PubMed2000

[Advantages and limitations of whole-body bone marrow MRI using Turbo-STIR sequences in comparison to planar bone scans] .

UNLABELLED: At modern MRI tomographs the whole body can be screened for bone marrow metastases within 45 min. AIM of this study was to evaluate the diagnostic advantages and disadvantages of a whole-body bone marrow MRI protocol using Turbo Short Tau Inversion Recovery [STIR] sequences in comparison to planar bone scintigraphy (SZ). PATIENTS AND METHODS: In order to screen for bone metastases within two weeks SZ and whole-body MRI with Turbo-STIR-sequences were performed in 20 patients with known breast cancer. For further evaluation five regions were defined: skull, spine including the pelvis, femora, humeri and ribs including scapulae and sternum. RESULTS: In 9/20 patients neither with SZ nor with MRI bone metastases were detected (staging M0). Among the remaining 11 patients SZ detected 109 and MRI 150 lesions which were typical for bone metastases. All of these 11 patients were staged M1 correspondingly with both methods. Within the thorax (ribs, sternum, scapulae) MRI discovered only 6/17 and within the skull 0/6 lesions which were suspicious for metastases in SZ. Inversely MRI identified much more metastatic lesions than SZ within the femora (20/16), the humeri (14/12) and the spine including the pelvis (110/58). CONCLUSIONS: Susceptibility-, truncation-, chemical-shift-, third arm- and particularly pulsation artifacts along with the impossibility to chose slice orientation equally advantageous for all regions of the body cause impaired image quality of MRI whole body scanning. Therefore, concerning the detection rate of bone metastases within the thorax (ribs, sternum and scapulae) and the skull, conventional Turbo-STIR-MRI whole-body scans are even less accurate than conventional planar bone scintigraphy in those regions.

Bone Marrow↗
PubMed1996

Long echo time STIR sequence MRI of optic nerves in optic neuritis.

MRI of the optic nerves was obtained in 13 patients with acute optic neuritis and 13 with a previous optic neuritis (ON), assessed by clinical features, visual fields and visual evoked potentials. Results of the conventional short tau inversion recovery (STIR) sequence obtained with a short echo time (STE-STIR; 22 ms) were compared with those of a long echo time (LTE-STIR: 80 ms) sequence. The conventional STE-STIR sequence revealed lesions in the optic nerves in 78.5% of acute and 58.8% of previous ON. The LTE-STIR sequence showed abnormalities in 92.8% of acutely symptomatic nerves and 94.1% of nerves with previous ON. The optic nerve lesions appeared significantly longer with the LTE-STIR sequence than with the conventional STE-STIR sequences, in both acute and previous ON.

Adult↗
PubMed1990

Genetic structure and DNA sequences at junctions involved in the rearrangements of Bacillus subtilis strains carrying the trpE26 mutation.

Studies on the region upstream to ribosomal operon rrnD of Bacillus subtilis led to the characterization of two of the four chromosomal junctions involved in the rearrangements (a translocation and an inversion) of the strains carrying the trpE26 mutation. Genetic analysis, by integrative mapping, showed linkage of rrnD to cysB and hisA (both on segment A) in the trpE26-type strains. Physical analysis showed that the region upstream to rrnD is now linked to the trpE-ilvA chromosome segment as demonstrated by analyzing restriction site-polymorphism between 168 and trpE26-type strains. Similar experiments confirmed the previous genetic data on linkage in these areas in strains carrying novel rearrangements derived from the trpE26-type strains: stable merodiploids and inversions. The nucleotide sequence of the area 5' to rrnD in both types of strains (168 and trpE26), the region downstream of the citG gene and the region carrying the trpE26 mutation (made available to us by D. Henner) provided evidence for the molecular basis of the differences in structure, allowed the identification of the break points and revealed the presence of a polypurine region upstream to rrnD as seen in other systems in B. subtilis. No extensive homology was found between pairs of junctions so far sequenced. The models proposed by C. Anagnostopoulos for the role of DNA sequences of intrachromosomal homology involved in the transfer of the trpE26 mutation and the formation of novel arrangements require therefore reevaluation.

Amino Acid Sequence↗
PubMed1996

Lesion discrimination in optic neuritis using high-resolution fat-suppressed fast spin-echo MRI.

Fast spin-echo (FSE) is a new sequence with acquisition times currently down to one-sixteenth of those obtained with conventional spin-echo sequences, which allows high-resolution (512 x 512 matrix) images to be acquired in an acceptable time. We compared the higher resolution of FSE with the medium resolution of a short inversion-time inversion-recovery (STIR) sequence in depicting the optic nerves of healthy controls and patients with optic neuritis. Optic nerve MRI examinations were performed in 18 patients with optic neuritis and 10 normal controls. Two sequences were obtained coronally: fat-suppressed FSE (FSE TR 3250 ms/TEef 68 ms, echo-train length 16, 4 excitations, 24 cm rectangular field of view, 3 mm interleaved contiguous slices, in-plane resolution 0.5 x 0.5 mm) and STIR (TR 2000 ms/TE 50 ms/TI 175 ms, in-plane resolution 0.8 x 0.8 mm, slice thickness 5 mm). FSE demonstrated much more anatomical detail than STIR, e.g. distinction of optic nerve and sheath. Lesions were seen in 20 of 21 symptomatic nerves using FSE and in 18 of 21 using STIR. Nerve swelling or partial cross-sectional lesions of the optic nerve were each seen only on FSE in 3 cases. Fat-suppressed FSE imaging of the optic nerve improves anatomical definition and increases lesion detection in optic neuritis.

Adult↗
PubMedDate not supplied

Turbo short tau inversion recovery imaging for metastatic node screening in patients with head and neck cancer.

BACKGROUND AND PURPOSE: A rapid and sensitive MR imaging technique would be beneficial for screening of metastatic nodes in the neck. We preliminarily evaluated the coronal MR imaging with a turbo short tau inversion recovery (STIR) sequence for that purpose. METHODS: The coronal turbo STIR imaging (repetition time [TR]/echo time [TE]/inversion time [TI] = 3850 ms/20 or 80 ms/180 ms) and axial fat-suppressed spectral presaturation with inversion recovery (SPIR) T2-weighted imaging (fsT2WI) (TR/TE = 3500 ms/80 ms) were performed on 29 patients with head and neck cancer. We obtained coronal turbo STIR images and axial fsT2WI of the necks. The section thickness, intersection gap, matrix size, and field of view were the same in both techniques. The diagnostic ability for metastatic nodes was assessed at each neck level by using various cutoff size criteria. The nodal involvement was confirmed by histologic examination. RESULTS: The image acquisition time for the whole neck by coronal turbo STIR and axial fsT2WI techniques was approximately 2 minutes and 4 minutes, respectively. When the size criteria (cutoff sizes of short axis diameter were 8 mm at level I and 5 mm at levels II and III) were used, the STIR imaging yielded compromised diagnostic ability having 100% sensitivity and 100% negative predictive value (NPV). fsT2WI technique yielded 100 sensitivity and 100% NPV by using cutoff sizes of 6 mm at levels I and II and 5 mm at level III. CONCLUSION: Coronal STIR imaging provided a rapid screening technique for cervical metastatic nodes and could be a diagnostic tool before detailed MR studies of the neck.

Adult↗
PubMedDate not supplied

A phantom study of intracranial CSF signal loss due to pulsatile motion.

MR imaging of the head often reveals localized areas of decreased signal intensity (flow voids) within the CSF. These flow voids are caused by turbulence within the CSF resulting from its pulsatile back-and-forth flow through the cerebral aqueduct and foramina. We describe a phantom that mimics the essential features of the CSF flow, and discuss its use in studying the dependence of the CSF flow void (CFV) on spin-echo (SE) and inversion-recovery pulse sequence parameters. The phantom had fluid-filled spaces to represent ventricles, and channels connecting these spaces to represent the aqueduct and foramina. A pump pushed the fluid in a pulsing manner through the phantom at various rates. The CFV was quantified by measuring signal loss relative to nonflowing fluid. The CFV did not appear to depend on repetition time or inversion time. The CFV was, however, strongly dependent on echo time (TE), and for single-echo SE sequences CFV became less severe as TE decreased. An even-echo rephasing effect was observed for multiecho sequences. Slice thickness and field of view also affected the appearance of the CFV, as did gating with respect to the pulsatile motion. These results imply that TE, field of view, slice thickness, and gating must be considered when using the appearance or absence of the CFV in diagnosis.

Cerebrospinal Fluid↗
PubMed1992

Detection of acute avascular necrosis of the femoral head in dogs: dynamic contrast-enhanced MR imaging vs spin-echo and STIR sequences.

OBJECTIVE: Spin-echo MR imaging has been shown to be highly sensitive in the detection of avascular necrosis. Very early avascular necrosis can, however, appear normal on MR images. We compared dynamic contrast-enhanced MR imaging with conventional spin-echo and short Tl inversion-recovery (STIR) sequences for detecting acute osteonecrosis in an animal model. MATERIALS AND METHODS: Avascular necrosis was induced unilaterally in the femoral heads of five dogs that were imaged with a 1.5-T system within 3 hr of devascularization. After standard T1-weighted, T2-weighted, and STIR images, gradient-recalled echo images, 28/5 (TR/TE) with a 45 degrees flip angle, were obtained at 6-sec intervals for 90 sec synchronous with the IV administration of 0.2 mmol of gadoteridol per kilogram of body weight at a rate of 2 ml/sec via an automated injector. Two animals were reimaged after 7 days. RESULTS: Spin-echo and STIR images did not show any acute changes in the ischemic femoral heads. In contrast, significant differences were present in the enhancement profiles of the marrow spaces in the normal and ischemic femoral heads (p = .005). Normal marrow was characterized by rapid enhancement, with an average signal intensity increase of 83% peaking at 36 sec; no measurable enhancement was seen in the marrow of the ischemic femoral head. Spin-echo images, obtained 7 days after devascularization (n = 2), showed changes characteristic of avascular necrosis. Dynamic contrast-enhanced MR images showed persistent lack of enhancement in the avascular marrow of the ischemic femoral head. A junctional zone, characterized by rapid contrast enhancement in excess of 120% without early washout, was identified at the interface between normal and avascular marrow. CONCLUSION: In this experimental model, dynamic contrast-enhanced MR imaging proved significantly more sensitive than conventional spin-echo and STIR imaging in the detection of acute avascular necrosis.

Acute Disease↗
PubMed1998

Optic neuritis: MR imaging with combined fat- and water-suppression techniques.

PURPOSE: To examine the benefits of combined fat- and water-suppressed T2-weighted magnetic resonance (MR) images in the diagnosis of optic neuritis. MATERIALS AND METHODS: MR imaging was performed with a 1.5-T unit in five healthy volunteers and 18 patients (21 nerves). All patients had abnormalities of visual evoked potentials and fulfilled the clinical criteria for the diagnosis of optic neuritis. Imaging was performed within 4 weeks of diagnosis (n = 12) or between 3 and 6 months after diagnosis (n = 6). Coronal images were obtained throughout the course of the optic nerve with use of three sequences: (a) short inversion time inversion recovery with fast spin-echo (SE) acquisition, (b) selective partial inversion-recovery (SPIR) prepared T2-weighted fast SE acquisition, and (c) SPIR-fluid-attenuated inversion recovery (FLAIR) with fast SE acquisition. RESULTS: Neuritic segments were demonstrated in all 21 symptomatic nerves. The extent of neuritic involvement (number of images showing abnormality) was significantly greater with the SPIR-FLAIR sequence (P < .01). The contrast ratio between neuritic optic nerve and orbital fat, normal nerve, and cerebral spinal fluid was significantly greater with SPIR-FLAIR than with the other sequences (P < .001). SPIR-FLAIR images also improved demonstration of optic nerve atrophy in chronic neuritis when compared with the other sequences. CONCLUSION: The SPIR-FLAIR sequence offers important advantages over current methods in the demonstration of optic neuritis.

Adult↗
PubMed2006

Localization and characterization of X chromosome inversion breakpoints separating Drosophila mojavensis and Drosophila arizonae.

Ectopic exchange between transposable elements or other repetitive sequences along a chromosome can produce chromosomal inversions. As a result, genome sequence studies typically find sequence similarity between corresponding inversion breakpoint regions. Here, we identify and investigate the breakpoint regions of the X chromosome inversion distinguishing Drosophila mojavensis and Drosophila arizonae. We localize one inversion breakpoint to 13.7 kb and localize the other to a 1-Mb interval. Using this localization and assuming microsynteny between Drosophila melanogaster and D. arizonae, we pinpoint likely positions of the inversion breakpoints to windows of less than 3000 bp. These breakpoints define the size of the inversion to approximately 11 Mb. However, in contrast to many other studies, we fail to find significant sequence similarity between the 2 breakpoint regions. The localization of these inversion breakpoints will facilitate future genetic and molecular evolutionary studies in this species group, an emerging model system for ecological genetics.

Animals↗
PubMed1990

The use of Gd-DOTA in magnetic resonance imaging of experimentally induced mammary tumors.

Gd-DOTA contrast enhancement of MR images was evaluated on induced mammary tumors in female rats. A single intravenous injection of the carcinogenic N-nitrosourea ENU was administered to Wistar rats; this simple treatment led to a high percentage of mammary tumors without causing death. All the induced tumors were adenocarcinoma and their heterogeneousness depended on their size. The induced tumors did not have intra- or extravascular inflammatory spaces caused by heterotopic lesions, as is the case with implanted tumors. Before injection of Gd-DOTA, appearance of the patchy internal structure was clearly demonstrated on spin-echo images performed with long repetition times. Three doses of the paramagnetic contrast agent (0.1, 0.2, and 0.5 mmol/kg) were evaluated on two different T1-weighted MR sequences. Images were recorded before and repeatedly after intravenous injection of Gd-DOTA, and signal intensities and relaxation times were measured. On images acquired with the spin-echo 500/28 as well as the inversion-recovery 928/26/300 sequences, the results showed that 0.2 mmol/kg Gd-DOTA was the optimal dose for contrast enhancement and for clear visualization of the heterogeneousness of the mammary tumor.

Adenocarcinoma↗