Biomedical subjects
B Appel
Publications and source records attributed to B Appel.
MRI approach of multiple sclerosis. 449 cases examined at 0.15 Tesla.
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MRI of the spine and spinal cord: infectious and inflammatory pathology.
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White matter diseases or leuko-araiosis of degenerative origin. MRI at 0.15 Tesla.
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Xenopus tropicalis U6 snRNA genes transcribed by Pol III contain the upstream promoter elements used by Pol II dependent U snRNA genes.
We have cloned and sequenced a 977bp DNA fragment, pXTU6-2, that represents the transcription unit for a Xenopus tropicalis U6 RNA gene. This basic repeating unit is reiterated ca.500-fold per haploid genome. Oocyte injections of pXTU6-2 led to the transcription of a mature-sized U6 RNA that, however, lacked internal 2'-O-methylations. These posttranscriptional modifications of U6 RNA might be cytoplasmic and could require its association with U4 RNA to be accomplished. The low alpha- amanitin sensitivity of U6 RNA synthesis in oocytes suggested that U6 RNA is transcribed by RNA polymerase III, consistent with features of the U6 RNA molecule which also contains a Box A- like intragenic control region. Inspection of X. tropicalis, mouse and human U6 DNA upstream sequences revealed the presence of a TATA box as well as of the proximal and enhancer (octamer motif) elements contained in snRNA genes transcribed by RNA polymerase II. We propose that U6 RNAs are synthesized by a specialized transcription complex consisting of RNA polymerase III and transcription factors, some of which are very likely shared with RNA polymerase II promoters.
Magnetic resonance imaging and cognitive functioning in multiple sclerosis.
The relationship between cognitive impairment in multiple sclerosis and brain lesions seen on magnetic resonance imaging (MRI) was studied. Three groups of 11 patients with multiple sclerosis, matched for the variables of disability, duration of illness, age and sex, were included. On the basis of neuropsychological testing, the groups were seen to differ in their level of cognitive impairment. The first group showed no cognitive impairment, the second group a moderate, and the third group a serious cognitive impairment. These differences between the groups were reflected by MRI, which revealed more abnormalities in the groups with cognitive impairment compared with the group with normal cognitive function. However, by MRI it was not possible to distinguish between the groups with moderate and that with serious cognitive impairment.
Radiation exposure to patients during extracorporeal shock wave lithotripsy.
Extracorporeal shock wave lithotripsy is rapidly becoming an accepted treatment of renal calculi. Since fluoroscopy is involved to image the stones it is important to know how much radiation the patient receives during this proCedure. Surface radiation exposure to the patient was measured in more than 300 fluoroscopic and radiographic procedures using thermoluminescent dosimeters. Initial results showed an average skin exposure of 10.1 rad per procedure for each x-ray unit, comparing favorably with exposure rates for percutaneous nephrostolithotomy and other routine radiological procedures. Factors influencing exposure levels include stone characteristics (location, size and opacity), physician experience and number of shocks required. Suggestions are given that may result in a 50 per cent reduction of radiation exposure.
[Relaxation-time measurements of the white and gray substances in multiple sclerosis patients].
In a patient population of some 450 with definite, probable, and possible multiple sclerosis referred to us for MRI, some 40 suffering from definite MS were chosen randomly for relaxation time measurements of plaque-free grey and white matter. T1 values could not be used for diagnostic purposes owing to their broad standard deviation. Overall white matter T2 was slightly higher in MS patients than in a non-MS population (94 ms versus 89 ms). Because these changes are not visible in MR images, relaxation time measurements may prove valuable for differential diagnosis.
Posttraumatic diabetes insipidus.
The authors report seven patients with fractures of the sella turcica. Four of them developed Diabetes Insipidus as a consequence of their traumata. The importance of computed tomography as a diagnostic procedure is paramount in order to make early diagnosis of this potential life-threatening condition possible.
CT and NMR in craniocerebral trauma.
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Rounded atelectasis. A case report.
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Localization of a base-paired interaction between small nuclear RNAs U4 and U6 in intact U4/U6 ribonucleoprotein particles by psoralen cross-linking.
The small nuclear RNAs U4 and U6 display extensive sequence complementarity and co-exist in a single ribonucleoprotein particle. We have investigated intermolecular base-pairing between both RNAs by psoralen cross-linking, with emphasis on the native U4/U6 ribonucleoprotein complex. A mixture of small nuclear ribonucleoproteins U1 to U6 from HeLa cells, purified under non-denaturing conditions by immune affinity chromatography with antibodies specific for the trimethylguanosine cap of the small nuclear RNAs was treated with aminomethyltrioxsalen. A psoralen cross-linked U4/U6 RNA complex could be detected in denaturing polyacrylamide gels. Following digestion of the cross-linked U4/U6 RNA complex with ribonuclease T1, two-dimensional diagonal electrophoresis in denaturing polyacrylamide gels was used to isolate cross-linked fragments. These fragments were analysed by chemical sequencing methods and their positions identified within RNAs U4 and U6. Two overlapping fragments of U4 RNA, spanning positions 52 to 65, were cross-linked to one fragment of U6 RNA (positions 51 to 59). These fragments show complementarity over a contiguous stretch of eight nucleotides. From these results, we conclude that in the native U4/U6 ribonucleoprotein particle, both RNAs are base-paired via these complementary regions. The small nuclear RNAs U4 and U6 became cross-linked in the deproteinized U4/U6 RNA complex also, provided that small nuclear ribonucleoproteins were phenolized at 0 degree C. When the phenolization was performed at 65 degrees C, no cross-linking could be detected upon reincubation of the dissociated RNAs at lower temperature. These results indicate that proteins are not required to stabilize the mutual interactions between both RNAs, once they exist. They further suggest, however, that proteins may well be needed for exposing the complementary RNA regions for proper intermolecular base-pairing in the course of the assembly of the U4/U6 RNP complex from isolated RNAs. Our results are discussed also in terms of the different secondary structures that the small nuclear RNAs U4 and U6 may adopt in the U4/U6 ribonucleoprotein particle as opposed to the isolated RNAs.
Point mutational analysis of the Xenopus laevis 5S gene promoter.
We have introduced C to T transitions into GC and CG base pairs of the Xenopus laevis somatic 5S gene coding region and its 5' flank in order to analyse their effects on transcription activity and regulation. These studies allow us to differentiate between the two promoter elements and their spacer, within the internal control region. Mutations within the 5' element which dissent from the corresponding tRNA consensus sequence reduce transcription activity substantially without significantly affecting transcription factor (TF) III A binding. Mutations in the spacer region have no pronounced effect on transcription. The 3' promoter element is found to extend to position 97, since mutations in this region interfere with transcription activity. This may be, at least partially, attributable to a reduced competition strength for TF III A.
Novel structure of a human U6 snRNA pseudogene.
A genomic DNA library containing human placental DNA cloned into phage lambda Charon 4A was screened for snRNA U6 genes. In vitro 32P-labeled U6 snRNA isolated from HeLa cells was used as a hybridization probe. A positive clone containing a 4.6-kb EcoRI fragment of human chromosomal DNA was recloned into the EcoRI site of pBR325 and mapped by restriction endonuclease digestion. Restriction fragments containing U6 RNA sequences were identified by hybridization with isolated U6[32P]RNA. The sequence analysis revealed a novel structure of a U6 RNA pseudogene, bearing two 17-nucleotide(nt)-long direct repeats of genuine U6 RNA sequences arranged in a head-to-tail fashion within the 5' part of the molecule. Hypothetical models as to how this type of snRNA U6 pseudogene might have been generated during evolution of the human genome are presented. When compared to mammalian U6 RNA sequences the pseudogene accounts for a 77% overall sequence homology and contains the authentic 5'- and 3'-ends of the U6 RNA.
Localization and structure of snRNPs during mitosis. Immunofluorescent and biochemical studies.
The distribution of U snRNAs during mitosis was studied by indirect immunofluorescence microscopy with snRNA cap-specific anti-m3G antibodies. Whereas the snRNAs are strictly nuclear at late prophase, they become distributed in the cell plasm at metaphase and anaphase. They re-enter the newly formed nuclei of the two daughter cells at early telophase, producing speckled nuclear fluorescent patterns typical of interphase cells. While the snRNAs become concentrated at the rim of the condensing chromosomes and at interchromosomal regions at late prophase, essentially no association of the snRNAs was observed with the condensed chromosomes during metaphase and anaphase. Independent immunofluorescent studies with anti-(U1)RNP autoantibodies, which react specifically with proteins unique to the U1 snRNP species, showed the same distribution of snRNP antigens during mitosis as was observed with the snRNA-specific anti-m3G antibody. Immunoprecipitation studies with anti-(U1)RNP and anti-Sm autoantibodies, as well as protein analysis of snRNPs isolated from extracts of mitotic cells, demonstrate that the snRNAs remain associated in a specific manner with the same set of proteins during interphase and mitosis. The concept that the overall structure of the snRNPs is maintained during mitosis also applies to the coexistence of the snRNAs U4 and U6 in a single ribonucleoprotein complex. Particle sedimentation studies in sucrose gradients reveal that most of the snRNPs present in sonicates of mitotic cells do not sediment as free RNP particles, but remain associated with high molecular weight (HMW) structures other than chromatin, most probably with hnRNA/RNP.
NMR approach of the periventricular white matter.
From a series of 117 neurological patients presenting a pathological periventricular white matter signal on NMR, the authors discuss the differential diagnosis possibilities based on the configuration of the lesions, on their localization in the brain, and on the calculated apparent T2 (T2**) values achieved with the single multi-echos technique.
[Indications and limitations of ultrasound and axial computed tomography in urologic oncology].
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Inadvertent puncture of a syringohydromyelia cavity after C1-C2 latero-cervical approach.
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