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Biomedical subjects

B Appel

Publications and source records attributed to B Appel.

At least 73 records · Page 4Linked to original sources
PubMed1987

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.

Adult↗
PubMed1987

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.

Humans↗
PubMed1987

[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.

Brain↗
PubMed1987

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.

Adolescent↗
PubMed1985

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.

Animals↗
PubMed1985

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.

Animals↗
PubMed1985

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.

Bacteriophage lambda↗
PubMed1985

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.

Animals↗
PubMed1985

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.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Morphogenesis of the inner ear. Correlation between CT-findings and macrosections.

The development of the temporal bone has been studied on macerated foetuses. For a comprehensive understanding two dissimilar techniques have been linked: CT scan and anatomical dissection technique on frozen tissue. CT scanning has been proved a good method to compare the different stages of maturity. There is also a good correlation between CT images and the anatomical slices obtained by dissection. Both methods are complementary to each other in the study of the morphogenesis of the inner ear.

Adult↗
PubMed1984

Structural requirements for the interaction of 5S rRNA with the eukaryotic transcription factor IIIA.

In order to study the binding of the eukaryotic transcription factor IIIA to heterologous 5S rRNAs with a low degree of overall sequence conservation (less than 20%) we have utilized a transcription competition assay involving eubacterial, archaebacterial and eukaryotic 5S rRNAs. All the molecules inhibit Xenopus 5S rRNA transcription specifically, which suggests that only a small amount of specific conserved RNA sequences, if indeed any, are essential for the interaction of the transcription factor with the 5S rRNA molecule, whereas universal 5S rRNA secondary structure elements seem to be required. A fragment of Xenopus laevis oocyte 5S rRNA (nucleotides 41-120), which partially maintains the original 5S rRNA structure, also competes for TF III A. In vitro transcription of a naturally occurring mutant of the Xenopus laevis oocyte 5S rRNA gene, the pseudogene, which carries several point mutations within the TF III A binding domain is equally inhibited by exogenous Xenopus 5S rRNA.

Animals↗
PubMed1984

The 5'-terminal sequence of U1 RNA complementary to the consensus 5' splice site of hnRNA is single-stranded in intact U1 snRNP particles.

The 5'-terminal region of U1 snRNA is highly complementary to the consensus exon-intron regions of hnRNA and it has been suggested that U1 snRNP might play a role in the splicing of the pre-mRNA by intermolecular base-pairing between these regions. Here the secondary structure of the 5' terminus of U1 RNA in the isolated native U1 snRNP particle has been investigated by site-directed enzymatic cleavage of the RNA. Individual oligodeoxynucleotides complementary to various sequences within the first 15 nucleotides of the 5' terminus of U1 RNA have been tested for their ability to form stable DNA X RNA hybrids, with subsequent cleavage of the U1 RNA by RNase H. Our results show unequivocally that the 9 nucleotides at the 5' terminus which are complementary to a consensus 5' splice site are indeed single-stranded in the intact U1 snRNP particle, and are not protected by snRNP proteins. However, they also indicate that the U1 sequence complementary to an intron's consensus 3' end is not readily available for intermolecular base-pairing, either in the intact U1 snRNP particle or in the deproteinized U1 RNA molecule. Therefore our data favour the possibility that U1 snRNP plays a role only in the recognition of a 5' splice site of hnRNA, rather than being involved in the alignment of both ends of an intron for splicing.

Autoantibodies↗
PubMed1984

Evidence for the existence of snRNAs U4 and U6 in a single ribonucleoprotein complex and for their association by intermolecular base pairing.

Small nuclear ribonucleoprotein particles (snRNPs) from eucaryotic cells can be fractionated on affinity columns prepared with antibodies of high affinity for 2,2,7-trimethyl-guanosine (m3G), which is present in the 5'-terminal caps of the snRNAs. While the snRNPs U1, U2 and U5 are eluted with the nucleoside m3G in the presence of 0.1 M salt, the snRNP species U4 and U6 are only desorbed when the salt concentration is increased. The same fractionation pattern was likewise observed for snRNPs from HeLa or Ehrlich ascites tumor cells. Since U6 RNA lacks the m3G residue and its RNA does not react with anti-m3G, its co-chromatography with U4 RNP on anti-m3G affinity columns suggests either that discrete snRNPs U4 and U6 are intimately associated in nuclear extracts or that both RNAs are organized in one ribonucleoprotein particle. Further evidence for a U4/U6 RNP particle is obtained by sedimentation studies with purified snRNPs in sucrose gradients. Gel fractionation of RNAs shows identical distributions of snRNAs U4 and U6 in the gradient, and the U4/U6 RNP particle sediments faster than the snRNPs U1 or U2. Physical association between snRNPs U4 and U6 during sedimentation is shown by their co-precipitation with anti-m3G IgG from the gradient fractions. Finally, experimental evidence is provided that snRNAs U4 and U6 are associated by intermolecular base pairing in the U4/U6 RNP particle, as demonstrated by our finding that anti-m3G IgG co-precipitates U6 RNA with U4 RNA following phenolization of U4/U6 RNPs at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

5'-Terminal caps of snRNAs are reactive with antibodies specific for 2,2,7-trimethylguanosine in whole cells and nuclear matrices. Double-label immunofluorescent studies with anti-m3G antibodies and with anti-RNP and anti-Sm autoantibodies.

Antibodies specific for 2,2,7-trimethylguanosine (m3G), which do not cross-react with m7G-capped RNA molecules were used to study, by immunofluorescence microscopy, the reactivity of the m3G-containing cap structures of the snRNAs U1 to U5 in situ. In interphase cells, immunofluorescent sites were restricted to the nucleus, whilst nucleoli were free of fluorescence. This indicates that the 5' terminal of most of the nucleoplasmic snRNAs are not protected by an m3G cap-recognizing protein and that the snRNA caps are not necessarily required for the binding of snRNPs to subnuclear structures. The snRNAs in the nucleoplasm appeared as distinct units in the light microscope, and this allowed the comparison of the distribution of snRNP proteins by double label studies with anti-RNP or anti-Sm antibodies within the same cell. The three antibody classes produced superimposable fluorescent patterns. Taking into account that the various IgGs react with antigenic sites on snRNAs or snRNP proteins not shared by all the snRNP species, these data suggest that U1 snRNP particles are distributed in the same way as the other snRNPs in the nucleus. Qualitatively the same results were obtained with DNase-treated nuclear matrices indicating that intact snRNPs are part of the nuclear matrix. Our data are consistent with proposals that the various snRNPs may be involved in processing of hnRNA and that this may take place at the nuclear matrix.

Animals↗