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B Meissner

Publications and source records attributed to B Meissner.

8 recordsLinked to original sources
PubMed1991

Faithful in vivo transcription termination of Xenopus laevis rDNA. Correlation of electron microscopic spread preparations with S1 transcript analysis.

DNA sequencing and subsequent functional in vitro analysis of the Xenopus laevis rDNA transcription termination has led to the identification of three transcription termination sequence elements: T1, located at the 3' end of the 28S rDNA; T2, a putative processing site 235 bp downstream of T1; T3, the principal terminator positioned 215 bp upstream of the gene promoter. As demonstrated for nuclear run-off assays, T3 was found to be the main terminator for Xenopus rDNA transcription. These in vitro data are in obvious contradiction to results obtained by electron microscopic (EM) spread preparations from rapidly isolated amplified oocyte nucleoli, i.e., an rDNA chromatin probe thought to represent the in vivo situation, indicative of transcription termination at sites T1-2. However, most interestingly, T3 had--again by the EM method--been identified as the exclusive terminator for NTS spacer transcription units. In order to answer the question of whether read-through transcription of the complete rDNA spacer sequence is obligatory for 40S pre-rRNA in vivo transcription, we analyzed several hundreds of spread rRNA genes from Xenopus oocyte nucleoli in great detail, applying two different spreading procedures, e.g., dispersal of amplified oocyte nucleoli shortly in detergent-free or detergent containing low-salt media prior to the EM spreading technique. Quantitation of EM spreads resulted in the finding that read-through rDNA spacer transcription beyond T1-2 termination sites (i.e., indicative of T3 transcription termination) can be visualized for the in vivo situation at a frequency of less than 3% of rRNA genes analyzed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Structural organization of an active, chromosomal nucleolar organizer region (NOR) identified by light microscopy, and subsequent TEM and STEM electron microscopy.

The three-dimensional arrangement of the chromatin components within the nucleolar organizer regions (NORs) from living oocyte nuclei was investigated. As a suitable cell system we chose vitellogenic oocytes of the orthopteran insect Acheta. This cell type is particularly attractive for analysis of nucleolar chromatin, since structural and functional aspects of NORs during early oogenic stages (including the association of NORs with amplified rDNA copies) are particularly well known (Lima-de-Faria 1974). In the course of the present study we first identified putative chromosomal NORs in isolated nuclei of mid-diplotene oocytes according to morphological characteristics using differential interference contrast (DIC) or phase contrast light microscopy. The presence of actively transcribing chromosomal NORs during this late stage of Acheta oogenesis obviously had been overlooked by previous investigators, probably due to difficulties of chromosome visualization. For a more detailed ultrastructural analysis, NORs were gently sedimented from opened nuclei and processed for sectioning using a modified "end-embedding" procedure (Mott and Callan 1975; Spring and Franke 1981). A small number of thick and thin sections could be made from individual NORs. Sections were analyzed by light microscopy, conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Whereas the structural connection of NORs to the chromosome axis and also the general arrangement of active nucleolar genes within the NOR complex could be seen with TEM, the visualization of individual nucleolar genes and the organization of transcription complexes was only possible using bright field STEM of thick sections at low temperature.

Animals↗
PubMed1978

Fluorescein angiography of the corneal limbus--drug effects on capillary blood flow.

By means of fluorescein angiography, plasma flow through the capillaries at the limbus corneae is demonstrated. The number of stained capillaries at a given time served as a measure of capillary perfusion. Even without drug the entire capillary system is perfused at least by plasma. Tolazoline enhanced the velocity of perfusion (P = 2alpha less than 0.01), epinephrine caused a marked capillary constriction (P = 2alpha less than 0.01), as well as--to a lesser extent--did dexamethasone (P = 2alpha less than 0.05). Dionine caused hyperemia, but the data varied much more than after tolazoline. In addition, dionine enhanced the dye leakage from the vessels.

Adult↗
PubMed1978

[Experiences with small groups in a psychiatric hospital (author's transl)].

The author reports on her experience collected over a period of almost three years with psychoanalytic groups in an open ward of the Psychiatric (Land Government-financed) Hospital at Düren. The special feature of this study is that the groups remained together for a short period only (10-12 sessions), so that it was necessary to limit the subjects covered. The problems which came up in these groups were partly due to the specific character of groups made up of in-patients, and partly due to the structure of such short-lived groups. An attempt was made to take advantage of the opportunity of the dual function of the head of an in-patient group, namely, to be the object of reference and transference for the small group and a member of the team for the entire ward, to offer a chance to the group members of focusing conflicts based on the Oedipus complex. In this connection, it was found to be very useful to enlist the help of the nurse or male nurse as co-leader of the group. Patients with a subsiding psychosis derived the greatest benefit from participating in such groups, whereas in the case of patients suffering from depression, participation in such a short-lived group should be discouraged.

Germany, West↗