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W Steffen

Publications and source records attributed to W Steffen.

69 records · Page 4Linked to original sources
PubMed1986

Relationship between the arrangement of microtubules and chromosome behaviour of syntelic autosomal univalents during prometaphase in crane fly spermatocytes.

During meiotic prometaphase of crane fly spermatocytes, syntelic autosomal univalents are able to move between the spindle poles several times. The relationship between the behaviour of chromosomes and the arrangement of microtubules during this stage was studied using a fixation technique (Nicklas et al. 1979) which makes it possible to examine a certain cell in an electron microscope after live observation. After reorientation, when a syntelic univalent had started moving towards the opposite spindle pole, a short chromosome fibre was found. When a univalent had reached the equator, a chromosome fibre could be traced up to the spindle apex. During the movement towards the opposite spindle pole the degree of disorder in the chromosome fibre was high, whereas it was low in the fibre of a motionless univalent. The degree of disorder was determined by the relative proportion of skew fibre microtubules. At the beginning of reorientation a chromosome fibre was still present, but later, it was no longer possible to recognize such a fibre. Instead of a chromosome fibre, a bundle of microtubules laterally associated with the kinetochore was observed. Some microtubules of this bundle had a direct contact with the kinetochore. These observations strongly hint that the laterally associated microtubules have an important function in the reorientation of syntelic autosomal univalents.

Centromere↗
PubMed1986

Aster-free spindle poles in insect spermatocytes: evidence for chromosome-induced spindle formation?

Tipulid spermatocytes form normally functioning bipolar spindles after one of the centrosomes is experimentally dislocated from the nucleus in late diakinesis (Dietz, R., 1959, Z. Naturforsch., 14b:749-752; Dietz, R., 1963, Zool. Anz. Suppl., 23:131-138; Dietz, R., 1966, Heredity, 19:161-166). The possibility that dissociated pericentriolar material (PCM) is nevertheless responsible for the formation of the spindle in these cells cannot be ruled out based on live observation. In studying serial sections of complete cells and of lysed cells, it was found that centrosome-free spindle poles in the crane fly show neither pericentriolar-like material nor aster microtubules, whereas the displaced centrosomes appear complete, i.e., consist of a centriole pair, aster microtubules, and PCM. Exposure to a lysis buffer containing tubulin resulted in an increase of centrosomal asters due to aster microtubule polymerization. Aster-free spindle poles did not show any reaction, also indicating the absence of PCM at these poles. The results favor the hypothesis of chromosome-induced spindle pole formation at the onset of prometaphase and the dispensability of PCM in Pales.

Animals↗
PubMed1986

[A food-borne infection caused by Campylobacter jejuni serotype Lauwers 19].

Report on a outbreak due to contaminated food involving 556 schoolchildren who got their lunch from a school kitchen. The outbreak occurred abruptly without any secondary infectious. Examinations for Salmonellae, Shigellae, Enteritis-coli, Yersiniae and Rotaviruses were negative. However, Campylobacter jejuni were isolated from 105 specimens of faeces in Rostock. Sixty of these strains and another 2 that had been isolated at the same time but had no relation to the outbreak in Rostock, were further differentiated in Berlin-Buch. All of them proved to be Campylobacter jejuni biotype 2. Serotyping according to Lauwers revealed that 58 out of the 60 strains isolated belong to serotype 19. One of the two remaining strains could not be typed, the other was identified as serotype 1. One of the two cultivated strains that were not related to the outbreak in Rostock, was untypable, the other being of serotype 2. Therefore it can be assumed that the outbreak came from the same source of infection. Epidemiological investigations pointed to some food which had been served 6 days prior to the outbreak. The meal had consisted of white cabbage stew with beef. The kitchen supplies the cooked food to several institutions; 3 different dishes being prepared each day, referred to as dish, A, B and C. The institutions receiving dish A - which on November 1, 1985 was the above-mentioned white cabbage stew - actually included several classes of a school as well as a kindergarten. On that particular day however the kindergarten had not been supplied with dish A but, as an exception, with dish B.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Immunostaining of spindle components in tipulid spermatocytes using a serum against pericentriolar material.

First meiotic division of tipulid (Pales ferruginea) spermatocytes was investigated by double immunostaining with anti-tubulin IgG and scleroderma 5051 serum against pericentriolar material (PCM). PCM-like material became visible in late diakinesis in centrosomal areas as well as in kinetochores. Anti-PCM fluorescence was most pronounced in metaphase and diminished again in anaphase. Displacement of one of the centrosomes from the nucleus at diakinesis in Pales spermatocytes leads to the formation of a bipolar, normally functioning spindle possessing one aster and centriole-free spindle pole (AFP). In about 80% of the AFPs observed there were no traces of anti-PCM staining detectable. This finding supports the assumption based on previous studies that polar PCM is not obligatory for spindle pole formation. The chromosomes seem to be able to induce the organization of a half-spindle. The strong anti-PCM fluorescence of the kinetochores observed here may be taken as further indication of tipulid chromosome autonomy regarding spindle formation.

Anaphase↗
PubMed1985

A model for chromosome movement based on lateral interaction of spindle microtubules.

Quantitative morphological studies of meiotic spindles in the crane fly Pales ferruginea (Fuge, 1980, 1984, 1985) were the basis for the development of a model explaining anaphase chromosome transport in higher eukaryotes. Two main features of chromosome fibres were important for the model: (1) the existence of microtubules oriented obliquely with respect to kinetochore microtubules, and (2) a higher degree of disorder in fibres exerting a pulling force. It is postulated that microtubules of the same polarity being inclined to each other at a certain angle are able to slide past each other by means of mechano-chemically active side-arms working in alternate succession. Sliding is suggested to lead to a displacement of microtubules and chromosomes in direction towards the poles. Furthermore, it is suggested that the chromosome fibre in anaphase becomes progressively disintegrated by fragmentation and disassembly of microtubules. Fragmentation may be induced by bending stress within the dynamic system.

Anaphase↗
PubMedDate not supplied

Immunogold localisation of the intermediate chain within the protein complex of cytoplasmic dynein.

It was our goal to determine the location of the intermediate chain within the complex of cytoplasmic dynein by immunoelectron microscopy. To do so we generated two monoclonal antibodies (m74-1 and m74-2) specific for the intermediate chain. Both antibodies recognised the intermediate chain by sodium dodecyl sulphate-polyacrylamide gel electrophoresis immunoblot and ELISA assays of native and denatured proteins. When sucrose density gradient-purified cytoplasmic dynein from bovine brain was incubated with the gold-conjugated monoclonal antibodies, m74-1 and m74-2, and examined by negative staining, the gold label was found opposite the globular heads at the base of the V-shaped stalk of the motor complex. The labelling of the intermediate chain is the first mapping of a component within cytoplasmic dynein. The identification of the intermediate chain at the base of the complex supports a possible docking function of the intermediate chain.

Animals↗