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Biomedical subjects

A Forer

Publications and source records attributed to A Forer.

At least 73 records · Page 4Linked to original sources
PubMed1976

Spindle birefringence of isolated mitotic apparatus: further evidence for two birefringent spindle components.

We studied sea-urchin zygote mitotic apparatus (MA) isolated in hexylene glycol, transferred immediately to a glycerol-dimethylsulphoxide medium, and stored for 2 weeks at room temperature. Treatment with 0-5 M KC1 caused loss of 45% of the birefringence, but microtubules remained intact (as seen electron microscopically in glutaraldehyde-fixed MA), and tubulin was not extracted (as determined by polyacrylamide gel electrophoresis). These results suggest that a non-tubulin component which is extracted by the KC1 contributes 45% of the MA birefringence. Further evidence for this conclusion came from indirect immunofluorescence experiments. Non-extracted (control) MA were fixed with formaldehyde and reacted with antibody against tubulin; there was intense staining of the spindle fibres and astral rays. Electron microscopically, however, microtubules were not present in formaldehyde-fixed MA. Since formaldehyde fixation caused breakdown of microtubules but the tubulin remained in the MA (as judged by reaction with antibodies) we suggest that after microtubule breakdown the tubulin remains in the MA because it is bound to a peri-microtubule spindle component (which we call 'substance gamma'). When KCl-extracted MA were fixed with formaldehyde and reacted with antibody against tubulin there was very little staining of spindle fibres and astral rays. Electron microscopically, formaldehyde caused microtubule breakdown, and since the tubulin is lost from formaldehydefixed, KC1-extracted MA (as judged by reaction with antibodies), we suggest that the tubulin-binding component, substance gamma, is extracted by the 0-5 M KC1. Pressure treatment caused the asters not to stain with antibody against tubulin, suggesting that the stability of substance gamma is different in different regions of the mitotic apparatus.

Animals↗
PubMed1975

Contractile proteins. Major components of nuclear and chromosome non-histone proteins.

Two of the major non-histone proteins from Physarum polycephalum have been isolated under nondenaturing conditions and identified as actin and myosin. A third protein has been purified from crude nuclear actomyosin and from residual nonhistone fractions and found to bind actomyosin in the presence of Mg2+. In Physarum these proteins are not components of the nuclear membrane. Based on sodium dodecylsulfate-polyacrylamide gel electrophoresis, similar proteins are also present in nuclei of HeLa cells and mouse embryo fibroblasts. Isolated metaphase chromosomes from Physarum show a several-fold enrichment in myosin and an altered ratio of actin to the Mg2+-dependent actomyosin binding protein as compared to interphase nuclei. When non-proliferative states are induced in any of these cells, the Mg2+-dependent actomyosin binding protein decreases while actin increases several fold in intranuclear concentration; concomitantly, there is a generalized condensation and inactivation of chromatin. Experiments with added purified radioactive nuclear actomyosin; comparative studies on nuclear protein during stepwise nuclear purification; and studies on isolated metaphase chromosomes indicate that these proteins exist in nuclei in vivo. These observations suggest that contractile proteins may function in the structural interconversions of chromatin and in the regulation of cell proliferation;

Actins↗
PubMed1975

Appearances of microtubules after various fixative procedures, and comparison with the appearances of tobacco mosaic virus.

Microtubules in crane-fly spermatids appeared altered when the glutaraldehyde-fixed cells were not postfixed with osmium tetroxide. The cytoplasmic microtubules were altered more than the doublet microtubules. Addition of osmium tetroxide after dehydration did not produce appearances identical with those of microtubules postfixed directly after glutaraldehyde, and thus at least some alterations occurred during dehydration, possibly due to extraction of microtubule-associated lipid. The omission of osmium tetroxide postfixation did not cause drastic alterations in the appearances of either tobacco mosaic virus (TMV), or polymerized tobacco mosaic virus protein (without RNA), suggesting that microtubule stability is different from TMV stability (with respect to the embedment procedure). The electron-dense stain associated with embedded-sectioned TMV is predominantly outside the TMV protein, as demonstrated by the known distribution of TMV protein compared with the dimensions of sectioned TMV and negatively stained TMV. The same might hold true for microtubules, as evidenced by the dimensions of negatively stained, isolated brain microtubules compared with those of embedded and sectioned brain microtubules.

Acetates↗
PubMed1972

Cytochalasin B: does it affect actin-like filaments?

An in vitro system was used to test the purported action of cytochalasin B. At concentrations 100 times those used for experiments in vivo, cytochalasin B did not cause the breakdown of F-actin, did not inhibit the transformation of G-actin to F-actin, did not inhibit the binding of heavy meromyosin to F-actin, and did not inhibit the adenosine triphosphate-induced release of heavy meromyosin from F-actin.

Actins↗