Biomedical subjects

L Wordeman

Publications and source records attributed to L Wordeman.

23 records · Page 2Linked to original sources

PubMed1990

Cytokinesis by furrowing in diatoms.

We have found that nocodazole reversibly inhibits nuclear migration and can be used to induce karyokinesis before the completion of nuclear migration, resulting in spindles that are displaced toward the hypothecal end of the cell. Surprisingly, displacement of mitotic nuclei results in complete spatial uncoupling of karyokinesis from cytokinesis. Nocodazole-induced displacement of mitotic nuclei will neither alter the position of the original furrow nor induce additional furrows. This demonstrates that in S. turris the location of the presumptive cleavage furrow is not determined by the position of the spindle but is cortically determined before mitosis. Therefore, although cell division in S. turris resembles certain mechanochemical aspects of cleavage in animal cells, our evidence suggests that the spatial regulation of the cytokinetic apparatus relies on a mechanism of cortical determination that is characteristic of plant cells.

Cell Division↗

PubMed1989

Distribution of phosphorylated spindle-associated proteins in the diatom Stephanopyxis turris.

Mitotic spindles isolated from the diatom Stephanopyxis turris become thiophosphorylated in the presence of ATP gamma S at specific locations within the mitotic apparatus, resulting in a stimulation of ATP-dependent spindle elongation in vitro. Here, using indirect immunofluorescence, we compare the staining pattern of an antibody against thiophosphorylated proteins to that of MPM-2, an antibody against mitosis-specific phosphoproteins, in isolated spindles. Both antibodies label spindle poles, kinetochores, and the midzone. Neither antibody exhibits reduced labeling in salt-extracted spindles, although prior salt extraction inhibits thiophosphorylation in ATP gamma S. Furthermore, both antibodies recognize a 205 kd band on immunoblots of spindle extracts. Microtubule-organizing centers and mitotic spindles label brightly with the MPM-2 antibody in intact cells. These results show that functional mitotic spindles isolated from S. turris are phosphorylated both in vivo and in vitro. We discuss the possible role of phosphorylated cytoskeletal proteins in the control of mitotic spindle function.

Antibodies↗

PubMed1987

Reactivation of spindle elongation in vitro is correlated with the phosphorylation of a 205 kd spindle-associated protein.

Mitotic spindles isolated from the diatom Stephanopyxis turris consist of two half-spindles of closely interdigitating microtubules that slide relative to one another in the presence of ATP, reinitiating spindle elongation (anaphase B) in vitro. Purified spindles that have been exposed to ATP-gamma-S undergo ATP-dependent reactivation more readily than do control spindles. Thiophosphorylated proteins in such spindles are located in the spindle midzone, kinetochores, and a portion of the pole complex. One major thiophosphorylated peptide of 205 kd is detected in extracts prepared from spindles labeled with [35S]ATP-gamma-S, and is also localized in the spindle midzone by using an antibody that recognizes thiophosphorylated proteins. It is likely that this 205 kd peptide is either a positive regulator or mechanochemical transducer of microtubule sliding when it is in a phosphorylated state.

Adenosine Triphosphate↗

PubMed1986

The distribution of cytoplasmic microtubules throughout the cell cycle of the centric diatom Stephanopyxis turris: their role in nuclear migration and positioning the mitotic spindle during cytokinesis.

The cell cycle of the marine centric diatom Stephanopyxis turris consists of a series of spatially and temporally well-ordered events. We have used immunofluorescence microscopy to examine the role of cytoplasmic microtubules in these events. At interphase, microtubules radiate out from the microtubule-organizing center, forming a network around the nucleus and extending much of the length and breadth of the cell. As the cell enters mitosis, this network breaks down and a highly ordered mitotic spindle is formed. Peripheral microtubule bundles radiate out from each spindle pole and swing out and away from the central spindle during anaphase. Treatment of synchronized cells with 2.5 X 10(-8) M Nocodazole reversibly inhibited nuclear migration concurrent with the disappearance of the extensive cytoplasmic microtubule arrays associated with migrating nuclei. Microtubule arrays and mitotic spindles that reformed after the drug was washed out appeared normal. In contrast, cells treated with 5.0 X 10(-8) M Nocodazole were not able to complete nuclear migration after the drug was washed out and the mitotic spindles that formed were multipolar. Normal and multipolar spindles that were displaced toward one end of the cell by the drug treatment had no effect on the plane of division during cytokinesis. The cleavage furrow always bisected the cell regardless of the position of the mitotic spindle, resulting in binucleate/anucleate daughter cells. This suggests that in S. turris, unlike animal cells, the location of the plane of division is cortically determined before mitosis.

Benzimidazoles↗

PubMed1986

Comparison of spindle elongation in vivo and in vitro in Stephanopyxis turris.

The spindle in dividing cells of the diatom Stephanopyxis turris contains three distinct classes of microtubules: central spindle microtubules, which slide over each other and grow during anaphase spindle elongation; kinetochore-attached microtubules, which are located on the outer surface of the central spindle; and peripheral microtubules, which fan out from the spindle poles in astral-like arrays. The poles are multilayered structures, which remain attached to the spindle after isolation. In vitro, after addition of ATP, central spindles elongate and the two half-spindles slide completely apart with a concurrent decrease in the extent and magnitude of the zone of microtubule overlap. Spindle elongation takes place in spindles whose chromatin has been removed by enzymic digestion and the extent of elongation in vitro is increased by the addition of neurotubulin. After ATP addition the arrays of interdigitating microtubules in the zone of overlap become disordered and selectively depolymerize from the overlap zone polewards. In some reactivated spindles an unusual structure, a striated fibre, can be seen running from the pole plates part of the way towards the spindle midzone. The fibre has no precedent in mitotic ultrastructure and its function is unclear. These results demonstrate that we can duplicate the essential elements of anaphase B in vitro and that this system will be useful for further studies of the molecular basis of spindle elongation.

Anaphase↗