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Results for “Cell Nucleus Division”

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At least 91 records · Page 5Linked to original sources
PubMed2006

Linking cell division to cell growth in a spatiotemporal model of the cell cycle.

Cell division must be tightly coupled to cell growth in order to maintain cell size, yet the mechanisms linking these two processes are unclear. It is known that almost all proteins involved in cell division shuttle between cytoplasm and nucleus during the cell cycle; however, the implications of this process for cell cycle dynamics and its coupling to cell growth remains to be elucidated. We developed mathematical models of the cell cycle which incorporate protein translocation between cytoplasm and nucleus. We show that protein translocation between cytoplasm and nucleus not only modulates temporal cell cycle dynamics, but also provides a natural mechanism coupling cell division to cell growth. This coupling is mediated by the effect of cytoplasmic-to-nuclear size ratio on the activation threshold of critical cell cycle proteins, leading to the size-sensing checkpoint (sizer) and the size-independent clock (timer) observed in many cell cycle experiments.

Animals↗
PubMed1969

Mesosomes in Escherichia coli.

When Escherichia coli was grown in a synthetic medium and fixed with osmium, sections of the cells revealed clearly defined mesosomes. These mesosomes appeared to develop, in dividing cells, as coiled infoldings of the cytoplasmic membrane. Mature mesosomes formed a link between the cytoplasmic membrane and the nucleus of the cell. The arrangement of the mesosomes in dividing cells led to the hypothesis that division of the nucleus in these cells is accomplished by two separate polar mesosomes. One mesosome is derived from the parent cell and is present at one pole of the daughter cell. The other is freshly synthesized at or near the newly forming pole of the daughter cell. While the old mesosome remains attached to the chromosome received from the parent cell, the newly synthesized mesosome becomes attached to and initiates replication of the new chromosome. As the cell grows and elongates, the two mesosomes, attached to their respective chromosomes move apart, thus effecting nuclear division.

Cell Division↗
PubMed2005

Division-plane positioning: microtubules strike back.

Two groups have recently developed physical techniques to manipulate the position of the nucleus in fission yeast. Their studies reveal how microtubules confine the nucleus to the cell center, and indicate how the position of the cleavage plane during cell division is coordinated with that of the nucleus.

Cell Division↗
PubMed1981

Analysis of the variability in cleavage times and demonstration of a mitotic gradient during the cleavage stages of Nothobranchius guentheri.

Living embryos of the annual cyprinodont fish Nothobranchius guentheri were observed under the microscope. Detailed records were made of the time of cell division, disappearance of the nucleus and of the position of each cell within the blastoderm up to and includig the sixth cleavage. Combination of these data revealed the presence of a mitotic gradient, a cell division gradient and a gradient of cell cycle duration in the 8-cell, 16-cell and 32-cell stage. Comparison of the variabilities in the duration of the interphase and mitosis reveals that differences between sister cell intercleavage times in the 8-, 16- and 32-cell stage are, for the most part, due to the variability in the duration of the mitotic process. It is concluded that the DNA-division cycle is composed of at least two parallel series of events. We found the random transition model of cell cycle control, originally based on the analysis of intermitotic times of mammalian cells in tissue culture, helpful also in analysing intercleavage time variability in embryonic cells.

Animals↗
PubMed2000

Cytoplasm-to-nucleus translocation of a herpesvirus tegument protein during cell division.

We have previously shown that the herpes simplex virus tegument protein VP22 localizes predominantly to the cytoplasm of expressing cells. We have also shown that VP22 has the unusual property of intercellular spread, which involves the movement of VP22 from the cytoplasm of these expressing cells into the nuclei of nonexpressing cells. Thus, VP22 can localize in two distinct subcellular patterns. By utilizing time-lapse confocal microscopy of live cells expressing a green fluorescent protein-tagged protein, we now report in detail the intracellular trafficking properties of VP22 in expressing cells, as opposed to the intercellular trafficking of VP22 between expressing and nonexpressing cells. Our results show that during interphase VP22 appears to be targeted exclusively to the cytoplasm of the expressing cell. However, at the early stages of mitosis VP22 translocates from the cytoplasm to the nucleus, where it immediately binds to the condensing cellular chromatin and remains bound there through all stages of mitosis and chromatin decondensation into the G(1) stage of the next cycle. Hence, in VP22-expressing cells the subcellular localization of the protein is regulated by the cell cycle such that initially cytoplasmic protein becomes nuclear during cell division, resulting in a gradual increase over time in the number of nuclear VP22-expressing cells. Importantly, we demonstrate that this process is a feature not only of VP22 expressed in isolation but also of VP22 expressed during virus infection. Thus, VP22 utilizes an unusual pathway for nuclear targeting in cells expressing the protein which differs from the nuclear targeting pathway used during intercellular trafficking.

Animals↗
PubMed1994

Multiple roles of intermediate filaments.

The widespread distribution, diversity of types, and highly conserved features of intermediate filaments (IFs) and the diversity of associated proteins indicate multiple roles for IFs in the nucleus and the cytoplasm of eukaryotic cells. Traditional functions include maintenance of cell shape, cell locomotion, movement and positioning of organelles and guiding cell development. Recent studies indicate some of these functions can now be expanded. Currently available information shows that IFs are important to nuclear function and cell division, to transport between the nucleus and cytoplasm, to the mechanical integrity of cells and tissues, to reorganization of the cytoplasm and chromatin in response to intercellular signals, and to embryonic and cellular differentiation.

Animals↗
PubMed2005

Nuclear and division-plane positioning revealed by optical micromanipulation.

The position of the division plane affects cell shape and size, as well as tissue organization. Cells of the fission yeast Schizosaccharomyces pombe have a centrally placed nucleus and divide by fission at the cell center. Microtubules (MTs) are required for the central position of the nucleus. Genetic studies lead to the hypothesis that the position of the nucleus may determine the position of the division plane. Alternatively, the division plane may be positioned by the spindle or by morphogen gradients or reaction diffusion mechanisms. Here, we investigate the role of MTs in nuclear positioning and the role of the nucleus in division-plane positioning by displacing the nucleus with optical tweezers. A displaced nucleus returned to the cell center by MT pushing against the cell tips. Nuclear displacement during interphase or early prophase resulted in asymmetric cell division, whereas displacement during prometaphase resulted in symmetric division as in unmanipulated cells. These results suggest that the division plane is specified by the predividing nucleus. Because the yeast nucleus is centered by MTs during interphase but not in mitosis, we hypothesize that the establishment of the division plane at the beginning of mitosis is an optimal mechanism for accurate symmetric division in these cells.

Cell Division↗