PubMed Health⌕ Search

Biomedical subjects

U P Roos

Publications and source records attributed to U P Roos.

4 recordsLinked to original sources
PubMed1976

RNA virus in Allomyces arbuscula: ultrastructural localization during the life-cycle.

Strain Bali I of Allomyces arbuscula is infected with a RNA virus; strain North Carolina is not. The virus appears to be avirulent, for strain Bali I showed no signs of pathogenicity. Virus aggregates occurred mostly in the cytoplasm during different stages of the gametophytic and sporophytic generations. Small intra-nuclear aggregates were found only in differentiating gametophytic hyphae and immature gametangia. In motile cells (gametes and zoospores) the aggregates are exclusively contained within the nuclear cap. This represents a reliable mechanism of transmission throughout the life-cycle.

Cell Nucleus↗
PubMed1975

Mitosis in the cellular slime mold Polysphondylium violaceum.

Myxamebas of Polysphondylium violaceum were grown in liquid medium and processed for electron microscopy. Mitosis is characterized by a persistent nuclear envelope, ring-shaped extranuclear spindle pole bodies (SPBs), a central spindle spatially separated from the chromosomal microtubules, well-differentiated kinetochores, and dispersion of the nucleoli. SPBs originate from the division, during prophase, of an electron-opaque body associated with the interphase nucleus. The nuclear nevelope becomes fenestrated in their vicinity, allowing the build-up of the intranuclear, central spindle and chromosomal microtubules as the SPBs migrate to opposite poles. At metaphase the chromosomes are in amphitelic orientation, each sister chromatid being directly connected to the corresponding SPB by a single microtubule. During ana- and telophase the central spindle elongates, the daughter chromosomes approach the SPBs, and the nucleus constricts in the equatorial region. The cytoplasm cleaves by furrowing in late telophase, which is in other respects characterized by a re-establishment of the interphase condition. Spindle elongation and poleward movement of chromosomes are discussed in relation to hypotheses of the mechanism of mitosis.

Cell Nucleus↗
PubMed1975

Fine structure of an organelle associated with the nucleus and cytoplasmic microtubules in the cellular slime mould Polysphondylium violaceum.

Polysphondylium violaceum was grown in association with Escherichia coli. Vegetative amoebae and pseudoplasmodia were fixed under different conditions and processed for electron microscopy. An electron-opaque body (nucleus-associated body, NAB) lies in the cytoplasm near the tapered end of interphase nuclei. The NAB consists of a disk-shaped, multilayered core, approximately 200 nm in diameter and 150 nm thick, embedded in a granular matrix from which electron-opaque nodules protrude. The nodules are termination points of microtubules radiating from the NAB into the cytoplasm or running along the nucleus. On the average there are 16 nodules per NAB. One or two microtubules terminate in each nodule. Spindle pole bodies, arising by duplication of the NAB at the beginning of mitosis, are unstructured foci for spindle microtubules in mitotic cells. It is suggested that cytoplasmic microtubules do not determine cell shape, but they probably cause the tapering deformation of the nucleus. They may, furthermore, represent a storage form of subunits for utilization during the formation of the mitotic spindle. The nodules of the NAB are potential nucleation sites of cytoplasmic microtubules during interphase. Spindle pole bodies presumably acquire a microtubule organizing capability by integration of the decondensed nodules.

Cell Nucleus↗