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R Hubble

Publications and source records attributed to R Hubble.

5 recordsLinked to original sources
PubMed1984

Interconversion of metaphase and interphase microtubule arrays, as studied by the injection of centrosomes and nuclei into Xenopus eggs.

We have designed experiments that distinguish centrosomal , nuclear, and cytoplasmic contributions to the assembly of the mitotic spindle. Mammalian centrosomes acting as microtubule-organizing centers were assayed by injection into Xenopus eggs either in a metaphase or an interphase state. Injection of partially purified centrosomes into interphase eggs induced the formation of extensive asters. Although centrosomes injected into unactivated eggs (metaphase) did not form asters, inhibition of centrosomes is not irreversible in metaphase cytoplasm: subsequent activation caused aster formation. When cytoskeletons containing nuclei and centrosomes were injected into the metaphase cytoplasm, they produced spindle-like structures with clearly defined poles. Electron microscopy revealed centrioles with nucleated microtubules. However, injection of nuclei prepared from karyoplasts that were devoid of centrosomes produced anastral microtubule arrays around condensing chromatin. Co-injection of karyoplast nuclei with centrosomes reconstituted the formation of spindle-like structures with well-defined poles. We conclude from these experiments that in mitosis, the centrosome acts as a microtubule-organizing center only in the proximity of the nucleus or chromatin, whereas in interphase it functions independently. The general implications of these results for the interconversion of metaphase and interphase microtubule arrays in all cells are discussed.

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PubMed1983

Centrosome development in early mouse embryos as defined by an autoantibody against pericentriolar material.

A human autoantibody from a schleroderma patient was found to immunostain interphase and mitotic centrosomes in a variety of vertebrate cells. Electron microscopic immunocytochemistry localized this antigen in dense pericentriolar material (PCM) surrounding the centrioles. The meiotic spindle of the mouse egg has no centriole but it exhibited a broad PCM band at each pole. This pattern was also found from the first through fourth mitotic divisions. During this time PCM was found assembled at a single locus in the cell and exclusively in mitotic cells; it was not observable in interphase cells. In the blastocyst, only polar trophoblast cells had characteristic centrosomes throughout the cell cycle. Results suggest PCM can exist, disperse, and reorganize during the cell cycle independently of the centriole, and its distribution in the embryo differs in cells having different fates.

Animals↗
PubMed1982

Mitosis in a cell with multiple centrioles.

N115 mouse neuroblastoma cells possess a large number of microtubule organizing centers (MTOCs) which can be identified ultrastructurally as single centrioles. The distribution and activity of these organizing centers can be followed through all stages of the cell cycle by labeling microtubules with anti-tubulin and chromatin with the Hoechst dye, Bisbenzimid. We have found that multiple MTOCs persist and continue to organize microtubules during mitosis. They exhibit a well-defined sequence of movements, starting from a loose cluster during interphase, proceeding to a widely and evenly dispersed arrangement in prophase, gathering into small clusters and chains during prometaphase, and residing in two ring-shaped groups at the mitotic poles during metaphase and anaphase. Despite their large number of centrioles, virtually all N115 cells show a normal bipolar mitosis, but often with unequal numbers of centrioles at the two poles. Such observations bring into question the importance of the centriole in establishing bipolar division in this cell type.

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