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キーワード:
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要旨:
In my thesis I aimed to contribute to the understanding of the
mechanism of cytokinesis in C. elegans embryos. I wanted to analyze
the relative contributions of different spindle parts microtubule
asters and the midzone - to cytokinesis furrow positioning. I
developed a UV laser-based severing assay that allows the spatial
separation of the region midway between the asters and the spindle
midzone. The spindle is severed asymmetrically between one aster
and the midzone. I found that the spindle provides two consecutive
signals that can each position a cytokinesis furrow: microtubule
asters provide a first signal, and the spindle midzone provides a
second signal. The use of mutants that do not form a midzone
suggested that the aster-positioned furrow is able to divide the cell
alone without a spindle midzone. Analysis of cytokinesis in
hypercontracile mutants suggests that the aster-positioned cytokinesis
furrow and the midzone positioned furrow inhibit each other by
competing for cortical contractile elements. I then wanted to identify
the molecular pathway responsible for cytokinesis furrow positioning
in response to the microtubule asters. To this end, I performed an
RNAi screen, which identified a role for LET-99 in cytokinesis:
LET-99 appeared to be required for aster-positioned cytokinesis but
not midzone-positioned cytokinesis. LET-99 localizes as a cortical
band that overlaps with the cytokinesis furrow. Mechanical
displacement of the spindle demonstrated that the spindle positions
cortical LET-99 at the site of furrow formation. The furrow
localization of LET-99 depended on G proteins, and consistent with
this finding, G proteins are also required for aster-positioned
cytokinesis.
