Ultrastructural analysis and chemical inhibition studies were
carried out on first cleavage of Mytilus zygotes to determine possible
relationships between the mitotic apparatus and the cortex during
polar lobe formation.
The stages of mitosis correlated with the appearance of the
polar lobe were first determined by light microscopy. The polar lobe
does not appear until anaphase of first cleavage. The early polar
lobe is symmetrical in position at the vegetal pole, but at late anaphase
it shifts position towards the side of the future CD blastomere.
During cytokinesis the furrow at the vegetal pole is displaced by the
polar lobe resulting in an unequal division.
Ultrastructural study at anaphase shows astral microtubules
penetrating the polar lobe. At the animal pole microtubules reach
almost to the cortex. When furrowing begins cortical granules move
into the furrow region at both the animal and vegetal poles. An
amorphous electron dense area is present just below the plasma membrane
in all cell furrows. This region may correspond to a contractile
band of microfilaments.
Cell division inhibitors were used to analyze the role of microtubules
and microfilaments in Mytilus cleavage. Prior to anaphase,
mercaptoethanol, an inhibitor of microtubule function, halts cell division
in Mytilus. Before the mitotic apparatus is formed, mercaptoethanol
also prevents polar lobe formation. Polar lobe formation can
occur in the inhibitor once the mitotic apparatus has begun to form.
Cytochalasin B which destroys microfilaments inhibits both polar lobe
formation and cytokinesis in Mytilus. Once the polar lobe has appeared,
it is resorbed when the cells are placed in cytochalasin.
It is suggested that both microtubules and a contractile band of
microfilaments play a role in first cleavage. Initial polar lobe formation
could be triggered by microtubules of the mitotic apparatus
penetrating the vegetal pole whereas final constriction of the definitive
polar lobe and the cleavage furrow may be caused by microfilaments. / Graduation date: 1973
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28907 |
| Date | 30 November 1972 |
| Creators | Elvin, Patricia J. |
| Contributors | Harris, Patricia |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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