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Microtubule cycles in oocytes of the surf clam, Spisula solidissima: an immunofluorescence study
Abstract:
Oocytes of the surf clam, Spisula solidissima, underwent germinal vesicle breakdown and two meiotic divisions to give off polar bodies when they were fertilized or parthenogenetically activated with KCl. Fertilized eggs further proceeded to mitosis and cleaved, while parthenogenetically activated eggs remained uncleaved. We examined changes in microtubule-containing structures during meiotic divisions and subsequent mitotic processes by immunofluorescence. A monoclonal anti-tubulin antibody was applied to alcohol-fixed eggs from which the vitelline membrane had been removed by protease digestion. Up to the stage of second polar body formation, the pattern of microtubule organization in the first and second meiotic spindles was identical in both fertilized and parthenogenetically activated eggs. However, while fertilized eggs formed a sperm aster and mitotic spindles later, activated eggs formed only monaster- or ring-shaped microtubule-containing structures which underwent cycles of alternating formation and breakdown. Lactoorecin staining of parthenogenetically activated eggs revealed that the chromosome cycle could occur in these eggs, in phase with this microtubule cycle.
Insights
Surf clam oocytes show identical microtubule organization during meiosis whether fertilized or activated. However, only fertilized eggs form sperm asters and mitotic spindles for cleavage, while activated eggs exhibit cyclical microtubule structures.
Area of Science:
- Cell Biology
- Developmental Biology
- Marine Biology
Background:
- Oocyte maturation involves complex meiotic divisions.
- Understanding microtubule dynamics is crucial for cell division.
- Parthenogenetic activation offers a model to study oocyte developmental potential.
Purpose of the Study:
- To investigate microtubule organization during meiosis and early development in Spisula solidissima oocytes.
- To compare microtubule dynamics in fertilized versus parthenogenetically activated oocytes.
- To correlate microtubule behavior with chromosome cycles in activated oocytes.
Main Methods:
- Immunofluorescence using a monoclonal anti-tubulin antibody.
- Protease digestion to remove the vitelline membrane.
- Lactoorecin staining for chromosome analysis.
Main Results:
- Microtubule organization of meiotic spindles was similar in fertilized and activated oocytes up to second polar body formation.
- Fertilized eggs developed sperm asters and mitotic spindles, leading to cleavage.
- Activated eggs formed dynamic, cyclical microtubule structures (monasters/rings) without cleavage.
- Chromosome cycles in activated eggs occurred in synchrony with microtubule cycles.
Conclusions:
- Fertilization triggers specific microtubule organization (sperm aster, mitotic spindles) essential for cleavage.
- Parthenogenetic activation leads to aberrant microtubule dynamics that prevent proper embryonic development.
- Spisula oocytes provide a model for studying the interplay between microtubule organization and chromosome behavior during aberrant cell cycles.