A partial characterization of the cytoskeleton in the eggs of Urechis caupo
Date
1985
Authors
Nilson, Ellen Blythe
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Abstract
I have partially characterized the previously undescribed cytoskeleton of Urechis caupo (Fisher and MacGinitie, 1928) eggs by fluorescence microscopy and electron microscopy. Actin in fixed cells was made visible by labelling with NBD-Phallacidin (specific for F-actin) and by indirect immuno fluorescence. NBD-Phallacidin fluorescence is high in oocytes, but after fertilization the amount diminishes nearly to the level of the control by 2 minutes post-insemination (PI). By four minutes PI the amount increases, but not to the original level. The fluorescence of NBD-Phallacidin-labelled eggs is not eliminated by treatment with cytochalasin B, a drug which disrupts actin filaments, but the staining pattern is altered. This change in F-actin may be related to the change in shape which occurs during fertilization as the eggs lose their characteristic indentation and round out.
A continuous, occasionally filamentous, electron-dense band immediately subjacent to the plasma membrane is visible in transmission electron micrographs of the oocytes. This dense band may also be represented as a peripheral substructure of the cytoskeleton in detergent-extracted eggs. I examined eggs extracted with the non-ionic detergent Triton X-100 with scanning electron microscopy and found an extensive detergent-resistant cytoskeleton. The nucleus and cytoplasm contain an extensive array of filaments, possibly including the F-actin which is visible in NBD-Phallacidin treated eggs. The outer boundary of the cytoskeleton is an anastomosing web which is connected to the internal cytoskeleton. In thin sections of extracted cells, the peripheral component of the cytoskeleton is strikingly similar to the dense band of unextracted eggs, and they may represent the same cell structure.