Graduate Thesis Or Dissertation
 

The effects of versene on dividing sea urchin eggs

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  • Developing sea urchin eggs (Strongylocentrotus purpuratus), reared at 15° C, were subjected to single 15-minute treatments with disodium versenate in calcium-free sea water, applied at 10-minute intervals, from 4 minutes after insemination to the second cleavage. These versene pulses produced specific degrees of retardation in the mitotic process and delayed cleavage. The effects on mitotic events were cytologically monitored and the times of 50% cleavage were observed-following each exposure period to versene. The cleavage delays induced by versene applied at successive periods in development yielded a specific pattern of response (sensitivity). This pattern showed two sensitivity peaks, one at the streak stage and one at telophase. A slight cleavage delay was also produced by treatment during the period before pronuclear fusion. The action of versene resulting in delay of cleavage was related to its calcium chelating properties, the removal of calcium preventing the formation of gels associated with the achromatic figure. Versene applied before pronuclear fusion retarded the events that precede pronuclear fusion, probably inhibiting monaster development. The sensitivity period from the fusion nucleus stage to early prophase, with a peak at the streak stage, was related to an inhibition or retardation of protein gelation preceding formation of the metaphase achromatic figure. The sensitivity period from early prophase into interphase following the first cleavage, with a peak at telophase, was related to an inhibition or retardation in the formation of gel structures required for development of the definitive diasters, the interzonal spindle, and the post-furrowing subcortical gel. A close relationship was shown to exist between the pattern of response to versene and the cyclic uptake and release of Calcium-45 previously studied by Clothier (1961).
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  • File scanned at 300 ppi using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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