In this study nuclear and ooplasmic maturation of prepuberal calf oocytes was evaluated to determine a possible cause for their low developmental competency. Calf oocytes resumed meiosis and arrested at the metaphase II stage at rates similar to that of adult animals; however, zygotes derived from calf oocytes cleaved and developed at significantly lower rates. Ooplasmic maturation was assessed during oocyte maturation and fertilization. Transmission electron microscopy revealed that a majority of calf oocytes exhibited some delay in organelle migration and redistribution following maturation. Immunofluorescence microscopy showed that following in vitro fertilization, a higher percentage of calf oocytes had abnormal chromatin and microtubule configurations than those of adult cattle. Delayed formation of sperm aster and asynchronous pronuclear formation characterized these anomalies. Microfluorometry was used to characterize the Ca$\sp{2+}$ responses of calf oocytes to the addition of agonists. The addition of thimerosal demonstrated the presence of Ca$\sp{2+}$ stores in calf oocytes. Injection of near threshold concentrations of inositol 1,4,5-trishphosphate (InsP$\sb3),$ used to test the sensitivity of the InsP$\sb3$R, released significantly less Ca$\sp{2+}$ in calf than cow oocytes. Furthermore, injection of a porcine sperm factor elicited Ca$\sp{2+}$ release in calf oocytes, however, these responses did not exhibit the frequency or amplitude known to be characteristic of cow oocytes. These results suggested that the Ca$\sp{2+}$ content of the intracellular stores was similar, but the sensitivity of the Insp$\sb3$R may be different. The activity of histone H1 and MAP kinases, which are required for the initiation and completion of meiosis was evaluated, and the presence and maturation of the InsP$\sb3$R system. Results show that following in vitro maturation, the activity of both histone H1 and MAP kinases, as well as the relative amount of the InsP$\sb3$R protein, were substantially lower in prepuberal calf oocytes when compared to oocytes of adult cattle. Together, these findings suggest that the low developmental competence of calf oocytes can be attributed, at least in part, to incomplete or delayed ooplasmic maturation.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-3088 |
| Date | 01 January 1998 |
| Creators | Damiani, Philip |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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