Date of Award

January 2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Animal Science

First Advisor

Zoltan Machaty

Committee Member 1

Ryan Cabot

Committee Member 2

Paul Ebner

Abstract

Heat stress during oocyte maturation causes well-defined changes in the oocyte cytoplasm that leads to reduced developmental potential. Previous work has been done that supports this hypothesis, but the underlying reasons are still not fully understood. Our objective is to determine these underlying mechanisms that contribute to this reduction in overall development potential of the oocytes and the embryos. Oocytes underwent in vitro maturation (IVM) for 40-44 hours in one of two environments: 39°C (control), or 41°C (heat stress). The oocytes underwent multiple experiments: stage of meiosis after maturation, endoplasmic reticulum (ER) size, total amount of Ca2+ stored in the ER, pattern of Ca2+ signal following in vitro fertilization (IVF), and embryo development after IVF. After 40-44 hours of IVM, oocytes were stained and their chromatin configuration was recorded. Heat-stressed oocytes showed a significant decrease in the ability to reach metaphase II of meiosis compared to the control group. Heat stressed oocytes also lowered the percentage of embryos developing to the blastocyst stage. Mobilized Ca2+ from the ER affects fertilization and subsequent embryo development. Administration of ionomycin caused oocytes to, in Ca2+-free medium, released Ca2+ from the intracellular stores. The average amplitude of the Ca2+ peaks was significantly higher compared to that of the heat stressed group. However time of release and time to maximum peak did not seem to have a discernable affect between the groups. Lower Ca2+ store content could be caused by one of two events: reduction in ER size or an alteration in ER function. Literature suggests that the ER should emulate a spider web-type structure contained throughout the entire cytoplasm. In some cases, heat stress oocytes exhibited an incomplete reorganization of the ER as compared to the control group.

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