Doctor of Philosophy (PhD)
School of Animal Sciences
As the necessity to improve in vitro embryo production efficiency is ever increasing, so too is the prerequisite obligation to improve oocyte competence. The ability of an oocyte to successfully produce a viable embryo requires that it both completes meiotic maturation and synchronously achieves cytoplasmic competence; an encompassing term that refers to the oocytes correct accumulation and storage of mRNAs, proteins and factors as well as the development and reorganization of organelles and the cytoskeleton. The current research was designed to analyze those methods that go into oocyte collection and pre-maturation handling to determine if there are ways to ensure the cohort of oocytes being placed in in vitro maturation (IVM) are those with the highest potential to develop. It was found that collection during different phases of the follicular wave had negligible effects on oocyte competence. However oocytes collected from growing follicles had increased ability to respond to calcium release signals compared to those recovered from atretic follicles, which was found to be important for embryo production rates. Oocytes retrieved from post-mortem ovaries exhibited irregular gene expression in immature oocytes, but expression patterns were more similar to ovum pick-up (OPU) oocytes following IVM. However, oocytes that were recovered following super-stimulation, while initially similar in gene expression to other recovery methods, displayed a dramatic increase in the level of gene transcripts present in mature oocytes. Looking only at OPU oocytes, incubation in meiotic delay was not only irreversible in some oocytes but was also only mildly successful at improving cytoplasmic maturation dynamics. Further, mitochondrial abnormalities in both distribution (projects 1, 2 and 4) and shape (project 4) were frequent. This suggests that recovering oocytes prematurely arrests mitochondrial development, which may be a major factor in low embryo production rates. Current research found that oocyte pre-incubation is unnecessary, and that oocytes recovered from post-mortem ovaries are likely of the greatest developmental competence. When recovering oocytes by OPU, timing is unimportant but super-stimulation causes irregular gene expression, the long-term effect of which is yet to be established.
Foster, Brittany Alanna, "Characterizing Cytoplasmic Maturation and Improving Competence of Bovine In Vitro Matured Oocytes" (2018). LSU Doctoral Dissertations. 4672.
Available for download on Sunday, July 04, 2021