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Effects of oocyte bisphenol A exposure on aspects of oocyte maturation and early embryo development in Bos taurus

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Title: Effects of oocyte bisphenol A exposure on aspects of oocyte maturation and early embryo development in Bos taurus
Author: Ferris, Jacqueline
Department: Department of Biomedical Sciences
Program: Biomedical Sciences
Advisor: King, Allan
Abstract: The microenvironment of the oocyte can influence oocyte quality, competence, and developmental potential. Alterations in this environment can have negative effects on oocyte maturation and subsequent embryo development. Oocyte quality, which can determine embryonic viability, is easily perturbed, thus factors that can alter normal oocyte maturation are a considerable concern. Bisphenol A (BPA) is an endocrine disrupting chemical that has been found to elicit a variety of reproductive effects. Exposure to BPA is considered to be ubiquitous and it has been found in a variety of human samples, including follicular fluid. BPA has previously been found to disrupt meiosis in mouse and human oocytes, however the embryonic effect in mammals are not as well documented. In the current study, bovine oocytes were matured in vitro under various treatment conditions such as no-treatment control (IVM media), vehicle control (0.1% ethanol), estradiol (2 μg/mL E2), and 15 ng/mL and 30 ng/mL BPA. The mature oocytes or subsequent embryos were collected for various analyses to determine effects on quality and developmental potential. Exposure of groups of oocytes to 15 ng/mL and 30 ng/mL BPA resulted in an average oocyte uptake of 1.69 and 2.48 ng/mL BPA, respectively. Exposure of bovine oocytes in vitro to 30 ng/mL BPA during maturation induced meiotic perturbations as well as poor embryonic outcomes. Meiosis progression was reduced and abnormal spindle morphology and chromosome alignment were increased. Under the same treatment conditions, resulting embryos exhibited decreased embryonic development rates, increased apoptosis, and a skewed sex ratio. Gene expression in blastocysts were not altered, whereas treatment with 15 ng/mL BPA resulted in increased expression of CDC2, AURKA, DAZL, TRβ and p53 in MII oocytes relative to that of the IVM group. This increased p53 expression resulting from the 15 ng/mL BPA group was also significantly greater than the expression levels resulting from 30 ng/mL BPA. There appeared to be a slight vehicle effect, with the vehicle group (0.1% ethanol) resulting in significantly increased expression of AURKA mRNA and non-significant increases in several other genes analyzed. BPA exposure during oocyte maturation in vitro can therefore, in a dose-dependent way, decrease oocyte and embryo quality and developmental potential.
Date: 2015-05

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