Early embryonic development in vertebrates is directed in part by maternal mRNAs expressed in oocytes and stored in cytoplasmic messenger ribonucleoprotein particles (mRNPs). Abundant evidence demonstrates the importance of mRNPs in embryonic development and in post-embryonic cellular function; however their characterization has been hampered by lack of suitable methodologies. The Xenopus oocyte has been the primary model system for studies of mRNPs. YY1 is a well-studied transcriptional regulatory factor that is sequestered in the oocyte cytoplasm and present entirely in cytoplasmic oocyte mRNPs. The objective of this thesis was to examine the biochemistry of YY1 association with maternal mRNA molecules in order to shed light on the role of YY1 in development and the poorly understood biology of oocyte mRNPs. The initial working hypotheses were that association of YY1 with mRNPs is dependent on sequence-specific RNA-binding activity and, therefore, that YY1 associates with a definite subset of maternal mRNA. A number of unique methods were developed in this study to address these hypotheses. RNA immunoprecipitation-DNA microarray (RIP-CHIP) analysis establishes that YY1 associates with a subset of mRNAs in the oocyte pool. A novel sequence-specific RNA-binding activity of the YY1 protein is demonstrated, and the RNA-binding activity of YY1 is shown to be required for its association with oocyte mRNPs in vivo. The functional roles of YY1 mRNA substrates are discussed in the context of embryological development and the biological function of YY1 in oocyte mRNPs. Extension of the experimental approaches developed in this thesis to the entire set of mRNP proteins would significantly advance our understanding of mRNP composition and heterogeneity, as well as the biological function of maternal mRNAs and mRNPs in development.

Early embryonic development in vertebrates is directed in part by maternal mRNAs expressed in oocytes and stored in cytoplasmic messenger ribonucleoprotein particles (mRNPs). Abundant evidence demonstrates the importance of mRNPs in embryonic development and in post-embryonic cellular function; however their characterization has been hampered by lack of suitable methodologies. The Xenopus oocyte has been the primary model system for studies of mRNPs. YY1 is a well-studied transcriptional regulatory factor that is sequestered in the oocyte cytoplasm and present entirely in cytoplasmic oocyte mRNPs. The objective of this thesis was to examine the biochemistry of YY1 association with maternal mRNA molecules in order to shed light on the role of YY1 in development and the poorly understood biology of oocyte mRNPs. The initial working hypotheses were that association of YY1 with mRNPs is dependent on sequence-specific RNA-binding activity and, therefore, that YY1 associates with a definite subset of maternal mRNA. A number of unique methods were developed in this study to address these hypotheses. RNA immunoprecipitation-DNA microarray (RIP-CHIP) analysis establishes that YY1 associates with a subset of mRNAs in the oocyte pool. A novel sequence-specific RNA-binding activity of the YY1 protein is demonstrated, and the RNA-binding activity of YY1 is shown to be required for its association with oocyte mRNPs in vivo. The functional roles of YY1 mRNA substrates are discussed in the context of embryological development and the biological function of YY1 in oocyte mRNPs. Extension of the experimental approaches developed in this thesis to the entire set of mRNP proteins would significantly advance our understanding of mRNP composition and heterogeneity, as well as the biological function of maternal mRNAs and mRNPs in development.