P-TEFb Associates with Nucleolar Structure to Control Oocyte Meiosis Progression and Embryonic Genome Activation in the Pig

다국어 초록 (Multilingual Abstract)

Live offspring is obtained from in vitro production of porcine embryos, but the procedure is still associated with great inefficiencies. In mammalian oocytes, acquisition of meiotic competence coincides with a decrease in general transcriptional activity at the end of the oocyte growth phase. In this study, we investigated the expression and sub-cellular localization of positive transcription elongation factor P-TEFb (CDK9/Cyclin T1), a RNA polymerase II CTD kinase during pig oocyte growth and early embryonic development. Localization and expression of components involved in mRNA and rRNA transcription were assessed by immunocytochemistry in growing and fully-grown oocytes. In addition, meiotic resumption, germinal vesicle breakdown, nuclear transcription and embryonic genome activation (EGA) were analyzed in oocytes and embryos cultured in presence of a potent CDK9 inhibitor, flavopiridol. Our analyses, demonstrated that CDK9 became co- localized partially with phosphorylated Pol II CTD and mRNA splicing complexes. Surprisingly, CDK9 was co-localized with Pol I-specific transcription factor, UBF, and gradually localized in nucleolar peripheries at the final steps of oocyte growth. Later, CDK9 became associated with nucleolar structures at 4-cell stage. Treatment with flavopiridol resulted in arrest in meiotic resumption, germinal vesicle breakdown as well as a decline in global transcription. Flavopiridol also inhibited embryo development beyond EGA. All together, these data suggest that CDK9 has a dual role in both Pol I- and Pol II-dependent transcription in pig oocyte growth and embryonic development.