MicroRNA pathway activity in mammalian oocytes

(English) Oocyte-to-embryo transition (OET) is one of the most complex developmental events where a differentiated oocyte gives rise to a totipotent zygote. During the growth phase an oocyte prepares for fertilization and progression to zygotic genome activation. It does so by transcribing and storing the necessary mRNAs till a fully-grown oocyte attains transcriptional quiescence. Therefore, transcriptome regulation in a fully-grown oocyte is of utmost importance. Study of post-transcriptional regulatory pathways revealed that the small-RNA mediated regulatory pathways exist in a unique conformation in mouse oocytes. Endogenous RNAi pathway is essential for mouse female germline while miRNA pathway which is ubiquitously present in most cell types is dispensable for oocyte maturation and fertilization. My PhD project was aimed at understanding the constraints of the miRNA pathway in the oocyte which makes it non-functional. As a fully-grown oocyte is a huge cell with a proportionally large maternal transcriptome we analysed the miRNA: mRNA stoichiometry changes that occur from growing to the fully-grown mouse oocyte. Inability of miRNAs to accumulate during oocyte growth phase leads to their dilution in fully-grown oocyte rendering them inactive. Low miRNA concentrations were also observed in rat,..