TRANSCRIPTOMIC ANALYSIS REVEALS ALTERED GENE EXPRESSION IN MICE OOCYTES DURING THE PUBERAL TRANSITION

Abstract

Oocytes are increasingly being cryopreserved from pre-, peri- and early pubertal females for fertility preservation in the setting of cancer and other medical diagnoses. However, the quality of the oocytes is unknown in this age population. Using a mouse model of the pubertal transition and an experimental paradigm that mimics how gametes are obtained clinically for fertility preservation, our goal was to analyze the global gene expression profiles in the oocyte across the pubertal transition. In mice, puberty typically occurs more than 20 days after birth. To understand the molecular signatures that underlie meiotic competence and egg quality during the pubertal transition, we performed RNA-Seq on oocytes from postnatal day (PND) 13, 16, and PND 40 mice. The PND 16 animals were further sub-divided into those that weighed less (<9g) (PND 16 small) and those that weighed more (≥9g) (PND 16 large). Our group previously demonstrated that these ages broadly represent mice with oocytes that lack meiotic competence (PND 13, PND 16 small), oocytes that are meiotically competent but are of suboptimal quality (PND 16 large), and oocytes that are meiotically competent and of optimal quality (PND 40). Oocytes were collected from 3 mice per cohort to create three independent pools per group for RNA Seq analysis. To identify gene expression profiles that underlie meiotic competence, we compared differentially expressed genes between meiotically non-competent (PND 13, PND 16 small) and competent (PND 16 large, PND 40) oocyte cohorts. 2183 genes were differentially expressed between these groups. Gene Ontology analysis demonstrated that genes involved in phosphatidylinositide 3-kinase, mTOR, and Hippo signaling pathways were predominantly downregulated in the age cohort associated with oocyte meiotic competence. The comparison of gene expression profiles between two meiotically competent groups from peri- (PND16 large) and post-pubertal mice (PND 40) revealed that differentially expressed genes involved in cellular communication (i.e., cell periphery, plasma membrane, postsynapse, extracellular region, cell junction, extracellular vesicle, dense core granule) are upregulated in the oocytes from PND 40 mice. Pubertal transition in female mice is associated with suboptimal gamete quality. Through analysis of oocytes across this transition, we can extrapolate that repression of cellular growth pathways is associated with meiotic competence and increased expression of cellular communication pathways is associated with oocyte quality.