With the progressive delaying of childbearing age in western society, understanding and treating the decline in women's fertility associated with aging is becoming increasingly important. While the causes of premature aging of the ovary compared to other organs are largely unknown, it is widely accepted that a decline in oocyte competence to develop as an embryo is central to the decline in fertility in women over thirty-five. Several causes are thought to be at the basis of this decreased oocyte quality, the most widely accepted being an increase in age-related aneuploidy. Oocyte competence to complete meiosis and to develop as an embryo depends on complex programs of gene expression. At the end of its growth, oocyte's transcription is silenced and the control of gene expression is transferred to the cytoplasm, where a program of selective translation of maternal mRNA is executed. Thus, translational regulation is essential for the oocyte to become developmentally competent. Our laboratory has shown that this translation program activated in the final stages of oocyte maturation plays a critical role for the progression through the meiotic cell cycle, for chromosome trafficking and for preimplantation embryo development. Here we propose to test the hypothesis that this oocyte translation program becomes progressively defective during female aging. Preliminary data exploring the translation of candidate maternal mRNAs in oocytes from aging mouse females support this hypothesis. We propose to further these studies by exploring the functionality of the translation program during aging in mice and humans. The first Specific Aim will compare the pattern of maternal mRNA translation in oocytes from young and old females. We will use a mouse model where ribosomes are tagged in the oocyte, and translating mRNAs will be isolated by immunoprecipitation of ribosome/mRNA complexes followed by RNA-Seq. This genome-wide approach will define the extent of translational defects that develop with oocyte aging. The second Specific Aim will be devoted to understanding the molecular mechanisms at the basis of this defective translation. On the basis of genome- wide data suggesting defective expression of RNA binding protein networks and polyadenylation machinery, we will investigate the functionality of these components in aging oocytes. With the third Specific Aim, we will test the hypothesis that disruption of the translational program recapitulates the phenotype associated with aging. We will use genetic models of haploinsufficiency and SiRNA mediated knockdown to destabilize the translational program in young oocytes and determine whether oocyte developmental competence is compromised as it is during aging. To consolidate these findings, we will relate the observations made in a rodent model to human oocytes. We will explore whether translation is defective in oocytes from aging women and explore whether defects in biomarkers of translation are present using single cell assays. If confirmed, the hypothesis of compromised translation will open new avenues for understanding the decline in fertility in aging women and for developing new therapies.
The progressive decrease in fertility associated female aging is becoming a major social issue in Western countries. Considerable evidence points to a decline in oocyte quality as the major cause of the aging-related infertility. Understanding how oocyte quality becomes compromised with aging of a female is therefore central to women's health. Based on observations in rodents, we propose the novel hypothesis that defective gene expression consequent to compromised mRNA translation causes the decline in oocyte quality during aging. Exploring how mRNA translation is defective will provide new molecular correlates of oocyte quality and will pave the way to develop novel strategies to improve oocyte quality from older women.
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