Pioneering Quantitative Transcriptome Analysis on Single Human Oocytes to Uncover the Genetic Base for Oocyte Aging

The leading cause of human infertility, spontaneous miscarriages and congenital defects lies in abnormal chromosome segregation during oocyte development. Through decades of research, many molecular and cellular aberrations were suggested to contribute to this deleterious process. Advance maternal age is the critical factor leading to oocyte quality decline and limits assisted reproductive technologies (ART) success rates. Currently, there is no medical procedure that can improve oocyte’s quality.

The aim of this study is to find the genetic base for the age-related decrease in oocyte quality. To achieve this goal, we are characterizing the transcriptomes of single oocytes from young and advanced aged women. Unfertilized MII oocytes after IVF (without ICSI) from two groups of patients (25-35 and 35-45) were collected and subjected to transcriptomic analysis. We adapted the Smart-seq3 protocol to human oocytes, a revolutionary method which provides quantitative full-length transcriptome coverage with a 5′ unique molecular identifier RNA controlling for PCR amplification biases. Using this technique, we were able to build cDNA libraries of full-length 5’ UMI tagged transcripts from single human oocytes. Thus, for the first time, we can quantity the expression level of each transcript and its spliced isoforms. Uncovering the gene expression changes oocytes undergo during quality decline, both at the levels of expression and splicing, could prove to be the first stepping-stone for translational applications to improve oocyte quality.