I-8: Somatic Cell Nuclear Reprogramming byMouse Oocytes Endures Beyond ReproductiveDecline

Background: The mammalian oocyte has the unique feature of supporting fertilization and normal development while being able of reprogramming the nuclei of somatic cells towards pluripotency, and occasionally even totipotency. Whilst oocyte quality is known to decay with somatic ageing, it is not a given that different biological functions decay concurrently. In this study, we tested whether oocyte’s reprogramming ability decreases with somatic ageing, as previously reported for natural reproduction. Materials and Methods: We collected oocytes from B6C3F1 mice aged beyond the usual reproductive age (climacteric; 57-62 week-old) and from B6C3F1 mice in young age (6-8 week-old). We randomly allocated the oocytes of each age group to two subgroups: one subgroup to be analyzed for gene expression by the Agilent microarray, and the other subgroup to be used for somatic cell nuclear transfer (SCNT) from cumulus cells. Resultant cloned embryos were cultured to morula and blastocyst stage and analyzed for developmental rates, cell physiology and gene expression.Results: We show that oocytes isolated from climacteric mice yield ooplasts that retain reprogramming capacity after SCNT, at levels similar to ooplasts of young donors. Despite differences in transcriptome between ooplasts of old and young mice, gene expression profiles of the resultant SCNT blastocysts were very similar. Conclusion: Our observations strongly suggest that the outcome of oocyte-induced reprogramming is determined by 1) the dependence on the availability of intrinsic reprogramming factors tightly regulated throughout ageing, as well as 2) intracellular and environmental checkpoints during pre-implantation development, towards selection of the successfully reprogrammed embryos. While oocytes are not regenerated but rather last for life, we further propose that these cells can still be a resource for somatic reprogramming when they cease to be considered safe for sexual reproduction. Last, we note that while transcription factor-induced reprogramming becomes less efficient with somatic ageing, oocyteinduced reprogramming does not, hinting at intrinsic differences between these reprogramming methods.