The proteome, not the transcriptome, predicts that oocyte superovulation affects embryonic phenotypes in mice

Leila Taher,Yutaka Suzuki,Georg Fuellen,Hannes C A Drexler,Steffen Israel,Wojciech Makalowski,Michele Boiani

doi:10.1038/s41598-021-03054-9

Abstract

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans. However, whether a superovulated oocyte is normal, is an open question. This study establishes for the first time that superovulation is associated with proteome changes that affect phenotypic traits in mice, whereas the transcriptome is far less predictive. The proteins that were differentially expressed in superovulated mouse oocytes and embryos compared to their naturally ovulated counterparts were enriched in ontology terms describing abnormal mammalian phenotypes: a thinner zona pellucida, a smaller oocyte diameter, increased frequency of cleavage arrest, and defective blastocyst formation, which could all be verified functionally. Moreover, our findings indicate that embryos with such abnormalities are negatively selected during preimplantation, and ascribe these abnormalities to incomplete ovarian maturation during the time of the conventional superovulation, since they could be corrected upon postponement of the ovulatory stimulus by 24 h. Our data place constraints on the common view that superovulated oocytes are suitable for drawing general conclusions about developmental processes, and underscore the importance of including the proteins in a modern molecular definition of oocyte quality.

Highlights

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans
The dose of gonadotropins used in our mice was chosen to preserve the units-to-body weight ratio of the commonly used 5 I.U. Equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) given at the age of 4 weeks, when mice weigh 10–15 g6: our mice were given 10 I.U. at the age of 8–10 weeks, when they weigh 20–25 g
It is commonly held that mouse oocytes ripened via superovulation possess developmental abilities that are very similar to those obtained after natural ovulation, and that residual differences are due to unrelated causes

Summary

Introduction

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans. It has become the epitome for generating oocytes for experimental and molecular embryology in mice, in greater numbers than natural ovulation, by stimulation with exogenous gonadotropins Studies on both superovulation and pregnancy in mice set the stage for assisted human reproduction[3,4,5]. The protein – but not the transcript – data established that superovulated mouse oocytes are not equivalent to their natural counterparts: the extent of preovulatory development prior to the ovulatory stimulus is decisive. These results underscore the importance of including the proteins in a modern molecular definition of oocyte quality, and call for caution when relying on superovulated oocytes to draw general conclusions about developmental processes

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