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

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.

The Proteome, Not the Transcriptome, Predicts that Oocyte Superovulation Affects Embryonic Phenotypes in Mice

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans. Yet 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 bear on phenotypic traits in mice, whereas the transcriptome is far less predictive. The proteins that were differentially expressed in superovulated mouse oocytes and their derived embryos relative to their naturally ovulated counterparts were enriched in ontology terms describing abnormal mammalian phenotypes: a thinner zona pellucida, a smaller oocyte diameter, increased cleavage arrest, and defective blastocyst formation, which we could all verify 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 suited to draw conclusions of general validity about developmental processes, and underscore the importance of including the proteins in a modern molecular definition of oocyte quality.

Dissecting signalling hierarchies in the patterning of the mouse primitive streak using micro-patterned EpiLC colonies

Molecular embryology studies have established that the patterning of the gastrula-stage mouse embryo is dependent on a regulatory network where the WNT, BMP and NODAL signalling pathways cooperate. Still, important aspects of their respective contributions to this process remain unclear. Here, studying their impact on the spatial organization and the developmental trajectories of micro-patterned Epiblast Like Cells (EpiLC) colonies, we show that when BMP is present, it dominates NODAL and WNT and imposes a posterior character to the colonies differentiation. However, the use of two Nodal mutant cell lines allowed us to show that prior to BMP action, NODAL is required to establish the mesendodermal lineage. The fact that mutant phenotypes were more severe in vitro than in vivo suggests that embryonic phenotypes are partially rescued by ligands of extra-embryonic or maternal origin. Our work demonstrates the complementarity of micro-patterned EpiLC colonies to embryological approaches.

Fields, patterns and information: R.L. Brahmachary’s contributions during the infancy of molecular embryology

The contribution of Professor Ratan Lal Brahmachary’s research during the early years of molecular embryology, its theoretical underpinnings, and its connection with those of other contemporary research efforts, are traced in this article as a part of the history of developmental biology research in India.