In mammals fertilization triggers a series of Ca2+ oscillations that not only are essential for events of egg activation but also stimulate oxidative phosphorylation. Little is known, however, about the relationship between quantitative changes in egg metabolism and specific long-term effects in offspring. This study assessed whether post-natal growth is modulated by early transient changes in NAD(P)H and FAD2+ in zygotes. We report that experimentally manipulating the redox potential of fertilized eggs during the pronuclear (PN) stage affects post-natal body weight. Exogenous pyruvate induces NAD(P)H oxidation and stimulates mitochondrial activity with resulting offspring that are persistently and significantly smaller than controls. Exogenous lactate stimulates NAD+ reduction and impairs mitochondrial activity, and produces offspring that are smaller than controls at weaning but catch up after weaning. Cytosolic alkalization increases NAD(P)+ reduction and offspring of normal birth-weight become significantly and persistently larger than controls. These results constitute the first report that post-natal growth rate is ultimately linked to modulation of NAD(P)H and FAD2+ concentration as early as the PN stage.

The gene encodes one of the 'core' transcription factors necessary to establish and maintain pluripotency in mammals. Its function depends on its precise level of expression, so its transcription has to be tightly regulated. To date, few conserved functional elements have been identified in its 5' regulatory region: a distal and a proximal enhancer, and a minimal promoter, epigenetic modifications of which interfere with expression and function in -derived cell lines. Also, its permanent inactivation in differentiated cells depends on methylation of its promoter. However, little is known about the epigenetic regulation of expression in the embryo itself. We used the rabbit blastocyst as a model to analyze the methylation dynamics of the 5' upstream region, relative to its regulated expression in different compartments of the blastocyst over a 2-day period of development. We evidenced progressive methylation of the 5' regulatory region and the first exon accompanying differentiation and the gradual repression of Methylation started in the early trophectoderm before complete transcriptional inactivation. Interestingly, the distal enhancer, which is known to be active in naïve pluripotent cells only, retained a very low level of methylation in primed pluripotent epiblasts and remained less methylated in differentiated compartments than the proximal enhancer. This detailed study identified CpGs with the greatest variations in methylation, as well as groups of CpGs showing a highly correlated behavior, during differentiation. Moreover, our findings evidenced few CpGs with very specific behavior during this period of development.

During the last few years, several co-culture systems using either BOEC or VERO feeder cells have been developed to improve bovine embryo development and these systems give better results at high oxygen concentration (20%). In parallel, the SOF medium, used at 5% O, has been developed to mimic the oviduct fluid. Since 2010s, the SOF medium has become popular in improving bovine embryo development and authors have started to associate this medium to co-culture systems. Nevertheless, little is known about the putative benefit of this association on early development. To address this question, we have compared embryo transcriptomes in four different culture conditions: SOF with BOEC or VERO at 20% O, and SOF without feeders at 5% or 20% O Embryos have been analyzed at 16-cell and blastocyst stages. Co-culture systems did not improve the developmental rate when compared to 5% O Direct comparison of the two co-culture systems failed to highlight major differences in embryo transcriptome at both developmental stages. Both feeder cell types appear to regulate the same cytokines and growth factors pathways, and thus to influence embryo physiology in the same way. In blastocysts, when compared to culture in SOF at 5% O, BOEC or VERO seems to reduce cell survival and differentiation by, at least, negatively regulating STAT3 and STAT5 pathways. Collectively, in SOF medium both blastocysts rate and embryo transcriptome suggest no influence of feeder origin on bovine early development and no beneficial impact of co-culture systems when compared to 5% O.