The Mechanism of Oocyte Activation Influences the Cell Cycle–Related Genes Expression During Bovine Preimplantation Development

Abstract

The first cleavage divisions and preimplantation embryonic development are supported by mRNA and proteins synthesized and stored during oogenesis. Thus, mRNA molecules of maternal origin decrease and embryonic development becomes gradually dependent on expression of genetic information derived from the embryonic genome. However, it is still unclear what the role of the sperm cell is during this phase and whether the absence of the sperm cell during the artificial oocyte activation affects subsequent embryonic development. The objective of this study was to determine, in bovine embryos, changes in cell cycle-associated transcript levels (cyclin A, cyclin B, cyclin E, CDC2, CDK2, and CDK4) after oocyte activation in the presence or absence of the sperm cell. To evaluate that, in vitro-produced (IVP) and parthenogenetically activated (PA) embryos (2-4 cells (2-4C), 8-16 cells (8-16C) and blastocysts) were evaluated by real-time PCR. There was no difference in cleavage and blastocyst rates between IVP and PA groups. Transcript level was higher in oocytes than in IVP and PA embryos. Cleaved PA embryos showed higher expression of cyclin A, cyclin B, cyclin E, and CDK2 and lower expression of CDC2 when compared with that from the IVP group. At the time of activation, all transcripts were expressed less in PA than in IVP embryos, whereas at the blastocyst stage, almost all genes were expressed at a higher level in the PA group. These results suggest that in both groups there is an initial consumption of these transcripts in the early stages of embryonic development. Furthermore, 8-16C embryos seem to synthesize more cell cycle-related genes than 2-4C embryos. However, in PA embryos, activation of the cell cycle genes seems to occur after the 8-to 16-cell stage, suggesting a failure in the activation process.

Endoplasmic reticulum distribution during bovine oocyte activation is regulated by protein kinase C via actin filaments

“…Since in vitro fertilization is not a synchronized process, the oocyte was submitted to parthenogenetic activation to have the zygotes at the same stage of development. Thus, following in vitro maturation, oocytes were artificially activated as described early (Milazzotto et al, 2008, 2012). Briefly, the oocyte was incubated in 5 µM calcium ionophore for 5 min.…”

Expression of miRNAs in Bull Spermatozoa Correlates with Fertility Rates

“…; Milazzotto et al. ). Thus, expression profiling of spermatozoa has recently been used in attempts to identify novel biomarkers for the prediction of fertility (Govindaraju et al.…”

“…Evidence of transcriptional activity has long been available for human-ejaculated spermatozoa, and also the presence of translational activity has been demonstrated (Pessot et al 1989;Steger 1999;Dadoune et al 2005;Gur and Breitbart 2006;Pan et al 2007). The proteins resulting from these mRNAs are likely to affect the first steps of embryonic development (Miller et al 2005;Milazzotto et al 2012). Thus, expression profiling of spermatozoa has recently been used in attempts to identify novel biomarkers for the prediction of fertility (Govindaraju et al 2012).…”

In search of the transcriptional blueprints of a competent oocyte

“…It is now well known that the maternal contribution has a large impact on early embryo development. Indeed, maternally derived mRNAs present in the oocyte decrease rapidly following fertilization (Milazzotto et al, 2012) but the lack of some maternal mRNAs can determine a low oocyte competence and quality (Labrecque and Sirard, 2014). However, the detailed molecular mechanisms affecting oocytes developmental competence are unknown.…”