Paternal influence on the time of first embryonic cleavage post insemination and the implications for subsequent bovine embryo development in vitro and fertility in vivo

Abstract

The objectives of this study were: (1) to evaluate the effect of sire on the time from insemination to first cleavage following insemination in vitro and the relationship of this parameter to field fertility and (2) to establish the relationship between the kinetics of cleavage in vitro and oocyte developmental competence for bulls of known field fertility. Frozen semen from six bulls with 150-day non-return rates ranging from 57±78% was used. In experiment 1, after insemination with semen from one of the six bulls, presumptive zygotes were transferred to IVC in droplets of synthetic oviduct fluid. Droplets were examined at 24, 27, 30, 33, 36, 42, and 48 hr after insemination and the number of cleaved oocytes was recorded. Blastocyst yield was recorded on Days 6-, 7-, and 8-post insemination. In experiment 2, culture droplets were examined at 30, 36, and 48 hr after insemination. At each time point, the number of cleaved embryos was recorded and these embryos were transferred into new droplets and were cultured separately for the duration of the experiment. The proportion of embryos developing to the blastocyst stage was recorded for each of the groups for each bull. The best predictor of field fertility was a model containing 33-hpi-cleavage percentage only (r 0.689, P`0.0001). There was also a significant correlation between blastocyst yield and non-return rate, with Day 7 blastocyst yield having the highest correlation (r 0.356), although this was relatively low in comparison. In experiment 2, irrespective of sire, a significantly higher proportion of those early-cleaving oocytes (before 30 hpi) developed to blastocysts than those cleaving later. In most cases, a higher proportion of blastocysts derived from early-cleaving oocytes hatched from the zona pellucida suggesting that such blastocysts are of superior quality to those derived from late-cleaving oocytes. In conclusion these data confirm our earlier observations that earliest cleaving zygotes are more competent in terms of development to the blastocyst stage than those that cleave later. This phenomenon is independent of the sire used. However, we have demonstrated that the kinetics of early embryonic development as measured by the timing of the first cleavage division post insemination vary between different bulls and that these differences can be used to discriminate between bulls of high and low bull field fertility. Mol. Reprod. Dev. 60: 47±55,

Sequential (hFSH + recFSH) vs homogenous (hFSH or recFSH alone) stimulation: clinical and biochemical (cumulus cell gene expression) aspects

“…Note the strong down regulation of the Zinc transporter SLC30A7 (see [38]) contribution [23,24]: the paternal genome affects embryonic development between pronuclear formation and 2-cell stage before embryonic genome activation. Early cleavage or "early embryo morphology aspect" as a test for oocyte competence is highly unreliable and is therefore questionable.…”

“…The aim was to find proposed biomarkers that might be used to predict and screen for oocyte quality, with the implication that this could also predict embryo quality. These aspects will also be discussed with respect to sperm quality, especially its capacity to induce rapid oocyte activation [22][23][24] Materials & methods…”

Assessment of different in vitro sperm challenges and in vivo fertility of bovine semen batches

“…In this sense, several researchers have reported a marked variability in field fertility among sires and/or batches (CORREA et al, 1997;WARD et al, 2001;ANDERSSON et al, 2004;OLIVEIRA et al, 2012a). Differences in field fertility could be attributed to variations in sperm-qualitative characteristics (CORREA et al, 1997).…”

High incidence of multiple aster formation in vitrified-warmed bovine oocytes after in vitro fertilization

“…Higher potential of oocytes cleaving earlier, compared to those cleaving later, to reach blastocysts [24,25], to survive cryopreservation [26] and to achieve pregnancy [24] have been reported in cattle. Although genetic factor [30], bull individuals for sperm [25], chromosomal normality [31], embryonic sex [24,31,32], and culture conditions [33] are involved in the developmental kinetics of embryos, the principle factor that controls the timing of first cleavage remains unclear. Developmental arrest was observed more frequently in vitrified group than fresh control group ( Table 1), suggesting that oocyte activation by sperm penetration was suboptimal in the vitrified-warmed oocytes.…”

“…Hence, the oocytes use their own MTOC dispersed in the cytoplasm for aster formation; that is called cytoplasmic aster [22,23]. Timing of first cleavage in IVF-derived bovine oocytes is important for yield and quality of blastocysts, as oocytes cleaving earlier are more likely to become blastocysts [24,25], and the resulting blastocysts have higher cryosurvival potential [26] and higher pregnancy rates [24] than those cleaving later. Thus, developmental kinetics can be used as a proxy of embryo quality.…”