Culture protocols for horse embryos after ICSI: Effect of myo-inositol and time of media change

Oocyte holding and in vitro maturation duration between 28 and 34 hours do not affect equine OPU-ICSI outcomes

Previous studies in the horse highlight the potential benefit of prolonged in vitro maturation (IVM) (34 h) compared to short IVM (24 h) with or without prior oocyte holding, but little is known about the optimal IVM duration within this interval. To determine the effect of oocyte holding and duration of IVM ranged between 28 and 34 h on nuclear maturation, cleavage, blastocyst formation, and pregnancy rates, a retrospective study was performed in an equine clinical OPU-ICSI setting. The study included data of 2114 aspirated oocytes from 201 OPU-ICSI sessions. Duration of IVM was divided in three different time windows using quartiles, with 465 oocytes (22.0 %) between 28 and 30 h (first quartile), 1078 oocytes (51.0 %) >30 and 31.7 h (second and third quartiles), and 571 oocytes (27.0 %) >31.7 and 34 h (fourth quartile). Using logistic regression models, the effect of duration of IVM with and without holding was tested on nuclear maturation, cleavage, blastocyst, and pregnancy rates. The three IVM intervals did not show differences in nuclear maturation (respectively 64.5 ± 0.48 %, 65.7 ± 0.47 %, and 67.3 ± 0.47 %), cleavage (respectively 59.7 ± 0.49 %, 58.5 ± 0.49 %, and 64.8 ± 0.48 %), blastocyst (respectively 17.5 ± 0.38 %, 19.0 ± 0.39 %, and 20.8 ± 0.41 %) nor pregnancy rates (respectively 65.4 ± 0.49 %, 70.3 ± 0.46 %, and 74.2 % ± 0.44) (P ≥ 0.38). Oocyte holding prior to IVM did not affect the results either (P ≥ 0.15). In conclusion, oocyte holding and IVM duration between 28 and 34h do not significantly affect outcomes, allowing flexibility in the planning of clinical OPU-ICSI in horses.

A study on methods for preimplantation genetic testing (PGT) on in vivo- and in vitro-produced equine embryos, with emphasis on embryonic sex determination

Two methods for preimplantation genetic testing (PGT) have been described for equine embryos: trophoblast cell biopsy (TCB) or blastocoele fluid aspiration (BFA). While TCB is widely applied for both in vivo- and in vitro-produced embryos, BFA has been mostly utilized for in vivo-produced embryos. Alternative methods for PGT, including analysis of cell-free DNA (CFD) in the medium where in vitro-produced embryos are cultured, have been reported in humans but not for equine embryos. In Experiment 1, in vivo- (n = 10) and in vitro-produced (n = 13) equine embryos were subjected to BFA, cultured for 24 h, then subjected to TCB, and cultured for additional 24 h. No detrimental effect on embryonic diameter or re-expansion rates was observed for either embryo group (P > 0.05). In Experiment 2, the concordance (i.e., agreement on detecting the same embryonic sex using two techniques) among BFA, TCB, and the whole embryo (Whole) was studied by detecting the sex-determining region Y (SRY) or testis-specific y-encoded protein 1 (TSPY) (Y-chromosome), and androgen receptor (AR; X-chromosome) genes using PCR. Overall, a higher concordance for detecting embryonic sex was observed among techniques for in vivo-produced embryos (67-100 %; n = 14 embryos) than for in vitro-produced embryos (31-92 %; n = 13 embryos). The concordance between sample types increased when utilizing TSPY (77-100 %) instead of SRY (31-100 %) as target gene. In Experiment 3, CFD analysis was performed on in vitro-produced embryos to determine embryonic sex via PCR (SRY [Y-chromosome] and amelogenin - AMEL [X- and Y-chromosomes]). Overall, CFD was detected in all medium samples, and the concordance between CFD sample and the whole embryo was 60 % when utilizing SRY and AMEL genes. In conclusion, equine embryos can be subjected to two biopsy procedures (24 h apart) without apparent detrimental effects on embryonic size. For in vivo-, but not for in vitro-produced equine embryos, BFA can be considered a potential alternative to TCB for PGT. Finally, CFD can be further explored as a non-invasive method for PGT in in vitro produced equine embryos.

Characterization of preovulatory follicular fluid secretome and its effects on equine oocytes during in vitro maturation

In vitro maturation (IVM) of oocytes is clinically used in horses to produce blastocysts but current conditions used for horses are suboptimal. We analyzed the composition of equine preovulatory follicular fluid (FF) secretome and tested its effects on meiotic competence and gene expression in oocytes subjected to IVM. Preovulatory FF was obtained, concentrated using ultrafiltration with cut-off of 10 kDa, and stored at -80 °C. The metabolic and proteomic composition was analyzed, and its ultrastructural composition was assessed by cryo-transmission microscopy. Oocytes obtained post-mortem or by ovum pick up (OPU) were subjected to IVM in the absence (control) or presence of 20 or 40 μg/ml (S20 or S40) of secretome. Oocytes were then analyzed for chromatin configuration or snap frozen for gene expression analysis. Proteomic analysis detected 255 proteins in the Equus caballus database, mostly related to the complement cascade and cholesterol metabolism. Metabolomic analysis yielded 14 metabolites and cryo-transmission electron microscopy analysis revealed the presence of extracellular vesicles (EVs). No significant differences were detected in maturation rates among treatments. However, the expression of GDF9 and BMP15 significantly increased in OPU-derived oocytes compared to post-mortem oocytes (fold increase ± SEM: 9.4 ± 0.1 vs. 1 ± 0.5 for BMP15 and 9.9 ± 0.3 vs. 1 ± 0.5 for GDF9, respectively; p < 0.05). Secretome addition increased the expression of TNFAIP6 in S40 regardless of the oocyte source. Further research is necessary to fully understand whether secretome addition influences the developmental competence of equine oocytes.

Improving the developmental competences of porcine parthenogenetic embryos by Notoginsenoside R1-induced enhancement of mitochondrial activity and alleviation of proapoptotic events

Notoginsenoside R1 (NGR1), derived from the Panax notoginseng root and rhizome, exhibits diverse pharmacological influences on the brain, neurons, and osteoblasts, such as antioxidant effects, mitochondrial function protection, energy metabolism regulation, and inhibition of oxygen radicals, apoptosis, and cellular autophagy. However, its effect on early porcine embryonic development remains unclear. Therefore, we investigated NGR1's effects on blastocyst quality, reactive oxygen species (ROS) levels, glutathione (GSH) levels, mitochondrial function, and embryonic development-related gene expression in porcine embryos by introducing NGR1 during the in vitro culture (IVC) of early porcine embryos. Our results indicate that an addition of 1 μM NGR1 significantly increased glutathione (GSH) levels, blastocyst formation rate, and total cell number and proliferation capacity; decreased ROS levels and apoptosis rates in orphan-activated porcine embryos; and improved intracellular mitochondrial distribution, enhanced membrane potential, and reduced autophagy. In addition, pluripotency-related factor levels were elevated (NANOG and octamer-binding transcription factor 4 [OCT4]), antioxidant-related genes were upregulated (nuclear factor-erythroid 2-related factor 2 [NRF2]), and apoptosis- (caspase 3 [CAS3]) and autophagy-related genes (light chain 3 [LC3B]) were downregulated. These results indicate that NGR1 can enhance early porcine embryonic development by protecting mitochondrial function.

Cloning horses by somatic cell nuclear transfer: Effects of oocyte source on development to foaling

The cloning of horses is a commercial reality, yet the availability of oocytes for cloned embryo production remains a major limitation. Immature oocytes collected from abattoir-sourced ovaries or from live mares by ovum pick-up (OPU) have both been used to generate cloned foals. However, the reported cloning efficiencies are difficult to compare due to the different somatic cell nuclear transfer (SCNT) techniques and conditions used. The objective of this retrospective study was to compare the in vitro and in vivo development of equine SCNT embryos produced using oocytes recovered from abattoir-sourced ovaries and from live mares by OPU. A total of 1,128 oocytes were obtained, of which 668 were abattoir-derived and 460 were OPU-derived. The methods used for in vitro maturation and SCNT were identical for both oocyte groups, and the embryos were cultured in Dulbecco's Modified Eagle's Medium/Nutrient Mixture F-12 Ham medium supplemented with 10% fetal calf serum. Embryo development in vitro was assessed, and Day 7 blastocysts were transferred to recipient mares. The embryos were transferred fresh when possible, and a cohort of vitrified-thawed OPU-derived blastocysts was also transferred. Pregnancy outcomes were recorded at Days 14, 42 and 90 of gestation and at foaling. The rates of cleavage (68.7 ± 3.9% vs 62.4 ± 4.7%) and development to the blastocyst stage (34.6 ± 3.3% vs 25.6 ± 2.0%) were superior for OPU-derived embryos compared with abattoir-derived embryos (P < 0.05). Following transfer of Day 7 blastocysts to a total of 77 recipient mares, the pregnancy rates at Days 14 and 42 of gestation were 37.7% and 27.3%, respectively. Beyond Day 42, the percentages of recipient mares that still had a viable conceptus at Day 90 (84.6% vs 37.5%) and gave birth to a healthy foal (61.5% vs 12.5%) were greater for the OPU group compared with the abattoir group (P < 0.05). Surprisingly, more favourable pregnancy outcomes were achieved when blastocysts were vitrified for later transfer, probably because the uterine receptivity of the recipient mares was more ideal. A total of 12 cloned foals were born, 9 of which were viable. Given the differences observed between the two oocyte groups, the use of OPU-harvested oocytes for generating cloned foals is clearly advantageous. Continued research is essential to better understand the oocyte deficiencies and increase the efficiency of equine cloning.