Developmental competence of equine oocytes and embryos obtained by in vitro procedures ranging from in vitro maturation and ICSI to embryo culture, cryopreservation and somatic cell nuclear transfer

Use of excised ovaries for oocyte recovery by ultrasound guided follicular aspiration - Validation of an experimental model for research purposes in live mares ovum pick up

Ovum pick-up (OPU) by transvaginal ultrasound guided follicle aspiration in mares is a common assisted reproductive technique used for oocyte recovery and in vitro production of horse embryos. There has been relatively little research into the factors influencing oocyte recovery in OPU from live mares. The objective of this study was to compare oocyte recovery and morphology of ultrasound-guided follicle puncture and aspiration in live mares and in postmortem excised ovaries, in order to validate an experimental model for research purposes of the efficiency of OPU in mares. Data from OPU performed in 12 mares from a commercial program (follicle numbers, oocyte recovery and oocyte morphology) were compared to that obtained from ultrasound-guided follicle puncture of 13 postmortem excised ovaries from slaughtered mares processed within 2 h of slaughter. In both groups, the OPU was performed by the same operator using the same equipment and OPU technique. The recovered oocytes per aspirated follicle was higher (P < 0.05) in the postmortem group (105/166, 63.2 %) than in live mares (138/261, 52.9 %). There was more (P < 0.05) expanded cumulus oocyte complexes in the postmortem than in the live mares (18 % vs. 2.9 %). Several oocytes (5 oocytes from 81 aspirated follicles) were found in the leaked fluid which overflowed during follicle flushing of postmortem ovaries. In conclusion, the higher recovery rate obtained in the excised ovaries and the finding of oocytes in the leaked fluid during OPU, suggests that there is still room for improvement in the in vivo OPU technique. Utilizing postmortem excised ovaries could offer an alternative for further research into factors affecting oocyte recovery and oocyte leakage during OPU procedures.

Granulosa cells provide transcriptomic information on ovarian follicle dynamics in southern white rhinoceros

Much remains unknown about the reproductive physiology of southern white rhinoceros (SWR) and the effect of ovarian stimulation prior to ovum pickup (OPU) have not been fully elucidated. Granulosa cells (GC) provide valuable insight into follicle growth and oocyte maturation status. The goals of this study were to evaluate transcriptomic changes in GC from three stages of follicle development and to identify biomarkers possibly associated with follicular growth and maturation as a result of ovarian stimulation. GC collected from SWRs following OPU were assigned stages based upon follicle size. Total RNA was isolated, and cDNA libraries were prepared and sequenced on a NovaSeq 6000. All bioinformatics analyses were performed utilizing the Galaxy web platform. Reads were aligned to CerSimCot1.0, and the manual curation was performed with EquCab3.0. Overall, 39,455 transcripts (21,612 genes) were identified across follicle stages, and manual curation yielded a 61% increase in gene identification from the original annotation. Granulosa cells from preovulatory follicles expressed the highest number of unique transcripts. The following seven biomarkers were determined based upon cluster analysis and patterns of expression: COL1A1, JMY, FBXW11, NRG1, TMPO, MACIR and COL4A1. These data can be used to potentially evaluate the effects of different ovarian stimulation protocols on follicle dynamics, improve OPU results, and support conservation efforts in this species.

Effect of sperm treatment with lysolecithin on in vitro outcomes of equine intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) in horses is currently employed for clinical and commercial uses, but the protocol could be optimized to improve its efficiency. We have hypothesized that destabilization of plasma and acrosomal membranes prior to injection would positively impact the developmental potential of equine zygotes generated by ICSI. This study evaluated effects of the sperm treatment with lysolecithin on plasma and acrosomal membranes and on oocyte activation ability, initially following heterologous ICSI on bovine oocytes and subsequently employing equine oocytes. The effects of the lysolecithin -treatment on the efficiency of conventional and piezo-assisted equine ICSI were evaluated. To do this, the equine sperm were treated with different concentrations of lysolecithin and the sperm plasma membrane, acrosome and DNA integrity were evaluated by flow cytometry. The results showed that a lysolecithin concentration of 0.08 % destabilized the membranes of all sperm and affected DNA integrity within the range described for the species (8-30 %). In addition, the heterologous ICSI assay showed that lysolecithin treatment was detrimental to the sperm's ability to activate the oocyte, therefore, chemical oocyte activation was used after equine ICSI after injection with lysolecithin -treated sperm. This group showed similar developmental rate to the control group with and without exogenous activation. In conclusion, lysolecithin pre-treatment is not necessary when using ICSI to produce equine embryos in vitro. The results from the current study provide additional insight regarding the factors impacting ICSI in horses.

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.

Could assisted reproductive techniques affect equine fetal membranes and neonatal outcome?

Embryo transfer (ET) and intracytoplasmic sperm injection (ICSI) are widely used in equine species, but their effects on fetal adnexa and neonates have not been investigated yet. The aim of this study was to retrospectively evaluate whether pregnancies obtained by ET or ICSI could be associated with the presence of macroscopic alterations of fetal membranes (FM) and umbilical cord (UC) and if the use of these techniques could influence neonatal outcome. Sixty-six light breed mares hospitalized at the Veterinary Teaching Hospital, University of Bologna, for attending delivery were included in the study. Mares were divided into Artificial Insemination (AI; 32/66 mares, 48 %), Embryo Transfer (ET; 12/66 mares, 18.2 %) and Intracytoplasmic Sperm Injection (ICSI; 22/66 mares, 33 %) groups. All the medical reports of mares and their foals were reviewed and data about mare, pregnancy, foaling, fetal membranes, umbilical cord and foal were recorded. The occurrence of dystocia resulted statistically different between AI group and ICSI group (p = 0.0066), and between AI group and ET group (p = 0.044). Macroscopic examination of FM revealed alterations in 30/66 mares (46 %): 8/32 in AI (25 %), 7/12 in ET (58 %) and 15/22 in ICSI (68 %) with significant lower incidence in AI compared to ET (p = 0.04) and ICSI (p = 0.002) groups. Alterations reported were chorionic villi hypoplasia, chorioallantois edema, allantois cysts, necrotic areas and greenish-grey concretions. Total length of UC resulted significantly shorter in ICSI group (49 ± 9 cm; p < 0.03) compared to AI (60 ± 17 cm) and ET (59 ± 15 cm). However, there were no differences in the incidence of foals' diseases at birth and in foals' survival among groups (p > 0.05). The results demonstrate that transfer of in vivo or in vitro produced embryos may lead to alterations of placental development, as observed in other species, without being associated with a higher incidence of neonatal morbidity and mortality. Further studies about trophoblast development, FM histological evaluation, and placental gene expression should be carried out to clarify the mechanisms underlying the placental alterations.

Can Nicotinamide Adenine Dinucleotide (NAD+) and Sirtuins Be Harnessed to Improve Mare Fertility?

Years of sire and dam selection based on their pedigree and athletic performance has resulted in a reduction in the reproductive capability of horses. Mare age is considered a major barrier to equine reproduction largely due to an increase in the age at which mares are typically bred following the end of their racing career. Nicotinamide adenine dinucleotide (NAD+) and its involvement in the activation of Sirtuins in fertility are an emerging field of study, with the role of NAD+ in oocyte maturation and embryo development becoming increasingly apparent. While assisted reproductive technologies in equine breeding programs are in their infancy compared to other livestock species such as cattle, there is much more to be learnt, from oocyte maturation to early embryo development and beyond in the mare, which are difficult to study given the complexities associated with mare fertility research. This review examines what is already known about the role of NAD+ and Sirtuins in fertility and discusses how NAD+-elevating agents may be used to activate Sirtuin proteins to improve equine breeding and embryo production programs both in vivo and in vitro.

Transcriptome analyses reveal transcriptional profiles of horse oocytes before and after in vitro maturation

Oocyte in vitro maturation is necessary for the study and application of animal-assisted reproduction technology in animal reproduction and breeding. The comprehensive transcriptional profile of equine oocyte maturated in vitro has not been fully mined yet, which makes many key transcriptional events still unidentified. Here, Smart-seq2 was performed to analyse the gene expression pattern and the underlying regulatory mechanism of horse germinal vesicle (GV) and in vitro metaphase II (MII) oocytes. The results showed that 6402 genes (2640 up-regulated and 3762 down-regulated in MII samples compared to GV) and 4021 lncRNA transcripts (1210 up-regulated and 2811 down-regulated in MII samples compared to GV) were differentially expressed in GV and MII oocytes. Further, GO and KEGG analysis found that differentially expressed mRNAs and lncRNAs were mainly enriched in the pathways related to energy and lipid metabolism. In addition, LGALS3 was found a key gene in mediating the regulation of oocyte meiosis recovery and fertilization ability. This study provides novel knowledge about gene expression and energy metabolism during equine oocyte maturation and a reference for the further study and application of assisted reproductive technology in horse reproduction and breeding.

Transcriptome Signature of Immature and In Vitro-Matured Equine Cumulus-Oocytes Complex

Maturation is a critical step in the development of an oocyte, and it is during this time that the oocyte advances to metaphase II (MII) of the meiotic cycle and acquires developmental competence to be fertilized and become an embryo. However, in vitro maturation (IVM) remains one of the limiting steps in the in vitro production of embryos (IVP), with a variable percentage of oocytes reaching the MII stage and unpredictable levels of developmental competence. Understanding the dynamics of oocyte maturation is essential for the optimization of IVM culture conditions and subsequent IVP outcomes. Thus, the aim of this study was to elucidate the transcriptome dynamics of oocyte maturation by comparing transcriptomic changes during in vitro maturation in both oocytes and their surrounding cumulus cells. Cumulus-oocyte complexes were obtained from antral follicles and divided into two groups: immature and in vitro-matured (MII). RNA was extracted separately from oocytes (OC) and cumulus cells (CC), followed by library preparation and RNA sequencing. A total of 13,918 gene transcripts were identified in OC, with 538 differentially expressed genes (DEG) between immature OC and in vitro-matured OC. In CC, 13,104 genes were expressed with 871 DEG. Gene ontology (GO) analysis showed an association between the DEGs and pathways relating to nuclear maturation in OC and GTPase activity, extracellular matrix organization, and collagen trimers in CC. Additionally, the follicle-stimulating hormone receptor gene (FSHR) and luteinizing hormone/choriogonadotropin receptor gene (LHCGR) showed differential expressions between CC-MII and immature CC samples. Overall, these results serve as a foundation to further investigate the biological pathways relevant to oocyte maturation in horses and pave the road to improve the IVP outcomes and the overall clinical management of equine assisted reproductive technologies (ART).

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.

Optimization of recovery and maturation methods for cumulus-oocyte complexes in jennies

Embryo production in donkeys is inefficient compared with that in other livestock. Obtaining a sufficient number of MII oocytes is the first step to solving this problem. In this study, the number, morphology and maturation rates of cumulus-oocyte complexes (COCs) obtained from abattoir-derived ovaries or live jennies were compared. The diameter of follicles from abattoir-derived ovaries was measured and divided into group 1 (2-6 mm), group 2 (6-10 mm), group 3 (10-20 mm), group 4 (20-28 mm) and group 5 (>28 mm). The results showed that the number of follicles per ovary in group 2 (3.6 ± 0.28) and 3 (4.2 ± 0.90) was higher than that in the other groups (p < .05). The recovery rate in group 3 was higher than group 1 (48.8% vs. 26.8%, p = .00), but lower than group 5 (48.8% vs. 76.5%, p = .025). The percentage of grade A COCs in group 3 was higher than group 2 (59.3% vs. 39.5%, p = .00) and group 1 (59.3% vs. 26.7%, p = .00). Moreover, the percentage of grade A COCs in group 4 (55.0%, p = .710) and group 5 (46.2%, p = .351) was reduced compared with that in group 3. From the above results, the developing follicles (group ovum pick-up [OPU], 10-20 mm) and preovulation follicles (group OPU-Preov, >35 mm) were aspirated from live jennies using OPU. Although there was no difference in the recovery rates of COCs between group 3 and OPU (48.8% vs. 43.0%, p = .184), the percentage of grades A COCs in group OPU was higher than group 3 (72.5% vs. 59.3%, p = .036). There was no difference in the maturation rate between group 3 and OPU (60.3% vs. 69.3%, p = .171) after the COCs matured in vitro. The rates of recovery (72.2%) and maturation (92.3%) in group OPU-Preov were higher than those in other groups (p < .05). Moreover, the effects of maturation time and serum type on maturation rates were evaluated in groups B44 (44 h, FBS), B36 (36 h, FBS) and D44 (44 h, foetal donkey serum, FDS). These results indicated that the maturation rate in group B36 was lower than group B44 (13.1% vs. 47.0%, p = .00) and group D44 (13.1% vs. 53.3%, p = .00). In conclusion, the quality of donkey COCs from OPU was higher than that from abattoir-derived ovaries, the suitable time of donkey in vitro maturation (IVM) was 44 h, and FBS could be replaced with FDS in donkey IVM medium.

Metabolic profiling of preovulatory follicular fluid in jennies

Follicular fluid is formed from the transudation of theca and granulosa cells in the growing follicular antrum. Its main function is to provide an optimal intrafollicular microenvironment to modulate oocyte maturation. The aim of this study was to determine the metabolomic profile of preovulatory follicular fluid (PFF) in jennies. For this purpose, PFF was collected from 10 follicles of five jennies in heat. Then, PFF samples were analysed by nuclear magnetic resonance (NMR) and heteronuclear single quantum correlation (2D 1H/13C HSQC). Our study revealed the presence of at least 27 metabolites in the PFF of jennies (including common amino acids, carboxylic acids, amino acid derivatives, alcohols, saccharides, fatty acids, and lactams): 3-hydroxybutyrate, acetate, alanine, betaine, citrate, creatine, creatine phosphate, creatinine, ethanol, formate, glucose, glutamine, glycerol, glycine, hippurate, isoleucine, lactate, leucine, lysine, methanol, phenylalanine, proline, pyruvate, threonine, tyrosine, valine, and τ-methylhistidine. The metabolites found here have an important role in the oocyte development and maturation, since the PFF surrounds the follicle and provides it with the needed nutrients. Our results indicate a unique metabolic profile of the jennies PFF, as it differs from those previously observed in the PFF of the mare, a phylogenetically close species that is taken as a reference for establishing reproductive biotechnology techniques in donkeys. The metabolites found here also differ from those described in the TCM-199 medium enriched with fetal bovine serum (FBS), which is the most used medium for in vitro oocyte maturation in equids. These differences would suggest that the established conditions for in vitro maturation used so far may not be suitable for donkeys. By providing the metabolic composition of jenny PFF, this study could help understand the physiology of oocyte maturation as a first step to establish in vitro reproductive techniques in this species.

Past, present and future of ICSI in livestock species

During the past 2 decades, intracytoplasmic sperm injection (ICSI) has become a routine technique for clinical applications in humans. The widespread use among domestic species, however, has been limited to horses. In horses, ICSI is used to reproduce elite individuals and, as well as in humans, to mitigate or even circumvent reproductive barriers. Failures in superovulation and conventional in vitro fertilization (IVF) have been the main reason for the use of this technology in horses. In pigs, ICSI has been successfully used to produce transgenic animals. A series of factors have resulted in implementation of ICSI in pigs: need to use zygotes for numerous technologies, complexity of collecting zygotes surgically, and problems of polyspermy when there is utilization of IVF procedures. Nevertheless, there have been very few additional reports confirming positive results with the use of ICSI in pigs. The ICSI procedure could be important for use in cattle of high genetic value by maximizing semen utilization, as well as for utilization of spermatozoa from prepubertal bulls, by providing the opportunity to shorten the generation interval. When attempting to utilize ICSI in ruminants, there are some biological limitations that need to be overcome if this procedure is going to be efficacious for making genetic improvements in livestock in the future. In this review article, there is an overview and projection of the methodologies and applications that are envisioned for ICSI utilization in these species in the future.

Detection of Indiscriminate Genetic Manipulation in Thoroughbred Racehorses by Targeted Resequencing for Gene-Doping Control

The creation of genetically modified horses is prohibited in horse racing as it falls under the banner of gene doping. In this study, we developed a test to detect gene editing based on amplicon sequencing using next-generation sequencing (NGS). We designed 1012 amplicons to target 52 genes (481 exons) and 147 single-nucleotide variants (SNVs). NGS analyses showed that 97.7% of the targeted exons were sequenced to sufficient coverage (depth > 50) for calling variants. The targets of artificial editing were defined as homozygous alternative (HomoALT) and compound heterozygous alternative (ALT1/ALT2) insertion/deletion (INDEL) mutations in this study. Four models of gene editing (three homoALT with 1-bp insertions, one REF/ALT with 77-bp deletion) were constructed by editing the myostatin gene in horse fibroblasts using CRISPR/Cas9. The edited cells and 101 samples from thoroughbred horses were screened using the developed test, which was capable of identifying the three homoALT cells containing 1-bp insertions. Furthermore, 147 SNVs were investigated for their utility in confirming biological parentage. Of these, 120 SNVs were amenable to consistent and accurate genotyping. Surrogate (nonbiological) dams were excluded by 9.8 SNVs on average, indicating that the 120 SNV could be used to detect foals that have been produced by somatic cloning or embryo transfer, two practices that are prohibited in thoroughbred racing and breeding. These results indicate that gene-editing tests that include variant calling and SNV genotyping are useful to identify genetically modified racehorses.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section II

Simple Summary

In order to improve fertilization and pregnancy rates within artificial insemination or in vitro fertilization techniques in horses, producers may choose to select the best sperm within an ejaculate. In this paper, we review conventional and novel methods of sperm selection.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of available semen selection techniques. This segment of our two-section review will focus on the selection of spermatozoa based on quality and sex for equine intracytoplasmic sperm injection (ICSI), as well as current and future developments in sperm sorting technologies. Ultimately, novel methods of semen selection will be assessed based on their efficacy in other species and their relevance and future application towards ARTs in the horse.

The Mare: A Pertinent Model for Human Assisted Reproductive Technologies?

Although there are large differences between horses and humans for reproductive anatomy, follicular dynamics, mono-ovulation, and embryo development kinetics until the blastocyst stage are similar. In contrast to humans, however, horses are seasonal animals and do not have a menstrual cycle. Moreover, horse implantation takes place 30 days later than in humans. In terms of artificial reproduction techniques (ART), oocytes are generally matured in vitro in horses because ovarian stimulation remains inefficient. This allows the collection of oocytes without hormonal treatments. In humans, in vivo matured oocytes are collected after ovarian stimulation. Subsequently, only intra-cytoplasmic sperm injection (ICSI) is performed in horses to produce embryos, whereas both in vitro fertilization and ICSI are applied in humans. Embryos are transferred only as blastocysts in horses. In contrast, four cells to blastocyst stage embryos are transferred in humans. Embryo and oocyte cryopreservation has been mastered in humans, but not completely in horses. Finally, both species share infertility concerns due to ageing and obesity. Thus, reciprocal knowledge could be gained through the comparative study of ART and infertility treatments both in woman and mare, even though the horse could not be used as a single model for human ART.

Genetic Manipulation of the Equine Oocyte and Embryo

As standard in vitro fertilization is not a viable technique in horses yet, many different techniques have been used to create equine embryos for research purposes. One such method is parthenogenesis in which an oocyte is induced to mature into an embryo-like state without the introduction of a spermatozoon, and thus they are not considered true embryos. Another method is somatic cell nuclear transfer (SCNT), in which a somatic cell nucleus from an extant horse is inserted into an enucleated oocyte, creating a genetic clone of the donor horse. Due to limited availability of equine oocytes in the United States, researchers have investigated the potential for combining equine somatic cell nuclei with oocytes from other species to make embryos for research purposes, which has not been successful to date. There has also been a rising interest in producing transgenic animals using sperm exposed to exogenous DNA. The successful creation of transgenic equine blastocysts shows the promise of sperm mediated gene transfer (SMGT), but this method is not ideal for other applications, like gene therapy, because it cannot be used to induce targeted mutations. That is why technologies like CRISPR/Cas9 are vital. In this review, we argue that parthenogenesis, SCNT, and interspecies SCNT can be considered genetic manipulation strategies as they create embryos that are genetically identical to their parent cell. Here, we describe how these methods are performed and their applications and we also describe the few methods that have been used to directly modify equine embryos: SMGT and CRISPR/Cas9.

A high glucose concentration during early stages of in vitro equine embryo development alters expression of genes involved in glucose metabolism

BACKGROUND

Equine embryos exhibit an unusual pattern of glucose tolerance in vitro and are currently cultured in hyperglycaemic conditions.

OBJECTIVE

Our main objective was to analyse the effect of different glucose concentrations on in vitro-produced equine embryo development and quality.

STUDY DESIGN

Experiments comparing in vitro and in vivo produced embryos.

METHODS

Oocytes (n = 641) were collected from post-mortem ovaries, matured in vitro and fertilised by intracytoplasmic sperm injection (ICSI). Embryo culture was divided from Day 0 to Day 4 and from Day 4 to Day 9 in three groups: 5-10 (5 and 10 mmol/L glucose respectively; n = 87); 5-17 (5 and 17.5 mmol/L; n = 66); and 10-17 (10 and 17.5 mmol/L; n = 117). A control group of 20 in vivo produced blastocysts was included. Cleavage and blastocyst rates were evaluated and embryos were snap-frozen for analysis of the relative mRNA expression of genes related to mitochondrial function, DNA methylation, apoptosis, glucose transport and metabolism.

RESULTS

No differences were observed in the cleavage or blastocyst rates among in vitro groups. Under high glucose conditions in vitro (10-17 group), BAX/BCL2 was higher, and PFKP, LDHA and COX2 were overexpressed compared to all other groups. The two groups with 5 mmol/L glucose concentration during the first culture stage (5-10 and 5-17) displayed similar patterns which differed to the 10-17 group.

MAIN LIMITATIONS

Conclusions related to embryo quality are based on gene expression patterns. Transfer of in vitro-produced embryos would reveal whether the observed differences improve embryo developmental competence.

CONCLUSIONS

Five mM glucose during the first days of culture seems to be preferable to avoid over-activation of embryonic glycolytic pathways. Further studies are necessary to determine whether this improves embryo developmental competence.

Pregnancy obtained in a late gestational mare by in vitro embryo production

Recently, the demand for invitro embryo production in the horse has increased worldwide. Most clinical transvaginal ultrasound-guided ovum pick-up (OPU) procedures are performed in non-pregnant donor mares, and few experimental studies have described invitro embryo production from oocytes of pregnant donors 21-150 days in gestation. This report discusses OPU, follicular growth and invitro embryo production in a pregnant mare during late gestation.

Association of equine oocyte and cleavage stage embryo morphology with maternal age and pregnancy after intracytoplasmic sperm injection

In this retrospective study the morphological characteristics of oocytes and cleavage stage embryos were associated with pregnancy results from clinical intracytoplasmic sperm injection (ICSI) in mares. Oocytes were collected from preovulatory follicles, and images (×200; n=401) were captured for measurements of ooplasm, the perivitelline space and zona pellucida. After ICSI and before transfer into recipients' oviducts, cleavage stage embryos were imaged (n=178). Oocyte donor ages (3-13, 14-19, 20-23, 24-27 years) were compared, as were mares aged 3-13 years without versus with recent histories of performance or injury stress. Cleavage rates did not differ with age. However, pregnancy rates declined and pregnancy loss rates (11-50 days gestation) increased with mare age. Young mares with performance or injury stress had significantly lower pregnancy rates than young mares under management typical for broodmares. No morphological oocyte characteristic was consistently associated with age or pregnancy outcome. Cleavage stage embryo morphology was not associated with pregnancy outcome; however, the rate of embryo development before oviductal embryo transfer was faster (P<0.05) for embryos that resulted in an early pregnancy (≤17 days) and tended (P ≤ 0.1) to be higher for embryos that produced a 50-day pregnancy. Embryonic vesicles that had a more rapid increase in diameter were more often (P<0.05) maintained until 50 days gestation.

Laboratory Production of Equine Embryos

Assisted reproduction technologies (ART) are well developed in humans and cattle and are gaining momentum also in the equine industry because of the fact that the mare does not respond to superovulation but can donate large numbers of oocytes through ovum pick up (OPU). After collection, the oocytes can be fertilized by intracytoplasmic sperm injection (ICSI) using a variety of stallion semen samples, even of poor quality, and the resulting embryos can establish high pregnancy rates after cryopreservation and transfer. The discoveries that equine oocytes can be held at room temperature without loss of viability and that an increase in vitro maturation time can double the number of embryos produced are fueling the uptake of the OPU technique by several clinics that are shipping oocytes of their client's mares to specialized ICSI laboratories for embryo production and freezing. In this article, we present a retrospective analysis of 10 years of work at Avantea with a special focus on the last 3 years. Based on our data, an average production of 1.7 to 2 embryos per OPU-ICSI procedure can be obtained from warmblood donor mares with a pregnancy rate of 70% and a foaling rate in excess of 50%. OPU-ICSI offers the added value of freezing embryos that allows the development of embryo commercialization worldwide to the benefit of top horse breeders who are endorsing this technology as never before.

Clinical Application of in Vitro Embryo Production in the Horse

The first reports of in vitro embryo production (IVEP) by conventional in vitro fertilization and intracytoplasmic sperm injection in horses date respectively from approximately 30 and 25 years ago. However, IVEP has only become established in clinical practice during the last decade. The initial slow uptake of IVEP was largely because the likelihood of success was too low to make it an economically viable means of breeding horses. During the last decade, the balance has shifted, primarily because of significant improvements in the efficiency of recovering immature oocytes from live donor mares (historically <25%; now >50%) and in the successful culture of zygotes to the blastocyst stage in vitro (historically <10%; now >20%). It has also been established that immature oocytes can be "held" at room temperature for at least 24 hours, allowing overnight transport to a laboratory with expertise in IVEP. Moreover, because in vitro-produced embryos can be cryopreserved with no appreciable reduction in viability, they can be shipped and stored until a suitable recipient mare is available for transfer. Most importantly, in an established equine ovum pick-up intracytoplasmic sperm injection (OPU-ICSI) program, blastocyst production rates now exceed 1 per procedure, and posttransfer foaling rates exceed 50%, such that overall efficiency betters that of either embryo flushing or oocyte transfer. Moreover, OPU-ICSI can be performed year round and allows embryo production from mares with severe acquired subfertility and extremely efficient use of scarce or expensive frozen semen. Cumulatively, these factors have stimulated rapid growth in demand for IVEP among sport horse breeders.

Effect of warming method on embryo quality in a simplified equine embryo vitrification system

Equine embryo vitrification is still not a well-established technique in equine practice. Notably, little work has been done on the effect of the warming system on viability of vitrified embryos. Our goal was to evaluate the effect of warming without cryoprotectants on in vitro - produced (IVP) embryo viability in culture, quality assessment parameters, and pregnancy after transfer. Equine IVP blastocysts were vitrified using commercial embryo vitrification media and a semi-closed vitrification device. In Exp. 1, we evaluated two warming temperatures (room temperature, RT, ∼22 °C; and 38 °C) for each of three warming systems: commercial warming solution (Kit); commercial embryo holding medium (EHM) with decreasing concentrations of sucrose (EHM + SS); or EHM alone without added sucrose. Embryos (n = 9 to 14 per treatment) were cultured in vitro for 24 h, stained with DAPI, TUNEL, and fluorophore-labelled phalloidin, and evaluated for nucleus number, mitotic rate, apoptotic rate, and actin filament distribution. In Exp. 2, to survey embryo viability in vivo, vitrified IVP blastocysts were shipped to an embryo transfer facility, then warmed immediately before transfer to recipient mares, using the warming treatments associated with the nominally best (Kit-RT, Kit-38, EHM-RT) and poorest (EHM + SS-38) assessed embryo quality in Exp. 1 (n = 7 to 8 per treatment). Subsequently, IVP blastocysts produced as part of our clinical program were vitrified and shipped, then warmed in embryo holding medium at an embryo transfer facility before transfer to recipient mares; fresh IVP embryos were shipped and transferred as controls. In Exp. 1, embryos increased significantly in diameter after culture (P < 0.01), with no difference among treatments. There was no difference (P > 0.05) in the number of viable nuclei, apoptotic rate, or microfilament distribution among treatments, or between vitrified-warmed and Control embryos. The mitotic rate was higher (P = 0.021) for Kit-RT (3.6%) when compared with the other treatment groups (1.5-2.0%). In Exp. 2, there was no difference (P > 0.05) in initial pregnancy (71.4-87.5%) or heartbeat (57.1%-85.7%) rates among warming treatments. In the clinical trial, there was no difference (P > 0.05) between vitrified-warmed and Control embryos in initial pregnancy (90.9% and 66.6%, respectively) or heartbeat (81.8% and 66.6%, respectively) rates. These results indicate that a semi-closed vitrification system using commercially-available media, and incorporating warming in the field in a single step using commercial embryo holding medium without cryoprotectants, can provide high pregnancy rates with IVP equine embryos.

Advances in Holding and Cryopreservation of Equine Oocytes and Embryos

Methods for holding of oocytes and embryos during shipment as well as for their cryopreservation can greatly aid equine reproductive management. Oocytes can be held at room temperature overnight or at cooler temperatures for two nights without affecting maturation or embryo development after intracytoplasmic sperm injection. In contrast, methods for cryopreservation of equine oocytes that support high rates of embryo development have not yet been established. Equine embryos may be held overnight at temperatures from 5°C to 19°C without reduction in viability, but longer holding periods, or higher holding temperatures, may be detrimental. Small equine embryos (<300 μm), either in vivo derived or in vitro produced, can be slow frozen or vitrified successfully. In the last decade, methods have been developed to allow in vivo-derived expanded blastocysts, up to Day 8, to be vitrified successfully after blastocoele collapse. These methods of shipment and preservation allow mare owners in remote locations to have access to sophisticated assisted reproductive technologies.

Energy metabolism of the equine cumulus oocyte complex during in vitro maturation

Horses are one of the few species, beside humans, in which assisted reproductive technology has important clinical applications. Furthermore, the horse can serve as a valuable model for the study of comparative reproductive biology. Here we present the first comprehensive characterisation of energy metabolism and mitochondrial efficiency in equine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM), as determined using a combination of non-invasive consumption and release assays and mitochondrial function analysis. These data reveal notable species-specific differences in the rate and kinetics of glucose consumption and glycolysis throughout IVM. Approximately 95% of glucose consumed was accounted for by lactate production; however, high concurrent oxygen consumption indicated a comparatively increased role for non-glycolytic oxidative phosphorylation. Up to 38% of equine COC oxygen consumption could be attributed to non-mitochondrial activities and there was a significant loss of spare respiratory capacity over the course of IVM. Notably, our data also revealed that current IVM protocols may be failing to satisfy the metabolic demands of the equine COC. Our findings constitute the first report on mitochondrial efficiency in the equine COC and provide new insight into comparative gamete biology as well as metabolism of the COC during in vitro maturation.

Mitochondrial DNA replication is initiated at blastocyst formation in equine embryos

Intracytoplasmic sperm injection is the technique of choice for equine IVF and, in a research setting, 18-36% of injected oocytes develop to blastocysts. However, blastocyst development in clinical programs is lower, presumably due to a combination of variable oocyte quality (e.g. from old mares), suboptimal culture conditions and marginal fertility of some stallions. Furthermore, mitochondrial constitution appears to be critical to developmental competence, and both maternal aging and invitro embryo production (IVEP) negatively affect mitochondrial number and function in murine and bovine embryos. The present study examined the onset of mitochondrial (mt) DNA replication in equine embryos and investigated whether IVEP affects the timing of this important event, or the expression of genes required for mtDNA replication (i.e. mitochondrial transcription factor (TFAM), mtDNA polymerase γ subunit B (mtPOLB) and single-stranded DNA binding protein (SSB)). We also investigated whether developmental arrest was associated with low mtDNA copy number. mtDNA copy number increased (P<0.01) between the early and expanded blastocyst stages both invivo and invitro, whereas the mtDNA:total DNA ratio was higher in invitro-produced embryos (P=0.041). Mitochondrial replication was preceded by an increase in TFAM but, unexpectedly, not mtPOLB or SSB expression. There was no association between embryonic arrest and lower mtDNA copy numbers.

pH-dependent effects of procaine on equine gamete activation†

Procaine directly triggers pH-dependent cytokinesis in equine oocytes and induces hypermotility in stallion spermatozoa, an important event during capacitation. However, procaine-induced hyperactivated motility is abolished when sperm is washed to remove the procaine prior to sperm-oocyte co-incubation. To understand how procaine exerts its effects, the external Ca2+ and Na+ and weak base activity dependency of procaine-induced hyperactivation in stallion spermatozoa was assessed using computer-assisted sperm analysis. Percoll-washed stallion spermatozoa exposed to Ca2+-depleted (+2 mM EGTA) procaine-supplemented capacitating medium (CM) still demonstrated hyperactivated motility, whereas CM without NaCl or Na+ did not. Both procaine and NH4Cl, another weak base, were shown to trigger a cytoplasmic pH increase (BCECF-acetoxymethyl (AM)), which is primarily induced by a pH rise in acidic cell organelles (Lysosensor green dnd-189), accompanied by hypermotility in stallion sperm. As for procaine, 25 mM NH4Cl also induced oocyte cytokinesis. Interestingly, hyperactivated motility was reliably induced by 2.5-10 mM procaine, whereas a significant cytoplasmic cAMP increase and tail-associated protein tyrosine phosphorylation were only observed at 10 mM. Moreover, 25 mM NH4Cl did not support the latter capacitation characteristics. Additionally, cAMP levels were more than 10× higher in boar than stallion sperm incubated under similar capacitating conditions. Finally, stallion sperm preincubated with 10 mM procaine did not fertilize equine oocytes. In conclusion, 10 mM procaine causes a cytoplasmic and acidic sperm cell organelle pH rise that simultaneously induces hyperactivated motility, increased levels of cAMP and tail-associated protein tyrosine phosphorylation in stallion spermatozoa. However, procaine-induced hypermotility is independent of the cAMP/protein tyrosine phosphorylation pathway.

Analysis of the equine "cumulome" reveals major metabolic aberrations after maturation in vitro

Background

Maturation of oocytes under in vitro conditions (IVM) results in impaired developmental competence compared to oocytes matured in vivo. As oocytes are closely coupled to their cumulus complex, elucidating aberrations in cumulus metabolism in vitro is important to bridge the gap towards more physiological maturation conditions. The aim of this study was to analyze the equine “cumulome” in a novel combination of proteomic (nano-HPLC MS/MS) and metabolomic (UPLC-nanoESI-MS) profiling of single cumulus complexes of metaphase II oocytes matured either in vivo (n = 8) or in vitro (n = 7).

Results

A total of 1811 quantifiable proteins and 906 metabolic compounds were identified. The proteome contained 216 differentially expressed proteins (p ≤ 0.05; FC ≥ 2; 95 decreased and 121 increased in vitro), and the metabolome contained 108 metabolites with significantly different abundance (p ≤ 0.05; FC ≥ 2; 24 decreased and 84 increased in vitro). The in vitro “cumulome” was summarized in the following 10 metabolic groups (containing 78 proteins and 21 metabolites): (1) oxygen supply, (2) glucose metabolism, (3) fatty acid metabolism, (4) oxidative phosphorylation, (5) amino acid metabolism, (6) purine and pyrimidine metabolism, (7) steroid metabolism, (8) extracellular matrix, (9) complement cascade and (10) coagulation cascade. The KEGG pathway “complement and coagulation cascades” (ID4610; n = 21) was significantly overrepresented after in vitro maturation. The findings indicate that the in vitro condition especially affects central metabolism and extracellular matrix composition. Important candidates for the metabolic group oxygen supply were underrepresented after maturation in vitro. Additionally, a shift towards glycolysis was detected in glucose metabolism. Therefore, under in vitro conditions, cumulus cells seem to preferentially consume excess available glucose to meet their energy requirements. Proteins involved in biosynthetic processes for fatty acids, cholesterol, amino acids, and purines exhibited higher abundances after maturation in vitro.

Conclusion

This study revealed the marked impact of maturation conditions on the “cumulome” of individual cumulus oocyte complexes. Under the studied in vitro milieu, cumulus cells seem to compensate for a lack of important substrates by shifting to aerobic glycolysis. These findings will help to adapt culture media towards more physiological conditions for oocyte maturation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5836-5) contains supplementary material, which is available to authorized users.

Vitrifying immature equine oocytes impairs their ability to correctly align the chromosomes on the MII spindle

Vitrified-warmed immature equine oocytes are able to complete the first meiotic division, but their subsequent developmental competence is compromised. Therefore, the present study investigated the effects of vitrifying immature horse oocytes on the chromosome and spindle configuration after IVM. Cumulus-oocytes complexes (COCs) were collected and divided into two groups based on mare age (young ≤14 years; old ≥16 years). COCs were then either directly matured invitro or vitrified and warmed before IVM. Spindle morphology and chromosome alignment within MII stage oocytes were assessed using immunofluorescent staining, confocal microscopy and three-dimensional image analysis. Vitrification reduced the ability of oocytes to reach MII and resulted in ultrastructural changes to the meiotic spindle, including shortening of its long axis, and an increased incidence of chromosomes failing to align properly at the metaphase plate. We hypothesise that aberrant chromosome alignment is an important contributor to the reduced developmental competence of vitrified equine oocytes. Contrary to expectation, oocytes from young mares were more severely affected than oocytes from older mares; we propose that the reduced effect of vitrification on oocytes from older mares is related to pre-existing compromise of spindle assembly checkpoint control mechanisms in these mares.

A retrospective comparison of the efficiency of different assisted reproductive techniques in the horse, emphasizing the impact of maternal age

Advancing maternal age is known to negatively affect fertility in the horse. This age-related decrease in fertility has been linked primarily to reduced oocyte quality rather than to impaired uterine function. In the past decade, the use of ovum pick-up (OPU) and ICSI to produce foals has rapidly gaining popularity amongst sport horse breeders. However, it is not yet known how maternal age influences the efficiency of a commercial OPU-ICSI program and whether the age effect is similar to that observed for other ART in the horse. To answer this question, reproductive records of 289 mares bred by natural mating (NM), 328 mares bred by AI, 205 embryo donor mares (AI-EF-ET), and 473 mares submitted for OPU-ICSI and ET were analyzed retrospectively using a regression model to investigate the effects of maternal age and breeding technique on the likelihood of producing a viable pregnancy. The reproductive efficiency (quantified as the proportion of mares that yielded at least one Day 45 pregnancy) of the different breeding techniques NM, AI, AI-EF-ET and OPU-ICSI-ET was 63.3, 43.9, 45.8 and 37.4%, respectively (P < 0.05). However, the frequent production of multiple embryos per ICSI session (up to 10 embryos in one attempt), makes OPU-ICSI-ET as effective as AI-EF-ET when measured in terms of the mean number of Day 45 pregnant recipients per donor mare. Increasing maternal age was associated with a reduction (P < 0.05) in the reproductive efficiency of all breeding techniques (NM, AI, AI-EF-ET) except OPU-ICSI-ET (P > 0.05). In the OPU-ICSI-ET group, increasing maternal age was associated with a lower number of follicles aspirated and oocytes recovered per mare. Nevertheless, the percentage of blastocysts per injected oocyte, and post-ET likelihoods of pregnancy and pregnancy loss were not influenced by the age of the oocyte donor mare (P > 0.05).

In vitro-produced horse embryos exhibit a very narrow window of acceptable recipient mare uterine synchrony compared with in vivo-derived embryos

In recent years, the number of equine invitro-produced embryos (IVP) has increased markedly; as yet, there are few reports on what constitutes an 'ideal' recipient for an IVP embryo. This study retrospectively investigated the effects of recipient mare oestrous cycle characteristics on the likelihood of pregnancy after transfer of IVP (n=264) and invivo-derived embryos (n=262). IVP embryos tolerated only a narrow window of recipient mare 'synchrony', with transfer on Day 4 after ovulation resulting in a higher likelihood of ongoing pregnancy (69%) than transfer on Days 3, 5 or 6 (53.2%, 41.3% and 23.1% respectively; P=0.02). In contrast, Day 8 invivo-derived embryos tolerated a wide range of uterine (a)synchrony, with no difference in pregnancy or pregnancy loss for recipients that ovulated between Day 4 and Day 9 before transfer. However, transferring invivo-derived embryos to recipients that had a longer oestrus preceding transfer resulted in higher Day 12 and ongoing pregnancy rate (P<0.01). This effect was not significant in IVP embryos. In conclusion, Day 6-8 IVP blastocysts survive best after transfer to Day 4 recipient mares; Day 8 invivo-derived embryos survive equally well in Day 4-9 recipients, but do better in mares that have a long preceding oestrus.

In vitro developmental competence of horse embryos derived from oocytes with a different corona radiata cumulus-oocyte morphology

The increase in demand for in vitro produced horse embryos is fostering the development of commercial laboratories for this purpose. Nevertheless, blastocyst production after intracytoplasmic sperm injection (ICSI) is still not as great as desired in most of these laboratories. In relation to horse oocyte classification, both expanded and compact cumulus-oocyte-complexes (COCs) are used for in vitro embryo production. The aim of this study was to compare in vitro embryo developmental capacity of COCs from horses including those with only the corona radiata, frequently collected after aspiration procedures. Horse oocytes were collected by follicular aspiration of abattoir-derived ovaries. After classification as expanded, compact or corona radiata COCs, these were in vitro matured, fertilized by ICSI and in vitro cultured for 7.5 days. Maturation rate, cleavage rate and morula/blastocyst rates were recorded. No significant differences (P > 0.05) were detected among groups in maturation rate. Cleavage rate was less (P < 0.05) for embryos derived from oocytes with a corona radiata as compared to compact-derived embryos, but embryo development after 7.5 days of culture was similar among groups (P > 0.05). In conclusion, even if embryos derived from oocytes with corona radiata had a lesser cleavage rate after ICSI, the developmental capacity was similar to embryos derived from oocytes with a compact and expanded cumulus morphology, indicating these can be an useful source of embryos in horses.

Advanced mare age impairs the ability of in vitro-matured oocytes to correctly align chromosomes on the metaphase plate

Background

Advanced mare age is associated with declining fertility and an increased risk of early pregnancy loss. Compromised oocyte quality is probably the primary reason for reduced fertility, but the defects predisposing to embryonic death are unknown. In women, advanced age predisposes to chromosome segregation errors during meiosis, which lead to embryonic aneuploidy and a heightened risk of miscarriage.

Objectives

To evaluate the effect of advanced mare age on chromosome alignment and meiotic spindle morphology in in vitro‐matured (IVM) oocytes.

Study design

Morphometric and morphological analysis.

Methods

To investigate differences in spindle organisation and chromosome alignment between young and old mares, oocytes collected from slaughtered mares were divided into two groups depending on mare age (young, ≤14 years and old, ≥16 years), IVM and stained to visualise chromatin and alpha‐tubulin. Spindle morphology, morphometry and chromosome (mis)alignment were evaluated by confocal microscopy and 3D image analysis.

Results

Oocytes from old mares showed a higher incidence of chromosome misalignment (47.4% vs. 4.5%; P<0.001) and a thicker metaphase plate (mean ± s.d.: 5.8 ± 1.0 μm vs. 4.9 ± 0.9 μm; P = 0.04) than oocytes from young mares. Although no differences in spindle morphometry were detected between old and young mares, an increased major spindle axis length was associated with chromosome misalignment (mean ± s.d.: 25.3 ± 6.1 μm vs. 20.8 ± 3.3 μm; P = 0.01) irrespective of age.

Main limitations

The oocytes were IVM and may not exactly reflect chromosome misalignment in vivo.

Conclusions

Advanced mare age predisposes to chromosome misalignment on the metaphase II spindle of IVM oocytes. The compromised ability to correctly align chromosomes presumably predisposes to aneuploidy in resulting embryos and thereby contributes to the age‐related decline in fertility and increased incidence of early pregnancy loss.

The Summary is available in Portuguese – see Supporting Information

Embryos and embryonic stem cells from the white rhinoceros

The northern white rhinoceros (NWR, Ceratotherium simum cottoni) is the most endangered mammal in the world with only two females surviving. Here we adapt existing assisted reproduction techniques (ART) to fertilize Southern White Rhinoceros (SWR) oocytes with NWR spermatozoa. We show that rhinoceros oocytes can be repeatedly recovered from live SWR females by transrectal ovum pick-up, matured, fertilized by intracytoplasmic sperm injection and developed to the blastocyst stage in vitro. Next, we generate hybrid rhinoceros embryos in vitro using gametes of NWR and SWR. We also establish embryonic stem cell lines from the SWR blastocysts. Blastocysts are cryopreserved for later embryo transfer. Our results indicate that ART could be a viable strategy to rescue genes from the iconic, almost extinct, northern white rhinoceros and may also have broader impact if applied with similar success to other endangered large mammalian species.

Lower blastocyst quality after conventional vs. Piezo ICSI in the horse reflects delayed sperm component remodeling and oocyte activation

PURPOSE

The aim of this study was to evaluate the differential effects of conventional and Piezo-driven ICSI on blastocyst development, and on sperm component remodeling and oocyte activation, in an equine model.

METHODS

In vitro-matured equine oocytes underwent conventional (Conv) or Piezo ICSI, the latter utilizing fluorocarbon ballast. Blastocyst development was compared between treatments to validate the model. Then, oocytes were fixed at 0, 6, or 18 h after injection, and stained for the sperm tail, acrosome, oocyte cortical granules, and chromatin. These parameters were compared between injection techniques and between sham-injected and sperm-injected oocytes among time periods.

RESULTS

Blastocyst rates were 39 and 40%. The nucleus number was lower, and the nuclear fragmentation rate was higher, in blastocysts produced by Conv. Cortical granule loss started at 0H after both sperm and sham injection. The acrosome was present at 0H in both ICSI treatments, and persisted to 18H in significantly more Conv than Piezo oocytes (72 vs. 21%). Sperm head area was unchanged at 6H in Conv but significantly increased at this time in Piezo; correspondingly, at 6H significantly more Conv than Piezo oocytes remained at MII (80 vs. 9.5%). Sham injection did not induce significant meiotic resumption.

CONCLUSIONS

These data show that Piezo ICSI is associated with more rapid sperm component remodeling and oocyte meiotic resumption after sperm injection than is conventional ICSI, and with higher embryo quality at the blastocyst stage. This suggests that there is value in exploring the Piezo technique, utilized with a non-toxic fluorocarbon ballast, for use in clinical human ICSI.

Intracytoplasmic sperm injection in domestic and wild mammals

Intracytoplasmic sperm injection (ICSI) has become a useful technique for clinical applications in the horse-breeding industry. However, both ICSI blastocyst and offspring production continues to be limited for most farm and wild species. This article reviews technical differences of ICSI performance among species, possible biological and methodological reasons for the variable efficiency and potential strategies to improve the outcomes. One of the major applications of ICSI in animal production is the reproduction of high-value specimens. Unfortunately, some domestic species like the bovine show low rates of pronuclei formation after sperm injection, which led to the development of various artificial activation protocols and sperm pre-treatments that are discussed in this article. The impact of ICSI technique on equine breeding programs is considered in detail, since in contrast to other species, its use for elite horse reproduction has increased in recent years. ICSI has also been used to produce genetically modified animals; however, despite numerous attempts in several domestic species, only transgenic pigs have been consistently produced. Finally, the ICSI is a promising tool for genetic rescue of endangered and wild species. In conclusion, while ICSI has become a consistent ART for some species, it needs further development for others. The low results obtained for some domestic species, the high training needed and the equipment required have limited this technique to the production of elite specimens or for research purposes.

Use of Confocal Microscopy to Evaluate Equine Zygote Development After Sperm Injection of Oocytes Matured In Vivo or In Vitro

Confocal microscopy was used to image stages of equine zygote development, at timed intervals, after intracytoplasmic sperm injection (ICSI) of oocytes that were matured in vivo or in vitro. After fixation for 4, 6, 8, 12, or 16 h after ICSI, zygotes were incubated with α/β tubulin antibodies and human anticentromere antibody (CREST/ACA), washed, incubated in secondary antibodies, conjugated to either Alexa 488 or Alexa 647, and incubated with 561-Phalloidin and Hoechst 33258. An Olympus IX81 spinning disk confocal microscope was used for imaging. Data were analyzed using χ 2 and Fisher's exact tests. Minor differences in developmental phases were observed for oocytes matured in vivo or in vitro. Oocytes formed pronuclei earlier when matured in vivo (67% at 6 h and 80% at 8 h) than in vitro (13% at 6 and 8 h); 80% of oocytes matured in vitro formed pronuclei by 12 h. More (p=0.04) zygotes had atypical phenotypes, indicative of a failure of normal zygote development, when oocyte maturation occurred in vitro versus in vivo (30 and 11%, respectively). Some potential zygotes from oocytes matured in vivo had normal phenotypes, although development appeared to be delayed or arrested. Confocal microscopy provided a feasible method to assess equine zygote development using limited samples.

Maternal age and in vitro culture affect mitochondrial number and function in equine oocytes and embryos

Advanced maternal age and in vitro embryo production (IVP) predispose to pregnancy loss in horses. We investigated whether mare age and IVP were associated with alterations in mitochondrial (mt) DNA copy number or function that could compromise oocyte and embryo development. Effects of mare age (<12 vs ≥12 years) on mtDNA copy number, ATP content and expression of genes involved in mitochondrial replication (mitochondrial transcription factor (TFAM), mtDNA polymerase γ subunit B (mtPOLB) and mitochondrial single-stranded DNA-binding protein (SSB)), energy production (ATP synthase-coupling factor 6, mitochondrial-like (ATP-synth_F6)) and oxygen free radical scavenging (glutathione peroxidase 3 (GPX3)) were investigated in oocytes before and after in vitro maturation (IVM), and in early embryos. Expression of TFAM, mtPOLB and ATP-synth-F6 declined after IVM (P<0.05). However, maternal age did not affect oocyte ATP content or expression of genes involved in mitochondrial replication or function. Day 7 embryos from mares ≥12 years had fewer mtDNA copies (P=0.01) and lower mtDNA:total DNA ratios (P<0.01) than embryos from younger mares, indicating an effect not simply due to lower cell number. Day 8 IVP embryos had similar mtDNA copy numbers to Day 7 in vivo embryos, but higher mtPOLB (P=0.013) and a tendency to reduced GPX3 expression (P=0.09). The lower mtDNA number in embryos from older mares may compromise development, but could be an effect rather than cause of developmental retardation. The general down-regulation of genes involved in mitochondrial replication and function after IVM may compromise resulting embryos.

Glucocorticoid metabolism in equine follicles and oocytes

The objective of this study was to determine whether (1) systemic and intrafollicular cortisol concentrations in horses are directly related and (2) supraphysiological levels of glucocorticoids affect in vitro maturation (IVM) rates of oocytes. Specifically, we studied the (1) changes in the intrafollicular cortisol and progesterone in context with granulosa cell gene expression during maturation of equine follicles (from 5-9 mm, 10-14 mm, 15-19 mm, 20-24 mm, and ≥25 mm in diameter) and (2) effects of cortisol supplementation on IVM rates and gene expression of equine cumulus-oocyte complexes (COCs). For these purposes, follicular fluid, granulosa cells, and COCs were collected from 12 mares (mean age 8.6 ± 0.5 yr) by transvaginal aspiration. Cortisol and progesterone concentrations in follicular fluid from follicles ≥25 mm were greater (P < 0.05) than in all other follicle classes and were positively correlated (r = 0.8; P < 0.001). Plasma concentrations of cortisol and progesterone did not differ before and after follicle aspiration (P > 0.05). In granulosa cells, gene expression of NR3C1, HSD11B1, HSD11B2, and CYP21A2 did not differ (P > 0.05) among different follicle classes. Maturation rates were similar (P > 0.05) among groups, regardless of the cortisol concentration in the IVM medium. In cumulus cells, messenger RNA expression of genes involved in glucocorticoid mechanism and apoptosis was either increased (NR3C1 and BCL2) or decreased (HSD11B2) by treatment (P < 0.01). In oocytes, gene expression of maturation markers (BMP15 and GDF9) was affected (P < 0.001) by cortisol treatment. This study demonstrates the involvement of glucocorticoids in follicle and oocyte maturation and cortisol modulation by HSD11B2 in equine COCs. Our data provide further information for understanding the normal ovarian endocrine physiology which might in turn also help improve equine assisted reproduction techniques.

Dynamics of 5-methylcytosine and 5-hydroxymethylcytosine during pronuclear development in equine zygotes produced by ICSI

Background

Global epigenetic reprogramming is considered to be essential during embryo development to establish totipotency. In the classic model first described in the mouse, the genome-wide DNA demethylation is asymmetric between the paternal and the maternal genome. The paternal genome undergoes ten-eleven translocation (TET)-mediated active DNA demethylation, which is completed before the end of the first cell cycle. Since TET enzymes oxidize 5-methylcytosine to 5-hydroxymethylcytosine, the latter is postulated to be an intermediate stage toward DNA demethylation. The maternal genome, on the other hand, is protected from active demethylation and undergoes replication-dependent DNA demethylation. However, several species do not show the asymmetric DNA demethylation process described in this classic model, since 5-methylcytosine and 5-hydroxymethylcytosine are present during the first cell cycle in both parental genomes. In this study, global changes in the levels of 5-methylcytosine and 5-hydroxymethylcytosine throughout pronuclear development in equine zygotes produced in vitro were assessed using immunofluorescent staining.

Results

We were able to show that 5-methylcytosine and 5-hydroxymethylcytosine both were explicitly present throughout pronuclear development, with similar intensity levels in both parental genomes, in equine zygotes produced by ICSI. The localization patterns of 5-methylcytosine and 5-hydroxymethylcytosine, however, were different, with 5-hydroxymethylcytosine homogeneously distributed in the DNA, while 5-methylcytosine tended to be clustered in certain regions. Fluorescence quantification showed increased 5-methylcytosine levels in the maternal genome from PN1 to PN2, while no differences were found in PN3 and PN4. No differences were observed in the paternal genome. Normalized levels of 5-hydroxymethylcytosine were preserved throughout all pronuclear stages in both parental genomes.

Conclusions

In conclusion, the horse does not seem to follow the classic model of asymmetric demethylation as no evidence of global DNA demethylation of the paternal pronucleus during the first cell cycle was demonstrated. Instead, both parental genomes displayed sustained and similar levels of methylation and hydroxymethylation throughout pronuclear development.

Evaluation of equine oocyte developmental competence using polarized light microscopy

The purpose of this study was to observe in vitro-matured equine oocytes with an objective computerized technique that involves the use of a polarized light microscope (PLM) in addition to the subjective morphological evaluation obtained using a classic light microscope (LM). Equine cumulus-oocyte complexes (COCs, n = 922) were subjected to different in vitro maturation times (24, 36 or 45 h), however, only 36-h matured oocytes were analyzed using CLM. The 36-h matured oocytes that reached maturity were parthenogenetically activated to evaluate the quality and meiotic competence. Average maturation percentages per session in groups 1, 2 and 3 (24-, 36- and 45-h matured oocytes respectively) were 29.31 ± 13.85, 47.01 ± 9.90 and 36.62 ± 5.28%, whereas the average percentages of immature oocytes per session were 28.78 ± 20.17, 7.83 ± 5.51 and 22.36 ± 8.39% respectively. The zona pellucida (ZP) birefringent properties were estimated and correlated with activation outcome. ZP thickness and retardance of the inner layer of the zona pellucida (IL-ZP) were significantly increased in immature oocytes compared with mature oocytes (P < 0.001 and P < 0.01 respectively). The comparison between parthenogenetically activated and non-activated oocytes showed a significant increase in the area and thickness of the IL-ZP in parthenogenetically activated oocytes (P < 0.01). These results show that the 36-h in vitro maturation (IVM) protocol allowed equine oocytes to reach maturity, and PLM observation of ZP can be used to distinguish mature and immature oocytes as well as activated and non-activated oocytes.

In Vitro and In Vivo Development of Horse Cloned Embryos Generated with iPSCs, Mesenchymal Stromal Cells and Fetal or Adult Fibroblasts as Nuclear Donors

The demand for equine cloning as a tool to preserve high genetic value is growing worldwide; however, nuclear transfer efficiency is still very low. To address this issue, we first evaluated the effects of time from cell fusion to activation (<1h, n = 1261; 1-2h, n = 1773; 2-3h, n = 1647) on in vitro and in vivo development of equine embryos generated by cloning. Then, we evaluated the effects of using different nuclear donor cell types in two successive experiments: I) induced pluripotent stem cells (iPSCs) vs. adult fibroblasts (AF) fused to ooplasts injected with the pluripotency-inducing genes OCT4, SOX2, MYC and KLF4, vs. AF alone as controls; II) umbilical cord-derived mesenchymal stromal cells (UC-MSCs) vs. fetal fibroblasts derived from an unborn cloned foetus (FF) vs. AF from the original individual. In the first experiment, both blastocyst production and pregnancy rates were higher in the 2-3h group (11.5% and 9.5%, respectively), respect to <1h (5.2% and 2%, respectively) and 1-2h (5.6% and 4.7%, respectively) groups (P<0.05). However, percentages of born foals/pregnancies were similar when intervals of 2-3h (35.2%) or 1-2h (35.7%) were used. In contrast to AF, the iPSCs did not generate any blastocyst-stage embryos. Moreover, injection of oocytes with the pluripotency-inducing genes did not improve blastocyst production nor pregnancy rates respect to AF controls. Finally, higher blastocyst production was obtained using UC-MSC (15.6%) than using FF (8.9%) or AF (9.3%), (P<0.05). Despite pregnancy rates were similar for these 3 groups (17.6%, 18.2% and 22%, respectively), viable foals (two) were obtained only by using FF. In summary, optimum blastocyst production rates can be obtained using a 2-3h interval between cell fusion and activation as well as using UC-MSCs as nuclear donors. Moreover, FF line can improve the efficiency of an inefficient AF line. Overall, 24 healthy foals were obtained from a total of 29 born foals.

Advances in Collection, Transport and Maturation of Equine Oocytes for Assisted Reproductive Techniques

Assisted reproductive techniques that are based on oocyte manipulations have gained acceptance in the equine industry. Methods to collect and handle immature or maturing oocytes have been developed, and systems to ship oocytes now allow for collection in one location and intracytoplasmic sperm injection (ICSI) in another. Subsequently, ICSI-produced embryos can be transferred onsite, shipped to another location, or cryopreserved. Methods for the collection, identification, culture, maturation, and shipment of equine oocytes are reviewed, with an emphasis on procedures from laboratories providing clinical services with documented success.

Beta-mercaptoethanol supplementation of in vitro maturation medium does not influence nuclear and cytoplasmic maturation of equine oocytes

In vitro embryo production in the horse is still not as efficient as in other species. Oxidative stress negatively affects oocyte and embryo culture. To attenuate/minimize the oxidative stress, antioxidants such as low-molecular thiol compounds can be added to culture media. Beta-mercaptoethanol (BME) has been shown to improve maturation and embryo development in different species. The aim of this study was to investigate whether the addition to maturation medium of BME at common (0.1 mM) and high (0.7 mM) concentration could improve oocyte maturation also in the horse. Equine oocytes recovered from slaughterhouse ovaries were used. Meiotic configuration after in vitro maturation (IVM) and early embryo production after intracytoplasmic sperm injection (ICSI) were considered as criteria for assessing nuclear and cytoplasmic maturation, respectively. A total of 1,076 oocytes were analysed over two experiments: 848 (control n = 293, BME 0.1 n = 270, BME 0.7 n = 285) were stained with Hoechst 33342 and examined for nuclear stage after 26 hr of IVM, and 228 MII oocytes were fertilized by ICSI (control n = 83, BME 0.1 n = 65, BME 0.7 n = 80). Cleavage rates were determined after 60 hr of culture. Unlike results obtained in other species, the addition of BME did not influence maturation rates (51.9% control vs 55.6% BME 0.1 mM and 55.1% BME 0.7 mM), nor cleavage rates after ICSI (38.6% vs 38.5% and 41.3%, respectively). In conclusion, the addition of BME at 0.1 and 0.7 mM to the maturation medium, in our culture conditions, has no effect on nuclear and cytoplasmic maturation of equine oocytes.