Equine blastocyst development after intracytoplasmic injection of sperm subjected to two freeze-thaw cycles

Cryopreservation of equine spermatozoa reduces plasma membrane integrity and phospholipase C zeta 1 content as associated with oocyte activation

BACKGROUND

Phospholipase C zeta (PLCZ1) is considered the major sperm-borne oocyte activation factor. Cryopreserved stallion spermatozoa are commonly used for intracytoplasmic sperm injection (ICSI). However, plasma membrane damage and protein modifications caused by cryopreservation could impair sperm structure and function, leading to a reduction of PLCZ1 and oocyte activation after ICSI.

OBJECTIVES

We compared membrane integrity and PLCZ1 abundance in populations for fresh, frozen, and refrozen stallion spermatozoa, either thawed and refrozen at room or low temperature; and examined the effect of relative PLCZ1 content on cleavage after ICSI.

MATERIALS AND METHODS

Western blotting, ELISA, and immunofluorescence were conducted in stallion spermatozoa, freezing extenders, and detergent-extracted sperm fractions to detect and quantify PLCZ1. Retrospectively, PLCZ1 content and cleavage rate were analyzed. Fresh, frozen, and refrozen at room and low temperatures spermatozoa were evaluated for acrosomal and plasma membrane integrity and PLCZ1 content using flow cytometry.

RESULTS

Western blotting, ELISA, and immunofluorescence revealed significant reduction of PLCZ1 in spermatozoa after cryopreservation and confirmed PLCZ1 detection in extenders. After detergent extraction, a PLCZ1-nonextractable fraction remained in the postacrosomal region of spermatozoa. Plasma membrane integrity was significantly reduced after freezing. Acrosomal and plasma membrane integrity were similar between frozen and refrozen samples at low temperature, but both were significantly higher than samples refrozen at room temperature. Acrosomal and plasma membrane integrity significantly correlated to PLCZ1 content. Percentages of PLCZ1-labeled spermatozoa and PLCZ1 content were reduced after freezing but not after refreezing. Relative content and localization of PLCZ1 were associated with cleavage rates after ICSI.

DISCUSSION AND CONCLUSION

Sperm PLCZ1 content associates with cleavage rates after ICSI. Cryopreservation is detrimental to sperm plasma membrane integrity and PLCZ1 retention. However, refreezing did not result in additional PLCZ1 loss. Refreezing stallion spermatozoa at a low temperature resulted in better survival but did not improve PLCZ1 retention.

Effect of Melatonin and Caffeine Supplementation to Freezing Medium on Cryosurvival of Peruvian Paso Horse Sperm Using a Two-Step Accelerating Cooling Rate

This research examined the antioxidant and cryoprotective effects of melatonin (ME) and caffeine (CAF) supplementation in freezing medium on the cryosurvival of Peruvian Paso horse sperm using a two-step accelerating cooling rate. Twenty ejaculates from four adult and fertile stallions were recovered, initially diluted with INRA-96®, and finally frozen with INRA-Freeze® with either no supplementation (as control), 1 μM ME, or 2 mM CAF using a two-ramp freezing system content inside a cryogenic-box and liquid nitrogen vapors. The sperm kinematic parameters and integrity of the plasma and acrosomal membranes of fresh semen and cryopreserved samples were evaluated using the CASA system (SCA-Evolution® 2018) and PI/fluorescein isothiocyanate-conjugated peanut (Arachis hypogaea) agglutinin double fluorescent test, respectively. The oxidative stress of post-thaw sperm samples was also assessed using the CellRox Deep Red fluorescence test. The results showed that curvilinear velocity and average-path velocity were greater (p < 0.05) after freezing with CAF than the control group. In addition, there were significance differences (p < 0.01) between stallions (1-4) in post-thaw kinematic parameters regardless of ME or CAF addition. Both ME and CAF improved (p < 0.05) the proportion of sperm with intact plasma membranes and intact acrosomes. Nevertheless, neither CAF nor ME improved the oxidative stress after the cryopreservation process.

An Investigation of Equine Sperm Quality Following Cryopreservation at Low Sperm Concentration and Repeated Freeze-Thawing

Stallion spermatozoa are typically cryopreserved at 200 to 300 million sperm/ml; however recent advances such as intracytoplasmic sperm injection (ICSI) requires only one spermatozoon, wasting many, after thawing a whole straw. Cryopreserving at concentrations less than the current standard or refreezing thawed spermatozoa could maximize the use of genetically valuable animals and reduce waste. This investigation aimed to identify if lowering the sperm concentration for cryopreservation affected post-thaw quality after one and two freeze-thaw cycles. Nine ejaculates were collected from three fertile, "good freezer" stallions (post-thaw motility ≥35%) for experiment 1. Each ejaculate was split into eight treatments: five, 10, 20, 50, 100, 200, 300, 400 million sperm/ml and cryopreserved. Post-thaw: motility, viability, acrosome integrity and oxidative stress were assessed. Experiment 2, straws from experiment 1 (300 million sperm/ml) were thawed, diluted to 20 million sperm/ml or left undiluted (control) and refrozen. Post-thaw motility and viability were assessed. In experiment 1 sperm concentration did not affect post-thaw total motility (TM), progressive motility (PM) or viability at 50 to 400 million sperm/ml (P > .05). Whilst sperm concentrations of five to 20 million/ml did differ (post-thaw TM and PM). Both refreezing and reducing spermatozoa concentration, decreased TM, PM and viability (P < .05) after two freeze-thaw cycles. These results suggest cryopreserving at sperm concentrations as low as 50 million/ml maintains spermatozoa quality in good freezer stallions. Spermatozoa maintained some motility and viability when initially cryopreserved at 20 million sperm/ml and after two freeze-thaw cycles but research should investigate more optimal conditions.

Dimethyl sulfoxide and glycerol as cryoprotectant agents of stallion semen: effects on blastocyst rates following intracytoplasmic sperm injection of IVM equine oocytes

Numerous variables affect invitro blastocyst development following intracytoplasmic sperm injection (ICSI). The paternal factor is affected by initial semen quality, processing techniques and final selection of individual spermatozoon for injection. This study investigated whether there was an effect of sperm cryoprotectant agent (CPA) on equine invitro blastocyst production, and reviews recent developments examining how processing equine semen affects ICSI outcomes. Single ejaculates from five stallions were collected and processed in a freezing extender containing either 1M dimethyl sulfoxide (DMSO) or 3.5% glycerol. Immature equine oocytes were obtained from ovarian follicles of mares during diestrus by transvaginal aspiration (n=128). After invitro maturation, MII oocytes (n=90) were fertilised by ICSI with thawed stallion spermatozoa (n=45 in both the DMSO and glycerol groups). The embryo cleavage rate was greater in the DMSO than glycerol group (73.3% vs 46.7% respectively; P=0.0098), but the blastocyst development rate per fertilised oocyte was similar between the two groups (28.9% vs 15.6% respectively; P=0.128), as was the blastocyst production rate per cleaved embryo (39.4% vs 33.3% respectively; P=0.653). In this study, cryopreservation of equine spermatozoa in 1M DMSO was correlated with significantly higher cleavage rates in IVM oocytes fertilised by ICSI compared with spermatozoa cryopreserved using 3.5% glycerol. Although not statistically significant in this small number of stallions, increased blastocyst production and individual stallion variability was observed among CPA treatments. This warrants further critical examination of cryoprotectants used in equine sperm subpopulations used for ICSI in a larger number of stallions.

Morphokinetics of early equine embryo development in vitro using time-lapse imaging, and use in selecting blastocysts for transfer

The use of time-lapse imaging (TLI) in the evaluation of morphokinetics associated with invitro developmental competence is well described for human, cattle and pig embryos. It is generally accepted that embryos that complete early cleavage sooner are more likely to form blastocysts and that timing of later events, such as blastocyst formation and expansion, are predictive of implantation potential and euploid status. In the horse, morphokinetics as a predictor of developmental competence has received little attention. In this study we evaluated the morphokinetics of early equine embryo development invitro for 144 oocytes after intracytoplasmic sperm injection and report the timings of blastocyst development associated with ongoing pregnancy for the first time. There was a tendency for time of cytoplasmic extrusion and first cleavage to occur earlier in the embryos that went on to form blastocysts (n=19) compared with those that arrested, and for first cleavage to occur earlier in blastocysts that established pregnancies that were ongoing (n=4) compared with pregnancies that were lost (n=2). TLI was clinically useful in identifying blastocysts when evaluation of morphology on static imaging was equivocal.

Update on advanced semen-processing technologies and their application for in vitro embryo production in horses

The increased commercialisation of intracytoplasmic sperm injection (ICSI) in horses creates more opportunities to incorporate advanced reproductive technologies, such as sex-sorted, refrozen and lyophilised spermatozoa, into a breeding program. This paper reviews the status of these semen-handling technologies in light of their use in equine ICSI programs. Pregnancies have been achieved from each of these advanced technologies when combined with ICSI in horses, but refinements in the semen-handling processes underpinning these technologies are currently being explored to produce more reliable and practical improvements in the results from equine ICSI.

Use of time-lapse imaging to evaluate morphokinetics of in vitro equine blastocyst development after oocyte holding for two days at 15°C versus room temperature before intracytoplasmic sperm injection

Time-lapse imaging was used to establish the morphokinetics of equine embryo development to the blastocyst stage after invitro oocyte maturation (IVM), intracytoplasmic sperm injection (ICSI) and embryo culture, in oocytes held overnight at room temperature (22-27°C; standard conditions) before IVM. Embryos that developed to the blastocyst stage underwent precleavage cytoplasmic extrusion and cleavage to the 2-, 3- and 4-cell stages significantly earlier than did embryos that arrested in development. We then determined the rate of blastocyst formation after ICSI in oocytes held for 2 days at either 15°C or room temperature before IVM (15-2d and RT-2d treatment groups respectively). The blastocyst development rate was significantly higher in the 15-2d than in the RT-2d group (13% vs 0% respectively). The failure of blastocyst development in the RT-2d group precluded comparison of morphokinetics of blastocyst development between treatments. In any condition examined, development to the blastocyst stage was characterised by earlier cytoplasmic extrusion before cleavage, earlier cleavage to 2- and 4-cell stages and reduced duration at the 2-cell stage compared with non-competent embryos. In conclusion, this study presents morphokinetic parameters predictive of embryo development invitro to the blastocyst stage after ICSI in the horse. We conclude that time-lapse imaging allows increased precision for evaluating effects of different treatments on equine embryo development.

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.

Effects of extender, cryoprotectants and thawing protocol on motility of frozen-thawed stallion sperm that were refrozen for intracytoplasmic sperm injection doses

We examined the effects of different freezing extenders, cryoprotectant agents (CPA) and initial thawing temperatures for preparing doses of refrozen stallion sperm for intracytoplasmic sperm injection (ICSI). Single ejaculates, from twelve stallions, were frozen in lactose-EDTA-egg yolk extender (LE) with 5% glycerol. In experiment 1, sperm were initially thawed to 5 °C or 37 °C, before being diluted in LE or skim milk-egg yolk extender (SMEY) containing either 5% glycerol (GLY), 5% methylformamide (MF) or 5% of a combination of both (GMF). In experiment 2, frozen sperm were initially thawed to 5 °C, diluted and refrozen in SMEY containing 2, 4, 6 or 8% GLY or GMF. In Experiment 1, sperm motility was reduced after each cryopreservation cycle (P < 0.05). Extender type did not affect motility after refreezing (P > 0.05), but sperm initially thawed to 5 °C exhibited higher motility than sperm thawed to 37 °C (P < 0.05). In addition, sperm refrozen in SMEY containing MF or GMF exhibited higher motility than sperm refrozen in GLY alone (P < 0.05). In experiment 2, there was an interaction between CPA and CPA concentration (P < 0.05). Sperm refrozen with GMF had higher motility than refrozen sperm with GLY (P < 0.05), and while GLY concentration did not affect post-thaw motility (P > 0.05). Sperm refrozen with 6 or 8% GMF exhibited the highest motility (P < 0.05). In conclusion, sperm motility is best maintained when thawing and refreezing stallion sperm in low sperm concentration ICSI doses by initially thawing the sperm to 5 °C and diluting the sperm in a freezing extender with 8% GMF.

A way for in vitro/ex vivo egg production in mammals

Eggs are female germ cells that are required for producing offspring through sexual reproduction. In mammals, eggs are produced in the ovary and ovulated into the oviduct. It is well known that over 99% of eggs are degenerated without ovulation, so that many studies have attempted in vitro folliculogenesis to produce many eggs in different species for a few decades. Although many methods have been developed, a success of in vitro egg production with the resultant live birth of offspring has been limited, especially in livestock animals. More recently, we have succeeded in producing live pups derived from in vitro/ex vivo egg production in mice. This review aims to introduce our recent findings with a brief history of in vitro/ex vivo culture systems for follicles and ovaries.

Exposure to follicular fluid during oocyte maturation and oviductal fluid during post-maturation does not improve in vitro embryo production in the horse

Most wild equids and many domestic horse breeds are at risk of extinction, so there is an urgent need for genome resource banking. Embryos cryopreservation allows the preservation of genetics from male and female and is the fastest method to restore a breed. In the equine, embryo production in vitro would allow the production of several embryos per cycle. Intracytoplasmic sperm injection (ICSI) is used to generate horse embryos, but it requires expensive equipment and expertise in micromanipulation, and blastocyst development rates remain low. No conventional in vitro fertilization (IVF) technique for equine embryo production is available. The development of culture conditions able to mimic the maturation of the oocyte in preovulatory follicular fluid (pFF) and the post-maturation in oviductal fluid (OF) may improve embryo production in vitro. Our aim was to analyse the effect of in vitro maturation in pFF and incubation in OF on in vitro maturation of equine oocytes, fertilization using conventional IVF or ICSI, and embryo development after culture in synthetic oviductal fluid (SOF) or DMEM-F12. Oocytes collected from slaughtered mares or by ovum pick up were matured in vitro in pFF or semi-synthetic maturation medium (MM). The in vitro maturation, fertilization and development rates were not statistically different between pFF and MM. After in vitro maturation, oocytes were incubated with or without OF. Post-maturation in OF did not significantly improve the fertilization and development rates. Thus, in our study, exposure to physiological fluids for oocyte maturation and post-maturation does not improve in vitro embryo production in the horse.

Alternative procedures for the cryopreservation of brown bear ejaculates depending on the flexibility of the "in cooling" period (5°C)

The adaptability of cryopreservation protocols for brown bear spermatozoa collected under field conditions and frozen in a nearby laboratory (transported for a few hours) or shipped to a reference laboratory for sex sorting (transported for a few days) was evaluated. Forty-nine electroejaculates from 15 mature brown bears were extended to 100×10(6) sperm/mL in a TES-Tris-Fructose based extender and cryopreserved (-20°C/min to -100°C and stored at -196°C). After thawing, the quality of the seminal samples was assessed for total (TM), progressive (PM) motility and kinetic parameters - by CASA -, and viability (VIAB), viable and non-apoptotic status (YOPRO-), high membrane mitochondrial potential (MIT) and intact acrosomes (iACR) - by flow cytometry -. In Experiment 1, we assessed different storage times (0, 0.5, 1 - control -, 4-5, 7-8 and 11-12 h) at 5°C from final dilution to freezing. After thawing, non-equilibrated samples (0 h) showed lower values of iACR, TM and PM. No significant differences were found for the different periods of equilibration tested. In Experiment 2, we evaluated three long-term storage times (24, 48 and 72 h) at 5°C before freezing using storage for 1h as control. The post-thawing quality of brown bear spermatozoa declined markedly after 48-72 h of pre-freezing. In conclusion, our findings suggest the possibility of extending the pre-freezing cooling period up to 24h post-collection without freezing. This knowledge should enable the adaptation of the freezing protocols for when a special handling conditions are required such as the shipment of seminal samples to technological centers for the pre-freezing application of enhancer spermatic biotechnologies.

Effect of holding equine oocytes in meiosis inhibitor-free medium before in vitro maturation and of holding temperature on meiotic suppression and mitochondrial energy/redox potential

BACKGROUND

Evaluation of mitochondrial function offers an alternative to evaluate embryo development for assessment of oocyte viability, but little information is available on the relationship between mitochondrial and chromatin status in equine oocytes. We evaluated these parameters in immature equine oocytes either fixed immediately (IMM) or held overnight in an Earle's/Hank's' M199-based medium in the absence of meiotic inhibitors (EH treatment), and in mature oocytes. We hypothesized that EH holding may affect mitochondrial function and that holding temperature may affect the efficiency of meiotic suppression.

METHODS

Experiment 1 - Equine oocytes processed immediately or held in EH at uncontrolled temperature (22 to 27°C) were evaluated for initial chromatin configuration, in vitro maturation (IVM) rates and mitochondrial energy/redox potential. Experiment 2 - We then investigated the effect of holding temperature (25°C, 30°C, 38°C) on initial chromatin status of held oocytes, and subsequently repeated mitochondrial energy/redox assessment of oocytes held at 25°C vs. immediately-evaluated controls.

RESULTS

EH holding at uncontrolled temperature was associated with advancement of germinal vesicle (GV) chromatin condensation and with meiotic resumption, as well as a lower maturation rate after IVM. Holding did not have a significant effect on mitochondrial distribution within chromatin configurations. Independent of treatment, oocytes having condensed chromatin had a significantly higher proportion of perinuclear/pericortical mitochondrial distribution than did other GV configurations. Holding did not detrimentally affect oocyte energy/redox parameters in viable GV-stage oocytes. There were no significant differences in chromatin configuration between oocytes held at 25°C and controls, whereas holding at higher temperature was associated with meiosis resumption and loss of oocytes having the condensed chromatin GV configuration. Holding at 25°C was not associated with progression of mitochondrial distribution pattern and there were no significant differences in oocyte energy/redox parameters between these oocytes and controls.

CONCLUSIONS

Mitochondrial distribution in equine GV-stage oocytes is correlated with chromatin configuration within the GV. Progression of chromatin configuration and mitochondrial status during holding are dependent on temperature. EH holding at 25°C maintains meiotic arrest, viability and mitochondrial potential of equine oocytes. This is the first report on the effects of EH treatment on oocyte mitochondrial energy/redox potential.

Ovum pick up, intracytoplasmic sperm injection and somatic cell nuclear transfer in cattle, buffalo and horses: from the research laboratory to clinical practice

Assisted reproductive techniques developed for cattle in the last 25 years, like ovum pick up (OPU), intracytoplasmic sperm injection (ICSI), and somatic cell nuclear transfer, have been transferred and adapted to buffalo and horses. The successful clinical applications of these techniques require both the clinical skills specific to each animal species and an experienced laboratory team to support the in vitro phase of the work. In cattle, OPU can be considered a consolidated technology that is rapidly outpacing conventional superovulation for embryo transfer. In buffalo, OPU represents the only possibility for embryo production to advance the implementation of embryo-based biotechnologies in that industry, although it is still mainly in the developmental phase. In the horse, OPU is now an established procedure for breeding from infertile and sporting mares throughout the year. It requires ICSI that in the horse, contrary to what happens in cattle and buffalo, is very efficient and the only option because conventional IVF does not work. Somatic cell nuclear transfer is destined to fill a very small niche for generating animals of extremely high commercial value. The efficiency is low, but because normal animals can be generated it is likely that advancing our knowledge in that field might improve the technology and reduce its cost.

Equine oviduct explant culture: a basic model to decipher embryo–maternal communication

Equine embryos remain for 6 days in the oviduct and thus there is a need for an in vitro model to study embryo–oviductal interactions in the horse, since this subtle way of communication is very difficult to analyse in vivo. Until now, no equine oviduct explant culture model has been characterised both morphologically and functionally. Therefore, we established a culture system for equine oviduct explants that maintained epithelial morphology during 6 days of culture, as revealed by light microscopy and transmission electron microscopy. We demonstrated the presence of highly differentiated, tall columnar, pseudostratified epithelium with basal nuclei, numerous nucleoli, secretory granules and apical cilia, which is very similar to the in vivo situation. Both epithelium and stromal cells originating from the lamina propria are represented in the explants. Moreover, at least 98% of the cells remained membrane intact and fewer than 2% of the cells were apoptotic after 6 days of culture. Although dark-cell degeneration, which is a hypoxia-related type of cell death, was observed in the centre of the explants, quantitative real-time PCR failed to detect upregulation of the hypoxia-related marker genes HIF1A, VEGFA, uPA, GLUT1 and PAI1. Since the explants remained morphologically and functionally intact and since the system is easy to set up, it appears to be an excellent tool for proteome, transcriptome and miRNome analysis in order to unravel embryo–maternal interactions in the horse.

Equine bone marrow mesenchymal or amniotic epithelial stem cells as feeder in a model for the in vitro culture of bovine embryos

Various studies have shown that the in vitro culture environment is one of the key determinants of the blastocyst output. In the present study we investigated the effects of co-culturing bovine embryos with equine bone marrow mesenchymal stem cells (BM-MSCs) or equine amniotic epithelial stem cells (AE-SCs) on in vitro blastocysts development. BM specimens were obtained aseptically from sternal aspirates of horses under local anaesthesia and the isolated cells were resuspended in Dulbecco Modified Earle's Medium supplemented with 10 ng/ml of basic fibroblast growth factor (bFGF). Amniotic membranes were obtained from fresh placentas and, to release the AE cells, amniotic fragments were incubated with 0.05% trypsin for 45 min. Separated AE cells were plated in standard culture medium containing 10 ng/ml epidermal growth factor (EGF). Seven hundred and five cumulus–oocyte complexes were used and, after IVM and IVF, cumulus-free presumptive zygotes were randomly transferred into one of three co-culture systems in which they were cultured up to day 7: (1) co-culture with cumulus cells (control); (2) co-culture with BM-MSCs; and (3) co-culture with AE-SCs. Statistical analyses were performed by ANOVA. Blastocyst developmental rates were significantly different (p < 0.001) between control, AE-SCs and BM-MSCs (respectively 35.45, 41.84 and 30.09%). In conclusion, the AE-SC monolayer create a more suitable microenvironment necessary for inducing local cell activation and proliferation of the growing embryos in comparison with BM-MSCs and cumulus cells. It can be suggested that these cells secrete biologically active substances, including signalling molecules and growth factors of epithelial nature, different to those of the BM cells of mesenchymal origin.

Efficiency of embryonic development after intrafollicular and intraoviductal transfer of in vitro and in vivo matured horse oocytes

In vivo techniques, such as intraoviductal oocyte transfer (OT) and intrafollicular oocyte transfer (IFOT), can be considered as alternatives to bypass the lack of efficient superovulation treatments and the inadequacy of conventional in vitro fertilization techniques in the horse. We compared embryo production after transfer of in vivo recovered oocytes (1) into a recipient's oviduct or (2) into her preovulatory follicle either immediately after ovum pick-up or (3) after in vitro maturation (IVM). Recipients were inseminated with fresh semen of a stallion with a known normal fertility. Ten days after surgery, rates of embryos collected in excess to the number of ovulations were calculated and compared for each group. Embryo collection rates were 32.5% (13 of 40), 5.5% (3 of 55), and 12.8% (6 of 47) for OT, post-IVM IFOT, and immediate IFOT, respectively. Oocyte transfer significantly yielded more embryos than did immediate IFOT and post-IVM IFOT. We also showed that in vitro matured oocytes could successfully be used for IFOT. Our results also suggest that improvement of the IFOT technique could turn it into an inexpensive and easy-to-perform procedure that could be an answer to the inefficiency of superovulation treatments in the mare.

Influence of cysteamine on in vitro maturation, in vitro and in vivo fertilization of equine oocytes

Contents The effect of cysteamine on in vitro nuclear and cytoplasmic maturation of equine oocytes collected by transvaginal ultrasound guided follicular aspiration was assessed. Oocytes were matured in vitro with (cysteamine group) or without (control group) cysteamine. The nuclear stage after DNA Hoechst staining, penetration rates after two different in vitro fertilization (IVF) techniques (IVF media with ionophore and Hepes buffer with heparin) and the embryo yield following oocyte intra-oviductal transfer were used as a criterion for assessing nuclear and cytoplasmic maturation, respectively. Contrary to the data described in other domestic species, there was no effect of cysteamine on in vitro nuclear maturation, IVF or in vivo embryonic development under our conditions. Ovum pick up yields (52%) and maturation rates (control group: 47% and cysteamine group: 55%) were similar to those previously reported. From 57 oocytes transferred to the oviduct in each group, the number of embryos collected was 10 (17%) in the control group and five in the cysteamine group (9%). Those two percentages were not statistically different (p > 0.05). No effect of IVF technique was seen on the success rate (6%) in each group.

Intracytoplasmic sperm injection in livestock species: an update

Intracytoplasmic sperm injection (ICSI) is a powerful technique in the field of assisted reproduction (ART) and provides exciting opportunities for studying the basic mechanisms of fertilization and early embryo development. Nevertheless, its application in agriculture and conservation biology has been greatly hampered by the low success rate reported for this method in respect of economically important species. Specifically, the rates of blastocyst formation and live newborn are greatly reduced when zygotes are generated by ICSI. Except for humans, ICSI remains a low efficiency technology in comparison with alternatives such as in vitro fertilization (IVF) and its application is less widespread. In this paper, we discuss the present status, applications and factors affecting ICSI in pigs and other species.

Microinjection of mouse phospholipase Cζ complementary RNA into mare oocytes induces long-lasting intracellular calcium oscillations and embryonic development

Methods presently used to activate mare oocytes for assisted reproduction technologies provide low rates of advanced embryonic development. Because phospholipase Cζ (PLCζ) is the postulated sperm-borne factor responsible for oocyte activation at fertilisation, the aim of the present study was to investigate the pattern of [Ca2+]i oscillations and developmental rates achieved by microinjection of three concentrations of mouse PLCζ complementary (c) RNA (1, 0.5 or 0.25 μg μL–1) into mare oocytes. The frequency of [Ca2+]i oscillations was no different (P > 0.05) after injection of 1, 0.5 or 0.25 μg μL–1 PLCζ cRNA (41.1 ± 5.3, 47 ± 4.0 and 55.4 ± 9.0, respectively). However, [Ca2+]i oscillations persisted longest (P < 0.05) for oocytes injected with 0.5 μg μL–1 PLCζ cRNA (570.7 ± 64.2 min). There was no significant difference in cleavage rates after injection of the three concentrations of PLCζ (P > 0.05; range 97–100%), but the proportion of oocytes reaching advanced stages of embryonic development (>64 nuclei) was significantly lower for oocytes injected with 0.25 μg μL–1 PLCζ cRNA (3%) than for those injected with 1 μg μL–1 PLCζ cRNA (15%). Based on these results, microinjection of PLCζ may prove an effective and consistent method for the parthenogenetic activation of mare oocytes for nuclear transfer and provides a physiologically relevant tool with which to study fertilisation-dependent [Ca2+]i signalling in this species.

In vitro development of equine oocytes from preserved ovaries after intracytoplasmic sperm injection

In this study, we evaluated the meiotic competence of equine oocytes from ovaries preserved for one day. We also investigated fertilization, cleavage rate, developmental competence and freezability of equine embryos after intracytoplasmic sperm injection (ICSI). After collection from ovaries, the oocytes were classified into two groups comprised of those having compact cumulus layers (Cp) or those having expanded cumulus layers (Ex). Oocytes with a first polar body were subjected to fertilization by ICSI using frozen-thawed stallion spermatozoa and were then cultured in CR1aa medium. The rates of metaphase II-stage oocytes, normal fertilization and cleavage were not significantly different between the two oocyte categories (38.5, 70.0 and 48.7% for CP and 43.5, 60.0 and 58.8% for Ex, respectively). However, the blastocyst development rate of Ex was significantly (P<0.05) higher than that of Cp (25.5 vs. 7.7%). Three Cp-derived and 12 Ex-derived early blastocysts were cryopreserved using the slow cooling protocol, and all of them developed to hatching blastocysts after thawing. These results suggest that equine oocytes fertilized by ICSI can develop to the preimplantation stage in culture conditions similar to those used in the bovine. Furthermore, the Ex oocytes had higher developmental competence than the Cp oocytes, and the in vitro-produced blastocysts had high viability after freezing and thawing.

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

Development of assisted reproductive technologies in horses has been relatively slow compared to other domestic species, namely ruminants and pigs. The scarce availability of abattoir ovaries and the lack of interest from horse breeders and breed associations have been the main reasons for this delay. Progressively though, the technology of oocyte maturation in vitro has been established followed by the application of ICSI to achieve fertilization in vitro. Embryo culture was initially performed in vivo, in the mare oviduct or in the surrogate sheep oviduct, to achieve the highest embryo development, in the range of 18-36% of the fertilised oocytes. Subsequently, the parallel improvement of in vitro oocyte maturation conditions and embryo culture media has permitted high rates of embryo development from in vitro matured and in vitro cultured ICSI embryos, ranging from 5 to 10% in the early studies to up to 38% in the latest ones. From 2003, with the birth of the first cloned equids, the technology of somatic cell nuclear transfer has also become established due to improvement of the basic steps of embryo production in vitro, including cryopreservation. Pregnancy and foaling rates are still estimated based on a small number of in vitro produced equine embryos transferred to recipients. The largest set of data on non-surgical embryo transfer of in vitro produced embryos, from ICSI of both abattoir and in vitro-matured Ovum Pick Up (OPU) oocytes, and from somatic cell nuclear transfer, has been obtained in our laboratory. The data demonstrate that equine embryos produced by OPU and then cryopreserved can achieve up to 69% pregnancy rate with a foaling rate of 83%. These percentages are reduced to 11 and 23%, respectively, for cloned embryos. In conclusion, extensive evidence exists that in vitro matured equine oocytes can efficiently develop into viable embryos and offspring.