Effect of cryopreservation technique and season on the survival of in vitro produced cattle embryos

Melatonin Improves Quality of Repeated-Poor and Frozen-Thawed Embryos in Human, a Prospective Clinical Trial

OBJECTIVE

In this study, two experiments were performed to assess the effect and the role of melatonin on human in vitro embryo quality.

METHODS

Experiment I: A total of 42 repeated-poor-quality-embryo patients were enrolled, with a total of 181 oocytes retrieval cycles. After IVF, for the same patient, the MT cycles group (10^-7 M melatonin added to the culture medium; n=48) were compared with the previous non-MT cycles group (n=133), following by in vitro culture to blastocyst stage and embryo transfer. 31 patients were transplanted with 65 embryo transfer, including 24 MT embryo transfer, 41 non-MT embryo transfer. Cycle outcomes were compared between the two groups. Experiment II:A total of 143 supernumerary human cleavage-stage embryos (from non-repeated-poor-quality-embryo patients) vitrified on Day 3 after IVF were warmed and randomized into two groups: melatonin group (10^-7 M melatonin added to the culture medium; n=71) and control group (n=72), and then cultured for 72 h. Rate of blastocyst and high-quality blastocyst, reactive oxygen species (ROS) levels of culture media as well as embryonic GPX1, CAT, Mn-SOD, Cu/Zn-SOD, BCL-2, BAX gene expression levels were analyzed.

RESULTS

Experiment I: Results showed that the rate of Day 3 high-quality embryos (29.6% vs.19.5%) in the MT cycles group was significantly higher than that in the non-MT cycles group (P<0.05). The rate of available blastocysts (17.1% vs.12.7%) and clinical pregnancy rate (25.0% vs.17.1%) were in tendency higher in the group treated with melatonin (P>0.05). Experiment II:Results showed that the blastocyst rates in the melatonin administered group were significantly higher than in control group (42.25% vs.26.38%, P<0.05). There were no significant differences in high-quality blastocyst rates. In addition, quantitative PCR showed that the expression of CAT was significantly upregulated by melatonin treatment (P<0.05), while there were no significant differences in the expression of GPX1, Mn-SOD, Cu/Zn-SOD, BAX and BCL-2 gene as well as the levels of ROS.

CONCLUSION

These data showed that melatonin supplement in the culture medium will improve Day 3 high-quality embryos rate of repeated-poor-quality-embryo patients and improve blastocyst rate of vitrified-warmed cleavage-stage embryos, suggesting that melatonin intervention may provide a potential rescue strategy for IVF failures.

CLINICAL TRIAL REGISTRATION

identifier [ChiCTR2200059773].

PGE2 Supplementation of Oocyte Culture Media Improves the Developmental and Cryotolerance Performance of Bovine Blastocysts Derived From a Serum-Free in vitro Production System, Mirroring the Inner Cell Mass Transcriptome

The culture media used throughout the in vitro production (IVP) of bovine embryos remain complex. The serum added to culture media in order to improve embryo development negatively impacts the cryotolerance of blastocysts. Periconceptional prostaglandin E2 (PGE2) signaling is known to exert prosurvival effects on in vitro-generated blastocysts. The purpose of the present study was to evaluate the effects on developmental and cryotolerance performance of a serum-free (SF) IVP system that included defined oocyte culture media supplemented or not with PGE2, versus serum-containing (SC) IVP. RNA-sequencing analysis was used to examine the gene expression of ICM derived under the different IVP conditions. We assessed the degree of cryotolerance of grade-I blastocysts during a three-day post-thaw culture by measuring survival and hatching rates, counting trophectoderm and inner cell mass (ICM) blastomere numbers. We also determined the proportion of ICM cells expressing octamer-binding transcription factor 4 protein (OCT4/POU5F1). We showed that grade-I blastocyst development rates under SF + PGE2 conditions were similar to those obtained under SC conditions, although the cleavage rate remained significantly lower. SC IVP conditions induced changes to ICM gene expression relative to several metabolic processes, catabolic activities, cell death and apoptosis. These alterations were associated with significantly higher levels of ICM cell death at day 7 post-fertilization, and lower survival and hatching rates after thawing. SF IVP conditions supplemented or not with PGE2 induced changes to ICM gene expression related to DNA replication, metabolism and double-strand break repair processes, and were associated with significantly larger ICM cell populations after thawing. SF + PGE2 IVP induced changes to ICM gene expression related to epigenetic regulation and were associated with a significantly higher proportion of ICM cells expressing OCT4. For the first time, our study thus offers a comprehensive analysis of the ICM transcriptome regulated by IVP culture conditions in terms of the cellular changes revealed during culture for three days after thawing.

Reproductive Seasonality Affects In Vitro Embryo Production Outcomes in Adult Goats

Reproductive seasonality may have a considerable influence on the efficiency of assisted reproductive technologies in seasonal species. This study evaluated the effect of season on cleavage, blastocyst rates and quality of in vitro produced (IVP) goat embryos. In total, 2348 cumulus-oocyte complexes (COCs) were recovered from slaughterhouse ovaries and subjected to the same IVP system throughout 1.5 years (49 replicates). The odds ratio (OR) among seasons was calculated from values of cleavage and blastocyst rates in each season. Cleavage rate was lower (p < 0.05) in spring (anestrus), in comparison with either autumn (peak of breeding season) or summer, while the winter had intermediate values. Furthermore, lower OR of cleavage was observed in spring. Blastocyst formation rate (from initial number of COCs) was higher (p < 0.05) in autumn (52 ± 2.5%) when compared with the other seasons (combined rates: 40 ± 1.9%). Moreover, its OR was higher (p < 0.05) in autumn compared to all other seasons and impaired in the spring compared to winter (OR: 0.54) and summer (OR: 0.48). Embryo hatchability and blastocyst cell number were similar (p > 0.05) among seasons. In conclusion, the breeding season leads to improved oocyte developmental competence, resulting in higher cleavage and blastocyst yield, whereas embryo quality remained similar throughout the years.

Effect of season on the in vitro fertilizing ability of frozen-thawed Spanish bovine spermatozoa

The purpose of the present study was to evaluate the effects of season on the in vitro fertilizing ability of bovine spermatozoa and subsequent embryo development. Bovine oocytes were matured and fertilized in vitro with Holstein dairy bull sperm cells collected and frozen in different seasons (winter, spring, and summer). On d 2 and 8 postinsemination, cleavage and blastocyst rates, respectively, were recorded; the blastocysts were graded for morphology. The number of sperm cells binding to the zona pellucida of oocytes, together with the number of nuclei in the developing blastocysts, were assessed after staining with Hoechst. No significant differences were observed among seasons in cleavage and embryo development rate. However, the proportion of "advanced blastocysts" was significantly higher in spring compared with winter and summer, with a corresponding decrease in the proportion of early blastocysts in spring compared with winter and summer. The number of sperm cells binding per oocyte was significantly lower in the oocytes inseminated with sperm samples collected in summer compared with winter or spring. Moreover, a significant interaction was observed in the number of sperm cells binding per oocyte between bull and season. Although no significant differences were observed among seasons in the number of nuclei per blastocyst, a significant interaction was observed between bull and season for this variable. Embryo development rate in in vitro fertilization appeared to be affected by season of semen collection, with sperm samples collected in spring being associated with a higher proportion of advanced blastocysts and better morphology than those collected at other times of the year.

Efficient one-step direct transfer to recipients of thawed bovine embryos cultured in vitro and frozen in chemically defined medium

Direct transfer (DT) of cryopreserved embryos to recipients facilitates on-farm application. We analyzed a new freezing/thawing (F/T) procedure for in vitro produced (IVP) embryos, integrating: 1) an ethylene-glycol based system; 2) a culture step without protein; and 3) a synthetic protein substitute (CRYO3) in cryopreservation medium. IVP embryos from abattoir ovaries were cultured in groups in BSA-containing synthetic oviduct fluid with or without 0.1% fetal calf serum (FCS) until Day-6. Morulae and early blastocysts were subsequently cultured without protein from Day-6 onwards. Day 7 and Day 8 expanded blastocysts (EXB) were subjected to F/T or vitrification/warming (V/W). Thawed and warmed EXB were cultured in vitro, and development rates, cell counts and dead cells were analyzed in surviving embryos. V/W improved survival over F/T (live and hatching rates at 2 h, 24 h and 48 h) (P < 0.0001), and FCS before Day 6 did not affect in vitro survival. After F/T, embryos had lower cell counts in the ICM, TE and total cells than after V/W. Day-7 embryos after F/T showed % apoptotic, % pycnotic and % total dead cells higher (p < 0.05) than their Day-8 counterparts, probably because F/T reduced the numbers of ICM cells within Day-8 embryos. Thereafter, Day-7 blastocysts were transferred to heifers in an experimental herd. There were no differences in birth rates with frozen (-FCS [n = 40]: 45%; +FCS [n = 14]: 28%), vitrified (-FCS [n = 47]: 53%; +FCS [n = 11]: 36%) and fresh (-FCS [n = 30]: 47%; +FCS [n = 17]: 53%) embryos. However, frozen embryos produced with FCS showed 5/9 miscarriages after Day-40. Calves born from frozen (n = 22), vitrified (n = 29) and fresh (n = 22) transfers did not differ in birth weight, gestation length and daily gain weight (P > 0.10). Subsequently, transfer of frozen embryos (n = 29) derived from oocytes collected from live, hormonally stimulated cows in experimental herd, led to pregnancy rates of 57% (heifers) and 40% (dry cows). with EXB on Day-62 Finally, embryos produced with BSA were transferred to cows in an on-field trial (frozen [n = 80]; fresh [n = 58]), with no differences in pregnancy rates (days 30-40). Pregnancy and birth rates could not be predicted from in vitro approaches. The new F/T system yields pregnancy and birth rates comparable to vitrified and fresh embryos without birth overweight. The absence of products of animal origin, defined chemical composition, and direct transfer entail sanitary, manufacturing and application advantages.

Update on the vitrification of bovine oocytes and invitro-produced embryos

The combined use of reproductive technologies, such as transvaginal ovum-pick up and invitro embryo production followed by direct transfer of cryopreserved embryos, has great potential for enhancing genetic selection and optimising cross-breeding schemes in beef and dairy cattle production systems. This, along with an effective cryopreservation procedure for cow oocytes, will enable the long-term conservation of female genetic traits and the advance of embryo biotechnology in this species. However, the low fertilisation rates and developmental competence of cryopreserved oocytes still need to be improved. Over the past two decades, many research efforts tried to overcome individual features of the bovine oocyte that make it notoriously difficult to cryopreserve. In addition, pregnancy rates associated with invitro-produced (IVP) embryos remain lower than those obtained using invivo counterparts. This, together with a lack of a standard methodology for IVP embryo cryopreservation that provides easier and more practical logistics for the transfer of IVP embryos on farms, has hindered international genetic trade and the management of embryo banks. This review updates developments in oocyte and IVP embryo vitrification strategies targeting high production efficiency and better outcomes.

Transcriptomic difference in bovine blastocysts following vitrification and slow freezing at morula stage

Cryopreservation is known for its marked deleterious effects on embryonic health. Bovine compact morulae were vitrified or slow-frozen, and post-warm morulae were cultured to the expanded blastocyst stage. Blastocysts developed from vitrified and slow-frozen morulae were subjected to microarray analysis and compared with blastocysts developed from unfrozen control morulae for differential gene expression. Morula to blastocyst conversion rate was higher (P < 0.05) in control (72%) and vitrified (77%) than in slow-frozen (34%) morulae. Total 20 genes were upregulated and 44 genes were downregulated in blastocysts developed from vitrified morulae (fold change ≥ ± 2, P < 0.05) in comparison with blastocysts developed from control morulae. In blastocysts developed from slow-frozen morulae, 102 genes were upregulated and 63 genes were downregulated (fold change ≥ ± 1.5, P < 0.05). Blastocysts developed from vitrified morulae exhibited significant changes in gene expression mainly involving embryo implantation (PTGS2, CALB1), lipid peroxidation and reactive oxygen species generation (HSD3B1, AKR1B1, APOA1) and cell differentiation (KRT19, CLDN23). However, blastocysts developed from slow-frozen morulae showed changes in the expression of genes related to cell signaling (SPP1), cell structure and differentiation (DCLK2, JAM2 and VIM), and lipid metabolism (PLA2R1 and SMPD3). In silico comparison between blastocysts developed form vitrified and slow-frozen morulae revealed similar changes in gene expression as between blastocysts developed from vitrified and control morulae. In conclusion, blastocysts developed form vitrified morulae demonstrated better post-warming survival than blastocysts developed from slow-frozen morulae but their gene expression related to lipid metabolism, steroidogenesis, cell differentiation and placentation changed significantly (≥ 2 fold). Slow freezing method killed more morulae than vitrification but those which survived up to blastocyst stage did not express ≥ 2 fold change in their gene expression as compared with blastocysts from control morulae.

Chapter 18 Vitrification: A Reliable Method for Cryopreservation of Animal Embryos

The impact of cryopreservation in assisted reproduction is increasingly appreciated. Cells, oocytes, and embryos preserved under ultralow temperature can endure storage for indefinite time with almost no alteration in their metabolic and genetic components. Advances in cryopreservation and its applications to preserve cells, gametes, and embryos offer opportunities in conservation of biodiversity and dissemination of elite livestock germplasm. This chapter describes the vitrification for cryopreservation of livestock embryos.

Vitrification of in vitro-produced and in vivo-recovered equine blastocysts in a clinical program

There is a clinical demand for cryopreservation of both in vivo-recovered and in vitro-produced (IVP) equine embryos. We previously reported successful vitrification of expanded equine blastocysts in fine-diameter microloader pipette tips (MPTs) after blastocoel collapse, in a research setting. Here, we report the results of clinical application of the MPT vitrification technique for both in vivo-recovered and IVP blastocysts. In vivo-recovered blastocysts were obtained by referring veterinarians on Days 6 to 8 after ovulation, and shipped 1 to 10 hours to the laboratory before vitrification. IVP blastocysts (<300 μm in diameter) were produced by intracytoplasmic sperm injection and in vitro embryo culture. All vitrified-warmed embryos were shipped (0.5-12 hours) for transfer to recipient mares. In experiment 1, 47 IVP embryos from our clinical intracytoplasmic sperm injection program were vitrified using the MPT and transferred. The rates of initial pregnancy (59%) and foaling (45%) were equivalent to those for 52 IVP embryos from the same mare aspiration sessions and shipped for the same duration but transferred fresh (75% and 45%, respectively). The pregnancy and foaling rates for in vivo-recovered embryos were 76 and 71%, respectively for 17 small blastocysts (<300 μm in diameter), and 55 and 45%, respectively for 11 large blastocysts (303-608 μm in diameter, collapsed before vitrification; P > 0.1). In experiment 2, the MPT was cut lengthwise to form an open vitrification device, designated "Sujo". Research IVP blastocysts were vitrified at 1, 2, or 3 embryos per Sujo (n = 34 embryos), or singly on a commercial open device (Cryolock; n = 11). After warming, 97% and 91% of embryos, respectively, grew in culture. Similarly, culture of two in vivo-recovered large blastocysts after collapse and vitrification on Sujos both resulted in embryo growth. However, transfer of four in vivo-recovered expanded blastocysts after collapse, vitrification on Sujos, and warming resulted in only one foal. These data indicate that vitrification of equine IVP embryos and small in vivo-recovered embryos is efficient under clinical conditions. Collapse and vitrification of in vivo-recovered large blastocysts in MPT under our clinical conditions resulted in a 45% foaling rate. While numbers are low, use of an open vitrification system did not appear to improve results for these embryos.