The potential for modification in cloning and vitrification technology to enhance genetic progress in beef cattle in Northern Australia

Recent advances of oocyte/embryo vitrification in mammals from rodents and large animals

Vitrification is a valuable technology that enables semipermanent preservation and long-distance or international transportation of genetically modified and native animals. In laboratory mice, vitrification maintains and transports embryos, and many institutions and companies sell vitrified embryos. In contrast, despite numerous papers reporting on vitrification in livestock over the past decade, practical implementation has yet to be achieved. However, with advances in genome editing technology, it is anticipated that the number of genetically modified domestic animals will increase, leading to a rise in demand for vitrification of oocytes and embryos. Here, we provide an objective overview of recent advancements in vitrification technology for livestock, drawing a comparison with the current developments in laboratory animals. Additionally, we explore the future prospects for vitrification in livestock, focusing on its potential benefits and drawbacks.

Melatonin promotes in vitro maturation of vitrified-warmed mouse GV oocytes potentially by modulating MAD2 protein expression of SAC component through MTRs

Previous studies have shown that melatonin (MT) can ameliorate vitrification-inflicted damage in mouse germinal vesicle (GV) oocytes, however, the key mechanistic basis of this improvement still remains poorly understood. This study was conducted to investigate whether MT can improve in vitro developmental potential of vitrified-warmed GV oocytes through its receptors. The fresh oocytes were randomly divided into four groups: untreated (control group, F), vitrified by open-pulled straw method (vitrification group, V), vitrification group with 100 nmol/L MT supplementation (vitrification + MT group, VM), and with 100 nmol/L MT plus 100 nmol/L luzindole administration (vitrification + MT + luzindole group, VML) or with 50 nmol/L ramelteon addition (vitrification + ramelteon group; VR). After warming, oocytes were cultured in vitro, and MT receptors (MTRs), MAD2 (mitotic arrest deficient 2), Securin and CyclinB1 protein levels and spindle morphology were evaluated. The ratio of oocytes developed to the metaphase I (MI) and metaphase II (MII) stages was also assessed. The results showed that after vitrification-warming, the in vitro maturation rate of GV oocytes was significantly lower compared to the control (F) group. Vitrification also significantly impaired the spindle morphology, decreased the protein level of MTRs and Securin, and decreased MAD2 levels in MI oocytes. However, when MT or ramelteon (MTRs agonist) were added (group wise) to warming and maturation media, the maturation rate of GV oocytes was significantly increased, the normal proportion of the spindle morphology increased, and the expression level of MAD2 increased in their resulting MI oocytes compared to the vitrification group. However, following addition of both MT and ramelteon, the maturation rate of GV oocyte showed no significant difference between VML and vitrification groups. The spindle morphology and MAD2 levels in MI oocytes were comparable to the vitrification group but differed significantly from the VM group. Taken together, finding of the present study shows that MT (100 nmol/L) can ameliorate the in vitro maturation of vitrified-warmed mouse GV oocytes, potentially by improving the spindle morphology, modulating MAD2 protein level and promoting the development of MI stage oocytes through MTRs.

Effects of ovary storage temperature and embryo vitrification on somatic cell nuclear transfer outcomes in goats

Improving the genetic potential of farm animals is one of the primary aims in the field of assisted reproduction. In this regard, somatic cell nuclear transfer (SCNT) can be used to produce a large number of embryos from genetically elite animals. The aims of the present study were to assess the effects of: (1) ovary storage conditions on preimplantation development of recovered oocytes and the freezability of the derived blastocysts; and (2) vitrification of goat SCNT-derived blastocysts on postimplantation development. Goat oocytes were recovered from ovaries and stored under warm (25°C-27°C) or cold (11°C-12°C) conditions before being used to produce SCNT embryos. There were no differences in oocytes recovered from ovaries kept under cold versus warm storage conditions in terms of cleavage (mean (±s.d.) 95.68±1.67% vs 95.91±2.93% respectively) and blastocyst formation (10.69±1.17% vs 10.94±0.9% respectively) rates. The re-expansion rate of vitrified blastocysts was significantly lower for cold- than warm-stored ovaries (66.3±8.7% vs 90±11% respectively). To assess the effects of vitrification on postimplantation development, blastocysts from cold-stored ovaries only were transferred from fresh and vitrified-warmed groups. The pregnancy rate was comparable between the fresh and vitrified-warmed groups (41.65% and 45.45% respectively). In addition, established pregnancy in Day 28-38 and full-term pregnancy rates were similar between the two groups. In conclusion, this study shows similar invitro preimplantation developmental potential of warm- and cold-stored ovaries. This study introduces the vitrification technique as an appropriate approach to preserve embryos produced by SCNT for transfer to recipient goats at a suitable time.

Vitrification of in vitro-derived bovine embryos: targeting enhancement of quality by refining technology and standardising procedures

Bovine invitro fertilisation technology has been widely exploited in commercial settings. The majority of invitro-derived cattle embryos are transferred into recipient cows as recently collected (i.e. 'fresh') embryos due to the lack of a reliable cryopreservation method that results in favourable pregnancy rates following transfer of thawed embryos. This is a primary reason for the poor industry uptake of this extreme temperature freezing process. Numerous investigations into vitrification have revealed the importance of rapid cooling and warming rates, enhancing embryo viability after cryopreservation compared with conventional slow freezing. Those studies spawned a considerable assortment of cryovessels and diversity of procedures, delivering variable rates of success, which makes performing vitrification consistently a practical challenge. Hence, further research is required in order to both optimise and standardise vitrification methodology and to design a cryovessel that enables direct transfer of vitrified embryos to recipients after warming. In parallel with improvements in vitrification, it is important to continue to raise the quality of invitro-derived cattle embryos through modifications in laboratory culture techniques. The twin goals of methodology refinement and standardisation, leading to embryo quality enhancement, are each imperative if invitro fertilisation technology is to be adopted in the field.

Melatonin Improves Parthenogenetic Development of Vitrified⁻Warmed Mouse Oocytes Potentially by Promoting G1/S Cell Cycle Progression

This study aimed to investigate the effect of melatonin on the cell cycle of parthenogenetic embryos derived from vitrified mouse metaphase II (MII) oocytes. Fresh oocytes were randomly allocated into three groups: untreated (control), or vitrified by the open-pulled straw method without (Vitrification group) or with melatonin (MT) supplementation (Vitrification + MT group). After warming, oocytes were parthenogenetically activated and cultured in vitro, then the percentage of embryos in the G1/S phase, the levels of reactive oxygen species (ROS) and glutathione (GSH), and the mRNA expression of cell cycle-related genes (P53, P21 and E2F1) in zygotes and their subsequent developmental potential in vitro were evaluated. The results showed that the vitrification/warming procedures significantly decreased the frequency of the S phase, markedly increased ROS and GSH levels and the expression of P53 and P21 genes, and decreased E2F1 expression in zygotes at the G1 stage and their subsequent development into 2-cell and blastocyst stage embryos. However, when 10⁻⁹ mol/L MT was administered for the whole duration of the experiment, the frequency of the S phase in zygotes was significantly increased, while the other indicators were also significantly improved and almost recovered to the normal levels shown in the control. Thus, MT might promote G1-to-S progression via regulation of ROS, GSH and cell cycle-related genes, potentially increasing the parthenogenetic development ability of vitrified–warmed mouse oocytes.

Comparison of pregnancy in cattle when non-vitrified and vitrified in vitro-derived embryos are transferred into recipients

The present study was conducted in cattle to test the null hypothesis that the pregnancy rate of recipient females is similar when in vitro-derived embryos are transferred either fresh (non-vitrified) or after being subjected to vitrification. Cumulus-oocyte complexes, collected twice (6 weeks apart) from 10 donor cows were matured in vitro and inseminated with frozen-thawed sperm from a single proven bull per donor collection. Cleaved embryos were cultured in vitro until day 7 and any resulting blastocysts were graded for stage [early (unexpanded), advanced (expanded, hatching, hatched)] and/or quality and either discarded (poor quality), or, if deemed suitable, transferred fresh or vitrified for later warming and transfer. All blastocysts were transferred singly to oestrus-synchronized cows and pregnancy monitored by transrectal palpation on days 35, 60 and 90. From 20 collections, 818 cumulus-oocyte complexes were aspirated; however, after grading, only 462 (56.5%) were ranked as suitable quality for maturation and insemination. From those 462 complexes inseminated, 363 (78.6%) cleaved during the process and 243 (52.6%) developed to the blastocyst stage with 194 (42.0%) deemed utilizable, of which 85 were vitrified and 109 were transferred fresh. There was a median of 13 (range 0-24) utilizable blastocysts per cow. Of the 109 non-vitrified blastocysts transferred, there were 45 (41.3%) and 41 (37.6%) recipients that were detected to be pregnant on day 35 and day 90, respectively, subsequent to transfer. Thus, an 8.9% abortion rate was observed (4/45). Of the 85 transferred vitrified-warmed blastocysts, 34 were detected to be pregnant (40.0%) on day 35 following transfer, and all pregnancies were maintained at day 90 (0% abortion rate), which was similar to non-vitrified transfers (P > 0.05, Chi-square test). There was no significant difference in pregnancy rate on day 90 in advanced compared to early blastocysts for either the non-vitrified transfers (9/23, 39.1% vs 33/86, 38.3%) or the vitrified transfers (30/72, 41.6% vs 4/13, 30.8%) (P > 0.05 in each case). In summary, these data show that vitrification of in vitro-derived early and advanced blastocysts is a suitable method of cryopreservation of bovine embryos, and, furthermore, that subsequent transfer of all vitrified/warmed blastocysts into recipient females results in pregnancy rates no different to those attained by non-vitrified transfers into recipient females.

Reproductive performance and expression of imprinted genes in somatic cell cloned boars

To assess the performance of boars derived by somatic cell cloning, we analyzed various aspects of their reproductive characteristics and the expression of two imprinted genes. Cloned boars (cloned Duroc × Jinhua) were analyzed for birth weight, growth rate, age at first ejaculation, semen characteristics and fertility, in comparison with naturally bred control boars of the same strain. The expression of imprinted genes was analyzed using the microsatellite marker SWC9 for the paternally expressed gene insulin-like growth factor -2 (IGF2) and with single nucleotide polymorphisms (SNPs) for the gene maternally expressed 3 (MEG3). The cloned boars had high production of semen and were nearly equal in level of fertility to conventional pigs; they showed similar characteristics as naturally bred boars of the same strains. The expression of IGF2 was partially disturbed, but this disturbed expression was not linked to a change in developmental fate or reproductive performance. These results indicate that use of cloned boars could be highly effective for proliferation of pigs with desirable characteristics, preservation of genetic resources and risk reduction against epidemic diseases, such as foot-and-mouth disease, through storage of somatic cells as a precautionary measure for use in regenerating pig populations after a future pandemic.

A comparative analysis of the efficacy of three cryopreservation protocols on the survival of in vitro-derived cattle embryos at pronuclear and blastocyst stages

The effectiveness of three cryopreservation protocols (slow freezing, short equilibration vitrification and long equilibration vitrification) on in vitro-derived cattle embryos at expanded blastocyst and pronuclear stages was compared. 199 expanded blastocysts of good quality were assigned randomly into four treatment groups [control, non-cryopreserved (fresh, unfrozen); and the three cryopreservation methods]. The re-expansion of the cryopreserved blastocysts after 24 h in vitro culture was similar to that of the fresh control group. However, the hatching rate of expanded blastocysts after 48 h culture was significantly less for the slow freezing group (31/47; 66.0%) than for both the short equilibration vitrification (46/51; 90.2%) and long equilibration vitrification groups (42/50; 84.0%). Denuded presumptive zygotes at the pronuclear stage (14-18 h post-insemination) were assigned randomly to the same four treatment groups and, following thawing, embryos were assessed for their capacity to cleave and to develop into a blastocyst. Overall, cleavage rates of cryopreserved zygotes were significantly less than those of the fresh control. The blastocyst formation rate of slow-frozen zygotes (4/81; 4.9%) was significantly less than that of zygotes subjected either to short equilibration vitrification (18/82; 22.0%) or long equilibration vitrification (16/74; 21.6%). All cryopreservation groups showed rates of blastocyst formation that were significantly less than that of the fresh control (51/92; 55.4%). Collectively, our findings indicate that vitrification is the preferred technology to cryopreserve in vitro-derived cattle embryos at expanded blastocyst and pronuclear stages. Moreover, short equilibration vitrification technology can improve outcomes and be more efficient by taking less time to perform.

Handmade cloning: recent advances, potential and pitfalls

Handmade cloning (HMC) is the most awaited, simple and micromanipulator-free version of somatic cell nuclear transfer (SCNT). The requirement of expensive micromanipulators and skilled expertise is eliminated in this technique, proving it as a major revolution in the field of embryology. During the past years, many modifications have been incorporated in this technique to boost its efficiency. This alternative approach to micromanipulator based traditional cloning (TC) works wonder in generating comparable or even higher birth rates in addition to declining costs drastically and enabling cryopreservation. This technique is not only applicable to intraspecies nuclear transfer but also to interspecies nuclear transfer (iSCNT) thus permitting conservation of endangered species. It also offers unique possibilities for automation of SCNT which aims at production of transgenic animals that can cure certain human diseases by producing therapeutics hence, providing a healthier future for the wellbeing of humans. The present review aims at highlighting certain aspects of HMC including recent advancements in procedure and factors involved in elevating its efficiency besides covering the potentials and pitfalls of this technique.