Vitrified before and after genome editing via electroporation

BACKGROUND

Cryopreservation of bovine zygotes allows for a flexible schedule of genome editing via electroporation. However, vitrification-induced cell membrane damage may not only affect embryonic development but also genome mutation.

OBJECTIVE

To investigate the effects of vitrification of zygotes before and after electroporation treatments on the development and genome mutation of bovine presumptive zygotes.

MATERIALS AND METHODS

In vitro-derived bovine zygotes were electroporated with the CRISPR/Cas9 system immediately (Vitrified-EP) or 2 h after incubation (Vitrified-2h-EP) following vitrification and warming, or electroporated before vitrification (EP-vitrified).

RESULTS

The development rates of vitrified-warmed zygotes were significantly lower (p < 0.05) than those of control zygotes that were not vitrified. Moreover, no differences were observed in the mutation rates and mutation efficiency of the blastocysts resulting from electroporated zygotes, irrespective of the timing of electroporation treatment.

CONCLUSION

Our results suggest that vitrification before and after electroporation treatments does not affect the genome editing of zygotes.

In vitro Development of Zona Pellucida-free Porcine Zygotes Cultured Individually after Vitrification

BACKGROUND

Cryopreservation of zona pellucida (ZP)-free embryos provides more options for somatic cell nuclear transfer, particularly during handmade cloning.

OBJECTIVE

This study investigated whether the removal of the ZP affects the development of porcine zygotes after vitrification and warming.

MATERIALS AND METHODS

We determined the appropriate volume of the corresponding medium for the individual culture of ZP-intact and -free embryos and evaluated the protection effect of ZP during cryopreservation on the resulting development of the vitrified-warmed zygotes.

RESULTS

The volume of culture medium influenced the development of ZP-intact zygotes, and a volume of 15 µL was most suitable for their development. However, the volume of culture medium did not modify the development of ZP-free zygotes. The removal of the ZP before vitrification did not adversely affect embryonic development or quality of the resulting blastocysts.

CONCLUSION

Our results suggest that the removal of the ZP does not cause detrimental effects to the development of vitrified-warmed zygotes.

28 EFFECT OF TRICHOSTATIN A ON IN VITRO EMBRYO DEVELOPMENT OF INTERSPECIES NUCLEAR TRANSFER EMBRYOS RECONSTRUCTED FROM CAT DONOR NUCLEI AND BOVINE CYTOPLASM

Interspecies somatic cell nuclear transfer (iSCNT) is an invaluable tool for studying nucleus-cytoplasm interactions and may provide an alternative for cloning endangered animals whose oocytes are difficult to obtain. The developmental ability of iSCNT embryos decreases with increases in taxonomic distance between the donor and recipient species. The development of cat-bovine iSCNT embryos is reportedly blocked at the 8-cell stage (Thongphakdee et al. 2008 J. Reprod. Dev. 54, 142–147). Abnormal epigenetic reprogramming, such as DNA methylation or histone modifications, may cause low iSCNT efficiencies. The present study was conducted to evaluate the effect of the histone deacetylase inhibitor trichostatin A (TSA), previously used to enhance nuclear reprogramming following SCNT, on the developmental ability of cat iSCNT embryos using bovine oocytes matured in vitro. The matured bovine oocyte was enucleated by the glass needle and the domestic cat fetal fibroblast used as the donor nuclei was then placed into the perivitelline space adjacent to the plasma membrane of the oocyte. Couplets with bovine ooplasm were fused and activated simultaneously with a single DC pulse of 2.3 kV cm–1 for 30 µs, respectively, using an electro cell fusion generator followed by cycloheximide treatment. Reconstructed cat-bovine embryos were treated with 0, 25, 50, and 100 nM concentrations of TSA for 24 h following fusion. The percentages of embryos cleaved and embryos developed to the blastocyst stage were subjected to arc sin transformation before ANOVA. The TSA treatment at 50 nM contributed significantly higher rates of cleavage and blastocyst formation (n = 139; 84.3 and 4.6%, respectively) compared with untreated embryos (n = 187; 63.8 and 0%, respectively) and embryos treated with 100 nM TSA (n = 172; 71.4 and 0%, respectively; P < 0.05). Development to the morula stage of iSCNT embryos was observed in the TSA treatment groups, whereas no embryos developed beyond the 16-cell stage in the untreated group. In conclusion, our results indicate that TSA treatment for 24 h following fusion improves the development of iSCNT embryos. Specifically, 50 nM TSA treatment provides a beneficial effect on cleavage and development to the blastocyst stage of cat iSCNT embryos using bovine oocytes matured in vitro as recipients and domestic cat fibroblasts as donor nuclei.

187 EFFECTS OF OVARY STORAGE TIME ON THE QUALITY AND MEIOTIC COMPETENCE OF CAT OOCYTES

Unlike the oocytes of other species, cat oocytes have a unique characteristic in that they can mature in vitro after temporary storage at 5°C. Temporal storage of ovaries can aid in preserving oocytes from the ovaries of endangered felids that sometimes die suddenly in the field. The present study was conducted to evaluate the effects of the duration of cold storage of cat ovaries on the quality and meiotic competence of their oocytes. Domestic cat ovaries were collected from sexually mature queens (40 ovary pairs) at various stages of the reproductive cycle, after routine ovariohysterectomy performed at local veterinary clinics. After excision, the ovaries were stored at 5°C in physiological saline for 0, 1, 2, 3, 4 and 5 days until oocyte recovery. The cumulus–oocyte complexes with uniform and dark-pigmented ooplasm and more than 2 layers of cumulus cells were collected (n = 526) and then cultured for 24 h in maturation medium. This maturation medium consisted of tissue culture medium 199 supplemented with 4 mg mL–1 of bovine serum albumin, 0.1 IU mL–1 of human menopausal gonadotropin, 10 IU mL–1 of hCG, 1 μg mL–1 of 17 β-oestradiol and 50 μg mL–1 of gentamicin. The status of meiosis and fragmented chromatin in the oocytes after the 24-h maturation culture was assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling and Hoechst 33342 staining. Data were analyzed using analysis of variance. The percentage of oocytes that reached metaphase II was greater for ovaries kept without cold storage (control group; 60.5%) than for ovaries kept for 1, 2, 3, 4 and 5 days in cold storage (maturation of 28.6, 38.3, 23.2, 1.6 and 2.2%, respectively; P < 0.05). In the cold storage group, the maturation rates (1.6–2.2%) of oocytes from ovaries stored for more than 4 days were significantly lower (P < 0.05) than those (23.2–38.3%) of oocytes from ovaries stored for less than 3 days. Moreover, oocytes with fragmented chromosomes after the maturation culture were not observed in the case of the control group, whereas 24.4 to 51.8% of the oocytes in the cold storage group had fragmented chromosomes, irrespective of the storage period. These results indicate that cold storage of cat ovaries decreases the meiotic competence of oocytes and influences the quality of oocytes matured in vitro.

50 EFFECTS OF VITAMINS ON THE QUALITY AND FERTILITY OF BOAR SEMEN AFTER LIQUID PRESERVATION AT 5°C

Liquid preservation can be used as an alternative to freeze-thawing for preserving semen for AI. The efficiency of some boar semen extenders has been studied over storage periods of 5 to 7 days. The objective of this study was to evaluate the viability and penetrability of boar spermatozoa preserved at 5°C in a modified Modena-based extender supplemented with either 100 μM vitamin C (Vc), 100 μM vitamin E (Ve), or 100 μM Vc + 100 μM Ve (Vc + e). The final sperm concentration was adjusted to cells mL–1 and the semen was then stored at 5°C for 4 weeks. In Experiment 1, the semen samples were assessed every week during the 4-week storage in each extender for the following factors: motility, by using computer-assisted semen analysis (CASA); viability, by using the Live/Dead fluorescence viability assay; plasma membrane integrity, by using the hypoosmotic swelling test (HOST); and acrosome integrity, by using fluorescein isothiocyanate (FITC)-labelled peanut agglutinin staining. In Experiment 2, we examined the penetrability of spermatozoa that had been stored in each extender for 4 weeks and the development of fertilized oocytes. Data were analysed using ANOVA. In Experiment 1, when the semen was stored for 2 weeks, the mean percentage values of total sperm motility and viability for semen stored with Ve were significantly higher than those for semen stored without Vc and Ve (control group) (84.3 vs 67.9% and 59.8 vs 51.2%, respectively; P < 0.05). Moreover, the percentage sperm motility for semen stored for 4 weeks tended to be higher in the Ve group than in the control group (44.2 vs 32.7%; P < 0.1). Storage with Vc or Vc + e did not improve sperm motility and viability of semen. The plasma membrane integrity and acrosome integrity of semen did not significantly differ among the groups during the 4-week storage. In Experiment 2, the rates of sperm penetration and of development to blastocysts of fertilized oocytes did not differ between the Ve and control groups (33.0 vs 28.5% and 14.9 vs 10.1%, respectively; P > 0.05). However, storage with Vc reduced the rate of oocyte development compared with the Ve and control groups (1.1%; P < 0.05). In conclusion, adding Ve to the semen extender may improve the motility and fertility of boar semen stored at 5°C. However, adding Vc has a harmful effect on the quality and fertility of stored boar semen.

Effects of cryoprotectant agents and equilibration methods on developmental competence of porcine oocytes

Chemical toxicity of cryoprotectants to in vitro developmental competence of porcine oocytes was examined. In vitro-matured oocytes were exposed to 40 percent ethylene glycol (EG), glycerol (GLY), or 1,2-propanediol (PD), fertilized with spermatozoa, and cultured for 8 days. Compared to treatment with other cryoprotectants, exposure to EG resulted in the development of significantly more blastocysts, but the rate was significantly lower than that of non-exposed control oocytes. In vitro-matured oocytes were also equilibrated in 40 percent EG by 3 multi-step methods, after which their developmental competence was evaluated. The rate of blastocyst development was higher in the 4-step method than in the 2- and 3-step methods of equilibrium. These results indicate that cryoprotectants and equilibration methods affect the developmental competence of porcine oocytes and that EG may be a superior cryoprotectant for vitrification of these cells.

Assessment of canine ovaries autografted to various body sites

The influence of graft site on the survival of canine follicles and oocytes after autografting was investigated. Hemi-ovaries were autografted to three locations (quadriceps femoris muscle fascia, kidney capsule, and gastrosplenic ligament), and grafted ovaries were recovered (under anesthesia) 28 to 31 d after transplantation. The grafted hemi-ovaries were bisected: one-quarter ovary was used for histological assessment and another quarter for evaluation of oocyte viability. As controls, the remaining fresh hemi-ovaries were used to assess the viability of follicles and oocytes in non-transplanted ovaries. Most follicles in the histological sections of the grafts were classified as primordial or primary follicles. Antral follicles were not observed in the grafts, irrespective of the graft site. The percentages of viable follicles in the sections from control ovaries, and the ovaries grafted to the kidney capsule, the quadriceps femoris muscle fascia, and the gastrosplenic ligament were 17.4, 22.9, 18.3, and 32.4%, respectively. A total of 12 oocytes was recovered from the 15 hemi-ovaries grafted in five bitches, of which five (41.7%) oocytes from the ovaries grafted to the quadriceps femoris muscle fascia and the kidney capsule were cultured for assessment of meiotic competence. Three oocytes were viable but remained in the germinal vesicle stage after 72 h of maturation culture. The quadriceps femoris muscle fascia might be useful for grafting like the kidney capsule, but improvement of follicle survival and meiotic competence of oocytes in the grafts is necessary.

18 EFFECTS OF SKIM MILK ON THE QUALITY AND FERTILITY OF BOAR SEMEN FOLLOWING LIQUID PRESERVATION AT 5°C AND 15°C

Liquid preservation of semen can be an alternative to frozen–thawed semen for artificial insemination. The success of a selection of boar semen extenders has been studied over storage periods of 5 to 7 days. The objective of this study was to evaluate the effects of skim milk on the viability and in vitro fertility of boar spermatozoa preserved in Modena-based extenders at 5°C and 15°C for 2 weeks. A total of 7 ejaculates were collected from one boar. The sperm-rich fraction of each ejaculate was centrifuged and diluted in Modena extenders supplemented with 0 (control), 7.5, and 15 mg mL–1 of dry skim milk. The final sperm concentration was adjusted to 1 × 108 cells mL–1, and then the semen was stored at 5°C and 15°C for 2 weeks. In the first experiment, the motility, viability (live/dead fluorescence viability assay), plasma membrane integrity (hypoosmotic swelling test; HOST), and acrosome integrity (FITC-labelled peanut agglutinin staining) of semen stored for 2 weeks were assessed. In the second experiment, the fertilization of stored semen after 20 h of co-incubation with in vitro matured oocytes and their development were examined. Data were analysed using ANOVA. When the semen was stored at 5°C for 2 weeks, the mean total sperm motility of semen stored with 7.5 and 15 mg mL–1 of dry skim milk was significantly higher than that of semen in the control group (41.4% and 41.5% v. 17.4%; P < 0.05). However, the beneficial effects of skim milk on the sperm motility were not observed in the semen stored at 15°C. Moreover, there were no significant differences in the other parameters of semen quality among the groups in each storage temperature. Significantly higher penetration rates of semen stored with 7.5 and 15 mg mL–1 of dry skim milk were observed in the storage at 5°C (41.1% and 34.8% v. 19.8%; P < 0.05) but not at 15°C (38.9% and 26.0% v. 30.0%; P > 0.05) when compared with the control group. When the semen was stored at 5°C, the development rate to the blastocyst stage of oocytes fertilized with semen stored with 7.5 mg mL–1 of dry skim milk was significantly higher than that with control and 15 mg mL–1 of dry skim milk (15.4% v. 1.1% and 7.8%; P < 0.01). However, there were no significant differences in the development rates of oocytes fertilized with semen stored at 15°C among the groups (9.6–11.9%). In conclusion, our results indicate that the effect of skim milk on the viability and in vitro fertility of liquid-stored boar spermatozoa is dependent on the storage temperature. The addition of 7.5 mg mL–1 of dry skim milk may be effective for the improvement of viability and fertility of semen stored at 5°C but not at 15°C.

271 VIABILITY OF OOCYTES FROM CANINE OVARIES GRAFTED IN THE PROXIMAL PORTION OF THE BODY SURFACE

Numerous studies have reported that follicles in ovarian tissue are not only able to survive ovarian grafting but also to grow from the early to advanced stages of follicular development. The site of grafting is very important for tissue survival and follicle development after transplantation. Several grafting techniques have been reported, basically differing only in the location to which the ovarian grafts have been transplanted, such as the bursal cavity, kidney capsule, and subcutaneous sites. The objective of the present study was to determine the viability of canine oocytes from ovaries transplanted in the proximal portion of the body surface. Bilateral ovariectomy was performed using a ventral midline abdominal approach with routine techniques and materials. After excision of ovaries from 10 bitches (4–7 y of age), each ovary of the pairs was cut approximately in half using a scalpel blade. The hemi-ovaries were kept in physiological saline, maintained at 38°C, and then transplanted to the animal of origin in each body site. The ovaries were transplanted under the fascia of the left quadriceps femoris muscle, the left thoracolumbar fascia, and the deltoid muscle in left scapular region. As control, a remaining hemi-ovary was used to examine the morphology and viability of oocytes from fresh ovaries without transplantation. All grafted ovaries were recovered from animals at 28 to 31 days after transplantation under the anesthesia. After collection, each ovary was sliced repeatedly to release oocytes. All oocytes collected from ovaries were examined microscopically for morphological quality and categorized by the classification as previously described (Hewitt et al. 1998 Theriogenology 49, 1083–1101). Grade A oocytes were darkly pigmented and surrounded by one or more layers of cumulus cells, Grade B oocytes were lightly pigmented with incomplete layers of cumulus cells, and Grade C oocytes were pale coloured and irregularly shaped without any cumulus cells. Only Grade A oocytes were cultured in maturation medium for 72 h at 38.5°C in a humidified atmosphere of 5% CO2 in air. After incubation for 72 h, the oocytes were denuded, fixed, and stained by Hoechst 33342 to examine the nuclear maturation. After grafting for 28 to 31 days, a total of 5, 7, and 4 oocytes were recovered, respectively, from hemi-ovaries transplanted into quadriceps femoris fascia, thoracolumbar fascia, and scapular deltoid muscle, of which 1 and 2 oocytes from quadriceps femoris fascia and thoracolumbar fascia were classified into Grade A, respectively. After maturation culture of 3 oocytes, one oocyte reached the metaphase II stage. In the control group, a total number of 183 oocytes were collected from fresh ovaries, and 20.8% of these oocytes were classified into Grade A, of which 6.1% of oocytes reached the metaphase II stage after maturation culture. These results indicate that some oocytes from grafted ovaries can develop and maintain meiotic competence even when the ovaries are transplanted under the fascia in the proximal portion of the body surface.

39 IN VITRO DEVELOPMENT OF CANINE EMBRYOS PRODUCED BY INTERSPECIES SOMATIC CELL NUCLEAR TRANSFER USING ENUCLEATED BOVINE OOCYTES

Interspecies somatic cell nuclear transfer (iSCNT) is an invaluable tool for studying nucleous-cytoplasm interactions, and may provide an alternative for cloning endangered animals, whose oocytes are difficult to obtain. Using readily available oocytes from domestic/farm animals as recipients for iSCNT would greatly benefit ongoing research on somatic cell reprogramming. However, little information is available concerning the development of canine iSCNT embryos reconstructed with bovine oocyte cytoplasm. In the first experiment, we investigated the influence of donor cell type on the development of canine iSCNT embryos reconstructed with enucleated bovine oocytes. Canine mammary gland tumour (MGT) cells and cumulus cells were used as donor cell. The bovine oocytes matured for 22 h were enucleated by the micromanipulator, and the donor cells were transferred into the perivitelline space adjacent to the plasma membrane of the oocyte. The couples were fused and activated simultaneously with a single DC pulse of 2.3 kV cm–1 for 30 μs, using an electro cell fusion generator. The reconstructed embryos were cultured for 72 h in the mSOF medium supplemented with 0.4% BSA. After 72 h of culture, only cleaved embryos were further co-cultured with bovine cumulus cells in mSOF supplemented with 5% fetal bovine serum (FBS) for an additional 5 days. In the second experiment, we examined the effects of serum type on the development of canine iSCNT embryos. The embryos reconstructed with canine cumulus cells were co-cultured with canine cumulus cells in mSOF supplemented with 5% FBS, and canine oestrous and diestrous serum for 5 days after 72 h of culture with 0.4% BSA. Data were analysed by chi-square analysis with a Yates’ correction. More than 75% of the canine somatic cells successfully were fused with bovine enucleated oocytes following electrofusion, irrespective of the types of the donor cells. There were no significant differences in the cleavage rates of iSCNT embryos between the cumulus cell and MGT cell (66.2% v. 62.6%). Although none of the embryos reconstructed with MGT cells (n = 123) developed to the 16-cell stage, 6% of embryos with cumulus cells (n = 133) reached at least the 16-cell stage. There were no significant differences in the cleavage rates of iSCNT embryos among the types of serum. The iSCNT embryos could not develop to the blastocyst stage, irrespective of the type of donor cell and serum. In conclusion, our results indicate that the bovine oocytes partly supported the remodelling and reprogramming of the canine somatic cell nuclei, but they were unable to support the development to the blastocyst stage of canine iSCNT embryos. Moreover, the development to the late embryonic stage of iSCNT embryos may be influenced by the type of donor cell but not serum.

Formation of an antral follicle-like structure of bovine cumulus-oocyte complexes embedded individually or in groups in collagen gels

Culture techniques of antral follicle-like structure (AFLS) derived from cumulus-oocyte complexes (COCs) might provide important insights into follicular development and oocyte maturation. This study was undertaken to investigate the effects of embedding bovine COCs individually (one COC) or in groups (4-5 COCs) in collagen gels on the formation of AFLS and the meiotic status of oocytes. The observations of AFLS formation were performed every second day for 14 days. The AFLS was formed at Day 2 or 4 after the start of culture (Day=0), irrespective of the culture methods. The mean diameters of AFLS during Days 4-14 using the individual culture method were significantly higher (p<0.05) than those using the group culture method. However, the AFLS formation rate in the individual culture method was significantly lower compared to that in the group culture method (26.1% vs 62.7%, p<0.01). Almost all oocytes had undergone the germinal vesicle breakdown stage, irrespective of the culture method or AFLS formation. In conclusion, comparison with the individual culture method revealed that the mean diameters of AFLS in the group culture method were smaller, but more COCs formed AFLS. The group culture method might be useful for evaluating the various hypotheses of follicular formation and interfollicular communication. However, improvement of the group culture system is necessary to prevent the meiotic resumption of oocytes, because the AFLS formation is dependent on the cumulus/granulosa cells surrounding oocytes.