Quality analysis of buffalo blastocysts derived from oocytes vitrified before or after enucleation and reconstructed with somatic cell nuclei

Current status of assisted reproductive technologies in buffaloes

Buffaloes are raised by small farm holders primarily as source of draft power owing to its resistance to hot climate, disease, and stress conditions. Over the years, transformation of these animals from draft to dairy was deliberately carried out through genetic improvement program leading to the development of buffalo-based enterprises. Buffalo production is now getting more attention and interest from buffalo raisers due to its socioeconomic impact as well as its contribution to propelling the livestock industry in many developing countries. Reproduction of buffaloes, however, is confronted with huge challenge and concern as being generally less efficient to reproduce compared with cattle due to both intrinsic and extrinsic factors such as poor estrus manifestation, silent heat, marked seasonal infertility, postpartum anestrus, long calving interval, delayed puberty, inherently low number of primordial follicles in their ovaries, high incidence of atresia, and apoptosis. Assisted reproductive technologies (ARTs) are major interventions for the efficient utilization of follicle reserve in buffaloes. The present review focuses on estrus and ovulation synchronization for fixed time artificial insemination, in vitro embryo production, intracytoplasmic sperm injection, cryopreservation of oocytes and embryos, somatic cell nuclear transfer, the factors affecting utilization in various ARTs, and future perspectives in buffaloes.

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.

Effective Oocyte Vitrification and Survival Techniques for Bovine Somatic Cell Nuclear Transfer

Bovine somatic cell nuclear transfer (SCNT) using vitrified-thawed (VT) oocytes has been studied; however, the cloning efficiency of these oocytes is not comparable with that of nonvitrified (non-V) fresh oocytes. This study sought to optimize the survival and cryopreservation of VT oocytes for SCNT. Co-culture with feeder cells that had been preincubated for 15 h significantly improved the survival of VT oocytes and their in vitro developmental potential following SCNT in comparison to co-culture with feeder cells that had been preincubated for 2, 5, or 24 h (p<0.05). Spindle assessment via the Oosight Microscopy Imaging System and microtubule staining revealed that vitrified metaphase II oocytes (VT group) were not suitable for SCNT. However, enucleating and/or activating oocytes prior to freezing enhanced their developmental potential and suitability for SCNT. The cloning efficiency of the enucleated-activated-vitrified-thawed (EAVT) group (21.6%) was better than that of the other vitrification groups [enucleated-vitrified-thawed (EVT) group, 13.7%; VT group, 15.0%; p<0.05] and was comparable with that of the non-V group (25.9%). The reactive oxygen species level was significantly lower in the EAVT group than in the other vitrification groups (p<0.05). mRNA levels of maternal genes (ZAR1, BMP15, and NLRP5) and a stress gene (HSF1) were lower in the vitrification groups than in the non-V group (p<0.05), whereas the level of phospho-p44/42 mitogen-activated protein kinase did not differ among the groups. Among the vitrification groups, blastocysts in the EAVT group had the best developmental potential, as judged by their high mRNA expression of developmental potential-related genes (POU5f1, Interferon-tau, and SLC2A5) and their low expression of proapoptotic (CASP3) and stress (Hsp70) genes. This study demonstrates that SCNT using bovine frozen-thawed oocytes can be successfully achieved using optimized vitrification and co-culture techniques.

Cryopreservation of immature buffalo oocytes: effects of cytochalasin B pretreatment on the efficiency of cryotop and solid surface vitrification methods

The aim of the present study was to compare the efficiency of the solid surface (SSV), cryotop (CT) vitrification methods and cytochalasin B (CB) pretreatment for cryopreservation of immature buffalo oocytes. Cumulus-oocyte complexes (COCs) were placed for 1 min in TCM199 containing 10% dimethylsulfoxide (DMSO), 10% ethylene glycol (EG), and 20% fetal bovine serum, and then transferred for 30 s to base medium containing 20% DMSO, 20% EG and 0.5 mol/L sucrose. CB pretreated ((+)CB) or non-pretreated ((-)CB) COCs were vitrified either by SSV or CT. Surviving vitrified COCs were selected for in vitro maturation (IVM) and in vitro fertilization (IVF). The rate of viable oocytes after vitrification in CT groups (82%) was significantly lower (P < 0.05) than that in a fresh control group (100%), but significantly higher (P < 0.05) than those in SSV groups (71-72%). Among vitrified groups, the highest maturation rate was obtained in the CT (-)CB group (32%). After IVF, the cleavage and blastocyst formation rates were similar among vitrified groups but significantly lower than those of the control group. In conclusion, a higher survival rate of oocytes after vitrification and IVM was obtained in the CT group compared with that in the SSV group, indicating the superiority of the CT method. Pretreatment with CB did not increase the viability, maturation or embryo development of vitrified oocytes.

Effect of donor cell types on developmental potential of cattle (Bos taurus) and swamp buffalo (Bubalus bubalis) cloned embryos

This study investigated the effect of donor cell types on the developmental potential and quality of cloned swamp buffalo embryos in comparison with cloned cattle embryos. Fetal fibroblasts (FFs), ear fibroblasts (EFs), granulosa cells (GCs) and cumulus cells (CCs) were used as the donor cells in both buffalo and cattle. The cloned cattle or buffalo embryos were produced by fusion of the individual donor cells with enucleated cattle or buffalo oocytes, respectively. The reconstructed (cloned) embryos and in vitro matured oocytes without enucleation were parthenogenetically activated (PA) and cultured for 7 days. Their developmental ability to the blastocyst stage was evaluated. The total number of trophectoderm (TE) and inner cell mass (ICM) cells and the ICM ratio in each blastocyst was determined by differential staining as an indicator of embryo quality. The fusion rate of CCs with enucleated oocytes was significantly lower than for those of other donor cell types both in cattle and buffalo. The rates of cleavage and development to the 8-cell, morula and blastocyst stages of cloned embryos derived from all donor cell types did not significantly differ within the same species. However, the cleavage rate of cloned cattle embryos derived from FFs was significantly higher than those of cattle PA and cloned buffalo embryos. The blastocyst rates of cloned cattle embryos, except for the ones derived from CCs, were significantly higher than those of cloned buffalo embryos. In buffalo, only cloned embryos derived from CCs showed a significantly higher blastocyst rate than that of PA embryos. In contrast, all the cloned cattle embryos showed significantly higher blastocyst rates than that of PA embryos. There was no difference in ICM ratio among any of the blastocysts derived from any of the donor cell types and PA embryos in both species. FFs, EFs, GCs and CCs had similar potentials to support development of cloned cattle and buffalo embryos to the blastocyst stage with the same quality.

Nuclear transfer and oocyte cryopreservation

Somatic cells can be reprogrammed to a totipotent state through nuclear transfer or cloning, because it has been demonstrated that the oocyte has the ability to reprogramme an adult nucleus into an embryonic state that can initiate the development of a new organism. Therapeutic cloning, whereby nuclear transfer is used to derive patient-specific embryonic stem cells, embraces an entire new opportunity for regenerative medicine. However, a key obstacle for human therapeutic cloning is that the source of fresh human oocytes is extremely limited. In the present review, we propose prospective sources of human oocytes by using oocyte cryopreservation, such as an oocyte bank and immature oocytes. We also address some potential issues associated with nuclear transfer when using cryopreserved oocytes. In the future, if the efficacy and efficiency of cryopreserved oocytes are comparable to those of fresh oocytes in human therapeutic cloning, the use of cryopreserved oocytes would be invaluable and generate a great impact to regenerative medicine.

Reproductive biotechniques in buffaloes (Bubalus bubalis): status, prospects and challenges

The swamp buffalo holds tremendous potential in the livestock sector in Asian and Mediterranean countries. Current needs are the faster multiplication of superior genotypes and the conservation of endangered buffalo breeds. Recent advances in assisted reproductive technologies, including in vitro embryo production methodologies, offer enormous opportunities to not only improve productivity, but also to use buffaloes to produce novel products for applications to human health and nutrition. The use of molecular genomics will undoubtedly advance these technologies for their large-scale application and resolve the key problems currently associated with advanced reproductive techniques, such as animal cloning, stem cell technology and transgenesis. Preliminary success in the application of modern reproductive technologies warrants further research at the cellular and molecular levels before their commercial exploitation in buffalo breeding programmes.