The effect of electrical field strength on activation and development of cloned caprine embryos

Hand-made cloned goat (Capra hircus) embryos—a comparison of different donor cells and culture systems

Nuclear transfer is a very effective method for propagation of valuable, extinct, and endangered animals. Hand-made cloning (HMC) is an efficient alternative to the conventional micromanipulator-based technique in some domestic species. The present study was carried out for the selection of suitable somatic cells as a nuclear donor and development of an optimum culture system for in vitro culture of zona-free goat cloned embryos. Cleavage and blastocyst rates were observed 72.06 ± 2.94% and 0% for fresh cumulus cells, 81.95 ± 3.40% and 12.74 ± 2.12% for cultured cumulus cells, and 92.94 ± 0.91% and 23.78 ± 3.33% for fetal fibroblast cells, respectively. There was a significant (p < 0.05) increase in blastocyst production in goats when cultured on a flat surface (FS) (23.78 ± 3.33 %) than well of wells (WOW) (15.84 ± 2.12 %) and microdrops (MD) (0.7 ± 0.7%). Furthermore, cleavage and blastocyst production rates were significantly (p < 0.05) more in the WOW (15.84 ± 2.12%) than the MD (0.7 ± 0.7%) system. The quality of HMC blastocysts was studied by differential staining. Genetic similarity was confirmed by polymerase chain reaction (PCR)-based amplification of the second exon of the MHC class II DRB gene, which gave similar bands in electrophoresis (286 bp) both in cloned embryos and donor cells. In conclusion, the present study describes that the fetal fibroblast cell is a suitable candidate as nuclear donor, and the flat surface culture system is suitable for zona-free blastocyst development by the hand-made cloning technique in the goat.

Applications of RNA interference-based gene silencing in animal agriculture

Classical genetic selection, recently aided by genomic selection tools, has been successful in achieving remarkable progress in livestock improvement. However, genetic selection has led to decreased genetic diversity and, in some cases, acquisition of undesirable traits. In order to meet the increased demands of our expanding population, new technologies and practices must be developed that contend with zoonotic and animal disease, environmental impacts of large farming operations and the increased food and fibre production needed to feed and clothe our society. Future increases in productivity may be dependent upon the acquisition of genetic traits not currently encoded by the genomes of animals used in standard agricultural practice, thus making classical genetic selection impossible. Genetic engineering of livestock is commonly used to produce pharmaceuticals or to impart enhanced production characteristics to animals, but has also demonstrated its usefulness in producing animals with disease resistance. However, significant challenges remain because it has been more difficult to produce animals in which specific genes have been removed. It is now possible to modify livestock genomes to block expression of endogenous and exogenous genes (such as those expressed following virus infection). In the present review, we discuss mechanisms of silencing gene expression via the biology of RNA interference (RNAi), the technology of activating the RNAi pathway and the application of this technology to enhance livestock production through increased production efficiency and prevention of disease. An increased demand for sustainable food production is at the forefront of scientific challenges and RNAi technology will undoubtedly play a key role.

In vitrodevelopment of goat parthenogenetic and somatic cell nuclear transfer embryos derived from different activation protocols

Oocyte activation is an essential step in animal cloning to allow subsequent development of the reconstructed embryos. A special activation protocol is required for different animal species. The present study investigated low temperature, electrical pulses, ethanol, ionomycin and strontium for goat oocyte activation in order to optimize the protocols. We found, as a result, effective activation and parthenogenetic development of goat oocytes that had been derived from ionomycin, strontium and electrical pulse groups. Within each group 79.3–81.6%, 2.2–78.8% and 65.5% of the oocytes cleaved and 16.2–24.8%, 0–15.6% and 11.1% of the cleaved embryos developed into blastocysts when the oocytes were activated by ionomycin combined with 6-dimethylaminopurine, strontium plus cytochalasin B and electrical pulses combined with cytochalasin B, respectively. However, low temperature and ethanol were both unable to activate goat oocytes under our experimental conditions. When ionomycin combined with 6-dimethylaminopurine and strontium plus cytochalasin B was applied to activate somatic cell nuclear transfer embryos derived from cultured cumulus, 51.0% and 72.5% of the embryos cleaved, respectively. After transfer of 4-cell embryos into recipients, one (1/19 and 1/7) of the recipients from each group was found to be pregnant as detected by ultrasound, but both of these recipients lost the embryos between 45 and 60 days of pregnancy.

Optimized combined electrical–chemical parthenogenetic activation for in vitro matured bovine oocytes

Sperm-mediated oocyte activation is a complex procedure, both in steps and duration, not yet been completely mimicked during in vitro studies, e.g., parthenogenesis or somatic cell nuclear transfer. Furthermore, parthenogenetic studies have been recognized as a suitable model for studying activation efficiency for nuclear transfer cloning. This study, therefore, was conducted to develop an optimized artificial activation method, based on bovine cloning. In vitro matured bovine oocytes were initially exposed to electrical pulse, used for cell fusion during cloning, and then treated with 15 temporal sequential combinations of 3 chemical activators [calcium ionophore (CI), strontium (SR) and ethanol (ET)], followed by exposure to a protein kinase inhibitor or used for in vitro fertilization as control group. Treated and naturally fertilized oocytes were further cultured for up to 8 days. Embryo development was scored daily and blastocyst cell counting was carried out using differential staining at day 8 of culture. Among 15 temporal sequential combinations of three chemical activators, the best cleavage rates were associated with double (SR-CI, 84.4%), triple (CI-SR-ET, 79.4%) and single (CI, 73.7%) compounds, respectively, which were not significantly different with each other and with in vitro fertilized (IVF) (85.5%). The highest blastocyst rates were gained with ET-SR (24.5%), SR-CI-ET (20.4%) and CI (24.5%) accordingly which were not significantly different with each other but significantly lower than IVF (47%). Embryo cell counting further confirmed reasonably better quality of blastocysts produced using double, triple and single compounds. Although most of the sequential artificial activation compounds induced high cleavage rate, close to IVF, but this did not assure comparable further embryo development to the blastocyst stage. Nevertheless, the results suggest exposure of in vitro matured bovine oocytes to electrical pulse, followed by exposure to CI-6-dimethylaminopurine (6-DMAP) or ET-SR-6-DMAP could be regarded as the optimal artificial activation protocol for in vitro development of parthenogenic bovine oocytes or as a step for activation protocol in cloning procedure.

The effect of activation treatments on the development of reconstructed bovine oocytes

The purpose of this study was to investigate the effect of different activation treatments on the development of IVM-derived and cloned bovine embryos. The effect of oocyte age (20h versus 24h after IVM) on the blastocyst rate was also investigated. No differences in the percentage of blastocyst development were observed between the oocytes matured for 20 and 24h (15% versus 27%, p>0.05). Reconstructed oocytes activated 4h after fusion (fusion before activation, FBA) had a higher blastocyst rate than those oocytes activated immediately after electrofusion (fusion and activation simultaneously, FAS) (26% versus 5%, p<0.01). Blastocyst rates were significantly greater (p<0.01) for the reconstructed oocytes activated by calcium ionophore (A23187) combined with 6-dimethylaminopurine (6-DMAP) (51.6%) than for those activated with cycloheximide (CHX) plus cytochalasin B (CB) treatment (1h, 8.2%; 5h, 14.3%). However, the blastocyst rates were similar among reconstructed oocytes activated by electric pulses and A23187 (30.5% versus 42.2%) or by A23187 and ionomycin (36.7% versus 33.3%) combined with 6-DMAP, respectively. Blastocysts that developed from reconstructed oocytes activated by A23187 and 6-DMAP resulted in three pregnancies (3/9) and one live birth from 18 embryos transferred to recipient cows. Genotypic analysis of six bovine microsatellite markers by polymerase chain reaction confirmed that the cloned calf was genetically identical to the nuclear donor. In conclusion, reconstructed oocytes that derived from oocytes exposed to activation treatment 4h after electrofusion are more likely to develop to the blastocyst stage. The best treatment to activate reconstructed bovine oocytes in this study was A23187 combined with 6-DMAP.

Suppression of prion protein in livestock by RNA interference

Given the difficulty of applying gene knockout technology to species other than mice, we decided to explore the utility of RNA interference (RNAi) in silencing the expression of genes in livestock. Short hairpin RNAs (shRNAs) were designed and screened for their ability to suppress the expression of caprine and bovine prion protein (PrP). Lentiviral vectors were used to deliver a transgene expressing GFP and an shRNA targeting PrP into goat fibroblasts. These cells were then used for nuclear transplantation to produce a cloned goat fetus, which was surgically recovered at 81 days of gestation and compared with an age-matched control derived by natural mating. All tissues examined in the cloned fetus expressed GFP, and PCR analysis confirmed the presence of the transgene encoding the PrP shRNA. Most relevant, Western blot analysis performed on brain tissues comparing the transgenic fetus with control demonstrated a significant (>90%) decrease in PrP expression levels. To confirm that similar methodologies could be applied to the bovine, recombinant virus was injected into the perivitelline space of bovine ova. After in vitro fertilization and culture, 76% of the blastocysts exhibited GFP expression, indicative that they expressed shRNAs targeting PrP. Our results provide strong evidence that the approach described here will be useful in producing transgenic livestock conferring potential disease resistance and provide an effective strategy for suppressing gene expression in a variety of large-animal models.