High rate of activation and fertilisation following intracytoplasmatic sperm injection (ICSI) in cattle

Combined Exogenous Activation of Bovine Oocytes: Effects on Maturation-Promoting Factor, Mitogen-Activated Protein Kinases, and Embryonic Competence

Oocyte activation via dual inhibition of protein synthesis and phosphorylation has improved in vitro embryo production in different mammalian species. In this study, we evaluated the effects of the combination of cycloheximide (CHX), dimethyl amino purine (DMAP), and anisomycin (ANY) on the activation of bovine oocytes, particularly on dynamics of MPF and MAPKs, embryonic developmental potential, and quality. The results showed that the cleavage and blastocyst rates, as well as levels of CCNB1, CDK1, p-CDK1Thr161, and p-CDK1Thr14-Tyr15, were similar among groups; ANY and ANY + CHX reduced the expression of ERK1/2 compared to DMAP-combinations (p < 0.05), whereas ANY + DMAP, CHX + DMAP, and ANY + CHX + DMAP reduced p-ERK1/2 compared to ANY and ANY + CHX treatments (p < 0.05). The quality of blastocysts in terms of cell counts, their allocation, and the numbers of TUNEL-positive cells did not differ among groups. However, transcript levels of POU5F1 were higher in embryos derived from ANY + CHX + DMAP treatment compared to other groups, while expression levels of CDX2 did not show differences. In addition, the BCL2A1/BAX ratio of the ANY + CHX + DMAP treatment was significantly low compared to the ANY treatment (p < 0.05) and did not differ significantly from the other treatments. In conclusion, oocyte activation by dual inhibition of protein synthesis and phosphorylation induces MPF inactivation without degradation of CCNB1, while MAPK inactivation occurs differentially between these inhibitors. Thus, although the combined use of these inhibitors does not affect early developmental competence in vitro, it positively impacts the expression of transcripts associated with embryonic quality.

Effect of anisomycin, a protein synthesis inhibitor, on the in vitro developmental potential, ploidy and embryo quality of bovine ICSI embryos

Increasing the efficiency of intracytoplasmic sperm injection (ICSI) in domestic animals has been attempted by many researchers, however embryonic development to the blastocyst stage remains low compared with that of in vitro fertilization (IVF) embryos. One of the main problems observed in cattle is inadequate oocyte activation after ICSI. The present study compared the effect of cycloheximide (CHX), 6-dimethylaminopurine (DMAP), and anisomycin (ANY) on the fertilization rate, development, ploidy and quality of bovine embryos generated by ICSI. Although no differences were observed between treatments in terms of cleavage, higher blastocyst rates were observed for ANY (37.3%) compared with CHX (21.8%, P 0.05) treatments. No differences were observed in the quality of embryos as assessed by the total number of cells, their distribution to the different embryo compartments [inner cell mass (ICM) and trophectoderm (TE)], the proportion of ICM cells to the total cell numbers and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL)-positive cells. Similarly, no differences were observed in the normal ploidy of embryos (56, 67, and 55%) for ANY, CHX and DMAP, respectively. However, higher fertilization rates were observed for ANY (75%) and CHX (87%) treatments compared with DMAP (35%). In conclusion, ANY showed a superior developmental rate compared with CHX treatment. Although no significant differences were observed compared with an improved protocol of DMAP (2Io-DMAP), the lower fertilization rate recorded with DMAP strongly suggests that ANY could be a better alternative for oocyte activation than traditional chemical compounds used currently in ICSI.

Improved embryo development in Japanese black cattle by in vitro fertilization using ovum pick-up plus intracytoplasmic sperm injection with dithiothreitol

The purpose of this study was to determine whether dithiothreitol (DTT) treatment of sperm and ethanol activation improve embryo production by intracytoplasmic sperm injection (ICSI). Further, we compared ICSI with standard in vitro fertilization (IVF) in oocytes obtained from cattle. We demonstrated that DTT reduced the disulfide bond in the bovine sperm head. Using oocytes obtained from a slaughterhouse, ICSI-DTT treatment without ethanol showed the highest rate of blastocyst formation. We applied these results to fertilization using ovum pick-up (OPU). Eleven Japanese black cattle served as donors for OPU plus standard IVF (OPU-IVF). Of them, four donors with low embryo development rates were selected to determine whether embryo development was enhanced by OPU plus ICSI (OPU-ICSI). We assessed effects on embryo development following IVF and ICSI in oocytes obtained using OPU. Blastocyst rates were significantly higher for OPU-ICSI than for OPU-IVF. Our results suggest that OPU-ICSI improves the blastocyst development rate in donors with low embryo production compared with the standard OPU-IVF.

Bovine embryo development following ICSI: effect of activation, sperm capacitation and pre-treatment with dithiothreitol

The development of bovine embryos obtained by intracytoplasmic sperm injection (ICSI) was studied in relation to various treatments applied to the sperm and to the early embryo. We investigated the effect of different activation protocols on ICSI-embryos and the influence of sperm capacitation with heparin and D-penicillamine, hypotaurine, and epinephrine (PHE) prior to ICSI. Finally, we studied the effect of dithiothreitol (DTT) pre-treatment of sperm or of injected oocytes. The activation of ICSI-embryos by ionomycin (Io)-cycloheximide (CHX) and sperm pre-treatment with heparin in combination with PHE did not increase the developmental capacity of ICSI-embryos. By contrast, the treatment of injected oocytes with 2 mM DTT resulted in increased cleavage and blastocyst rates in the group of non-activated embryos and in acceleration of blastocyst development in the group of activated embryos. Similarly, pre-treatment of sperm with DTT, followed by ICSI and activation, determined an increase of embryo development on Day 7 although the total number of blastocysts recorded on Day 8 was not different from untreated controls. The transfer of 11 ICSI-blastocysts, produced without activation, in six recipients gave rise to two pregnancies of which one went to term with the birth of an healthy calf.

Comparison of microinjection (piezo-electric) and cell fusion for nuclear transfer success with different cell types in cattle

Amongst the many variables that can determine success of cloning, the source of nuclei, the procedure used for nuclear transfer, and the activation of the reconstructed embryo are very important aspects. In this study, we have compared the two most common procedures for transferring nuclei to enucleated oocytes--cell fusion (CF) and piezoelectric microinjection (PEM) using different somatic cells--and we have investigated the effect of different activation procedures. Granulosa cells and fibroblasts were grown to confluency or in low serum to induce a quiescent state, while lymphocytes were thawed immediately prior to use. Enucleated oocytes were reconstructed either with CF or PME by 21-23 h postmaturation. For cell fusion, one pulse of 1 kVolt/cm for 30 microsec was used; for PEM, the cell membrane was broken by repeated pipetting and transferred in a 12% PVP solution to facilitate injection. Manipulated oocytes were activated with ionomycin and cycloheximide (CHX) or 6-DMAP (DMAP) and cultured in microdrops of SOF-BSA-AA. On day 7 (day 0: nuclear transfer), embryo development was evaluated and embryos were either transferred fresh or were frozen. More embryos were successfully reconstructed with PEM than CF, but a higher number of reconstructed embryos by CF developed to blastocyst at D + 7. In addition, in both systems more embryos were obtained after activation with DMAP than with CHX. The transfer of 141 embryos to recipients resulted in a pregnancy rate of 50%, and no differences were observed between the source of donor cell, the reconstruction methods, or the activation protocol. Six calves were delivered at term, and four survived. High pregnancy losses were observed throughout the gestation period.

Activation of bovine oocytes following intracytoplasmic sperm injection (ICSI)

In the human and the mouse, intracytoplasmic sperm injection (ICSI) apparently triggers normal fertilization and may result in offspring. In the bovine, injection of spermatozoa must be accompanied by artificial methods of oocyte activation in order to achieve normal fertilization events (e.g., pronuclear formation). In this study, different methods of oocyte activation were tested following ICSI of in vitro-matured bovine oocytes. Bovine oocytes were centrifuged to facilitate sperm injection, and spermatozoa were pretreated with 5 mM dithiothreitol (DTT) to promote decondensation. Sperm-injected or sham-injected oocytes were activated with 5 microM ionomycin (A23187). Three hours after activation, oocytes with second polar bodies were selected and treated with 1.9 mM 6-dimethylaminopurine (DMAP). The cleavage rate of sperm-injected oocytes treated with ionomycin and DMAP was higher than with ionomycin alone (62 vs 27%, P < or = 0.05). Blastocysts (2 of 41 cleaved) were obtained only from the sperm-injected, ionomycin + DMAP-treated oocytes. Upon examination 16 h after ICSI, pronuclear formation was observed in 33 of 47 (70%) DMAP-treated oocytes. Two pronuclei were present in 18 of 33 (55%), while 1 and 3 pronuclei were seen in 8 of 33 (24%) and 7 of 33 (21%) oocytes, respectively. In sham-injected oocytes, pronuclear formation was observed in 15 of 38 (39%) with 9 (60%) having 2 pronuclei. Asa single calcium stimulation was insufficient and DMAP treatment could result in triploidy, activation by multiple calcium stimulations was tested. Three calcium stimulations (5 microM ionomycin) were given at 30-min intervals following ICSI. Two pronuclei were found in 12 of 41 (29%) injected oocytes. Increasing the concentration of ionomycin from 5 to 50 microM resulted in a higher rate of activation (41 vs 26%). The rate of metaphase III arrest was lower while the rate of pronuclear formation and cleavage development was higher in sperm-injected than sham-injected oocytes, suggesting that spermatozoa contribute to the activation process. Further improvements in oocyte activation following ICSI in the bovine are necessary.