Changes in MPF and MAPK activities in porcine oocytes activated by different methods

Chemical activation of mammalian oocytes and its application in camelid reproductive biotechnologies: A review

Mammalian oocyte activation is a critical process occurring post-gamete fusion, marked by a sequence of cellular events initiated by an upsurge in intracellular Ca2+. This surge in calcium orchestrates the activation/deactivation of specific kinases, leading to the subsequent inactivation of MPF and MAPK activities, alongside PKC activation. Despite various attempts to induce artificial activation using distinct chemical compounds as Ca2+ inducers and/or Ca2+-independent agents, the outcomes have proven suboptimal. Notably, incomplete suppression of MPF and MAPK activities persists, necessitating a combination of different agents for enhanced efficiency. Moreover, the inherent specificity of activation methods for each species precludes straightforward extrapolation between them. Consequently, optimization of protocols for each species and for each technique, such as PA, ICSI, and SCNT, is required. Despite recent strides in camelid biotechnologies, the field has seen little advancement in chemical activation methods. Only a limited number of chemical agents have been explored, and the effects of many remain unknown. In ICSI, despite obtaining blastocysts with different chemical compounds that induce Ca2+ and calcium-independent increases, viable offspring have not been obtained. However, SCNT has exhibited varying outcomes, successfully yielding viable offspring with a reduced number of chemical activators. This article comprehensively reviews the current understanding of the physiological activation of oocytes and the molecular mechanisms underlying chemical activation in mammals. The aim is to transfer and apply this knowledge to camelid reproductive biotechnologies, with emphasis on chemical activation in PA, ICSI, and SCNT.

Effects of triton X-100 pretreatment of lyophilized and frozen-thawed ram sperm on preimplantation embryo developmental competence

In this study, it was aimed to determine the effect of destruction of lyophilized and frozen-thawed ram sperm plasma and acrosomal membrane on development of embryos produced by intracytoplasmic sperm injection (ICSI). Semen samples were divided into two groups for lyophilization (L) and freezing (F). For the removal of the plasma membrane, L and F groups were incubated with Triton X-100 (LTX-100 and FTX-100, respectively). Integrities of the plasma membrane, acrosome and chromatin structure were evaluated. Oocytes were injected with these sperm groups. Although no plasma membrane and acrosome integrities of the L (0.0%) group were detected, the plasma membrane integrity of the F group (69.4%) was significantly higher than the FTX-100 group (23.6%) (p < 0.05). The acrosome integrity of the FTX-100 group (3.80%) was significantly lower than the F group (55.6%) (p < 0.05). The chromatin integrities of L and F groups were higher than the Triton X-100 treated groups (p < 0.05). ICSIs with L, LTX-100, F and FTX-100 sperm were produced similar cleavage and blastocyst rates. In conclusion, data presented here confirm that ram spermatozoa can effectively be lyophilized and injected into oocytes for initiation of embryonic development and Triton X-100 pretreatment is not necessary while using lyophilized and frozen semen.

Design of novel oocyte activation methods: The role of zinc

Oocyte activation occurs at the time of fertilization and is a series of cellular events initiated by intracellular Ca2+ increases. Consequently, oocytes are alleviated from their arrested state in meiotic metaphase II (MII), allowing for the completion of meiosis. Oocyte activation is also an essential step for somatic cell nuclear transfer (SCNT) and an important tool to overcome clinical infertility. Traditional artificial activation methods aim to mimic the intracellular Ca2+ changes which occur during fertilization. Recent studies emphasize the importance of cytoplasmic Zn2+ on oocyte maturation and the completion of meiosis, thus suggesting artificial oocyte activation approaches that are centered around the concentration of available Zn2+in oocytes. Depletion of intracellular Zn2+ in oocytes with heavy metal chelators leads to successful oocyte activation in the absence of cellular Ca2+ changes, indicating that successful oocyte activation does not always depends on intracellular Ca2+ increases. Current findings lead to new approaches to artificially activate mammalian oocytes by reducing available Zn2+ contents, and the approaches improve the outcome of oocyte activation when combined with existing Ca2+ based oocyte activation methods. Here, we review the important role of Ca2+ and Zn2+ in mammalian oocyte activation and development of novel oocyte activation approaches based on Zn2+ availability.

The developmental competence of oocytes parthenogenetically activated by an electric pulse and anisomycin treatment

OBJECTIVE

The aim of this study was to investigate the developmental competence of oocytes parthenogenetically activated by an electric pulse (EP) and treated with anisomycin and to determine whether this method is applicable to somatic cell nuclear transfer (SCNT).

RESULTS

Embryos derived from porcine oocytes parthenogenetically activated by an EP and treatment with 0.01 µg/mL anisomycin had a significantly improved in vitro developmental capacity. Furthermore, 66.6% of blastocysts derived from these embryos had a diploid karyotype. The blastocyst formation rate of cloned embryos was similar between oocytes activated by an EP and treated with 2 mM 6-dimethylaminopurine for 4 h and those activated by an EP and treated with 0.01 µg/mL anisomycin for 4 h. The level of maturation-promoting factor was significantly decreased in oocytes activated by an EP and treated with anisomycin. Finally, the mRNA expression levels of apoptosis-related genes (Bax and Bcl-2) and pluripotency-related genes (Oct4, Nanog, and Sox2) were checked by RT-PCR.

CONCLUSION

Our results demonstrate that porcine oocyte activation via an EP in combination with anisomycin treatment can lead to a high blastocyst formation rate in parthenogenetic activation and SCNT experiments.

An Improved System for Generation of Diploid Cloned Porcine Embryos Using Induced Pluripotent Stem Cells Synchronized to Metaphase

Pigs provide outstanding models of human genetic diseases due to their striking similarities with human anatomy, physiology and genetics. Although transgenic pigs have been produced using genetically modified somatic cells and nuclear transfer (SCNT), the cloning efficiency was extremely low. Here, we report an improved method to produce diploid cloned embryos from porcine induced pluripotent stem cells (piPSCs), which were synchronized to the G2/M stage using a double blocking method with aphidicolin and nocodazole. The efficiency of this synchronization method on our piPSC lines was first tested. Then, we modified our traditional SCNT protocol to find a workable protocol. In particular, the removal of a 6DMAP treatment post-activation enhanced the extrusion rate of pseudo-second-polar bodies (p2PB) (81.3% vs. 15.8%, based on peak time, 4hpa). Moreover, an immediate activation method yielded significantly more blastocysts than delayed activation (31.3% vs. 16.0%, based on fused embryos). The immunofluorescent results confirmed the effect of the 6DMAP treatment removal, showing remarkable p2PB extrusion during a series of nuclear transfer procedures. The reconstructed embryos from metaphase piPSCs with our modified protocol demonstrated normal morphology at 2-cell, 4-cell and blastocyst stages and a high rate of normal karyotype. This study demonstrated a new and efficient way to produce viable cloned embryos from piPSCs when synchronized to the G2/M phase of the cell cycle, which may lead to opportunities to produce cloned pigs from piPSCs more efficiently.

Pig oocyte activation using a Zn²⁺ chelator, TPEN

Artificial oocyte activation is a critical step during SCNT. Most current activation protocols focus on inducing an increase in the intracellular free Ca(2+) concentration of the oocyte. Here, we have used a zinc chelator, TPEN, to enhance the efficiency of oocyte activation during SCNT. TPEN treatment of matured pig oocytes resulted in the reduction of available Zn(2+) in pig oocytes; however, the cytosolic Ca(2+) concentration in the oocytes was not affected by the TPEN treatment. When various concentrations (100-250 μM) and incubation durations (45 minutes-2.5 hours) of TPEN were used to activate oocytes, the efficiency of oocyte activation was not different from conventional activation methods. When oocytes that were activated by conventional activation methods were incubated with a lower concentration of TPEN (5-10 μM), a significant increase in embryos developing to the blastocyst stage was observed. In addition, when oocytes receiving a small Ca(2+) stimulus were further activated by higher concentration of TPEN (100-200 μM), a significant increase in the frequency of blastocyst formation was observed, compared to a conventional activation method. This result indicated that TPEN can be a main reagent in oocyte activation. No increase in the cytosolic Ca(2+) level was detected when oocytes were exposed to various concentrations of TPEN, indicating the ability of TPEN to induce oocyte activation is independent of an intracellular Ca(2+) increase. We were able to produce clones through SCNT by using the TPEN-assisted activation procedure, and the piglets produced through the process did not show any signs of abnormality. In this study, we have developed an efficient way to use TPEN to increase the developmental potential of cloned embryos.

Short-term treatment with 6-DMAP and demecolcine improves developmental competence of electrically or Thi/DTT-activated porcine parthenogenetic embryos

Treatment with 6-dimethylaminopurine (6-DMAP) or demecolcine (DE) for several (at least 2) hours after artificial activation is known to improvein vitrodevelopment of porcine embryos. However, several reports have also shown that treatments with these chemicals induce apoptosis. The aim of this study was to find out whether short-term treatment with 6-DMAP and DE combined with electrical or thimerosal/dithiothreitol (Thi/DTT) activation had a beneficial effect on development of parthenogenetically activated porcine oocytes. We additionally treated embryos with 6-DMAP (2 mM) and/or DE (0.4 μg/ml) for a short time (40 min) after an electrical pulse (EP) or Thi/DTT. As a result, short-term treatment with 6-DMAP and DE successfully induced development of electrically or Thi/DTT-activated porcine parthenogenetic embryos with no significant difference in cleavage rate, blastocyst formation rate and total cell number compared with long-term treatment. To find optimal activation protocol, cleavage rate, blastocyst formation rate and total cell number were compared between EP and Thi/DTT treatments. Thi/DTT + 6-DMAP + DE showed significantly higher blastocyst formation rate (36.1 ± 3.5%) and total cell number (46.9 ± 1.0) than other groups (EP + 6-DMAP + DE, EP + Thi/DTT + 6-DMAP + DE: 23.3 ± 3.0%, 42.2 ± 1.1 and 17.2 ± 2.7%, 36.7 ± 1.5, respectively). In conclusion, this study demonstrates that short-term treatment with 6-DMAP and DE is as effective as the standard long-term treatment and Thi/DTT + 6-DMAP + DE exerts a synergistic effect.