Effects of Different Activation Regimens on Pronuclear Formation and Developmental Competence of In Vitro-Matured Porcine Oocytes After Intracytoplasmic Sperm Injection

Effect of chemical activators after intracytoplasmic sperm injection (ICSI) on embryo development in alpacas

Low motility and low sperm concentration are characteristics of alpaca semen. Thus, the intracytoplasmic sperm injection (ICSI) technique represents an alternative to improve the reproductive capacity of the male. However, the effect of post-ICSI activation in alpaca is not yet known. The aim of the present study was to compare the effect of chemical activators on alpaca embryo development after ICSI. Alpaca ovaries were collected from a local slaughterhouse and transported to the laboratory. Category I, II and III oocytes were matured for 30 h at 38.5 °C. After ICSI, injected oocytes were randomly divided and activated as follows: i) 5 μM ionomycin for 5 min, ii) 7% ethanol for 4 min, iii) 5 μM ionomycin for 5 min, window period 3 h plus 7% ethanol for 4 min, iv) 5 μM ionomycin for 5 min, window period 3 h, a second ionomycin treatment for 5 min, followed by 1.9 mM 6-DMAP for 3 h, v) 10 mM SrCl2 for 3 h. Culture was carried out for 5 days in SOFaa at 38.5 °C. The cleavage rate was the lowest in the SrCl2 group, morula development was the lowest in the SrCl2 and without activation groups, and blastocyst stage was not different between groups (P<0.05). The rates with SrCl2 were lower in total embryos produced, whereas in transferable embryos they were lower with 2Io/6-DMAP and with SrCl2 (P<0.05). In conclusion, alpaca oocyte activation is more efficient with ionomycin and ethanol to produce transferable embryos.

A fast and reliable protocol for activation of porcine oocytes

Oocyte activation is physiologically triggered by the sperm during fertilization, however, production of porcine embryos by somatic cell nuclear transfer (SCNT), intracytoplasmic sperm injection (ICSI) or parthenogenetic activation (PA) requires artificial oocyte activation. Although effective protocols for artificial oocyte activation have been developed, current protocols require long exposures to non-specific inhibitors, which do not mimic the physiological process and may have detrimental consequences for embryo development. This study attempted to mimic the physiological activation events induced by fertilization, through the manipulation of Ca²⁺ and Zn²⁺ levels, and protein kinase C (PKC) as well as cyclin dependent kinase 1 (CDK1) activities, with the aim of developing an improved protocol for activation of porcine oocytes. In the first experiment, matured oocytes were exposed to ionomycin (Ion) for 5 min, and then treated with a specific CDK1 inhibitor (RO-3306) and/or PKC activator (OAG) for different time intervals. The highest rate of pronuclear (PN) formation (58.8%) was obtained when oocytes were treated with PKCa + CDK1i for 4 h. Second, PN formation and embryo development were evaluated in oocytes exposed for different times to a Zn²⁺ chelator (TPEN) following Ion treatment. This revealed that 15 min was the minimal exposure time to TPEN required to maximise oocyte activation and embryo development. Next, we observed that treatment with PKCa + CDK1i for 4 h after TPEN for 15 min decreased embryo development compared to TPEN alone. Lastly, we compared the efficiency of the Ion (5 min) plus TPEN (15 min) protocol (IT-20) with a control protocol used in our laboratory (CT-245) for production of PA, SCNT and ICSI embryos. In PA embryos, IT-20 resulted in higher cleavage (72% vs 49.2%) and blastocyst from cleaved embryos (65.5% vs 46.2%) compared to CT-245. In ICSI embryos, higher PN rates were obtained with the IT-20 protocol compared with CT-245 and the non-activated (N-A) group. Moreover, the two protocols were equally efficient for activation of SCNT embryos. Based on these findings, we propose that IT-20 is a fast and effective protocol for activation of porcine oocytes.