Electrical Activation Enhances Pre-Implantation Embryo Development Following Sperm Injection into <i>In Vitro</i> Matured Pig Oocytes

Abstract

ABSTRACT. The objective of this study was to evaluate the effect of electrical stimulation (EST) on pronuclear formation, chromosomal constitution, and developmental capability among in vitro matured pig oocytes following intracytoplasmic sperm injection (ICSI). After ICSI, the oocytes were randomly distributed and cultured into 3 groups: the EST activated ICSI group, non-activation ICSI group, and in vitro fertilization (IVF) group. The proportion of oocytes in which 2 pronuclei were formed in ICSI groups was significantly higher in the former groups than in the IVF group (96.2 and 93.5 vs. 64.5%, respectively, P<0.05). The cleavage rate was significantly higher in EST activated ICSI group (78.6%) than in the IVF and non-activated ICSI groups (51.8 and 46.0%, respectively, P<0.05), as was the proportion of oocytes that developed to the blastocyst stage at day 7 (18.9 vs. 11.6 and 9.1%, respectively, P<0.05). Diploid blastocysts were observed in 52.4, 63.0, and 65.2% of oocytes in the IVF, activated, and non-activated ICSI groups, respectively. Eight out of 23 gilts (34.8%) were confirmed to be pregnant in activated ICSI groups, but none of these pregnancies were carried to term. These results show that oocyte activation after ICSI is effective in elevating the cleavage rate and blastocyst development, while ensuring normal chromosome composition. Further research is needed to determine the pregnancy maintenance requirements for ICSI-embryos in pigs. KEY Intracytoplasmic sperm injection (ICSI) is a valuable assisted reproduction technology for studying fertilization, treating human infertility, and producing transgenic animals. In humans, ICSI has become a widely applied means of overcoming infertility. In addition to its clinical usefulness, ICSI can be a valuable research tool for studying the fundamental aspects of interaction between 2 gametes during fertilization. Since the first report of the use of ICSI in mammals [38], several successful attempts to produce live offspring with ICSI using both in vivo matured [27,37] and in vitro matured [2] oocytes have been reported. In pigs, successful production of offspring after ICSI has been reported mostly with in vivo matured oocytes [12,21]. The use of ICSI-fertilized porcine in vitro matured oocytes resulted in the death of a piglet immediately after birth [17]. Recently, Nakai et al. [24] reported 3 healthy piglets produced by ICSI for the first time using in vitro matured porcine oocytes. In several species such as rabbits [19], hamsters [5], and mice [15,26], injection of the sperm itself is apparently sufficient to activate the oocyte, as the sperm nucleus can undergo decondensation and form a pronucleus (PN).Compared with other species, the ICSI procedure has not been well established in pigs, partially because of activation of in vitro matured oocytes after ICSI, which lowers the fertilization rate and results in abnormal development of ICSI-fertilized porcine and bovine oocytes [18]. Thus, it appears that sperm preparation and post-ICSI oocyte activati...

Recent advances in critical nodes of embryo engineering technology

“…Electrical stimulation is also widely used in ICSI to stimulate oocytes. Experimental studies have been conducted on many animals, such as rabbits 137 , 138 , pigs 139 , and humans 140 - 142 . The specific research content and conclusions are summarized in Table 4 .…”

Developmental and Degenerative Characterization of Porcine Parthenogenetic Fetuses during Early Pregnancy

“…In assisted reproductive technology (ART) programs, physicians and scientists have used a variety of mechanical, electrical, and chemical stimuli that mimic the induction of cytoplasmic calcium oscillation needed to activate oocytes after intracytoplasmic sperm injection (ICSI) or round spermatid injection (ROSI), resulting in high fertilization and pregnancy rates [1,2].…”