Abstract
Simple SummaryTo increase the early implantation rate, oocytes and zygotes have been subjected to various artificial stimulations before and/or after in vitro fertilization, nuclear transfer, or sperm (spermatid) injection, etc. However, the stimulation process may induce parthenogenetic development. It is difficult to identify whether the embryo or fetus is normally fertilized or parthenogenetically activated in early pregnancy. In the present study, the porcine parthenotes originated from electric stimulation implanted and developed normally during the first month, in a manner similar to artificially inseminated embryos and fetuses. There were no statistical differences in the formation of the major organs such as the brain, liver, kidney, or heart in both groups. However, the implanted parthenotes radically ceased their development and degenerated after one month. It can be postulated that the parthenotes are one of the reasons for the gap between early pregnancy and delivery rate in assisted reproduction techniques.The difference between early pregnancy and delivery rate is quite large in assisted reproduction techniques (ARTs), including animal cloning. However, it is not clear why the implanted fetuses aborted after the early pregnancy stage. In the present study, we tried to evaluate the developmental and morphological characteristics of porcine parthenogenetically activated (PA) embryos or fetuses by electric stimulation during the early pregnancy period. The implanted PA and artificially inseminated (AI) embryos and fetuses were collected at day 26 and 35 after embryo transfer, respectively. The developmental and morphological parameters in the PA embryos at day 26 were similar to the AI embryos. The size, weight, formation of major organs, and apoptotic cells were not statistically different in both embryos at day 26. However, the PA fetuses at day 35 showed ceased fetal development and degenerated with abnormal morphologies in their organs. The day 35 PA fetuses showed significantly higher apoptotic cells and lower methylation status in three differentially methylated regions of the H19 gene compared to their comparators. Therefore, the normal development of PA embryos and fetuses during early gestation could lead to these pregnancies being misinterpreted as normal and become one of the main reasons for the gap between early pregnancy and delivery rate.
Highlights
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].Electrical stimulation is commonly used to activate mammalian oocytes, along with other methods, including other assisted reproduction techniques (ARTs) methods [3,4,5] and cell fusion for somatic cell nuclear transfer (SCNT)in mammals [6,7]
The influence of paternal factors derived from sperm during fertilization is very important in embryonic and placental development, parthenogenetic embryos and fetuses can be generated to serve as robust models to study embryonic development and embryonic-maternal recognition during pre- and post-implantation stages
Pig parthenogenetically activated (PA) embryos derived from oocytes obtained by in vitro maturation (IVM) and activated by electrical stimulation could still be detected by ultrasonography after one month of gestation [12]
Summary
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].Electrical stimulation is commonly used to activate mammalian oocytes, along with other methods, including other ART methods [3,4,5] and cell fusion for somatic cell nuclear transfer (SCNT)in mammals [6,7]. Electrical stimulation triggers calcium influx by forming pores in the plasma membrane to initiate a second meiotic cell cycle [8,9]. It can activate oocytes for the generation of parthenogenetically activated (PA) embryos. The influence of paternal factors derived from sperm during fertilization is very important in embryonic and placental development, parthenogenetic embryos and fetuses can be generated to serve as robust models to study embryonic development and embryonic-maternal recognition during pre- and post-implantation stages. Parthenogenetic embryos without paternally expressed imprinted genes can be implanted and developed to the fetus stage up to early pregnancy [11]. Pig PA embryos derived from oocytes obtained by in vitro maturation (IVM) and activated by electrical stimulation could still be detected by ultrasonography after one month of gestation [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
