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Introduction
Maternal effect genes (MEG) regulate oocyte nuclear maturation, successful processing the sperm nucleus, the organization of the two pronuclei, first embryo cleavages and finally, activation of the embryonic genome (Heikinheimo & Gibbons, 1998). Among these genes, zygote arrest 1 ( ZAR-1) that encodes a transcription regulator, seems to play an essential role in oocyte to embryonic transition. Embryos were recovered from the Zar-1 knockout mice arrested before the 1- or 2-cell transition, which corresponds with the activation of embryonic transcription (Wu et al., 2003). In the pig, mRNA expression for this gene was reported up to the 5- to 8-cell stage and then it declined sharply in the morulae and blastocysts (Uzbekova et al., 2006). Nucleoplasmin 2 (NPM2) appears to be essential for proper histone deacetylation and heterochromatin formation surrounding nucleoli in oocytes/early embryos, and developmentally associated protein 3 (DPPA3) appears to be essential for maintaining the correct pattern of chromatin methylation after fertilization (Burns et al., 2003; Nakamura et al., 2007). Npm 2 knockout mice embryos failed preimplantation development resulting from improper nuclear and nucleolus organization (Burns et al., 2003; Lingenfelter et al., 2011), whereas it was reported that Dppa3-deficient mice embryos are characterized by impaired DNA replication and abnormal segregation of maternal chromosomes (Nakatani et al., 2015). Nevertheless, no information is available concerning the expression of these genes during porcine oocyte maturation and embryo development.
One of the common practices for improving in vitro embryo production (IVP) efficiency is the introduction of supplements into the culture system (Neira et al., 2010). Among the employed supplements, epidermal growth factor (EGF) has been reported mainly as a key mediator of gonadotropin-induced oocyte nuclear maturation and ovulation in vitro (Richani et al., 2014). Moreover, EGF may also participate in post-fertilization embryonic development because the EGF receptor (EGFR) has been found in porcine embryos (Lee et al., 2005). However, the role of cytokines and their associated mechanisms of action has been explored less extensively, particularly regarding porcine IVP. IL-1 activity was found in the preovulatory porcine follicular fluid, and in vitro studies revealed that this factor is able to...