There are two main methods by which activation can be performed: (i) physical methods and (ii) chemical methods. Physical methods include electrical stimulation, temperate and mechanical ways, whereas the chemical methods comprise of different artificial chemical agents, including strontium chloride, calcium ionophores, ethanol that promote to rise in intracellular Ca2+ oscillations, cycloheximide, that inhibit protein synthesis and 6-DMAP (6-dimethyl amino purine) which inhibit protein phosphorylation.
The contribution of both maternal and paternal genomes is required for thedevelopment to full term of mammalian embryos. However, the percentage of parthenogeneticallyactivated embryos developing to blastocyst stage is lower as compared to normal fertilized embryos. (Renard et al. 1991).In mouse, strontium chloride has been successfully employed in manydifferent studies to induce artificial oocyte activation. The role of strontium to induce calcium oscillations appears to be more physiologically sound than alternativemethods of oocyte activation that produce a monotonic rise in calcium.Strontium chloride (SrCl2) is recognized as one of the most popular parthenogenetic agents for mouse oocytes activation and induces calcium oscillations leads to improved activation rate and blastocyst formation. (Locham-kaplan et al. 2003) (Satoshi et al. 2006).
The diploid parthenogenetic oocytes have more developmental competence as compared to haploid form(Liu et al. 2002). A substancecytochalasin B (CB) prevents the release of the second polar body after activation of mammalian oocyte which results in diploid form of embryo (Fukui et al. 1992) and it may also contribute to prevent fragmentation and degradation of embryos ( Yi and Park 2005).
Parthenogenetic oocyte activation technique is mainly used in cloning and is a key step for nuclear transfer for cloning. The technique is also useful for understanding of physiological mechanisms of fertilization and early embryonic development. Embryonic stem cells can be derived from fertilized embryos. The stem cells which are produced by parthenogenetic activation have the same totipotency and proliferation as formed by normal sperm-egg fertilization..( Ju et.al 2008). Resultantly, parthenogenetic activation technology has become a target of reproductive biology. This technology can also be used to establish embryonic stem cell lines (Mizutani et al. 2004) and embryonic stems cells are the fundamental source in field of regenerative medicine; used to treat many diseases such as diabetes, beta thalassemia, heart infarction etc by providing patient specific replacement cells.
Mouse is one of the most commonly animal models used for parthenogenetic activation. The other animals which have been used for parthenogenetic activation include rabbits, cattle, sheep, horses, monkeys and pigs. Parthenogenetic embryos are failed to develop to term, due to genomic imprinting, an epigenetic change of certain genes, depending on the parent of origin.(Uranga and Arechaga 1997). The studies pertaining to parthenogenetic activation technology for mouse oocytes is extremely limited at present (Mizutani et al. 2004).