Developmental Competence Of Somatic Cell Nuclear Transfer Embryos Reconstructed From Small Bovine Oocytes By Pre-Maturation Culture

Abstract

Somatic cell nuclear transfer (SCNT) is a technique used to create cloning embryos and has a variety of applications. However, the availability of oocytes at fully grown stage is scarce. Oocytes obtained from ovaries are mainly at antral stage. While large antral follicles-derived oocytes can become mature and show great ability to generate embryos after SCNT by in vitro maturation (IVM) culture, their smaller counterparts face more challenges. Therefore, a pre-IVM culturing process prior to IVM was suggested. Nevertheless, the pre-IVM protocol that proves to be effective in supporting oocytes and can displace high developmental competence post-SCNT are not yet to be established. Thus, this study was conducted to complete such task. As the results indicated, pre-IVM culture did enhance meiosis rate in small-sized oocyte which was comparable to fully grown ones at approximately 80%. Improvements also showed in the developmental competence of parthenogenetic embryos reconstructed from small oocytes. The proportion of good-quality blastocyst based on the blastomere number was recorded even higher in group of pre-IVM and L-ascorbic acid treatment than positive control group (55.70% versus 53.90, respectively). Alike outcome was observed in the histone H3K9 acetylation intensity measured in parthenogenetic blastocysts after immunostaining. Such results indicated establishment of a pre IVM protocol that may support small antral follicles-derived oocytes for SCNT. Regarding to the developmental ability of SCNT embryos derived from small-sized oocytes after pre-IVM culture, the percentages were comparable to the positive control group despite large deviation. Nonetheless, such pre-IVM protocol was able to generate embryo reached late blastocyst stage. Taken together, the pre-IVM medium used in this study might have the potential to improve developmental competence of small oocytes undergoing SCNT and yet, more tests need to be carried out.