Reproduction Abstracts

It has been proven that treatment of cloned embryos with a histone deacetylase inhibitor (HDACi) such as trichostatin A (TSA) following somatic-cell nuclear transfer (SCNT), significantly improves subsequent development to a blastocyst as well as full-term development (Kishigami et al. BBRC 2006). Recently, we have shown that lysine acetylation levels in both the nucleus and cytoplasm are significantly increased after oocyte activation (Matsubara et al. BBRC 2013) or with oocyte aging (Lee et al. JRD 2013), which are more enhanced by TSA treatment. To get insight into the mechanism underlying HDACi requirement for SCNT embryos, we looked into the dynamics of lysine acetylation during one-cell stage mouse cloned embryos. First, we observed that high acetylation levels in somatic cells disappeared within 3 h after SCNT without oocyte activation, suggesting high HDAC activities in oocytes erasing the lysine acetylation derived from somatic cells. Next we found lower accumulation of acetylation in SCNT nuclei than control embryos (parthenogenetically-activated oocytes), which is consistent with previous reports showing lower acetylation of histones in SCNT embryos. Further, to directly compare the acetylation levels of nuclei within the same oocyte cytoplasm, we injected somatic cells into oocytes without enucleating, revealing that somatic-cell derived nuclei showed significantly lower acetylation level than the female pronuclei. Thus, lysine-acetylation in SCNT embryos is dynamically changed as in fertilized embryos but distinct at the acetylation level, suggesting an intrinsic property of SCNT nuclei which require HDACi for further development.