Timing and Uniformity of Embryonic Gene Activation Affect Subsequent Pre-implantation Development of Cloned Bovine Embryos

Treatment with a histone deacetylase inhibitor after nuclear transfer improves the preimplantation development of cloned bovine embryos

We examined the effects of treatment with histone deacetylase inhibitors (HDACi), trichostatin A (TSA) and scriptaid (SCR), on the blastocyst formation rate in bovine somatic cell nuclear transferred (SCNT) embryos derived from fibroblast cells. Three fibroblast cell lines (L1, L2 and L3) were used as somatic cell donors to produce SCNT embryos (L1, L2 and L3 embryos, respectively). In Experiment 1, we compared the in vitro developmental competence of L1 embryos treated with various concentrations of TSA for different time periods following chemical activation. Embryos treated with 5 nM TSA for 20 h showed a significantly increased blastocyst formation rate compared with untreated controls. In Experiment 2, we examined the effect of TSA (5 nM) treatment of L1, L2 and L3 embryos as well as the effect of treatment of L1, L2 and L3 embryos with various concentrations of SCR on in vitro developmental competence. It was found that 5 nM TSA treatment significantly increased the blastocyst formation rate in L1 and L3 embryos but did not have an influence on the development of L2 embryos. On the other hand, 5 nM SCR treatment significantly increased the blastocyst formation rates of L1 and L2 embryos compared with controls. However, there was no significant increase in the blastocyst formation rate of L3 embryos when they were treated with SCR. In Experiment 3, acetylation of H4K12 was examined in donor cells and pronuclear-stage L1, L2 and L3 embryos treated with 5 nM TSA or 5 nM SCR by immunostaining. The level of H4K12 acetylation was different among donor cells. The staining intensities in the TSA-treated L1 and L3 embryos and SCR-treated L2 embryos were significantly higher than those of untreated embryos. These results suggest that HDACi treatment of bovine SCNT embryos improves the blastocyst formation rate; however, the optimal treatment conditions may differ among donor cell lines.

Enhancement of histone acetylation by trichostatin A during in vitro fertilization of bovine oocytes affects cell number of the inner cell mass of the resulting blastocysts

Histone acetylation is one of the major mechanisms of epigenetic reprogramming of gamete genomes after fertilization to establish a totipotent state for normal development. In the present study, the effects of trichostatin A (TSA), an inhibitor of histone deacetylase, during in vitro fertilization (IVF) of bovine oocytes on subsequent embryonic development were investigated. Cumulus-enclosed oocytes obtained from slaughterhouse bovine ovaries were matured in vitro and subjected to IVF in a defined medium supplemented with 0 (control), 5, 50, and 500 nM TSA for 18 h. After IVF, presumptive zygotes were cultured in modified synthetic oviductal fluid (mSOF) medium until 168 h postinsemination (hpi). Some oocytes were immunostained using antibody specific for histone H4-acetylated lysine 5 at 10 hpi. Cleavage, blastocyst development and cell number of inner cell mass (ICM) and trophectoderm (TE) of blastocysts were assessed. TSA treatment enhanced histone acetylation that was prominent in decondensed sperm nuclei. TSA did not affect the postfertilization cleavage, blastocyst rates, and TE cell number. However, it significantly enhanced ICM cell number (p < 0.05). These results indicate that TSA treatment during IVF of bovine oocytes does not affect blastocyst development but alters the cell number of ICM, suggesting that overriding epigenetic modification of the genome during fertilization has a carryover effect on cell proliferation and differentiation in preimplantation embryos. Thus, further environmental quality controls in assisted reproductive technologies are needed in terms of factors which affect chromatin remodelling.

Resurrection of a bull by cloning from organs frozen without cryoprotectant in a -80 degrees c freezer for a decade

Frozen animal tissues without cryoprotectant have been thought to be inappropriate for use as a nuclear donor for somatic cell nuclear transfer (SCNT). We report the cloning of a bull using cells retrieved from testicles that had been taken from a dead animal and frozen without cryoprotectant in a −80°C freezer for 10 years. We obtained live cells from defrosted pieces of the spermatic cords of frozen testicles. The cells proliferated actively in culture and were apparently normal. We transferred 16 SCNT embryos from these cells into 16 synchronized recipient animals. We obtained five pregnancies and four cloned calves developed to term. Our results indicate that complete genome sets are maintained in mammalian organs even after long-term frozen-storage without cryoprotectant, and that live clones can be produced from the recovered cells.

A unique method to produce transgenic embryos in ovine, porcine, feline, bovine and equine species

Transgenesis is an essential tool in many biotechnological applications. Intracytoplasmic sperm injection (ICSI)-mediated gene transfer is a powerful technique to obtain transgenic pups; however, most domestic animal embryos do not develop properly after ICSI. An additional step in the protocol, namely assistance by haploid chemical activation, permits the use of ICSI-mediated gene transfer to generate transgenic preimplantation embryos in a wide range of domestic species, including ovine, porcine, feline, equine and bovine. In the present study, spermatozoa from five species were coincubated with pCX-EGFP plasmid and injected into metaphase II oocytes. The chemical activation protocol consisted of ionomycin plus 6-dimethylaminopurine. We detected high proportions of fluorescent EGFP embryos for all five species (23–60%), but with a high frequency of mosaic expression (range 60–85%). To our knowledge, this is the first study to produce exogenous DNA expression in feline and equine embryos. Chemical activation reduces the lag phase of egfp expression in ovine embryos. Our results show that this unique method could be used to obtain ovine, porcine, feline, bovine and equine transgenic preimplantation embryos.