Live birth of somatic cell-cloned rabbits following trichostatin A treatment and cotransfer of parthenogenetic embryos

Somatic cell nuclear transfer (SCNT) efficiency is still low in rabbit. Previous studies indicated that trichostatin A (TSA) treatment could improve cloning efficiency and term development in the mouse, and cotransfer of parthenogenetic (PA) embryos benefited the pregnancy of cloned embryos in porcine and the mouse. In this study we investigated the effect of TSA treatment on the term development of the SCNT rabbit embryos, and the possibility of the pregnancy maintenance of clones by cotransfer of PA embryos. The SCNT embryos were produced by fusing cumulus cells with enucleated cytoplasts before activation by electrical stimulation, and Dimethylaminopurine (6-DMAP) and Cyclohexamide (CHX) treatments. They were cultured in EBSS-complete medium regardless of their treatment with or without TSA. In vitro developmental data showed no differences in the cleavage and the blastocyst rates, and the blastocyst cell number between the TSA-treated and the untreated SCNT embryos. Two of the six recipients became pregnant after the embryo transfer (ET) in the TSA-treated group, and one pregnant female delivered seven live and three stillborn pups. The death of all live pups occurred within an hour to 19 days. Four of the seven recipients became pregnant in the TSA-untreated group. Three of them gave birth to six live and eight stillborn pups. Four pups of the TSA-untreated group have grown into adulthood, and three of them produced progeny. Cotransfer of three to four PA embryos with 26-32 SCNT embryos to the same recipient resulted in pregnancy and birth rates statistically no different compared to the control SCNT ET group. In conclusion, our results indicate that TSA treatment has a limited effect on the in vitro development of the SCNT embryos; furthermore, both the TSA-treated and the untreated clones can develop to term in rabbits, but none of the offspring from TSA-treated embryos survived to adulthood in our experiment.

Somatic cell nuclear transfer: Past, present and future perspectives

It is now over a decade since the birth, in 1996, of Dolly the first animal to be produced by nuclear transfer using an adult derived somatic cell as nuclear donor. Since this time similar techniques have been successfully applied to a range of species producing live offspring and allowing the development of transgenic technologies for agricultural, biotechnological and medical uses. However, though applicable to a range of species, overall, the efficiencies of development of healthy offspring remain low. The low frequency of successful development has been attributed to incomplete or inappropriate reprogramming of the transferred nuclear genome. Many studies have demonstrated that such reprogramming occurs by epigenetic mechanisms not involving alterations in DNA sequence, however, at present the molecular mechanisms underlying reprogramming are poorly defined. Since the birth of Dolly many studies have attempted to improve the frequency of development, this review will discuss the process of animal production by nuclear transfer and in particular changes in the methodology which have increased development and survival, simplified or increased robustness of the technique. Although much of the discussion is applicable across species, for simplicity we will concentrate primarily on published data for cattle, sheep, pigs and mice.