Since the first report of live mammals produced by nuclear transfer from a cultured differentiated cell population in 1995 (ref. 1), successful development has been obtained in sheep, cattle, mice and goats using a variety of somatic cell types as nuclear donors. The methodology used for embryo reconstruction in each of these species is essentially similar: diploid donor nuclei have been transplanted into enucleated MII oocytes that are activated on, or after transfer. In sheep and goat pre-activated oocytes have also proved successful as cytoplast recipients. The reconstructed embryos are then cultured and selected embryos transferred to surrogate recipients for development to term. In pigs, nuclear transfer has been significantly less successful; a single piglet was reported after transfer of a blastomere nucleus from a four-cell embryo to an enucleated oocyte; however, no live offspring were obtained in studies using somatic cells such as diploid or mitotic fetal fibroblasts as nuclear donors. The development of embryos reconstructed by nuclear transfer is dependent upon a range of factors. Here we investigate some of these factors and report the successful production of cloned piglets from a cultured adult somatic cell population using a new nuclear transfer procedure.

The influence of various in vitro procedures on embryo survival and the production of normal offspring was investigated in sheep. Zygotes with both in vivo cultured IVM\p=n-\IVF zygotes and control zygotes 25\p=n-\35% versus 51\p=n-\60%, respectively, P < 0.05). Day 6.5 IVM\p=n-\IVFmorulae had a lower survival rate than did control morulae regardless of culture treatment (P < 0.05), while survival rates of day 6.5 IVM\p=n-\IVF blastocysts cultured in vivo did not differ from those of control blastocysts (P > 0.1). Both the gestation period and birth weight of IVM\p=n-\IVFlambs were increased when compared with controls, the former significantly in all groups (154.0\p=n-\154.9days versus 150.6 days; P < 0.01), while the latter increase was on the borderline of significance (4\ m=. \ 5\ p=n-\ 4\ m=. \ 8 kg versus 4.0 kg; 0.01 \m=le\P \m=le\0.1, respectively) and dependent on the prolongation of the gestation period. It is concluded that in vitro maturation and fertilization compromise subsequent embryonic and fetal development in sheep irrespective of the subsequent in vivo or in vitro culture treatment. Subjecting IVM\p=n-\IVF zygotes to in vivo culture for 6.5 days minimizes only some of these effects, thus leading to the aberrant production of some offspring.

The efficiency of cloning by somatic cell nuclear transfer (SCNT) is poor in livestock with w5% of transferred cloned embryos developing to term. SCNT is associated with gross placental structural abnormalities. We aimed to identify defects in placental histology and gene expression in failing ovine cloned pregnancies to better understand why so many clones generated by SCNT die in utero. Placentomes from SCNT pregnancies (nZ9) and age matched, naturally mated controls (nZ20) were collected at two gestational age ranges (105-134 days and 135-154 days; termZ147 days). There was no effect of cloning on total placental weight. However, cloning reduced the number of placentomes at both gestational ages (105-134 days: control 55.0G4.2, clone 44.7G8.0 and 135-154 days: control 72.2G5.1, clone 36.6G5.1; P!0.001) and increased the mean individual placentome weight (105-134 days: control 10.6G1.3 g, clone 18.6G2.8 g and 135-154 days: control 6.6G0.6 g, clone 7.0G2.0 g; P!0.02). Placentomes from cloned pregnancies had a significant volume of shed trophoblast and fetal villous hemorrhage, absent in controls, at both gestational age ranges (P!0.001) that was shown to be apoptotic by activated caspase-3 immunoreactivity. Consequently, the volume of intact trophoblast was reduced and the arithmetic mean barrier thickness of trophoblast through which exchange occurs was altered (P!0.001) at both gestational age ranges in clones. In addition, cloning reduced placental expression of key genes in placental differentiation and function. Thus, cloning by SCNT results in both gross and microscopic placental abnormalities. We speculate that trophoblast apoptosis, shedding, and hemorrhage may be causal in fetal death in ovine clones. Reproduction (2007) 133 243-255

Abstract. With the increasing difficulties associated with meeting the required needs for organs used in transplantation, alternative approaches need to be considered. These include the use of stem cells as potential sources of specialized cells, the ability to transdifferentiate cell types in culture, and the development of complete organs that can be used in humans. All of the above goals will require a complete understanding of the factors affecting cell differentiation and nuclear reprogramming. To make this a reality, however, techniques associated with cloning and genetic modifications in somatic cells need to be continued to be developed and optimized. This includes not only an enhancement of the rate of homologous recombination in somatic cells, but also a thorough understanding of the nuclear reprogramming process taking place during nuclear transfer. The understanding of this process is likely to have an effect beyond the area of nuclear transfer and assist with better methods for transdifferentiation of mammalian cells.The ever-expanding gap between availability of organs and the number of patients awaiting an organ transplant is of great concern. In 2003, 14,880 transplantations were carried out between January and August, yet more than 83,000 patients were in the organ waiting list (based on data from the Organ Procurement and Transplantation Network as of November 1, 2003). This increasing divergence between availability of organ donors and the increasing number of patients in waiting lists has caused researchers to look into alternative methods to fulfill these needs. Whereas for complete organ replacement, xenotransplantation with pig organs is the main alternative, for tissue repair, other alternatives exist. The most promising to date is the use of embryo-derived and adult-derived stem cells (1). Cloning by nuclear transfer has a key role to play both by assisting in the generation of swine with complex genetic manipulations, and in the generation of human stem cells. Although ethical concerns need to be considered for the application of these technologies, such discussion is beyond the scope of this review. This review will focus on the development of the cloning technology, the basic concept in nuclear reprogramming, and recent advances in both understanding the epigenetic process of nuclear reprogramming and in enhancing the ability to undertake complex genetic manipulation in this species.The goals of generating a complete organism by nuclear transfer of a nuclei into an oocyte, or reproductive cloning, has been pursued for many years. By use of frog (Rana pipiens) eggs, Briggs and King (2) described the first nuclear transfer experiment. Briefly, ovulated MII eggs were enucleated with a handmade needle, and cells from a developing frog were lysed and their nuclei injected into the egg. Over the next 4 to 11 d, the majority of the cleaved blastulae developed into normal postneurula and tadpole stages, demonstrating the ability of the injected nuclei to at least partially complete normal de...

The processes of cellular differentiation were studied in somatic cell nuclear transfer (SCNT), in vitro cultured (IVC) and in vivo developed (in vivo) ovine embryos on days 7, 9, 11, 13, 17 and 19. SCNT embryos were constructed from in vitro matured oocytes and granulosa cells, and IVC embryos were produced by in vitro culture of in vivo fertilized zygotes. Most SCNT and IVC embryos were transferred to recipients on day 6 while some remained in culture for day 7 processing. In vivo embryos were collected as zygotes, transferred to intermediate recipients and retransferred to final recipients on day 6. All embryos were processed for examination by light and transmission electron microscopy or immunohistochemical labelling for alpha-1-fetoprotein and vimentin. Overall, morphological development of in vivo embryos was superior to IVC and SCNT embryos. Day 7 and particularly day 9 IVC and SCNT embryos had impaired hypoblast development, some lacking identifiable inner cell masses. On day 11, only in vivo and IVC embryos had developed an embryonic disc, and gastrulation was evident in half of in vivo embryos and one IVC embryo. By day 13, all in vivo embryos had completed gastrulation whereas IVC and SCNT embryos remained retarded. On days 17 and 19, in vivo embryos had significantly more somites and a more developed allantois than IVC and SCNT embryos. We conclude that IVC and particularly SCNT procedures cause a retardation of embryo development and cell differentiation at days 7-19 of gestation.