Showing papers by "Ian Wilmut published in 2000"

Growth and Antrum Formation of Bovine Preantral Follicles in Long-Term Culture In Vitro

Abstract: Culture of preantral follicles has important biotechnological implications through its potential to produce large quantities of oocytes for embryo production and transfer. A long-term culture system for bovine preantral follicles is described. Bovine preantral follicles (166 +/- 2.15 micrometer), surrounded by theca cells, were isolated from ovarian cortical slices. Follicles were cultured under conditions known to maintain granulosa cell viability in vitro. The effects of epidermal growth factor (EGF), insulin-like growth factor (IGF)-I, FSH, and coculture with bovine granulosa cells on preantral follicle growth were analyzed. Follicle and oocyte diameter increased significantly (P < 0.05) with time in culture. FSH, IGF-I, and EGF stimulated (P < 0.05) follicle growth rate but had no effect on oocyte growth. Coculture with granulosa cells inhibited FSH/IGF-I-stimulated growth. Most follicles maintained their morphology throughout culture, with the presence of a thecal layer and basement membrane surrounding the granulosa cells. Antrum formation, confirmed by confocal microscopy, occurred between Days 10 and 28 of culture. The probability of follicles reaching antrum development was 0.19 for control follicles. The addition of growth factors or FSH increased (P < 0.05) the probability of antrum development to 0.55. Follicular growth appeared to be halted by slower growth of the basement membrane, as growing follicles occasionally burst the basement membrane, extruding their granulosa cells. In conclusion, a preantral follicle culture system in which follicle morphology can be maintained for up to 28 days has been developed. In this system, FSH, EGF, and IGF-I stimulated follicle growth and enhanced antrum formation. This culture system may provide a valuable approach for studying the regulation of early follicular development and for production of oocytes for nuclear/embryo transfer, but further work is required.

In-utero overgrowth in ruminants following embryo culture: lessons from mice and a warning to men

Abstract: Unusually large offspring have been born in ruminants following the transfer to recipients of embryos that have either been subjected to some form of manipulation, e.g. nuclear transfer, or have been exposed to an unusual in-vivo or in-vitro environment. Overgrowth syndromes have been reported in other species, including humans and mice, but these have arisen from chromosomal abnormalities and spontaneous or experimentally induced genetic mutations. Overgrowth phenotypes across the species, however, exhibit many common features, including alterations in organ and tissue development, and placental anomalies. Our current working hypothesis is that the causative agent(s) alter(s) the expression of a gene or genes associated with growth and development. Imprinted genes have been implicated in this syndrome because: (i) similar phenotypes are observed in both humans and mice when the expression of such genes has been altered; and (ii) they may be more vulnerable to epigenetic modification during the period (oocyte to blastocyst) when embryos are cultured in vitro. Evidence supporting this hypothesis is reviewed and the implications for assisted reproduction in humans discussed.

Large offspring syndrome and other consequences of ruminant embryo culture in vitro: Relevance to blastocyst culture in human ART

Abstract: In vitro production of embryos from domestic animals is used to augment conventional genetic improvement programmes in agriculture and to facilitate advances in gene transfer and cloning. However, production of embryos in vitro exposes them to hazards not normally encountered in vivo and, as a result, there have been unforeseen consequences including the large offspring syndrome. This syndrome is manifest as abnormal growth and development at fetal, neonatal and later stages after transfer of embryos cultured in vitro for up to 1 week after fertilization. Our embryo culture and fetal development studies have begun to characterize many of the genetic, metabolic and developmental features associated with the syndrome. This review considers the findings of these studies in the context of blastocyst production in vitro, emphasizing the impact of culture strategies on ruminant (cattle and sheep) embryo composition and developmental competence. The need to alter in vitro production strategies to safeguard oocytes and embryos during culture is discussed. Finally, the implications of experiences gained in domestic animal studies are considered in the context of current options for human embryo culture. The need for an appreciation of the sensitivity of the embryo to its environment and the possible short- and long-term consequences of inappropriate in vitro production strategies are considered.

The second creation : Dolly and the age of biological control

Abstract: The cloning of Dolly in 1996 from the cell of an adult sheep was a pivotal moment in history. For the first time, a team of scientists, led by Ian Wilmut and Keith Campbell, was able to clone a whole mammal using a single cultured adult body cell, a breakthrough that revolutionized three technologies - genetic engineering, genomics, and cloning by nuclear transfer from adult cells - and brought science ever closer to the possibility of human cloning. In this definitive account, the scientists who accomplished this stunning feat explain their hypotheses and experiments, their conclusions, and the ethical and scientific ramifications of their work. Written with award-winning science writer Colin Tudge. The Second Creation is a landmark work that details the most exciting and challenging scientific discovery of the twentieth century.

The Second Creation : The Age of Biological Control by the Scientists Who Cloned Dolly

Abstract: Recounts how Dolly the clone sheep was created and covers the techniques for her predecessors, Megan and Morag, who were cloned from embryo cells. The authors explain the scientific reasons behind their research, discuss where they believe this technology will lead, and address the ethical issues that have been raised by Dolly's creation.

The effects of cell size and ploidy on cell allocation in mouse chimaeric blastocysts.

Abstract: In a previous study of mouse tetraploid[harr ]diploid chimaeric blastocysts, tetraploid cells were found to be more abundant in the trophectoderm than the inner cell mass (ICM) and more abundant in the mural trophectoderm than the polar trophectoderm. This non-random allocation of tetraploid cells to different regions of the chimaeric blastocyst may contribute to the restricted tissue distribution seen in postimplantation stage tetraploid[harr ]diploid chimaeras. However, the tetraploid and diploid embryos that were aggregated together differed in several respects: the tetraploid embryos had fewer cells and these cells were bigger and differed in ploidy. Each of these factors might underlie a non-random allocation of tetraploid cells to the chimaeric blastocyst. A combination of micromanipulation and electrofusion was used to produce two series of chimaeras that distinguished between the effects of cell size and ploidy on the allocation of cells to different tissues in chimaeric blastocysts. When aggregated cells differed in cell size but not ploidy, the derivatives of the larger cell contributed significantly more to the mural trophectoderm and polar trophectoderm than the ICM. When aggregated cells differed in ploidy but not cell size, the tetraploid cells contributed significantly more to the mural trophectoderm than the ICM. In both experiments the contributions to the polar trophectoderm tended to be intermediate between those of the mural trophectoderm and ICM. These experiments show that both the larger size and increased ploidy of tetraploid cells could have contributed to the non-random cell distribution that was observed in a previous study of tetraploid[harr ]diploid chimaeric blastocysts.

Laying hold on eternal life

Abstract: Since “eternal life” comes from God, it is best understood and defined by looking to Him. Paul, in Romans 16:26, speaks of the “everlasting God” (i.e., “the eonian God”). This word “everlasting” is the same word as “eternal,” also being the word “aionios.” That He is the “everlasting God,” or the “eonian God,” does not refer to the fact that God will never die. This is a truth that is taught elsewhere in Scripture by other terms, such as: