Page 4 of 4
Normal telomere lengths found in cloned cattle.
Success of cloning using adult somatic cells has been reported in sheep, mice and cattle. The report that “Dolly” the sheep, the first clone from an adult mammal, inherited shortened telomeres from her cell donor and that her telomeres were further shortened by the brief culture of donor cells has raised serious scientific and public concerns about the ‘genetic age’ and potential developmental problems of cloned animals. This observation was challenged by a recent report that showed calves cloned from fetal cells have longer telomeres than their age-matched controls. The question remains whether Dolly’s short telomeres were an exception or a general fact, which would differ from the telomeres of fetal-derived clones.
Nat Genet 2000 Nov;26(3):272-3
Extension of cell life span and telomere length in animals cloned from senescent somatic cells.
The potential of cloning depends in part on whether the procedure can reverse cellular aging and restore somatic cells to a phenotypically youthful state. Here, we report the birth of six healthy cloned calves derived from populations of senescent donor somatic cells. Nuclear transfer extended the replicative life span of senescent cells (zero to four population doublings remaining) to greater than 90 population doublings. Early population doubling level complementary DNA-1 (EPC-1, an age-dependent gene) expression in cells from the cloned animals was 3.5- to 5-fold higher than that in cells from age-matched (5 to 10 months old) controls. Southern blot and flow cytometric analyses indicated that the telomeres were also extended beyond those of newborn (<2 weeks old) and age-matched control animals. The ability to regenerate animals and cells may have important implications for medicine and the study of mammalian aging.
Science 2000 Apr 28;288(5466):665-9
Stem cells: progress in research and edging towards the clinical setting.
Mouse embryonic stem cells have been shown to differentiate into a variety of tissues in vitro and in transplantation experiments can produce many different cell types. Multipotent stem cells in adult humans have also shown a high degree of plasticity: haemopoietic stem cells, for example, have been shown to contribute to several other tissues, such as liver. From these simple observations there has been considerable extrapolation into the use of such putative totipotent stem cells in the clinical setting, with the development of ‘designer’ tissue engineering, whose aim is to create large tissues or even whole organs for clinical use. In practical terms, however, there are many limitations and difficulties and clinical use has been restricted to a very few settings, eg the use of fetal cells in Parkinson’s disease. Nonetheless, there is enormous potential in this area, and also in the application of embryonic or adult stem cells as carriers for gene therapy; but the limitations of such treatment, in particular the stability of manipulated cells, and the problems of aging and Ooncogenicity, not to mention a host of ethical and regulatory issues, all need to be considered.
Clin Med 2001 Sep-Oct;1(5):378-82
Medical perspectives on cloning, preimplantation genetic diagnosis, therapeutic use of pluripotent stem cells and the availability of molecular information on the genome.
The progress in biological techniques of cloning, preimplantation genetic diagnosis (PGD) and stem cell production and application of genomic information being generated on human diseases and traits will profoundly influence our lives and progeny produced during the next century. These procedures are controversial with a restricted social acceptance. Cloning by splitting of the fertilized preimplantation stage embryo or by nuclear transplantation procedures will benefit both the agriculture and biotechnology industries. Although monozygotic twins are natural human clones presumably derived from splitting of the single ovum, benefits of human cloning remain unclear. This procedure may not be acceptable near term to a large population. The PGD is a safe procedure for prevention of genetic diseases due to chromosomal anomalies and gene mutations. It can be performed before transfer of the embryo to the recipient natural or foster mother avoiding the trauma of induced abortion when the embryo is found to be abnormal. This technique also improves human fertility caused by anomalous embryo as they may be sorted out by genetic screening before transfer into the maternal uterus. Finally, the therapeutic application of stem cells derived from embryonic cells is wide and novel. They are to be used for therapy of defective organs. Availability of in-depth genomic information will permit characterization of cells for use in all these procedures. Thus, a cautious application of these biological procedures, and the use of genetic information in the future medical practice will undoubtedly help eradication of human diseases and enhance the quality of our lives.
Early Pregnancy 2001 Jan;5(1 Pt 1):16-17
Bioethics: cloning announcement sparks debate and scientific skepticism.
A small U.S. biotech firm made headlines around the world last week when it announced that it had cloned several human embryos for transplantation research, prompting strong reactions. President George W. Bush denounced the research as unethical, European leaders discussed national controls on cloning, and the furor could spur efforts to pass a law in the United States that would ban research on human cloning. All this fuss over results whose scientific significance is questionable: Some scientists note that the six-cell clusters created by ACT barely qualify as embryos.
Science 2001 Nov 30;294(5548):1802-3
Human cloning from the perspective of The Council of Europe bioethical standards
Allegations negating the role of law in the resolving the controversial problem of human cloning are unjustified. Human rights, implying the magnitude and value of human person and deeply rooted inherent dignity of the human being, constitute the very foundation of every legal order. Every lawyer, as well as every specialist in medicine or biology must be aware of his own human dignity and the ethical consequences. Among the standards of the Council of Europe in the context of human cloning there must be mentioned the Additional Protocol of January 12, 1998 on the Prohibition of Cloning Human Beings. It is the integral element of the normative system of the mother convention, the European Bioethical Convention of April 4, 1997. It has the distinguished place - within this system as far as its substantial provisions exclude the possibilities of limitations and derogation. The system of the Convention and the Protocol must be viewed in the light of a broader normative environment, including the integral system of the European Convention on Human Rights and the set of recommended bioethical standards. The absolute prohibition embodied in the Protocol is limited to all the methods leading to the creation of genetically identical human beings. The protocol does not directly regulate cloning of human tissues and cells, including embryonic stem cells. However, some conclusions may be taken from the Convention and from the recommended standards. It is the assumption of the Convention and the Protocol that the guarantees embodied there must be apprehended as practical and effective ones, justifiable and not excluding the use of proper sanctions by the State. It is an unacceptable view that scientists are excluded from the sphere of the functioning of the above-mentioned prohibition. The real sense of this prohibition is to stop the unlimited liberty and arbitrary practice of such scientists. The freedom of scientific research is not absolute, and must be guided by the respect for human dignity and human rights, as by well as protective guarantees embodied in the Convention and recommended standards.
Med Wieku Rozwoj 2001;V(1 Suppl 1):213-225
Human cloning in the activities of the European Union.
The European Union has been concerned with human cloning since the late 80s. It resulted from inclusion of biotechnology into the sphere of European integration. The attitude of the European Union in the domain of human cloning was shaped, in principle in the second part of the 90s. As the Community law stands at present, the European Union is not able to regulate all aspects of the cloning of human beings. It has no general power to decide in that sphere, especially, as far as bioethic aspects are concerned. The cloning of human beings in the European Union is understood as a process aiming at producing new human being, genetically identical with another live or dead human being. Thus the notion of human cloning is reduced to reproductive cloning. Three instruments are at the disposal of the European Union in the domain of human cloning. The first is prohibition of reproductive cloning as a general principle of Community law. However, that principle is not the result of judicial activity of the European Court of Justice (as general principles normally are), but the logical consequence of views formally expressed by the European Parliament, the Council of the Europe as well as the Commission. The principle was finally included in the Charter of fundamental rights of the European Union. The second instrument is an imperative prohibition of patent granting to biotechnological inventions on human reproductive cloning. Last, but not least, the Union applies a prohibition of financing scientific research connected with human cloning from the budget of the European Communities within the V Framework Programme in the field of research and technological development.
Med Wieku Rozwoj 2001;V(1 Suppl 1):195-212
Reprogramming of telomerase activity and rebuilding of telomere length in cloned cattle.
Nuclear reprogramming requires the removal of epigenetic modifications imposed on the chromatin during cellular differentiation and division. The mammalian oocyte can reverse these alterations to a state of totipotency, allowing the production of viable cloned offspring from somatic cell nuclei. To determine whether nuclear reprogramming is complete in cloned animals, we assessed the telomerase activity and telomere length status in cloned embryos, fetuses and newborn offspring derived from somatic cell nuclear transfer. In this report, we show that telomerase activity was significantly (P < 0.05) diminished in bovine fibroblast donor cells compared with embryonic stem-like cells, and surprisingly was 16-fold higher in fetal fibroblasts compared with adult fibroblasts (P < 0.05). Cell passaging and culture periods under serum starvation conditions significantly decreased telomerase activity by approximately 30 to 50% compared with nontreated early passage cells (P < 0.05). Telomere shortening was observed during in vitro culture of bovine fetal fibroblasts and in very late passages of embryonic stem-like cells. Reprogramming of telomerase activity was apparent by the blastocyst stage of postcloning embryonic development, and telomere lengths were longer (15-23 kb) in cloned fetuses and offspring than the relatively short mean terminal restriction fragment lengths (14-18 kb) observed in adult donor cells. Overall, telomere lengths of cloned fetuses and newborn calves (approximately 20 kb) were not significantly different from those of age-matched control animals (P > 0.05). These results demonstrate that cloned embryos inherit genomic modifications acquired during the donor nuclei’s in vivo and in vitro period but are subsequently reversed during development of the cloned animal.
Proc Natl Acad Sci U S A 2001 Jan 30;98(3):1077-82