Part I: A brief description of the Early Life Issues
4. Cloning
The term “cloning” is not specific to one biological process but collectively refers to any process used to create copies of another organism, cell or tissue. Cloning can include the creation of identical DNA fragments (molecular cloning), cells (cell cloning), or whole organisms. It is the last with which this document is largely concerned.
In recent years, the media has almost exclusively referred to a single method of cloning whole organisms, somatic cell nuclear transfer, (SCNT), which has become synonymous in the public mind with cloning, an error that has found its way into legislation around the world.
The SCNT method was made famous by the creation, in March 1996, of “Dolly” the sheep by a team of scientists at the Roslin Institute in Edinburgh, Scotland, led by Dr. Ian Wilmut. Dolly, a Finn Dorset breed sheep, was the first cloned mammal to be brought to adulthood. She suffered some genetic abnormalities and died much earlier than is usual for a sheep of that breed, on February 14, 2003.
From the time of Dolly’s creation, the media has used the terms “cloning” and SCNT interchangeably, creating much confusion in the public and in various attempts to regulate or ban human cloning around the world.
In Canada, so ingrained was the idea that “cloning = SCNT”, that neither pro-life activists nor embryologists nor experts in bioethics were able to clarify to parliamentarians the linguistic problems of legislation proposing to regulate artificial procreation, embryo research and cloning. Critics of the bill insisted that any attempt to ban or restrict human cloning must accurately reflect the scientific realities of the field. These experts cautioned that the bill was riddled with inaccurate terms and therefore that its prohbition on cloning would prove ineffective.
The government’s Assisted Human Reproduction act passed in the House of Commons without significant amendments in October, 2003. It was passed unanimously in the Senate in signed into law in March 2004.
In the Canadian legislation, as with may others worldwide, the term “cloning” is defined only as Somatic Cell Nuclear Transfer, despite there being many different methods of creating a cloned cell or organism.
What is a Clone?
The group of definitions given below are subject to change given new information. They have been developed by Dr. Dianne Irving, PhD[1], with the purpose of clarifying common misunderstandings of the nature of human cloning research. They were developed from internationally recognized human embryology text books using standard scientific nomenclature.
- Human being: any organism who begins to exist immediately by means of sexual or a-sexual reproduction and who possesses a genome specific for and consistent with an individual member of the human species.
- Human genome: The total nuclear and cytoplasmic DNA genetic materials that constitute an organism as an individual member of the human species.
- Cloning: the duplication, or near-duplication, of molecules, any part(s) of a cell, a single cell, cells, tissues, organs, or organisms using any cloning technique.
- Cloning techniques: any technique used to duplicate, or to near-duplicate, molecules, part(s) of a cell, a single cell, cells, tissues, organs, or organisms.
- Human cloning: (a) organism: the duplication, or near-duplication, of a whole human being using any cloning technique; or, the use of part(s) of human cellular or artificial materials for the purpose of duplicating a whole human being using any technique; (b) molecules: permanently altering the human genome in successive reproductive generations by means of the duplication, or near duplication, of human genetic materials using any a-sexual reproductive technique and/or any sexual reproductive technique.
· Cloned human being: A human being at any stage of development who is a-sexually reproduced using any cloning technique.
These definitions cover some of the cloning that are currently being used, e.g., human cloning by means of "twinning" (blastomere separation and blastocyst splitting), somatic cell nuclear transfer (SCNT), germ line cell nuclear transfer (GLCNT), pronuclear transfer, mitochondrial transfer, and germ line gene transfer. They attempt to anticipate the near future use of legislation to cover advances in nanotechnology, (e.g., the artificial construction of parts of human cells, human cells, tissues, organs, and organisms starting with nano-molecules, etc.; this technology is in current development and the proposed legislation in New Zealand allows for the use of artificially constructed sperm and oocytes but does not specify the methods that may be used.) -- and in bioengineering and genetic engineering.
A Variety of Methods
Somatic Cell Nuclear Transfer: In SCNT the nucleus of an oocyte is removed and replaced with that of a somatic[2] cell (a cell that is not either a male or female gamete). After being inserted into the oocyte, the somatic cell nucleus is reprogrammed by the host cell. The resulting single-cell embryo is stimulated and will begin to divide and develop. After many mitotic divisions in culture, this single cell forms a blastocyst with almost identical DNA to the original organism.
Contrary to the popular conception, this technique does not create an exact genetic copy of the donor of the somatic cell since mitchondrial DNA is found in the enucleated oocyte that was not part of the nucleus. The resulting organism therefore, carries DNA from both the original oocyte and the donor of the nuclear DNA.
Pronuclear Transfer: Pronuclear Transfer is a form of a-sexual reproduction (cloning) in which male and/or female pronuclei[3] are transferred from one or more embryos to an enucleated oocyte. After electrical or chemical stimulation, the pronuclei merge, producing a new human embryo with 46 (or more) chromosomes. The extra female chromosomes which were initially ejected in a polar body from the oocyte during fertilization can also be “captured” and used as a female pronucleus in cloning.
In the ordinary process of fertilization, the oocyte (“ovum”) is at first diploid, that is it contains the full complement of 46 chromosomes, the normal number for any cell of a member of the human species.
When a sperm penetrates an oocyte, the 46 female chromosomes of the oocyte are reduced to 23. In this process, the extra 23 female chromosomes are extruded or ejected from the organism in a “polar body.”[4] The embryo now contains 23 male and 23 female chromosomes (the correct number for an individual member of the human species).
At first, after the sperm has penetrated the membranes of the oocyte, the male and female chromosomes are separately encased in a molecular aggregate called a “pronucleus”; each containing 23 chromosomes. Each pronucleus can be manipulated, isolated and removed from the newly fertilized embryo – a technique refined for years for IVF research.
This is a method that could be used to produce human/human chimeras (male and female pronuclei transferred from more than one human embryo), and human/animal chimeras.
Mitochondrial Transfer: “Mitochondrial Transfer” is an a-sexual form of manipulation of an embryo (cloning) in which the mitochondria (containing mitochondrial DNA) from a human donor female oocyte are transferred to another human female oocyte, or to a newly produced human embryo.
Every human cell contains small organelles that are found in the cytoplasm of the cell, outside of the nucleus. One kind of these organelles is called a mitochondrion, which contain human genetic material (DNA) – or “mDNA” (for “mitochondrial DNA”). Mitochondria are primarily concerned with energy production for the rest of the cell. Although the amount of mDNA is small compared to the nuclear DNA in the cell nucleus, small errors in mDNA can cause serious, even lethal, human diseases that are passed on by the mother’s oocyte during fertilization. One method of attempting to correct this genetic defect is to transfer healthy mitochondria from a donor oocyte into the diseased oocyte, or into a new human embryo reproduced with the diseased oocyte
This new human embryo would contain human genetic material (DNA) from more than one female and from one male, and the “foreign” mitochondrial DNA would continue to be replicated (cloned) with each new cell of the developing human being, including his/her own germ line (reproductive) cells. Thus the initial “foreign” mitochondrial DNA could be cloned throughout successive generations.
DNA-Recombinant Germ Line Gene Transfer: The injection of “foreign” DNA or genes into cells or embryos – “gene transfer” – can be used for “enhancement” or for “corrective” purposes. This is a form of eugenics, the effort to “improve” the human race by eliminating unwanted characteristics, or, as in the case of DNA Recombinant Germ Line Gene Transfer, by direct manipulation of the genetic make-up of successive generations of human beings.
It is accomplished by means of a “vector” or carrier, often a virus, into which the “foreign” gene is first inserted and which then “recombines” with the vector’s own genetic material. This vector, now containing the “foreign” gene, is then transferred into a germ line cell (male or female) of a patient.
The germ line cells of that patient will incorporate the “foreign” gene into its own DNA. When that patient later takes part in sexual reproduction, the “foreign” gene will be transferred again by being incorporated into the new human embryo’s own germ line cells.
Alternatively, the “foreign” gene in the vector can be transferred into a newly fertilized human embryo and thus be incorporated into the new embryo’s germ line cells. In either case, as the human embryo’s cells divide during growth and development, the “foreign” gene will likewise be incorporated into every cell of the growing embryo, including the new embryo’s own germ line cells. Therefore, when that human being matures and reproduces sexually, his/her descendants will also possess the “foreign” gene. Thus the “foreign” gene will be passed on throughout successive generations.
Blastomere separation (twinning): See Part I, Section 2. What are New Reproductive Technologies? Pg. 7
Altered Nuclear Transfer: In 2004, a controversy arose when Dr. William Hurlbut[5] a member of the President’s Council on Bioethics, made a presenation[6] suggesting a method called “Altered Nuclear Transfer” that he claimed would enable scientists to obtain embryonic stem cells without the creation of embryos.
He proposed the creation of life forms made from human oocytes and injected DNA that he termed “biological artifacts”. These would be capable of producing embryonic or embryonic-like stem cells, without the entity containing enough of a human genome to qualify as embryos, and therefore as persons. Hurlbut concluded that these “biological artifacts” could circumvent the ethical problem of killing embryonic human beings to obtain stem cells.
Hurlbut’s proposal was based on research by Rudolf Jaenisch a Professor of Biology at MIT and a pioneer in transgenic[7] science. Jaenisch isloated embryonic stem cells from what he called an “embryo-like entity” that was genetically incapable of implanting in a uterus, and that also had certain structural deficiencies. ANT uses the technology of nuclear transfer, but using a donor cell with an altered nucleus.
Dr. Hurlbut stated:
The resulting biological entity, while being a source of pluripotent stem cells, would lack the essential attributes and capacities of a human embryo. For example, the altered nucleus might be engineered to lack a gene or genes that are crucial for the cell-to-cell signaling and integrated organization essential for (normal) embryogenesis. It would therefore lack organized development from the very earliest stages of cell differentiation. Such an entity would be a 'biological artifact,' not an organism.
He said, “Even if they're human - without that principle of life, are not moral entities.”
Possibly due to the extremely rarified nature of the technical language, few reservations were raised at the meeting, and the proposal gained support even among pro-life advocates.
American Life League[8] responded that the proposal would indeed create embryos that were merely genetically modified to make them severely disabled. “While the experiment was successful in producing embryonic stem cells, it did so by producing disabled embryos. The original proposal envisioned the creation of entities without any developmental direction or organization; yet those created in this experiment were able to develop to the blastocyst stage before the genetic engineering resulted in their death.”
Dr. Clem Persaud, a retired Professor of Microbiology and Biotechnology, called[9] the proposal "deeply flawed." He said that the process would not create an unknown new entity, but a severely disabled, cloned human being. "The process amounts to a kind of germ-line genetic engineering combined with a type of cloning to produce an aberrant human embryo. Deliberately producing a deformed human being, then destroying it to harness stem cells is morally repugnant, and is a clear case of ends justifying means."[10]
Parthenogenesis: A form of asexual reproduction where an embryo develops without the fusion of sperm with the oocyte. Parthenogenesis occurs naturally in some species, including lower plants, invertebrates (e.g. water fleas, aphids, some bees and parasitic wasps), and vertebrates (e.g. some reptiles, fish, and, very rarely, birds and sharks). Some scientists have proposed artificially inducing parthenogenesis with human oocytes as a means to obtain stem cells without fertilization. It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize.
Chimera: a single individual that is a combination of two or more fused embryos or parts of embryos. Chimeras are formed from three or four parent cells (an embryo is fused with an unfertilized oocyte or an embryo is fused with an extra sperm). Each population of cells keeps its own character and the resulting animal is a mixture of mis-matched parts. An analogy is two jigsaw puzzles cut using an identical cutter, but with different pictures. A single puzzle can be made out of the mis-matched parts, but the completed puzzle will show parts of both different pictures.
Mosaic: or mosaicism, denotes the presence of two populations of cells with different genotypes in one individual, who has developed from a single fertilized egg. Mosaicism may result from a mutation during development which is propagated to only a subset of the adult cells.
Although the two can have some common charateristics, mosaicism is distinct from chimerism. In the latter, the two or more genotypes arise from more than one zygote, while in mosaics, these genotypes arise from only a single cell.
[1] Dr. Dianne Irving PhD a scientist and a philosopher, was in the first graduating class at The Kennedy Institute Of Ethics at Georgetown University. See Part V: Resources; Section 3. Prominent Figures in the Early Life Issues.
[2] Somatic cell: any cell forming the body of an organism. The word "somatic" is derived from the Greek word sōma (σώμα), meaning "body".
[3] Pronucleus: a molecular aggregate created from the haploid nuclei of sperm and oocyte at fertilization but before fusion; each contains 23 chromosomes.
[4] The polar body can also be combined with pronuclei to create chimeric embryos. This is also a form of cloning.
[5] Dr. William Hurlbut: a physician and Consulting Professor in the Neuroscience Institute at Stanford, Stanford University Medical Center. He currently serves on the President's Council on Bioethics. See Part V: Resources; Section 3. Prominent Figures in the Early Life Issues.
[6] Dr. Hurlbut’s commissioned working paper for the Council, titled, “Altered Nuclear Transfer as a Morally Acceptable Means for the Procurement of Human Embryonic Stem Cells,” was discussed in December 2004. http://www.bioethics.gov/background/hurlbut.html
[7] Transgenic: in recombinant DNA technology DNA molecules from different sources are combined in vitro to one molecule to create a new gene. This modified DNA is then transferred into an organism causing the expression of modified or novel traits. The product is also known as an Genetically Engineered Organism or GEO.
[8] http://www.lifesite.net/ldn/2006/jul/060714a.html
[10] See also Part II: The Ethics of the Early Life Issues, on the so-called “rustling bush” problem.
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