Reproductive Cloning

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Author: Barbara Wexler
Date: 2011
Publisher: Gale, a Cengage Company
Series: Information Plus Reference Series
Document Type: Topic overview
Length: 4,332 words
Content Level: (Level 5)
Lexile Measure: 1330L

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Human reproductive cloning should not now be practiced. It is dangerous and likely to fail. The panel therefore unanimously supports the proposal that there should be a legally enforceable ban on the practice of human reproductive cloning. For this purpose, we define human reproductive cloning as the placement in a uterus of a human blastocyst derived by the technique that we call nuclear transplantation.
—Committee on Science, Engineering, and Public Policy Board on Life Sciences, Scientific and Medical Aspects of Human Reproductive Cloning (2002)

AAAS endorses a legally enforceable ban on efforts to implant a human cloned embryo for the purpose of reproduction. The scientific evidence documenting the serious health risks associated with reproductive cloning, as shown through animal studies, make it unconscionable to undertake this procedure. At the same time, we encourage continuing open and inclusive public dialogue, in which the scientific community is an active participant, on the scientific and ethical aspects of human cloning as our understanding of this technology advances.
—American Association for the Advancement of Science Statement on Human Cloning, February 14, 2002

The Human Genome Project defines three distinct types of cloning. The first is the use of highly specialized deoxyribonucleic acid (DNA) technology to produce multiple, exact copies of a single gene or other segment of DNA to obtain sufficient material to examine for research purposes. This process produces cloned collections of DNA known as clone libraries. The second kind of cloning involves the natural process of cell division to create identical copies of the entire cell. These copies are called a cell line. The third type of cloning, reproductive cloning, is the one that has received the most attention in the mass media. This is the process that generates complete, genetically identical organisms such as Dolly, the famous Scottish sheep cloned in 1996 and named after the entertainer Dolly Parton (1946-).

Cloning may also be described by the technology that is used to perform it. For example, the term recombinant DNA technology describes the technology and mechanism of DNA cloning. Also known as molecular cloning, or gene cloning, it involves the transfer of a specific DNA fragment of interest to researchers from one organism to a self-replicating genetic element of another species such as a bacterial plasmid. (See Figure 8.1: Click here for the media record of Bacterial plasmid .) The DNA under study may then be reproduced in a host cell. This technology has been in use since the 1970s and is a standard practice in molecular biology laboratories.

According to Christina Ullman ("Cloning" in Genes & Society Graphics, Genetics & Public Policy Center at Johns Hopkins University with support from the Pew Charitable Trusts, 2008, http://www.dnapolicy.org/resources/cloning_infographic_final.pdf, accessed October 11, 2010) displays and describes the differences between different types of cloning. This graphic depiction was developed by the Johns Hopkins University's Genetics and Public Policy Center of the Phoebe R. Berman Bioethics Institute with support from the Pew Charitable Trusts. Also presented are some of the current and potential applications of therapeutic cloning, which produces stem cells that may be used to improve human health. This chapter focuses on cloning genes and reproductive cloning and the following chapter describes therapeutic cloning and stem cell research.

Just as GenBank is an online public repository of the human genome sequence, the Clone Registry database is a sort of "public library." Used by genome sequencing centers to record which clones have been selected for sequencing, which sequencing efforts are currently under way, and which are finished and represented by sequence entries in GenBank, the Clone Registry may be freely accessed by scientists worldwide. To effectively coordinate all of this information, a standardized system of naming clones is essential. The nomenclature used is shown in Figure 8.3: Click here for the media record of Standardized clone names .

Cloning Genes

Molecular cloning is performed to enable researchers to have many copies of genetic material available in the laboratory for the purpose of experimentation. Cloned genes allow researchers to examine encoded proteins and are used to sequence DNA. Gene cloning also allows researchers to isolate and experiment on the genes of an organism. This is particularly important in terms of human research; in instances where direct experimentation on humans might be dangerous or unethical, experimentation on cloned genes is often practical and feasible.

Cloned genes are also used to produce pharmaceutical drugs, insulin (a pancreatic hormone that regulates blood glucose levels), clotting factors, human growth hormone, and industrial enzymes. Before the widespread use of molecular cloning, these proteins were difficult and expensive to manufacture. For example, before the development of recombinant DNA technology, insulin used by people with diabetes was extracted and purified from cow and pig pancreases. Because the amino acid sequences of insulin from cows and pigs are slightly different from those in human insulin, some patients experienced adverse immune reactions to the nonhuman "foreign insulin." The recombinant human version of insulin is identical to human insulin so it does not produce an immune reaction.

Figure 8.4: Click here for the media record of Cloning DNA in plasmids shows how a gene is cloned. First, a DNA fragment containing the gene being studied is isolated from chromosomal DNA using restriction enzymes. It is joined with a plasmid (a small ring of DNA found in many bacteria that can carry foreign DNA) that has been cut with the same restriction enzymes. When the fragment of chromosomal DNA is joined with its cloning vector (cloning vectors, such as plasmids and yeast artificial chromosomes, introduce foreign DNA into host cells), it is called a recombinant DNA molecule. Once it has entered into the host cell, the recombinant DNA can be reproduced along with the host cell DNA.

Another molecular cloning technique that is simpler and less expensive than the recombinant cloning method is the polymerase chain reaction (PCR). PCR has also been dubbed "molecular photocopying" because it amplifies DNA without the use of a plasmid. Figure 6.5: Click here for the media record of Polymerase chain reaction (PCR) shows how PCR is used to generate a virtually unlimited number of copies of a piece of DNA.

A collection of clones of chromosomal and vector DNA (a small piece of DNA containing regulatory and coding sequences of interest) is called a library. These libraries of clones containing partly overlapping regions are constructed to show that two particular clones are next to one another in the genome. Figure 8.5: Click here for the media record of Construction of an overlapping clone library shows how, by dividing the inserts into smaller fragments and determining which clones share the same DNA sequences, clone libraries are constructed.

Organismal or Reproductive Cloning

Another way to describe and classify cloning is by its purpose. Organismal or reproductive cloning is a technology used to produce a genetically identical organism—an animal with the same nuclear DNA as an existing animal.

The reproductive cloning technology used to create animals is called somatic cell nuclear transfer (SCNT). In SCNT scientists transfer genetic material from the nucleus of a donor adult cell to an enucleated egg (an egg from which the nucleus has been removed). This eliminates the need for fertilization of an egg by a sperm. The reconstructed egg containing the DNA from a donor cell is treated with chemicals or electric current to stimulate cell division. Once the cloned embryo reaches a suitable stage, it is transferred to the uterus of a surrogate (female host), where it continues to grow and develop until birth. Figure 8.6: Click here for the media record of Reproductive cloning shows the entire SCNT process that culminates in the transfer of the embryo into the surrogate mother and ultimately the birth of a cloned animal.

Organisms or animals generated using SCNT are not perfect or identical clones of the donor organism or "parent" animal. The clone's nuclear DNA is identical to the donor's, but some of the clone's genetic materials come from the mitochondria in the cytoplasm of the enucleated egg. Mitochondria, the organelles that serve as energy sources for the cell, contain their own short segments of DNA called mtDNA. Acquired mutations in the mtDNA contribute to differences between clones and their donors and are believed to influence the aging process.

Dolly the Sheep Paves the Way for Other Cloned Animals

In 1952 scientists transferred a cell from a frog embryo into an unfertilized egg, which then developed into a tadpole. This process became the prototype for cloning. Ever since, scientists have been cloning animals. During the 1980s the first mammals were also cloned from embryonic cells. In 1996 cloning became headline news when, after more than 250 failed attempts, Ian Wilmut (1944-) and his colleagues at the Roslin Institute in Edinburgh, Scotland, announced they had successfully cloned a sheep, which they named Dolly. Dolly was the first mammal cloned from the cell of an adult animal, and since then researchers have used cells from adult animals and various modifications of nuclear transfer technology to clone a range of animals, including a gaur, sheep, goats, cows, horses, mules, oxen, deer, mice, rats, pigs, cats, dogs, and rabbits.

To create Dolly, the Roslin Institute researchers transplanted a nucleus from a mammary gland cell of a Finn Dorsett sheep into the enucleated egg of a Scottish blackface ewe and used electricity to stimulate cell division. The newly formed cell divided and was placed in the uterus of a blackface ewe to gestate. Born several months later, Dolly was a true clone—genetically identical to the Finn Dorsett mammary cells and not to the blackface ewe, which served as her surrogate mother. Her birth revolutionized the world's understanding of molecular biology, ignited worldwide discussion about the morality of generating new life through cloning, prompted legislation in dozens of countries, and launched an ongoing political debate in Congress.

Dolly was the object of intense media and public fascination. She proved to be a basically healthy clone and produced six lambs of her own through normal sexual means. Before her death by lethal injection in February 2003, Dolly had been suffering from lung cancer and arthritis. An autopsy (postmortem examination) of Dolly revealed that, other than her cancer and arthritis, which are common diseases in sheep, she was anatomically like other sheep.

In February 1997 Don Paul Wolf (1939-) and his colleagues at the Oregon Regional Primate Center in Beaverton successfully cloned two rhesus monkeys using laboratory techniques that had previously produced frogs, cows, and mice. It was the first time that researchers used a nuclear transplant to generate monkeys. The monkeys were created using different donor blastocysts (early-stage embryos), so they were not clones of one another—each monkey was a clone of the original blastocyst that had developed from a fertilized egg. Neither of the cloned monkeys survived past the embryonic stage.

An important distinction between the process that created Dolly and the one that produced the monkeys was that unspecialized embryonic cells were used to create the monkeys, whereas a specialized adult cell was used to create Dolly. The Oregon experiment was followed closely in the scientific and lay communities because, in terms of evolutionary biology and genetics, primates are closely related to humans.

In 2000 the Oregon researchers succeeded when one of four embryos that were created by splitting a blastocyst four ways and implanting the pieces into surrogate mothers survived. The survivor was named Tetra, from the Greek prefix for the number four. Researchers and the public speculated that if monkeys could be cloned, it might become feasible to clone humans.

In May 2001 BresaGen Limited, an Australian biotechnology firm, announced the birth of that country's first cloned pig. The pig was cloned from cells that had been frozen in liquid nitrogen for more than two years, and the company employed technology that was different from the process used to clone Dolly the sheep. The most immediate benefit of this new technology was to improve livestock—cloning enables breeders to take some animals with superior genetics and rapidly produce more. Biomedical scientists were especially attentive to this research because of its potential for xenotransplantation (the use of animal organs for transplantation into humans). Pig organs that have been genetically modified so that they will not be rejected by the human immune system could prove to be a boon to medical transplantation.

That same year the first cat was cloned, and the following year rabbits were successfully cloned. In January 2003 researchers at Texas A&M University reported that cloned pigs behaved normally—as expected for a litter of pigs—but were not identical to the animals from which they were cloned in terms of food preferences, temperament, and how they spent their time. The researchers explained the variation as arising from the environment and epigenetic (not involving DNA sequence change) factors, causing the DNA to line up differently in the clones. Epigenetic activity is defined as any gene-regulating action that does not involve changes to the DNA code and that persists through one or more generations, and it may explain why abnormalities such as fetal death occur more frequently in cloned species.

In May 2003 a cloned mule (the first successful clone of any member of the horse family) was born in Idaho. The clone was not just any mule, but the brother of the world's second-fastest racing mule. Named Idaho Gem, the cloned mule was created by researchers at the University of Idaho and Utah State University. The researchers attributed their success to changes in the culture medium they used to nurture the eggs and embryos.

In August 2003 scientists at the Laboratory of Reproductive Technology in Cremona, Italy, were the first to clone a horse. Cesare Galli et al. describe their cloning technique in "Pregnancy: A Cloned Horse Born to Its Dam Twin" (Nature, vol. 424, no. 6949, August 7, 2003).

The mule was cloned from cells that were extracted from a mule fetus, whereas the cloned horse's DNA came from her adult mother's skin cells. There were other differences as well. The University of Idaho and Utah State University researchers harvested fertile eggs from mares, removed the nucleus of each egg, and inserted DNA from cells of a mule fetus. The reconstructed eggs were then surgically implanted into the wombs of female horses. In contrast, Galli et al. harvested hundreds of eggs from mare carcasses, cultured the eggs, removed their DNA, and replaced it with DNA taken from either adult male or female horse skin cells.

In May 2004 the first bull was cloned from a previously cloned bull in a process known as serial somatic cell cloning or recloning. Before the bull, the only other successful recloning efforts involved mice. Chikara Kubota, X. Cindy Tian, and Xiangzhong Yang describe their cloning technique in "Serial Bull Cloning by Somatic Cell Nuclear Transfer" (Nature Biotechnology, vol. 22, no. 6, June 2004). Their effort was also cited in the Guinness Book of World Records as the largest clone in the world.

At the close of 2004 a South Korean research team reported cloning macaque monkey embryos, which would be used as a source of stem cells. Conservationists then focused research efforts on cloning rare and endangered species. In April 2005 Texas A&M University announced the first successfully cloned foal in the United States. That same month scientists at Seoul National University cloned a dog they named Snuppy. In May 2005 Embrapa, a Brazilian agricultural research corporation, reported the creation of two cloned calves from a Junquiera cow, which is an endangered species. In 2006 ferrets were cloned using somatic cell nuclear transfer.

In 2009 the first camel was cloned in Dubai, United Arab Emirates. In 2010 researchers in Spain reported cloning the first fighting bull. By the close of 2010, over 20 animal species had been successfully cloned using nuclear transfer and surrogate mothers, the same technique that was used to produce Dolly the sheep.

Cloning Endangered Species

Reproductive cloning technology may also be used to repopulate endangered species such as the African bongo antelope, the Sumatran tiger, and the giant panda, or animals that reproduce poorly in zoos or are difficult to breed. In January 2001 scientists at Advanced Cell Technology (ACT), a biotechnology company in Massachusetts, announced the birth of the first clone of an endangered animal, a baby bull gaur (a large wild ox from India and Southeast Asia). The gaur was cloned using the nuclei of frozen skin cells taken from an adult male gaur that had died eight years earlier. The skin cell nuclei were joined with enucleated cow eggs, one of which was implanted into a surrogate cow. The cloned gaur died from an infection within days of its birth. That same year scientists in Italy successfully cloned an endangered wild sheep. Cloning an endangered animal is different from cloning a more common animal because cloned animals need surrogate mothers to be carried to term. Furthermore, the transfer of embryos is risky, and researchers are reluctant to put an endangered animal through the rigors of surrogate motherhood, so they opt to use nonendangered domesticated animals whenever possible.

Cloning extinct animals is even more challenging than cloning living animals because the egg and the surrogate mother used to create and harbor the cloned embryo are not the same species as the clone. Furthermore, for most already extinct animal species such as the woolly mammoth (Mammuthus primigenius) or the smilodon (Smilodon populator), there is insufficient intact cellular and genetic material from which to generate clones. In the future, carefully preserving intact cellular material of imperiled species may allow for their preservation and propagation.

In 2003 ACT announced the birth of a healthy clone of a Javan banteng (an endangered cattlelike animal native to Asian jungles). The clone was created from a single skin cell that was taken from another banteng before it died in 1980. The skin cell was kept frozen until it was used to create the clone. The banteng embryo gestated in a standard beef cow in Iowa.

Born in April 2003, the cloned banteng developed normally, growing its characteristic horns and reaching an adult weight of about 1,800 pounds (816 kg). The banteng lived at the San Diego Zoo until it died in April 2010 at the age of seven, less than half of the anticipated lifespan of a uncloned banteng. Hunting and habitat destruction have reduced the number of banteng, which once lived in large numbers in the bamboo forests of Asia, by more than 75% from 1983 to 2003. In "Ecological-Economic Models of Sustainable Harvest for an Endangered but Exotic Megaherbivore in Northern Australia" (Natural Resource Modeling, vol. 20, no. 1, March 2007), Corey J. A. Bradshaw and Barry W. Brook of Charles Darwin University report that in 2007 a population of between 8,000 and 10,000 banteng lived on an isolated peninsula in northern Australia.

In August 2005 the Audubon Nature Institute in New Orleans, Louisiana, reported that two unrelated endangered African wildcat clones had given birth to eight babies. These births confirmed that clones of wild animals can breed naturally, which is vitally important for protecting endangered animals on the brink of extinction.

Rob Waters describes in "Animal Cloning: The Next Phase" (Bloomberg BusinessWeek, June 10, 2010) the Frozen Zoo, a laboratory repository of frozen skin cells and DNA from about 800 species that are housed at the San Diego Zoo's Institute for Conservation Research. Even though the lab was established in 1972, the technology necessary to use the cells to clone animals was still under development in 2010. In June 2010 tissue from the Frozen Zoo was used to create stem cells of an endangered African monkey and the stem cells successfully developed into brain cells, giving rise to the hope that in the not-too-distant future it will be possible to clone endangered animals and save them from extinction.

Despite this progress, ethicists caution that there are moral considerations around the issue of animal cloning. Several cloned animals, including two endangered cattle and the banteng, died prematurely. Furthermore, ethicists question whether the risks (deformed and short-lived animals) outweigh the benefits if just a few endangered animals that ultimately live in zoos are created using cloning. According to Waters, Autumn M. Fiester of the University of Pennsylvania observed, "There has been a lot of suffering with these early deaths and malformations."

Reproductive Human Cloning

In December 2002 a religious sect known as the Raelians made news when their private biotechnology firm, Clonaid, announced that it had successfully delivered the world's first cloned baby. The announcement, which could not be independently verified or substantiated, generated unprecedented media coverage and was condemned in the scientific and lay communities. At least some of the media frenzy resulted from the beliefs of the Raelians—namely, the sect contends that humans were created by extraterrestrial beings.

Clonaid's announcement, which ultimately was viewed as a hoax, brought attention to the fact that several laboratories around the world had embarked on clandestine efforts to clone a human embryo. For example, in 2002 Panayiotis Zavos (1944-), a U.S. fertility specialist, claimed to be collaborating with about two dozen international researchers to produce human clones. Another doctor focusing on fertility issues, Severino Antinori (1945-), attracted media attention when he maintained that hundreds of infertile couples in Italy and thousands in the United States had already enrolled in his human cloning initiative. As of January 2011, neither these researchers nor anyone else had offered proof of successful reproductive human cloning.

Moral and Ethical Objections to Human Cloning

The difficulty and low success rate of much animal reproductive cloning (an average of just one or two viable offspring result from every 100 attempts) and the as-yet-incomplete understanding of reproductive cloning have prompted many scientists to deem it unethical to attempt to clone humans. Many attempts to clone mammals have failed, and about one-third of clones born alive suffer from anatomical, physiological, or developmental abnormalities that are often debilitating. Some cloned animals have died prematurely from infections and other complications at rates higher than conventionally bred animals, and some researchers anticipate comparable outcomes from human cloning. Furthermore, scientists cannot yet describe or characterize how cloning influences intellectual and emotional development. Even though the attributes of intelligence, temperament, and personality may not be as important for cattle or other primates, they are vital for humans. Without considering the myriad religious, social, and other ethical concerns, the presence of so many unanswered questions about the science of reproductive cloning has prompted many scientists to consider any attempts to clone humans as scientifically irresponsible, unacceptably risky, and morally unallowable.

People who oppose human cloning are as varied as the interests and institutions they support. Religious leaders, scientists, politicians, philosophers, and ethicists argue against the morality and acceptability of human cloning. Nearly all objections hinge, to various degrees, on the definition of human life, beliefs about its sanctity, and the potentially adverse consequences for families and society as a whole.

In an effort to stimulate consideration of and debate about this critical issue, the President's Council on Bioethics examined the principal moral and ethical objections to human cloning in Human Cloning and Human Dignity: An Ethical Inquiry (July 2002, http://bioethics.georgetown.edu/pcbe/reports/cloningreport/pcbe_cloning_report.pdf). The council's report distinguished between therapeutic and reproductive cloning and outlined key concerns by trying to respond to many as yet unresolved questions about the ethics, morality, and societal consequences of human cloning.

The council determined that the key moral and ethical objections to therapeutic cloning (cloning for biological research) center on the moral status of developing human life. Therapeutic cloning involves the deliberate production, use, and destruction of cloned human embryos. One objection to therapeutic cloning is that cloned embryos produced for research are no different from those that could be used in attempts to create cloned children. Another argument that has been made is that the ends do not justify the means—that research on any human embryo is morally unacceptable, even if this research promises cures for many dreaded diseases. Finally, there are concerns that acceptance of therapeutic cloning will lead society down a slippery slope to reproductive cloning, a prospect that is almost universally viewed as unethical and morally unacceptable.

The unacceptability of human reproductive cloning stems from the fact that it challenges the basic nature of human procreation by redefining having children as a form of manufacturing. Human embryos and children may then be viewed as products and commodities rather than as sacred and unique human beings. Furthermore, reproductive cloning might substantially change fundamental issues of human identity and individuality, and allowing parents unprecedented genetic control of their offspring may significantly alter family relationships across generations.

The council concluded that "the right to decide 'whether to bear or beget a child' does not include a right to have a child by whatever means. Nor can this right be said to imply a corollary—the right to decide what kind of child one is going to have. ... Our society's commitment to freedom and parental authority by no means implies that all innovative procedures and practices should be allowed or accepted, no matter how bizarre or dangerous."

Nearly universal opposition to human cloning persisted in 2011. According to the Center for Genetics and Society, in "About Reproductive Cloning" (2011, http://www.geneticsandsociety.org/section.php?id=16), even though some researchers now believe that it may be possible to safely clone humans, many more researchers remain unconvinced. Other compelling arguments against human cloning focus on the psychological health of cloned children and the concern that if human reproductive cloning was permitted, it would also usher in the use of genetic manipulation techniques that could markedly alter the fabric of society and even change the definition of human life.

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Gale Document Number: GALE|EJ1529400108