genetics

to clone or not to clone?

margie sanchez, science contributor 

     On February 15, 2002 scientists working for the Department of Veterinary Sciences at Texas A&M announced the first successful cloning of a cat. The kitten, named CC after the old typist abbreviation for carbon copy, was born on December 22, 2001. Members of the team who performed the cloning had withheld announcement of the birth until they could verify genetic identity. This cloning breakthrough was published in the February 21, 2002 issue of Nature, the London based scientific journal.

As the first cloned companion animal, CC was an instant global sensation and celebrity. A team at the Audubon Nature Institute had been researching similar experiments in animal cloning, although their efforts were ultimately aimed at the preservation of endangered species. The team at the Institute had already successfully cloned a gaur, an endangered species of wild cattle native to India. Dr. Philip Damiani, a staff scientist at the Institute, said that the success of their colleagues in Texas would accelerate the institute’s research in cloning technology, including the protection of endangered species.

     Texas A&M continued to develop their cloning techniques, and have now cloned more species than any institution in the world.

                                                                                             Rainbow and C.C. the cloned cat!

                                                                                             Rainbow and C.C. the cloned cat!

Since 1999 their researchers have successfully cloned cattle, swine, goats, horses, a deer, and other animals. But CC the cat was ostensibly the defining moment in the history of cloning. Her birth proved that the technology of cloning could be applied to species that had previously proved difficult to replicate. Moreover, CC was a healthy, viable animal and never exhibited the health problems or short life spans of other cloned animals like Dolly the sheep. CC was healthy at birth, and continues to enjoy a full and healthy life at the home of Dr. Duane Kraemer, one of the scientists who helped clone her. In September 2006, CC gave birth to a litter of normal, healthy kittens.

Dr. Kraemer explained that she was allowed to reproduce once for scientific study. This event was another milestone in cloning technology.  Because she can reproduce, not only is CC a healthy cloned animal, but she is considered to be a viable one in terms of biology.  CC’s two sons and daughter live with their mother and father in a cat mansion at the Kraemer home. Indeed, CC the cat continues to be a crowning achievement for cloning technology thus far.

     Shortly after the announcement of her birth, CC was featured in National Geographic as a great contribution to science, opening the way to successfully replicating pets and other valued animals once the cloning technique was perfected. At the time, the research that produced CC was partially funded by a company that sought to use the cloning technology to provide commercial cloning of companion animals for pet owners. Richard Denniston of Lazaron Biotechnologies revealed that the company had several hundred customers who “banked” the DNA of their pets with Lazaron in the hope that they would be able to replicate their pets someday. Denniston shared that his company had banked “lots and lots” of cats as well as dogs, cattle, goats, horses, etc. He revealed that many people were interested in cloning animals.

 

However, until the success of CC, cloning had been limited to cattle, sheep, and pigs. Remember Dolly the sheep?  Born at the Roslin Institute in Scotland in 1997, Dolly the sheep was the world’s first cloned animal.  Just like CC the cat, Dolly’s birth was acclaimed as a phenomenal scientific breakthrough.  However, her birth also immediately heralded an outbreak of ethical discussion. Why clone a sheep? What will scientists attempt to clone now? Who will be the first to attempt to clone a human? Should humans be cloned?  Who will regulate or limit cloning?

The arrival of CC heated the debate even more. The Humane Society argued that cloning was dangerous to the animals involved. They were also opposed to cloning companion animals because it needlessly added to the overpopulation of animals in shelters waiting for homes. Brian Sodergren, who monitored the exploitation and abuse of animals at that time for the Society, pointed out that the large number of embryos used to obtain only one successful birth was “mind-boggling”.  So, how is cloning achieved? And what exactly is a clone?

      The answer to the second question is fairly simple to address. All we have to do is look at twins. Not fraternal twins, but identical twins, or triplets, etc. Each identical twin is a clone of the other twin. Therefore, human clones already exist naturally. These natural clones occur when a fertilized egg splits. This unusual cleavage of a fertilized egg (or sometimes a very early embryo) sets the stage for genetically identical babies. In contrast, fraternal twins are the result of two or more eggs fertilized at the same time.


Since they have genetic differences they are not identical twins, triplets, etc. and, therefore, are not genetic clones.  But even though she was verified as a genetic clone, CC demonstrated obvious differences from her genetic donor mother. That’s because the pattern of cats’ coats is only partially genetically determined. It also depends on factors during fetal development. This process also applies to humans. Identical twins almost always demonstrate differences, sometimes obvious, sometimes slight to imperceptible. It was obvious that CC was born with a color pattern similar to her cell donor, but not exactly the same.


Dr. Westhusin, the lead researcher for the Texas A&M team, explained that the patterns of pigmentation in multi-colored animals can be affected by developmental factors that cannot be controlled by genotype (genetic expression) alone.  A genotype is the description of a trait or traits at the genetic level. A phenotype is what is expressed physically, including traits that are visible to us like hair color. For instance, a person could carry one gene for red hair from his mother and one gene for black hair from his father. So his genotype for hair color can be represented as Bb, B for black hair, and b for red hair.


However, because B for black hair is dominant over b for red, he has black hair. And that is what we see, or that is what is expressed. In other words, that person’s phenotype for hair is black even though he also carries a gene for red hair in his genotype. (Actually, the genetics of human hair color (like skin and eye color) is more complicated than the above scenario, something like cats’ coats.) The difference between a genotype and phenotype illustrates only one of the challenges for cloning technology. Moreover, it’s impossible to control or limit developmental and environmental influences that affect genetic variances. So how does artificial cloning differ from natural cloning? And how much more difficult is artificial cloning?

     Artificial cloning is much more difficult to achieve. For instance, the successful cloning of CC was preceded by unrelenting perseverance of laborious attempts by trial and error before the scientists finally achieved their goal. Dr. Taeyoung Shin did the cloning by nuclear transfer with Drs. Duane Kraemer, Jim Rugila, and Lisa Howe assisting with the transfer of the cloned embryos into the surrogate mother (a cat named Allie) and delivery of the kitten. CC and her genetic donor are both female domestic shorthairs. CC’s cloning was achieved by transplanting DNA from Rainbow, a female three colored tortoise-shell (or calico) into an egg cell whose nucleus had been removed, then implanted this embryo into Allie, the surrogate mother. The procedure seems straightforward enough, but requires many attempts and many nuclear transfers to produce numerous embryos ready for transfer into surrogate mothers.

      In their first attempt, the researchers used skin cells of a donor cat to make the clone. Eggs from other cats were used for the next cloning step. Their chromosomes were removed, and then replaced with DNA from the frozen donor cells, creating cloned embryos which were finally transplanted into surrogate mothers. The researchers did 188 nuclear transfers which resulted in 82 cloned embryos that were transferred into 7 surrogate mothers. But only one cat became pregnant with a single embryo, and that pregnancy resulted in miscarriage. The embryo had to be surgically removed after 44 days, but at least it was determined to be a cloned embryo.

     For the next attempt, the research team used cells from ovarian tissue to receive the DNA from the cat to be cloned. Five cloned embryos produced from this attempt were then implanted into a single surrogate mother, Allie. Ultrasound confirmed pregnancy 22 days later and a single kitten, CC, was delivered by C-section on December 22, 2001- 66 days after the embryo was transferred. Although the kitten was healthy and normal at birth, the announcement was delayed until genetic identity could be verified. The announcement also had to wait until CC completed her shot series and her immune system was fully developed. In spite of this great triumph, the company that partially funded the team’s research cautioned that it would be difficult to estimate when the cloning of dogs and cats would be commercially available.

In fact, much more research will be required before we witness the routine cloning of pets, ala “Sixth Day”. For those of you who are not familiar with this movie starring Arnold Schwarzenegger, “The Sixth Day”, released in 2000, is about a man living in the near future (2015). The title of the movie refers to the laws prohibiting the cloning of humans, called the Sixth Day laws in reference to the 6th day of Creation when God created humans. The routine cloning of animals and the illegal cloning of humans sets up a plot with ethical and moral issues on both sides of the cloning debate.  At the time the movie was released, companion animals like CC had not yet been successfully cloned. And just like in the movie, cloning raises ethical and moral issues on several fronts.

Who determines which species could and should be cloned? Will cloning of pets be limited to the rich? Can cloning technology provide medical and scientific benefits? Is cloning humane to the animals used in the procedure? What about the cloning of endangered species? How practical is it? What happens if their natural habitat can no longer sustain the endangered species? Or worse, what if their natural habitat no longer exists? Is it ethical or humane to continue cloning an endangered species for scientific study? Can we justify placing a cloned species in zoos or private collections to prevent the extinction of the species? Should humans be cloned? Can human cloning ever be justified?

    At this time, there is a unanimous global moratorium on human cloning. Officially, that is. There’s no effective way to monitor or regulate research on human cloning.  But why clone a human in the first place? Ah, maybe you’re thinking someone could clone Einstein, or a supermodel, or Michael Jordan. Remember that CC is not an exact duplicate of her mother. And identical human twins also differ, sometimes even in intelligence and abilities. Developmental factors as well as environment make each human unique, even twins. Second, cloning humans isn’t very practical. Cloning a human is not as easy as “The Sixth Day” and other sci-fi stories imply. The moral implications alone of human cloning raise so many objections that most scientists will probably be prohibited from even attempting such a controversial feat of scientific advancement.  In contrast, cloning human tissues and organs is a field ripe with hopeful and exciting prospects. Successful organ and tissue cloning would eliminate the frustration of long waiting lists for donor organs as well as complications like Host vs. Graft disease.

     An argument could be made for the practicality of cloning farm animals like Dolly the sheep. Humans have been breeding sheep and cattle for thousands of years in an attempt to improve the species. Exact genetic duplication allows an improved animal to be shared and distributed very quickly. A flock or herd of genetically identical animals will give wool, milk, eggs, or meat in a more standardized quality. Cloning would also speed up the process of genetically engineering animals to produce pharmaceutical products for human use. At this time, research is being conducted on transgenic animals like goats. The research utilizes somatic cell nuclear transfer, otherwise known as cloning, to ensure that the animals will carry the desired genes for creating drug proteins which will be obtained by purifying the animals’ milk. The million dollar question is- how safe is cloning technology to the animals involved in the cloning procedure? And how safe are the products of cloning to humans?  

    By the time you read this article, scientists somewhere in some part of the world have already perfected a new cloning procedure, animal, or product. Despite ethical and moral issues regarding all cloning, it is likely that cloning will continue to be a hot project for researchers attempting to push the envelope in the advancement of science. The question with cloning, as with all scientific advances is this: Just because we can, does that mean we should?