THE CLONED SHEEP

Since 1997 when Dolly the cloned sheep was born, scientists have been successful in creating dozens of animal clones. Understanding chromosome duplication and cell division has resulted thus far in the births of cloned pigs, mice, cows, goats, and even a cat. However, scientists at the University of Pittsburgh have found that their most recent and ambitious attempt to clone a monkey has proven to be a disappointment.
Due to a basic obstacle in the molecular structure of primates – humans included – scientists have discovered that cloned primate cells have repeatedly failed to divide in the proper way. Accordingly, the process of pregnancy cannot even begin due to the chromosomal abnormalities that occur when there is an improper division of cells.
When scientists attempt to clone a species, they remove the portion of an animal’s cells, known as the nucleus, which bears the animal’s DNA. The nucleus of the cell is then ‘plopped’ into an egg that has not yet been fertilized. Ritter observes, “The implanted DNA drives the egg to develop into an embryo, which is placed in a surrogate mother, where it grows into a newborn – the genetic clone of the animal whose DNA you started with” (2003). Furthermore, each egg contains a nucleus of its own, which has to be removed before the egg is able to accept the new nucleus. In most animal species, this has not presented any difficulty. It does pose a problem with monkeys, however. With his research team at the University of Pittsburgh, Gerald Schatten’s work has revealed that when the nucleus is removed from a monkey egg, two essential proteins are also removed. Absent these proteins, there is no possibility that the egg will produce a new monkey. Researchers have discovered that the cloning of other animals has been possible because animals such as cows and mice have more than one copy of the two key proteins needed to help the cloned embryo develop and grow.
While this molecular obstacle to cloning primates will have scientists and researchers in the field of cloning trying to overcome this barrier, some experts suggest that this development may be for the best. The main concern is that it may be dangerous to clone human beings. Even though the scientific breakthrough that came about when Dolly was born received widespread media attention, the fact remains that the cloning of barnyard animals has not yet been perfected. What the media doesn’t seem to report quite so readily to the public are the numbers of cloned animals that are stillborn, or the percentage that do survive but have significant birth defects (AP, 2003). Additionally, researchers conducted no less than 277 attempts before succeeding with Dolly. In contrast, some 724 eggs were used when attempts were made to clone a rhesus monkey. Out of those 724 eggs, only 33 embryos developed. Still, despite that many attempts, not a single pregnancy resulted from those efforts to clone a monkey. Scientist Schatten makes this humorous observation, "It's almost like God in her wisdom said go ahead and clone cows and sheep, but if you clone a human I'm going to paralyse the egg" (Cohen, 2003).
Certainly, it seems likely that uncovering this molecular block should be giving researchers reason to pause. The problem they are now facing is an essential piece of information and will have a significant impact on the future of cloning. Given the fact that absolutely no pregnancies developed in the monkey experiments, that degree of failure seems to suggest a fundamental difference between the DNA of barnyard species and that of primates and/or humans.
Additionally, it should be noted that the emergence of this molecular block is not only a glitch in the research on reproductive cloning. What is perhaps an even more significant development is that this same glitch is also very likely to have a negative impact on embryonic stem cell research, and its subsequent application in the treatment of many serious medical conditions. Schatten makes a point of emphasizing that his primary interest in being able to clone monkeys, and eventually humans, is strictly for medical purposes. He contends, “Human reproductive cloning is unsafe, unethical and ought to be illegal everywhere in the world." With respect to his own work, the scientist admits that if he does find a way to overcome the molecular obstacle and is successful in his efforts to clone primates and humans, he also intends to safeguard his research so that his methods will not be used to produce human babies (Ritter, 2003)