The Legacy of Dolly the Sheep: A Review on Cloning

Have you ever encountered someone who looked exactly identical to another person? While you may have seen identical twins, they are not truly the same person despite their similar appearances. To achieve true identicality, we enter the realm of cloning: a process where organisms are created with the exact same DNA, genes, and everything in between. Cloning involves a variety of sophisticated techniques to produce precise genetic replicas of biological organisms. Although it might seem like a concept straight out of science fiction, cloning has been a subject of scientific research and practice for several decades.

The act of cloning was first proposed by German embryologist Hans Spemann in 1938. Unfortunately, scientists and researchers were unable to create successful clones until 1979, where they produced the first animal clone, creating genetically identical mice. They were able to achieve this by implanting split mouse embryos into the wombs of adult female mice. After this success, scientists produced other genetically identical mammals such as chickens, cows, and sheep through a similar method of implanting the nucleus of an early embryo into a reproductive egg with no nucleus. While scientists found success in cloning infant embryos, they struggled to find a way to clone mature adult cells.

However, on July 5, 1996, researchers at the Roslin Institute of the University of Edinburgh achieved a groundbreaking milestone: the creation of Dolly the Sheep, the first mammal cloned from an adult somatic cell. Interestingly, this experiment was originally intended to explore the production of therapeutic proteins in animal milk to treat human diseases. The researchers were using embryonic stem cells to create genetically modified animals and did not anticipate that the adult cells they harvested would develop into viable embryos. Dolly's unexpected birth marked one of the most significant scientific breakthroughs of our time, opening new doors in the field of genetics and biotechnology.

Fun Fact: Dolly the Sheep was named after the famous singer Dolly Parton!

But how was Dolly cloned? First let’s go over a few methods of cloning. Gene cloning involves producing copies of genes or segments of DNA. It is a common practice in molecular biology used for applications of sequencing, mutagenesis, and genotyping. One use of gene cloning involves transferring a DNA fragment from one organism to a self-replicating genetic entity such as bacteria. Nowadays, gene cloning is used to isolate peculiar and unstudied genes. Reproductive cloning involves the implementation of a mature somatic cell into an egg cell without any DNA traces. In this process, the egg develops into an early-stage embryo in an incubator before being implanted into a womb of some adult female organism. When the adult female gives birth, it gives birth to a clone of whatever animal donated the cell. Therapeutic cloning is a method that is used to clone an embryo for the purpose of producing embryonic stem cells with the same DNA as the donor. The cloned cells are then used in various experiments for finding treatments for diseases. Dolly the Sheep, as well as the cloned mammals before her, was cloned using the method of reproductive cloning. The somatic cell used for her cloning came from the udder cell of a six year old sheep.

In late 2001, Dolly suffered from some physical setbacks. She was seen to be walking very stiffly and rigidly. Later on, a few X-rays revealed that Dolly had arthritis, fuelling implications that cloned animals had lower life expectancies. Sadly, after around two years, Dolly passed away on February 14, 2003. However, she died from a lung infection that was found to be common among many other sheep at the institute. This discovery dispelled the myth about premature deaths and cloned animals. Despite her passing, Dolly the Sheep continued to influence scientists and researchers around the world.

Dolly the Sheep’s success unveiled unprecedented scientific possibilities. The Dolly Project not only pioneered the field of cloning but also significantly advanced stem cell biology. Inspired by the project's breakthroughs, stem cell biologist Shinya Yamanaka developed induced pluripotent stem cells from adult cells. This revolutionary achievement earned him the Nobel Prize in 2012 and has since become foundational in various research disciplines.

As cloning techniques improved, scientists began exploring the potential of cloning to save endangered species from extinction. In 2003, the first cloned endangered animal, a banteng (a species of cattle from Southeast Asia), was born. This success sparked further efforts to clone endangered and even extinct species. While some endangered species cloning projects have shown promise, cloning extinct species presents unique challenges because scientists must obtain preserved DNA from the extinct animals to initiate the cloning process. However, such DNA is often scarce or unavailable for many species. Despite this, the continued exploration of cloning holds promise for biodiversity conservation and scientific discovery.

Now, you may be wondering: Has anyone ever cloned a human being? Based on the information you have already read, you must think that this process has been executed before. However, despite the myriad of cloned animals, there have been no cloned humans to exist to this day. While there may have been claims of human cloning, no official reports have stated the existence of a human clone. For example, in 1998, South Korean researchers claimed to have successfully cloned a human embryo. However, this claim fell short when they revealed that the experiment was halted when the embryo became four cells. In 2002, a religious group claimed that the first cloned human was birthed. Due to lack of evidence to confirm the existence of the clone, this claim was also refuted. According to many researchers and scientists, it is actually more difficult to clone humans compared to other mammals because of the structure of the reproductive eggs. When removing the nucleus from an egg, the spindle proteins, proteins needed for cell division, are also removed. This damages the cell and prevents it from performing cell division, stunting its growth. This is most likely the reason why no one has ever cloned a human being before.

Although the science behind cloning has come a long way, we must always remember one sheep that forever transformed the field of cloning–Dolly the Sheep. Dolly's successful cloning was not just a scientific triumph; it was a pivotal moment that reshaped our understanding of genetics, development, and the potential of biological science. Her birth demonstrated that it was possible to create a living organism from an adult somatic cell, challenging previously held beliefs and opening up new avenues for research and application. I hope you learned something new! Keep a lookout for the next post!

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References

BIO RAD. (n.d.). Introduction to Gene Cloning and Analysis. BIO RAD. Retrieve August 7, 2022, from https://www.bio-rad.com/en-us/applications-technologies/introduction-gene-cloning-analysis?ID=LUSNKO4EH

National Human Genome Research Institute. (2020, Aug. 15). Cloning Fact Sheet. National Human Genome Research Institute. Retrieved August 7, 2022, from https://www.genome.gov/about-genomics/fact-sheets/Cloning-Fact-Sheet

Rozenbaum, M. (2022 Jan. 6). 25 years after Dolly the sheep – cloning today. Understanding Animal Research. Retrieved August 7, 2022, from https://www.understandinganimalresearch.org.uk/news/25-years-after-dolly-the-sheep-cloning-today