Before the famous Dolly the Sheep, cloning was not quite what it is considered today. The first example that could be considered “cloning” took place in 1885. Hans Adolf Edward Dreisch discovered that if he shook the two-celled embryos of sea urchins, the cells could separate and grow into two identical sea urchins. A couple decades later in 1902, Hans Spemann decided to find out if he could do the same, this time with salamander embryos. These embryos were stickier than those of sea urchins so Spemann took a strand of baby hair to wrap around the embryos and tighten until they split into two.
This lead to the same result of the previous experiment only with salamanders instead of sea urchins. When Spemann tried to split more advanced embryos, he had less success getting these “twin” salamanders to adulthood. Spemann did not stop testing there. In 1928, Spemann forced the embryo’s nucleus to one side and tied off the other, not enough to make it split but enough to keep the nucleus to the other side. The nucleus side went through cell division as normal, yet the side without a nucleus did not.
After the nucleus side had gone through cell division four times, which produces 16 cells, Spemann allows one of the cells, which has a nucleus, to go to the non dividing side before snipping the sides apart. Both of the embryos grew into normal salamanders, despite one not having its own nucleus and “borrowing” one. This experiment brought to light the idea of nucleus substitution. A couple more decades passed and in 1952 Robert Briggs and Thomas King decide to try their hand at cloning, this time with frogs.
Briggs and King wondered if they could take the nucleus of an early tadpole embryo and put it into a frog egg that did not have a nucleus. This turned out to be a success. Briggs and King continued to experiment with cloning frogs and learned that like with Spemann’s salamanders, the success was less likely with the further advanced embryos. In 1958, John Gurdon made another leap for cloning progress. Gurdon took the nucleus from a tadpole’s intestinal cell and implanted it into a frog’s egg that did not have a nucleus. This created a tadpole genetically identical to the one Gurdon stole a cell’s nucleus from.
The idea that one could make a clone from a fully developed organism was rather exciting, but research did not stop there. Over a decade later, in 1975, J. Derek Bromhall wanted to move past amphibians and echinoderms and towards mammals. Bromhall took the nucleus of a rabbit’s embryo and put it into an enucleated rabbit egg. The new embryo grew and developed but Bromhall did not put the embryo into a mother rabbit’s womb so it did not get past this point. It was not until a few years later that a cloned mammal made it past the embryonic stage.
In 1984, Steen Willadsen follows the normal procedure of making a clone by transferring a nucleus from an 8 cell embryo, this time with a sheep. At this point in time, in vitro fertilization had helped many couples have children. Using this process, Willadsen placed the embryo clones into a surrogate, this sheep gave birth to three lamb clones (4). Curious to see if this process would work on other mammals, Neal First, Randal Prather, and Willard Eyestone decided to use the exact same process Willadsen used 3 years before, this time with a cow.
The experiment was a success. In 1996, it was time to switch things up. All the former nuclei had come from early embryos and Ian Wilmut and Keith Campbell wanted to see if cloning would still work despite using cultured sheep cells from a laboratory. Wilmut and Campbell used the same procedure as the people before them and their surrogate gave birth to two lambs named Megan and Morag. Later that same year, the famous Dolly made her appearance. Wilmut and Campbell wanted to see if they could create a clone from an adult somatic cell.
To find out, they took the nucleus from an adult sheep’s udder cell and inserted it into enucleated egg. Unlike using the nucleus from an embryo and transferring it into enucleated egg, the adult cell nucleus needs its genetic information to be reset back to the embryonic state. This factor caused Wilmut and Campbell to lose 276 of their attempts at cloning a sheep using an adult somatic cell. Finally, one embryo made it far enough to be carried to term in a surrogate mother and the famous Dolly was born.
The following year, in 1997, Li Meng, John Ely, Richard Stouffer, and Don Wolf wanted to attempt cloning a primate. However, they knew how much trouble it was for Wilmut and Campbell to create a clone from an adult somatic cell and they deemed it best to fall back on the easier way of embryonic cell nuclear transfer. The team created 29 embryonic clones to place into surrogate mothers, but only two survived, a male and a female named Ditto and Neti. The ability to clone human’s closest relatives brought up the question on whether humans could be cloned as well.
In the same year, Angelika Schnieke, Keith Campbell, Ian Wilmut recalled the success of cloning sheep with cultured embryonic cells from the lab and expanded on this basic idea. They introduced the human Factor IX, which is a protein that aids in blood clotting, into the genome of sheep skin cells. After that, the team then took the nucleus from these cultured transgenic cells and placed them into the enucleated cells in the usual fashion. The result was Polly, a sheep with the ability to produce Factor IX protein in her milk.
This experiment showed promise for more medical advances with the assistance of cloning, In the following years, more scientists tried their hand at cloning with no real enormous advancements made. In 2001, different groups tried to fight the gaur and mouflon extinction through cloning. However, it is unclear as to how successful this process was and appears to need more research before saving endangered animals through cloning will become a sound reality. A couple of years passed and in 2007, Shoukhrat Mitalipov and his colleagues used a rhesus monkey to create embryonic stem cells through somatic cell transfer.
By fusing an adult monkey cell with an enucleated egg cell and allowing this embryo to develop for a while before moving its cells into a culture dish, researchers created embryonic stem cells. This was excited news that could possibly open the doors to therapeutic cloning for humans that could allow scientists to study and treat diseases. Only a few years ago, Mitalipov and his colleagues expanded their research further. In 2013, they created human embryonic stem cells. The patient was a baby with a rare genetic disorder from whom the researchers took skin cells from to be fused with a donated egg cell.
With a series of electrical pulses, the egg began dividing. Although the cloning process shows promise for medical advances, a controversy still arises over the issue. When asked why these people did not support cloning, 34 percent believed that it was against their religion, 22 percent believed that it interfered with distinctiveness and individuality, another 22 percent were concerned that cloning could be used for questionable purposes, 14 percent were worried about the technology used, 5 percent had a different reason not previously mentioned, and 3 percent were just against it for an unknown reason.
People are concerned scientists are “playing God” and these creatures are abominations. The question of ethics is often brought up to surround this topic, the quality of life for the clones is a big issue. Clones do not live as long as their “original copy” and often suffer more genetic disorders as well as other health issues (1). Other people worry that if human clones came into existence, they might be treated as second class citizens or be locked up waiting for their organs to be harvested.
For these reasons, “Scientific organizations like the American Academy for the Advancement of Sciences have spoken in favor of a ban on human cloning until it can be done safely. ” (7). However, most scientists are in favor of cloning, as long as it is under strict government control and ethical review. Others look forward to bringing extinct animals back into existence and helping endangered creatures from that fate. Although the ethics of cloning is still up to debate, the new outcoming science behind it is truly fascinating and time will only tell what will be discovered.
