Health Talk: Chimeras
The ability to combine animals is an idea common to mythology in many cultures. The best elements of each animal were taken, forming a novel creature usually more powerful than its constituents. This type of animal was given the name “chimera.” For example, the griffin, a combination of a lion and an eagle — both kings of their domains — was a legendary symbol of divine power. The pincoy is a combination of a man and a sea lion that brings fertility to the sea.
Although mythological chimeras do not exist, researchers have been able to combine features of animals using modern genetic technology. Animal chimeras are formed when zygotes of different animals are mixed and allowed to develop within a carrier organism.
This ability arises from our understanding of organism development. After an egg is fertilized, cell division occurs until a large number of cells are created. However, these cells are all the same, and have not yet “chosen” a developmental path. This is to say that different cells will develop into different parts of the body; for example, some cells will develop into components of the digestive system, and others will develop into the brain. Before the cells “choose” a developmental path, scientists are able to replace some cells with cells from another animal, which also have not “chosen” their developmental path.
Chimeras have many uses in biological research. According to www.timesonline.co.uk, research under Yutaka Hanazano, a professor in the Division of Regenerative Medicine at Jichi Medical University in Japan, has been able to grow chimpanzee pancreas in sheep. Further development in this field may yield promising results with other organs, and Hanazano believes this research may one day allow sheep to become “organ banks” for humans who need transplants. His work was inspired by the lack of organ donors in Japan compared to other countries around the world.
Mouse chimeras are popular among biologists, and can be used to study cellular processes. In one instance, mouse chimeras were created with human brain cells, which allowed researchers to observe human neural development. Researchers were able to use these genetically engineered cells in mice as therapy to Tay-Sachs disease, a genetic disorder that causes mental deterioration, and ultimately death, in children. Cellular chimeras also exist, where scientists mix genomes of different organisms to produce a new cell with the desired traits. An article on www.nature.com stated that a viral chimera has been developed that combines the genomes of the common cold and the polio virus. Although this may sound like an attempt to create a supreme virus, the chimera can actually be useful for treating malignant glioma, the most common and fatal form of brain cancer. This kind of cancer cannot be removed surgically, and chemotherapy has proven to be ineffective. The chimera virus destroys malignant glioma, but does not cause polio. However, there is always the darker side to research. Chimeras may also have uses in biological warfare. According to www.howstuffworks.com, geneticists have been able to increase the potency of various infectious diseases, such as smallpox and anthrax. During the time of the Soviet Union, a high-ranking biological warfare expert considered combining smallbox and ebola into one virus. The possibilities are endless when it comes to chimeras. Diseases can be created that can remain dormant in the body until an external source triggers its activation.
Research with human chimeras is only in its beginnings, as work with human organs would require experimentation using human stem cells. The debate about the ethics of using human cells for experimentation is divided. However, chimera research has shown promising results and its research is important to our understanding of cellular processes.