A group of scientists have successfully created a human-chicken embryo, a scientific feat previously made impossible because of strict ethical laws.
But by inventing a new technique to graft human embryonic stem cells into a chicken embryo, researchers at New York City's Rockefeller University were able to create the world's first human-chicken hybrid that bypasses regulation.
The researchers believe this could bring advances in human developmental medicine and pave the way for better methods in preventing birth defects and miscarriages.
What Are Organizer Cells?
When a clump of cells come together to form an embryo, it decides its future fate with what scientists call organizer cells. These cells, first discovered in 1924 in salamanders and have since been observed in other animals, direct the formation of the animal. In other words, these cells are responsible for organizing the formation of limbs, organs, and other body parts.
Up until now, scientists have not been able to find organizer cells in humans. Governments around the world have imposed an ethical ban on experimenting with human embryos after its 14th day. This is around the time organizer cells would appear in a natural pregnancy.
"No one knew what happens after the ball of cells attaches itself to the uterus," says stem cell biologist and lead researcher Ali Brivanlou.
How A Human-Chicken Embryo Was Formed
By using human embryonic stem cells, Brivanlou and his team circumvented the 14-day ban and created a new structure akin to a human embryo. The team cultured the stem cells, which could turn into any of the specialized cells, on small squares that forced them to come together instead of spreading apart.
They also exposed the cells to two proteins, causing them to form layers similar to a human embryo. Later testing showed the cells expressed genes also found in the organizer cells of other animals.
The team went on to graft the embryonic cells into a chicken embryo, which was taken from the egg at the 12-hour mark, a point similar to the 14-day point in human embryos. The result that followed was astonishing.
Hello, Human-Chicken Hybrid
It's not easy grafting human cells into other species. The team, for instance, had previously tried and failed to create a human-mouse hybrid embryo. However, their latest feat shows humans and birds may not be as evolutionary different as were once thought.
As soon as the human cells were transplanted, organizer cells immediately began directing the embryo to form a secondary spinal column and nervous system that were made entirely of chicken cells. Brivanlou says this is a clear indication that human organizers do exist.
"To my amazement, the graft not only survived, but actually gave rise to these beautifully organized structures," he says.
He also believes that the ability of human cells to organize new structures in a chicken, which is more closely related to dinosaurs than humans, is proof that animal cells' ability to create their destiny have survived hundreds of millions of years.
What Are The Medical Implications?
By understanding how stem cells can organize and generate various body parts, researchers could break ground into new avenues in regenerative medicine, where stem cells are used to heal damaged tissue or even generate new organs.
The study also provides a groundbreaking look into the early stages of human development. By opening up new insight about how cells form and organize into body parts, scientists can come up with new methods and techniques to prevent birth defects and miscarriages, as well as other diseases such as cancer and diabetes.
The study is published in Nature on May 23.
