A team of researchers at Universidad de Chile have grown tube-shaped, dinosaur-like fibulas – one of two long bones of the lower legs – on a regular chicken. To do so, they manipulate the gene of a regular chicken called IHH or Indian Hedgehog.
In dinosaurs, which are the ancestors of birds, the fibula bone was tube-shaped and reached all the way down to the ankle. Also, another bone called the tibia of same length grew beside it. But, as the evolution progressed ( from dinosaurs to birds), the fibula became shorter than the tibia, and it no longer reached the ankle. Modern birds embryos still show sign of developing long, dinosaur like-fibulae at early stage. But as the embryos grow, fibulae become shorter and they don’t make it to ankle.
Joâo Botelho, lead researcher of the study, decided to investigate the mechanisms that underlie this transformation with his team. In regular bone development, the shaft matures and stops growing (cell division) long before the ends do, but in modern birds, fibula’s growth stops first at the ends.
What Botelho found was that molecular mechanisms of maturation were active very early at the lower end, ceasing cell division and growth. So when they inhibited the expression of gene called IHH or Indian Hedgehog, it made the embryo of the chicken to grow tubular fibula as long as the tibia and connected to the ankle, exactly like a dinosaur.
The researchers believe that early maturation at the lower end of the fibula in modern chickens occurs because of the influence of a nearby bone in the ankle, known as the calcaneum. They explain that unlike other animals, the calcaneum in bird embryos presses against the lower end of the fibula, and some even confuse them with a single element because “they are so close.”
In regular chickens, interactions between the calcaneum and the end of the fibula influence the bone shaft to stop growing, and this prevents the fibula from reaching the ankle bone. However, when they turned of the gene Indian Hedgehog (IHH), the calcaneum strongly expresses PthrP, a gene that allows growth at the ends of bones. And, this made their chicken to grow long fibula that connected with the ankle.
Unfortunately, the chickens with experimentally dinosaur-like lower legs could not survive till the hatching stage. ScienceAlert notes that the researchers did not mean to raise them into full-grown “dino-chickens,” but to understand “the biological processes that led to the transition from dinosaur legs to modern bird legs.”
“The experiments are focused on single traits, to test specific hypotheses” says Alexander O. Vargas. “Not only do we know a great deal about bird development, but also about the dinosaur-bird transition, which is well-documented by the fossil record. This leads naturally to hypotheses on the evolution of development, that can be explored in the lab.”