Scientists Tweak Genes and Grow a Dinosaur Leg on a Chicken
by Jessica HallThis just in from the what-could-possibly-go-wrong department: Scientists from the Universidad de Chile, headed by Joâo Botelho, genetically manipulated chickens so that they would grow up with legs like dinosaurs. They apparently did not notice the major premise of the latest Jurassic Park movie, because this really looks like someone in a lab coat thought “Let’s make a creature grow up to express more velociraptor-like traits and just see what happens.”
But that’s not even the crazy part. The crazy part is that to do this, the researchers didn’t insert genes from any organism. They just silenced a gene the chickens already had.
Now, they didn’t build a chicken that looks like someone just cut-and-pasted a leathery green raptor leg onto it — but it’s close enough for government work. You see, chickens have a detached and diminished fibula. It’s the tiny pin-like (not a coincidence: fibula is Latin for pin) bone we hate in chicken legs. Suppressing one of the genes responsible for the differences between raptors and chickens — in this case, it’s a gene called Indian Hedgehog which is important to bone development — resulted in chickens that develop a full-length, tubular fibula connected at the ankle. They ended up with chickens possessed of bone structure that matches the lower leg anatomy of a raptor. The dino-chicken leg bones look just like raptor leg bones, as visible here:
The fibula bone (orange) in Dinosaurs is as long as the tibia and reaches down to the ankle (upper left), whereas in adult birds, it is splinter-like and shorter than the tibia, missing its lower end (upper right). However, bird embryos actually start out like dinosaurs, and then develop their adult anatomy (centre). The transformation can be stopped by experimental inhibition of Indian Hedgehog (IHH), a bone maturation gene, which leads to a bird with a dinosaur-like fibula (lower right).
(Image courtesy of Universidad de Chile)
Dinosaurs, which are the ancestors of chickens, had a tibia and fibula of the same length, connected at the ankle. In the evolution from dinosaurs to birds, the fibula retracted under lighter use and no longer connects to the ankle; it became shorter than the other bone in the lower leg, the tibia. Embryologists had already discovered that during the course of development, bird embryos first develop a tubular, full-length, dinosaur-like fibula. Only later does it become shorter than the tibia and acquire its mature, pin-like shape.
This is the second time Botelho has
tempted fate achieved an experimental reversion to a dinosaur-like trait in birds. Previously, he had managed to undo the evolution of the backward-facing perching toe of birds, using gene modification to produce birds with a non-twisted, non-opposed toe, also just like dinosaurs had — and another lab at Yale built a chicken with a dinosaur-like snout by altering gene expression in chicken embryos. But the scientists assure us that they aren’t trying to produce dinosaurs. You know, just parts of dinosaurs. Or things like dinosaurs. Not sure which is less terrifying.
“The experiments are focused on single traits, to test specific hypotheses,” says Alexander Vargas, in whose lab Botelho made the chickens. “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.”
Indominus Rex by DanteFitts
Sooner or later we’ll hear how this series of experiments plays out. Meanwhile, I’ll be busy being glad I don’t live on or near an island.