Clever Apes: Cooking up a dino-chicken
We bring you a guest post today from Faraz Hussain, who studies biochemistry at Illinois Institute of Technology. Faraz is a student of Joseph Orgel, the biologist researching preserved dinosaur tissue whom we profiled in the latest episode of Clever Apes. Here, Faraz introduces us to a completely different way of bridging the eons to bring dinosaurs into the present day. – Gabriel Spitzer
Dinosaurs’ 180 million-odd year reign may be considered a lively old romp by most, but some clever apes would prefer to study these fossils in the flesh. One particular suborder, the theropods, never really went extinct at all. The birds that descended from them are the nearest living relatives today of both raptors and tyrannosaurs—perhaps none more so than the humble hen. Paleontologist Jack Horner, one of the most vocal exponents of avian dinosaurs being all around us, would rather that hens' more imposing ancestors had not evolutionarily "chickened out" in the first place.
Instead of messing about with amber-encased mosquitoes gorged on dino-DNA and playing fill-in-the-blanks with frog and bird genomes à la Jurassic Park, Horner has been rallying his paleontologist pals and evolutionary developmental biologists to try a fresh tack on resurrecting a dinosaur: He wants to reverse-engineer a chickenosaurus. Hey, why start from scratch when you already have a fully-formed dinosaur in need of just a few minor genetic modifications? What follows is not your grandma's stuffed chicken recipe:
While birds may have opted for wings instead of claws, both the T. rex and the chicken have only three digits at the end of each. In birds, however, these fingers have fused together. Hans Larsson at McGill University's Redpath Museum is looking for ways to short-circuit the genetic pathway responsible for this process in the chicken's embryonic stage and allowing the digits to separate so that, instead of those delicious wings, it ends up with far deadlier talons instead.
A chicken has only a handful of vertebrae at the end of its spine that fuse to form what passes for its tail. In 2007, Larsson observed a tail in a developing chick embryo that had 16, although by the time it hatched these had dwindled to five. Turn off the genetic mechanism that triggers the breakdown and absorption of the tail, and voilà—you're well on your way to the 40 or so vertebrae found in some of the heftiest hindquarters ever: the T. rex tail.
Matthew Harris discovered the rudiments of teeth on a frankenchicken embryo called the talpid2 usually known for its polydactyl fingers. While a far cry from the toothy old tyrannosaur grin that we know and love—the genome of a chicken doesn’t contain genes coding for enamel, nor can they produce dentin, which made up the bulk of those formidable fangs—it’s finally a fighting chance for poultry to bite back!
The scaly skin covering chicken feet is the closest approximation we have to dinosaur dermis. Engineered so that it would be shorn of its feathers from birth and covered in this leathery skin, the one issue that would remain to be settled is whether you prefer your dinosaurs purple or green. The only real clues we have when it comes to coloration are possible hints about the plumage of the turkey-sized Sinosauropteryx.
Another gimme! Instead of picking your garden variety Rhode Island Red, which like most birds of its feather, is restricted to a horizontal femoral posture, start out with a heartier cousin like the Philippine gamecock instead, which has an upright femur robust enough to carry the weight of its eventual dino-tail.
Arkhat Abzhanov found that two signaling proteins—Fibroblast growth factor 8 and the creatively named Sonic hedgehog—mediate the fusion of different segments making up a bird’s jawbone to form what ends up as the core of its beak. In alligators, which are among the closest living relatives of birds, these bones remain separate, giving rise to their characteristic snouts. Using beads of proteins to block the expression of these signaling molecules at the appropriate stage of embryonic development, Abzhanov produced chicks with alligator-like snouts. Ultimately, he would like to revert a chick back to the state of its Maniraptoran forebears, but he says that ethical considerations currently prevent him from allowing any of his snouted chickens to hatch.
If the story of the snout rings a bell, see the required ingredients for chicken fingers above. The mechanisms triggering beak and wing formation are not too different; what worked for the beak may apply to winding back the clock on the wings, as well. Interestingly, even some of the biologists who are pioneering these approaches are dubious about whether they can be applied to a project of such outsized proportions, but Horner is not content to see these fantastic techniques being used for anything less than the creation of a poultrified protosaur—the first of its kind.
Faraz Hussain is a biochem major at IIT and a budding science writer.