One defective gene might turn some bunnies’ hops into handstands, a new study suggests.
To move quickly, a breed of domesticated rabbit called sauteur d’Alfort sends its back legs sky high and walks on its front paws. That strange gait may be the result of a gene tied to limb movement, researchers report March 25 in PLOS Genetics.
Sauteur d’Alfort rabbits aren’t the only animal to adopt an odd scamper if there’s a mutation to this gene, known as RORB. Mice with a mutation to the gene also do handstands if they start to run, says Stephanie Koch, a neuroscientist at University College London who was not involved with the rabbit work. And even while walking, the mice hike their back legs up to waddle forward, almost like a duck.
“I spent four years looking at these mice doing little handstands, and now I get to see a rabbit do the same handstand,” says Koch, who led a 2017 study published in Neuron that explored the mechanism behind the “duck gait” in mice. “It’s amazing.”
Understanding why the rabbits move in such a strange way could help researchers learn more about how the spinal cord works. The study is “contributing to our basic knowledge about a very important function in humans and all animals — how we are able to move,” says Leif Andersson, a molecular geneticist at Uppsala University in Sweden.
In the rabbit study, Andersson and colleagues bred hop-less sauteur d’Alfort male rabbits with New Zealand white female rabbits that can hop. The team then scanned the genetic blueprints of the offspring that couldn’t hop and looked for mutations that didn’t appear in offspring that could.
A mutation in the RORB gene popped up as a likely candidate for the rabbits’ acrobatic handstands. That change creates faulty versions of the genetic instructions that cells use to make proteins, the researchers found. As a result, there appears to be less of the RORB protein in specialized nerve cells in rabbits that have the mutation compared with rabbits that don’t.
Those spinal cord nerve cells, called interneurons, help coordinate the left and right side of the body and are crucial for a normal gait, Andersson says. Without the RORB protein in interneurons, the rabbits may lack the ability to coordinate what their hind limbs are doing, which restricts their ability to hop.
While moving slowly from place to place, rabbits with the defective gene can walk normally, alternating their front and hind legs. But rabbits hop to move fast or to travel over long distances. And hopping requires synchronized hind legs to jump at the same time, says study coauthor Miguel Carneiro, a molecular geneticist at Universidade do Porto in Vairão, Portugal.
Without that coordination, some hop-less bunnies might do a more drastic handstand than others. But all rabbits with a RORB mutation use their front paws to move quickly, Carneiro says.
It’s an interesting observation, although the study doesn’t reveal much about how the lack of the RORB protein in interneurons spurs the rabbits’ handstands, Koch says. “All they’re looking for is that mutation in one gene and how that gene is affecting the spinal cord, but it could be affecting everything in the rabbit. We have no idea.”
Uncovering how that genetic defect affects the body more broadly could be important for understanding the way all animals move. Even people can’t run without harmonized movements of our four limbs. “If you look at the 100-meter sprint — Usain Bolt or someone like that — there’s super coordination between limbs,” Andersson says. “If you lack the coordination between arms and legs… you could never compete for a gold medal.”
These handstand rabbits wouldn’t grab any golds either. But they could help researchers develop ways to repair the body when defects in RORB cause disease, Koch says.