Selective breeding by humans has resulted in some incredibly strange and unfortunate pets over the years, and the rabbit sauteur d’Alfort is one of the strangest of them all.
This rare breed of rabbit does not jump or walk like any other rabbit or hare in existence. When the sauteur is ready to go, he kicks his hind legs into the air and bounces forward on his front legs, like a human acrobat walking on their hands.
While this may seem like a funny trait, it unfortunately brings other debilitating issues as well. The only rabbit that cannot jump well helped us to better understand the genetics of jumping in mammals.
By crossing a single male sauté with a single female of the white New Zealand breed and then crossing the resulting offspring, researchers raised 52 bunnies, 23 percent of which carried two copies of the mutant gene that were similar to the original father. These numbers are consistent with the statistics expected when only one recessive gene is involved in a mutation.
By merging the DNA of the author and non-author young, researchers used whole genome sequencing to compare the two groups. In the end – as they expected – there was only one gene that stood out.
The cause of the author’s defective jumping appears to be a mutation in an evolutionarily conserved site of a gene known as RORB, which instructs mammalian cells to make certain proteins.
RORB proteins are generally found throughout the nervous system of rabbits, where they help convert the genetic code into a protein building template. However, this particular mutation causes a particularly sharp decrease in the number of neurons in the spinal cord that can actually produce this protein.
In fact, two copies of the RORB mutation did not result in spinal cord proteins at all, and this was linked to an inability to hop. Other rabbits in the litter that were able to jump with their hind legs did not show such protein loss.
The RORB gene, the authors conclude, must allow rabbits to bind. It may also be the key to other mammals hopping.
Over the years, there has been a lot of scientific interest in the special physiology and biomechanics that allow mammals – such as kangaroos, bunnies, hares, and some mice – to jump, but the genetics underlying this feat have rarely been considered.
One of the few studies out there recently found that mice with the same RORB mutation as sauteur rabbits also cannot jump as normal. Instead, these rodents waddle on their front legs like a duck, with their tails and hind legs in the air.
“I watched these mice do little handstands for four years, and now I see a rabbit doing the same handstand,” neuroscientist Stephanie Koch of University College London told Science News. “It is awesome.”
Koch’s research on rabbits is the first to describe a specific gene needed to jump or jump, and it is very similar to what she has seen in mutated mice.
Like mutated rodents, sauteur rabbits also exhibit other anatomical defects that go beyond their strange gait. Many are born blind and develop cataracts in their first year of life. RORB knockout mice also exhibit retinal degeneration.
In mice, the RORB gene appears to play an essential role in differentiating cells in both the cerebral cortex and retina. It can also do something similar in the spinal cord, which is involved in the regulation of sensory information and locomotion in mammals.
As such, this lack of protein can cause rabbits and mice’s hind legs to lift rather than jump. For example, in author rabbits, the RORB mutation appears to cause defects in the differentiation of spinal cord interneurons, although it remains unclear whether this causes the bizarre locomotion.
“In addition to its expression in the spinal cord, RORB is also expressed in many areas of the brain, such as the primary somatosensory, auditory, visual and motor cortex, in some thalamic and hypothalamic nuclei, in the pituitary and in the superior colliculus.”, write the authors.
“Thus, we cannot rule out that alteration of RORB function in the brain contributes to the locomotor phenotype characteristic of the sauteur rabbits.”
The effects of the RORB mutation require more research, but it is clear that it is somehow involved. This was the only variant identified in the whole rabbit genome sequence that had any effect on hopping.
While there may be more genes involved in rabbit hopping, it looks like poor sauteur rabbits have definitely pointed us in the direction of one.
The study is published in PLOS Genetics