Scientists have found that one gene is responsible for variability in locomotion in horses and mice. Traits such as height are controlled by the interaction of up to 700 genes. So it came as quite a shock to researchers from Uppsala University (UU) and their international collaborators that the mutation of just a single gene is responsible for variability in locomotion in horses and mice. Furthermore, the research team discovered that this gene, DMRT3, is expressed in a previously unknown set of neurons in the spinal cord. These findings provide insight into the neural circuits that coordinate movement in vertebrates.
Horses were the perfect choice for the researchers to test the genetic basis of variability in locomotion. This is because there are several naturally occurring gaits that these animals can perform, including walking, trotting, cantering and galloping. Icelandic horses can tölt, which is a sort of ambling gait and they can also perform flying pace. The scientists wanted to know why some horses have more variability in their gait than others and whether it could be genetically explained. First they demonstrated that a single base change in DMRT3, which resulted in the production of a truncated form of the gene, was the mutation associated with pacing in horses. They developed a diagnostic screening test and found that this mutation is common among horses bred for harness racing, such as the Tenessee Walking Horse and the Paso Fino breeds.
The Swedish scientists further explored the function of DMRT3 in a mouse neurobiological model. They showed that the neural circuits of knockout mice lacking the gene did not develop properly and had an altered pattern of locomotion. But fascinatingly these mice could eventually move somewhat normally, suggesting that other neural circuits compensate for the loss of DMRT3. This shows how the nervous system is flexible and capable of adapting to the absence of key genes.