The Chinese Dog Experiment That Had Never Been Done Before

In addition to being man's best friend, dogs are close enough to humans in their physiology that they are often used in studies of human diseases and their treatments. For instance, a better understanding of gene therapies through experiments with dogs could lead to breakthrough treatments for conditions like Parkinson's disease or muscular dystrophy. A novel experiment by Chinese scientists in 2015 took steps down that path by producing dogs that were twice as strong as they would be naturally.

In the study, researchers knocked out the gene responsible for a protein known as myostatin. First discovered in 1997, myostatin is a growth factor protein expressed in skeletal muscle. Myostatin essentially puts the brakes on muscle growth in mammals, keeping muscle mass within a reasonable range. However, animals without the necessary gene — or those with a gene mutation – can put on incredible amounts of muscle mass. Because of this, researchers have been looking toward various ways of inhibiting myostatin either to improve athletic performance or to treat diseases characterized by muscle loss.

The researchers in the Chinese dog experiment took an approach aimed at knocking out the gene for myostatin. To do this, they turned to a technology known as CRISPR-Cas9. This technological breakthrough has sped up research in gene editing around the world. CRISPR-Cas9 acts like molecular scissors that allow scientists to edit DNA, adding, removing, or changing sections of genetic material. This tool consists of a sequence of RNA (CRISPR) to guide an enzyme (Cas9) to a specific chain of DNA.

The scientists first created an RNA chain that would target the myostatin gene in dogs. They then used this RNA with a Cas9 enzyme to break the DNA chain at the beginning and end of the myostatin sequence. Once broken, the DNA chain would reconnect where it was cut, splicing out the myostatin gene. The researchers injected dozens of embryos and implanted them in 10 adult female dogs, resulting in the birth of 27 puppies. Of these 27, two puppies, Tiangou and Hercules, were born without the myostatin gene. Without a myostatin gene, these two dogs grew to be larger and more muscular than their litter mates.

The researchers in this study demonstrated how it is possible to knock genes out in dogs using a single CRISPR-Cas9 injection. This could open avenues to treat a variety of conditions. For instance, being able to splice out some of the genes associated with Parkinson's disease could lead to new therapies for the disease. Being able to remove the myostatin gene in particular could help with conditions that cause muscle weakness or loss of muscle or bone mass.

However, some scientists note that there can be ethical issues with genetic engineering. Creating genetically engineered animals can involve processes that are painful and invasive. It can also result in embryos that are larger than usual, which can lead to difficult or harmful pregnancies. Removing the myostatin gene could be used to make stronger or faster animals, which some people might find ethically objectionable. However, using such methods to treat serious medical conditions could justify potential downsides.

Ethical issues aside, this experiment showed what CRISPR-Cas9 technology can do. Further research in this area could one day lead to treatments for a variety of health conditions.