Gene Editing Starts the Eradication of Salmon Viruses

Great news coming from The Roslin Institute in Scotland! Researchers have identified genes associated with resistance to a disease known as Infectious Pancreatic Necrosis (IPN) in Atlantic Salmon. Seeing as how salmon represent 4.6% of the global food supply with almost all of that being from aquaculture farms, you can see how this would be a pretty big deal. IPN is among the list of several diseases that can greatly disrupt aquaculture centers by infecting their salmon production and causing high mortality rates. By finding the exact locations in Atlantic Salmon genomes that allows for some of them to be naturally resistant to IPN, farmers can more accurately test for and select naturally resistant brood stock: the animals in a farm used for breeding purposes. 

A dissected Salmon Parr infected with IPN (top) vs a healthy Parr (bottom)

But how exactly did scientists go about doing this? Well, first they performed what is called a "challenge experiment" in which they infected families of Atlantic Salmon and looked at the tanks that had the least amount of salmon dead. The salmon in those tanks were deemed resistant whereas the other ones were deemed susceptible or intermediate to IPN. They then took two of the intermediate families, tested for their parent's genotypes, and analyzed their gene expression patterns for IPN QTL-linked markers. 

QTL = Quantitative Trait Locus. It's an area on a chromosome region detected by statistical analysis that is significantly associated with variation for a quantitative trait. Often times to find QTLs scientists link them to specific genetic markers that exist in two distinguishable forms. 

After looking into the QTL pattern differences in the salmon, the authors found a specific gene within this area that was the most differentially expressed; a gene called nae1. They then used CRISPR-Cas9, a widely used method for gene editing, to block nae1 and see if it really caused a major difference in IPN resistance. Their results show that indeed, blocking nae1 significantly reduced the salmon's abilities to resist being infected by the virus! Exciting stuff!