Two genetically engineered farm animals reported today illustrate how far from Frankenstein’s stitched-together monster animal biotechnology has come. One of those animals, a cow, secretes milk that lacks an allergy-inducing protein because researchers accurately blocked its production using the technique of RNA interference. And in pigs, scientists have used an enzyme called a TALEN to scramble a gene that would normally help remove cholesterol.
RNA interference (RNAi) and TALENs are more accurate at targeting the gene in question than are earlier genetic engineering techniques. For years, researchers tried to remove the allergy-inducing milk protein beta-lactoglobulin from cow’s milk, which can cause diarrhea and vomiting in some toddlers. They tried replacing the gene encoding beta-lactoglobulin with a defective form, but this proved nearly impossible because the techniques available to introduce foreign genes into animal genomes were not precise, and misplaced genes failed to express themselves correctly.
In 2006, scientists at AgResearch in Hamilton, New Zealand began to experiment with molecules that interfere with the messenger RNA go-between that enables translation of a gene into protein. In mice, they discovered a short chunk of RNA, called a microRNA, that targeted beta-lactoglobulin messenger RNA directly to prevent its translation. They inserted DNA encoding a version of this microRNA into the genome to create genetically modified cow embryos that they hoped would grow into cows without the allergen in their milk. Out of 100 embryos, one calf yielded beta-globulin-free milk. “This isn’t a quick process,” says Stefan Wagner, a molecular biologist at AgResearch. That’s why it has taken so long to succeed in making an allergen-free cow, he says.