Cloned, genetically altered goats producing spider silk in their milk sounds like something out of The X-Files, but it was in all the papers last week when a company called Nexia revealed it had cloned three goats (Clint, Danny and Arnold), and explained why.
The cloning of goats brings to four (sheep, mice, cows and goats) the number of species that have been cloned since Dolly the sheep made headlines a couple of years ago, using a process called nuclear transfer.
A clone is an exact genetic copy of an existing animal. Every cell in an animal’s body contains the complete genetic information for the entire animal within its nucleus. In nuclear transfer cloning, cells are taken from the animal to be cloned, then the DNA is removed from the nuclei. The DNA is transferred into mature, unfertilized eggs, which begin developing, just as if they’d been fertilized. The embryos are then transferred into surrogate mothers.
Each of the Montreal goats is essentially an identical twin of the original goat. They all have the same markings and the same head and body shapes.
Nexia didn’t clone Clint, Danny and Arnold because of a shortage of goats. Nexia wants to create an entirely different breed of goats: goats that have been genetically altered to produce a substance similar to spider silk in their milk.
If you’ve just decided to swear off goat cheese, relax: the milk wouldn’t be for human consumption. The goal is to retrieve the spider-silk proteins from the milk and turn them into a substance called BioSteel, an incredibly light fabric both biodegradable and strong enough to stop bullets. Nexia thinks BioSteel could be used in everything from body armor to spacecraft construction. It could replace plastics and other materials the body typically rejects for artificial tendons, ligaments and other prostheses. It could make super-thin, biodegradable sutures for eye or brain surgery. It could even strengthen the structural steel used in buildings. (Although it would have to be carefully sealed from the environment so bacteria wouldn’t eat it.)
Spider silk is made of a protein whose molecules are capable of making lots of bonds with neighboring molecules. As spiders secrete this protein, it hardens and pulls taut, crystallizing into a strong cable able to withstand the impact of a hurtling fly.
There’s a strong similarity between the way mammals make milk proteins and spiders make silk proteins. Nexia believes they can introduce the gene from spiders that causes certain cells to produce silk into goats, tricking the goats’ mammary glands into producing silk along with milk. The goats would become biological factories.
Once Nexia has goats containing the spider-silk gene, it will clone them, then breed them normally to produce a herd of goats, all of which contain the spider-silk gene.
Nexia at first indicated they had been the first to clone goats, but it turns out three goats were cloned in the U.S. last fall, for a similar reason: they’ve been genetically modified to produce an anti-blood clotting protein, called Antithrombin III, in their milk. Antithrombin III is currently undergoing human tests.
These advances have many people concerned. Every advance in cloning makes it more likely that someone will try to clone a human, which critics feel threatens the integrity of being human. “Every human has a right to have their life as a surprise. We have a right not to be manufactured,” is how Dr. Margaret Somerville, an ethicist at McGill University, puts it.
Others see a nightmare world in which clones are created simply to provide body parts. Since the clones would be genetically identical, organs from them would not be rejected by the original’s body.
Many people are pushing for laws banning human cloning, and the federal government announced the day after the Montreal scientists announced the birth of Danny, Clint and Arnold that it will soon introduce such legislation.
The cloning of animals isn’t as big an ethical concern in most people’s minds, since we already use animals to provide food and clothing. But there are concerns about the cross-species exchange of genes. Critics point out that living systems are so much more complicated than we appreciate that we can’t know what consequences cross-species engineering will have.
But the beneficial possibilities of herds of dairy animals able to produce drugs and other valuable substances along with their milk are so great it’s such research will slow. Just like the old science fiction movies they evoke, the Spider-Goat Clones of Montreal will almost certainly spawn sequels.