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Musings on Cattle Cloning

by Thomas M. Zinnen

August 8, 1997

Plant breeders who chance upon a valuable individual plant, such as the original Delicious apple, the original Navel orange, or the original Russett Burbank potato, can make more plants by taking cuttings: snipping a piece of stem and rooting it.

The fancy word for this is cloning. It's a way to make more identical copies of a plant without going through flowering and seed production. It also avoids the genetic variation that goes along with seed production and the mixing of genes from two parents. And in many cases it's faster. Animal breeders with prize bulls or cows would like to be able to have that same kind of option for making quick and true copies of their prizes.

But it's been harder to find ways to clone cattle than coleus. You just can't lop off a tail and stick it in water.

American Breeders Service and its subsidiary, Infigen, announced yesterday (August 7, 1997) the cloning of a bull calf, a cloning that started with cells taken from a 30-day-old fetus.

But more important would be the cloning prize, full-grown animals. Significantly, Dr. Michael Bishop of Infigen also stated that cloning starting with cells from an adult animal is underway. Bishop said at least one cow is now pregnant with a fetal calf that originated with a cell from a full-grown animal.

What's the Story? Source, Sauce, Storage, and Speed

The advances announced by ABS can be viewed as:

  1. The source of the cells used to originate the clone: cells from adult cattle are now being used.
  2. The 'secret sauce' that converts ordinary cells from adults into cells that in test tubes can become embryos. ABS says the sauce will be secret until their pending patent is awarded.
  3. The cells that can become embryos can be stored, frozen, for a long time, and then thawed and used. The cells offer the same advantages as frozen semen and frozen embryos: storage over time, transport over great distances, a genetic reserve. This also means that once the cells have been collected, later rounds of cloning can start with taking cells out of the freezer, rather than taking them out of the prize bull.
  4. The process outlined by ABS means each cell is first allowed to form an embryo of 16 or 32 or 64 cells, and then each of those cells can be used to form a separate embryo--yielding 16 or 32 or 64 identical embryos. This could speed up the process of building a herd of identical cattle.
See Infigen's website at www.infigen.com for a color graphic of the 12-step method they developed.

Background

Cloning of cattle was done first a decade ago by Neal First and his colleagues at the University of Wisconsin-Madison.

But the starting cells were embryo cells. That means you're cloning something that's not a proven bull or a prize cow.

The embryo's parents might be prizes, but the embryo is an uncertain entity.

Starting with embryo cells also means you really haven't bypassed sexual reproduction--and genetic variation it introduces.

Cloning Does Not Bypass Pregnancy

Unlike plant breeders, who can lop off a branch of a coleus plant and stick it in a pot and wait for the cutting to root, animal breeders still have to get back to one cell in a test tube in the lab. That cell grows into an embryo and then the animal breeder moves the embryo from the test tube and puts it into the uterus of a cow. If all goes well, the embryo grows, attaches to the wall of the uterus, forms a placenta, develops into a fetus, and the cow is pregnant with a cloned calf. The cloned calf still takes about 280 days to complete its development before it is born in the usual way.

The ABS announcement yesterday signals that the dairy and beef industry is a step closer to routine reproduction of prize bulls and cows.

Although it involves pregnancy, cattle cloning is asexual reproduction: making more individuals of a species without fusion of sperm and egg, and without the genetic variation that goes along with making the sperm and egg (genetic recombination and reassortment at meiosis) and without the variation from new combinations of genes upon fusion of sperm and egg.

Why Clone? Pharmaceuticals and Organs for Transplants

Cloning makes sense if you have a precious individual animal. Prize bulls and cows are examples. Another example would be individual cattle that have received through genetic engineering a copy of an important new gene. The new gene could make the milk more valuable as a source of drugs or of nutrients.

Another possibility is to give an individual cow a gene that would let the cow make a new protein in her milk. The gene could be the genetic recipe for making a medicine such insulin that could be secreted in milk. With this idea, milk from that particular cow would be used as a source of insulin. The insulin would be purified from the milk and diabetics would inject themselves as usual with the purified insulin.

Other proteins might be kept in the milk intended for drinking. For example, milk might be made a way to fight cholera.

Cholera is a disease of the human gut. It's caused when humans drink water contaminated by the cholera bacterium. The best control is obviously clean water. But imagine an additional protection. Imagine if a cow were given the genetic recipe to make a cholera-fighting protein in her milk. In this case, a person who drinks the milk with the anti-cholera protein would be protected against any cholera bacterium in a drink of water.

Or imagine a calf given genes so that the calf's organs, such as the heart or liver or kidneys, could be transplanted to humans and not rejected by the human's system. That would be a valuable calf. But you would want to make many copies of it before you used the calf as a source of organs.

Linking Two Separate Tools: Cloning and Genetic Engineering

The value of cloning mature animals then is not solely in prize milk cows or dairy bulls. Cloning is valuable when you already have something that is powerful but rare. So cloning is like photocopying: you gotta have an original to copy.

Genetic engineering is the tool for making a valuable original. Cloning is the way to make many copies of the original. That's why ABS's subsidiary Infigen is negotiating with genetic engineering companies to link the new cattle cloning technology with gene transfer technology.

How is this different from Dolly the cloned sheep that made news in February?

  1. Dolly bulldozed a paradigm of biology. Dolly showed that cells from adult animals could be "reprogrammed" to start completely over and develop from a single cell into a complete adult.
  2. ABS's Gene the Bull doesn't plow any paradigms. It demonstrates some new techniques of cell culture. It presents another set of recipes for cattle cloning. It points the way to some new possibilities for cloning humans from cells of adult humans, but in this arena Gene's tune is just a variation on a theme played first by Dolly.

Related Links

Genetic Revolution Overview

Edgey about BioTecknowledgey: A Case Study of Cloning


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