Growing spermatozoa in a test tube opens a new way for genetic modification of animals and in the future can help to correct genetic diseases in humans before conception.

The procedure gives two advantages. First, you can create genetically modified animals in one generation, rather than in two, as in most conventional techniques.

Secondly, since genes are introduced into spermatozoids grown in the laboratory, it allows scientists to perform subtle genetic manipulations in many animals, and not just in mice, as has been so far.

Sean Burgess of the National Institutes of Health in Bethesda, Maryland, along with his Japanese counterparts, developed this technique to introduce new genes into a fish called zebra danio, which is a convenient object for genetic experiments.

Existing techniques (such as the introduction of DNA into eggs, spermatozoa or embryos shortly before fertilization or implantation) yield a high percentage of so-called "mosaic" fishes, t. Fish that have both genetically modified and normal cells.

To obtain animals that have new genes in each cell, researchers have to mate the mosaic fish and then test the offspring and select those whose parents had a genetically altered sperm or egg.

The new technique is based on a technique for growing male germ cells and converting them into spermatozoa in a test tube developed by Japanese scientists. Mr. Burgess then created retroviruses that infect spermatozoa and insert a new gene into their DNA.

Then the scientists used these sperm to fertilize the ova and create new animals. Only six eggs (from 1410), fertilized with altered spermatozoa, developed transgenic animals, but each cell in their body contained a new gene.

"This technique should be kept in mind," says geneticist Perry Hackett of Discovery Genomics in Minnesota.

However, he points out that the number of successful attempts was so small that, in the end, the usual method of selection could be faster. "And in this case you do not need to grow sperm and do not need viruses," he says.. - So I do not think that this method is ready for presentation yet ».

Biologists dealing with mammals are also unlikely to rush to this technique. First, they have not yet developed similar techniques for the cultivation and maturation of spermatozoa in mammals. In addition, existing transgenic technologies for many mammals are already much more effective now than for zebra zebrafish.

However, Mr. Berjess says that they are already improving technology. For example, they develop ways to grow spermatozoa for a longer time, so that spermatozoa that do not contain DNA can be eliminated. This will greatly improve the efficiency.

If successful, researchers will be able to destroy and replace existing genes, which now can only be done on mice.

Gene replacement is also one of the goals of cloning research, but cloning also has its own problems that still need to be addressed.

If a new technique can be applied to human spermatozoa, then, as Mr. Burgess says, it will allow to correct genetic defects even before fertilization.

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