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Tokyo scientists use fertilized toad egg to Successfully reproduce kidney.

A group of scientists at the University of Tokyo used a fertilized toad egg to successfully produce a kidney in the laboratory, which they then transplanted into a toad embryo with all functions intact.

The experiment is the first time an organ cultured in vitro has been shown to function normally inside a host body, said Makoto Asashima, one of the four group members from the state-run university's life sciences department. The results appear to signal a breakthrough in identifying what kinds of genes are involved in organ formation during early vertebrate development. And the findings raise hopes that one day human organs and tissues needed for transplant could be created in the laboratory.

"There is definitely the potential for generating organs for transplantation in the laboratory for different animal models and eventually for humans," said Dr. Igor Dawid, chief of the developmental biology section at the National Institutes of Health in Bethesda, Maryland, who characterized the experiments as "valuable and promising."

Asashima and his colleagues applied a technique they discovered earlier in the decade, which involves treating undifferentiated embryonic cell tissue with a protein-like substance called activin to induce organ formation. In those earlier experiments, the scientists were able to generate a beating heart by bathing cell tissue from a newt embryo in a high concentration of activin.

In the current experiment, the researchers extracted cells from the fertilized eggs of a Xenopus, a bisexual African clawed toad that is widely used in developmental biology investigations. These cells then were treated with a combination of activin and retinoic acid (vitamin A). By varying the doses of activin and retinoic acid, the group was able to produce red blood, muscle, kidney, heart, and liver cells from the same undifferentiated cell tissue.

To answer the question of whether these treated cells would function normally inside the body, the scientists cut off a small square of tissue and immersed it in a low concentration of activin and retinoic acid for three hours to induce kidney formation. Next, they transplanted the tissue into a toad embryo whose own kidney-producing tissue had been removed. A month later, the embryo had developed into a healthy tadpole with fully functioning kidneys. In contrast, another embryo implanted with untreated cell tissue failed to develop a kidney and died a week later.

"I think we have opened a new field of developmental engineering," Asashima said. "There is a possibility now to generate kidneys and other organs from cells of other vertebrates."

Dawid agreed that the group's work may provide an excellent model of the biology of kidney formation. But he added that before the technique can be applied in humans, much more must be learned about the cellular and molecular events that are required for kidney growth. At that point, he said, "the system developed by Asashima and his colleagues is likely to be very important in this context."
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Publication:Transplant News
Date:Sep 30, 1998
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