The technique could help grow human kidneys and combat a severe shortage of donors for people with renal disease. But scientists have cautioned that major barriers remain before it could be used in cases of humans.
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Scientists in Japan have successfully used mice stem cells to grow kidneys in rat embryos, a study published on Tuesday showed.
The process has previously been used to grow pancreases in rats, but it's the first time that scientists have grown kidneys.
The technique could in the future help grow human kidneys in animal embryos and combat a severe shortage of donors for people with renal disease.
But the scientists cautioned that the development was just a first step and that "serious technical barriers and complex ethical issues" remain before the technique could be used to develop human organs.
A New Heart Grown from Stem Cells
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The researchers first identified rat embryos in which the kidneys could be grown. They then genetically-modified the embryos to ensure they did not develop kidneys of its own.
The embryos were then injected with pluripotent stem cells from mice and implanted into rat wombs so they could be carried to term.
Pluripotent stem cells are a kind of "master" cell that can develop into any of the cells and tissue that make up the body.
Curious case of rats and mice
The mice stem cells produced functional kidneys in the rats, the study showed. But the scientists failed to grow functional kidneys when they injected rat stem cells into similarly modified mice embryos.
"Rat stem cells did not readily differentiate into the two main types of cells needed for kidney formation," said Masumi Hirabayashi, an associate professor at Japan's National Institute for Physiological Sciences, who supervised the study.
Conversely, "mouse stem cells efficiently differentiated... forming the basic structures of a kidney," he told AFP news agency.
It's not clear what caused the difference but the researchers believe "environmental cues" inside the mice are likely to blame and not the technique.
A human mini heart
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Rats die
The rats in which the kidneys were grown died shortly after birth because they did not suckle properly.
The scientists believe that removing the genes that allow kidneys to develop in the womb likely also removed their sense of smell, so the newborns failed to detect milk and died.
The short lives of the rats meant the researchers could not test the functioning of their kidneys. But Hirabayashi said the organs appeared functional "based on anatomical observations."
Ethical concerns
Developing human organs in animals also poses serious ethical questions because human stem cells could develop into brain or reproductive organ cells in the host.
"The main ethical concerns are the risk of consciousness and/or gamete (reproductive cell) production," said Hirabayashi.
"There are serious technical barriers and complex ethical issues that must be discussed and solved before producing human organs in animals," he added.
In the short-term, researchers are likely to focus on ways to genetically modify host rats without lethal side effects.
Last Tuesday was World Heart Day! DW takes a closer look at that amazing organ. Over the course of an average lifespan, the heart beats about three billion times. Simply incredible.
Image: Fotolia/Dmytro Tolokonov
More love for your heart
An international study found many of us believe only older people are at risk of heart attacks - and as a result, that only older people have to be careful. But the German Heart Foundation says that's not true. The earlier you start looking after your heart - through an active lifestyle and healthy diet - the better. After all, you've only got one heart!
Image: Fotolia/Jacek Chabraszewski
Nifty little pump
The heart is a marvel of technology. The fist-sized, hollow muscle contracts about 70 times per minute, pumping up to 10,000 liters of blood through the body. And it does that your whole life. If necessary, the heart can pump about five times that much blood - for instance, when we are jogging.
Image: Fotolia
Real muscle work
The heart may be "just" a muscle - but it's a very special one. Like the muscles in your legs and arms, it can contract as fast and with as much power. But the heart has incredible stamina, and never gets tired. What's more, all heart muscle cells are linked, so they contract in unison.
Image: picture-alliance/dpa
Life saver
If a heart beats slower than it should, a patient can be fitted with a pacemaker. First implanted in 1958, the device sends electrical impulses to the heart muscle. These days, pacemakers can function for from five to 12 years - on average, about eight.
Image: picture-alliance/dpa
Open-heart surgery
To operate on a heart, surgeons have to stop it temporarily. This halts the circulation of blood - which would technically be fatal. But in the 1950s, scientists were able to solve this problem by developing the heart-lung machine. That machine takes over the function of the heart and lungs, enriching the blood with oxygen and pumping it through the body.
Image: picture-alliance/dpa
The heart via the groin
Modern medicine allows doctors to examine and perform surgery on the heart without cutting open the patient's ribcage. Instead, an intracardiac catheter - more or less a thin plastic tube - is inserted through veins and arteries in the groin, the elbow or the wrist. This tube is then pushed into the heart, requiring only local anesthesia.
Image: picture-alliance/Andreas Gebert
Foldable heart valve
If a heart valve is not working or worn out, you need a new one. Doctors might use a biological replacement from pigs, and mechanical heart valves made from metal are also an alternative. Modern artificial heart valves are foldable (pictured above) and can be inserted in endoscopic surgery via a catheter. This way, no open-heart operation is needed.
Image: picture-alliance/dpa
Putting heart into it
The first heart transplantation took place in 1967 - quite a sensation, back then. Nowadays, this operation is no longer a rarity. Every year, surgeons around the world transplant several thousand donor hearts from people who have died. The patients who receive a donor heart, however, have to take medication for the rest of their lives to prevent their own body from rejecting the foreign organ.
Image: picture-alliance/dpa
A pump inside
Donor hearts are rare, and there are waiting lists for recipients. If a heart is not working properly anymore, an artificial heart may support it. In that case, the sick heart stays in the body, and is supported by an implanted pump. This pump is powered by an external energy supply.
Image: picture-alliance/dpa
Plastic heart
One research dream is to create an artifical heart that can replace the sick patient's heart completely. It would be inserted into the body, not require any external connection and would beat for many years without failure. Not an easy task - although some prototypes already exist.
