LONDON Cloned piglets that glow in the dark after jellyfish genes were inserted into their cells have upset experts who say they are a "perversion of science".

U.S. researchers say the work is a step towards growing animal organs for transplants which could save thousands of human lives.

The piglets were cloned using the same nuclear transfer technique pioneered by experts at the Roslin Institute in Edinburgh who created Dolly the first cloned sheep.

In the latest case genetic material containing the fluorescent jellyfish gene was inserted first into pig cells grown in a laboratory. Nuclei from these cells were then placed inside donor pig

eggs whose own DNA had been removed.

Five eggs were implanted into the womb of a surrogate mother which gave birth to a litter, labelled NT (nuclear transfer) one, two, three, four and five, in March.

Four of the litter had yellow snouts and hoofs. The tissue glowed when placed under an ultraviolet lamp. Professor Randy Prather, who led the experiment at the University of Missouri in Columbia, said: "They're transgenic, which means they have genetic material from another species.

"In this case, it's a fluorescent gene from a jellyfish. We use this gene because it provides us with a visual marker that proves the pigs are indeed transgenic."

The fifth piglet in the litter had a "normal" pink nose and feet. Prather said the animals showed it was possible to make genetic modifications to pig clones to express desired traits.

This had important implications for xenotransplantation -- the transfer of animal organs to humans. "It means it's possible to change the genetic make-up of the cells to prevent the body's rejection of transplanted organs," the professor added.

Dr Andre Menache, president of the Group Doctors and Lawyers for Responsible Medicine which urges caution over xenotransplantation, said: "I call it a perversion of science. These people are throwing stardust in the public face just to try and impress us. But we are still at square one with this research."

"These are retroviruses, which belong to the same class as the AIDS virus, so we are playing with fire,'' he added.