by Xinhua writer Huang Kun

"Xiao Xiao," which means "tiny" in Chinese but represents a big victory for scientists as the world's first cloned mouse from iPS cells, was highly praised by an expert at Britain's Roslin Institute where the first cloned mammal Dolly was born.

"Most research progresses in small steps. Xiao Xiao represents a jump forward," said Bruce Whitelaw, head of the Division of Developmental Biology at the Roslin Institute, and editor-in-chief of the journal Transgenic Research.

This is because Xiao Xiao finally proved that iPS cells, the abbreviation of induced pluripotent stem cells, are truly pluripotent. Stem cells are cells that can differentiate into specialized cell types for organisms to grow or repair themselves. In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues, therefore the embryonic stem cells are called pluripotent.

In 2007, Japanese and American scientists declared at the same time that they induced skin cells into the status of pluripotent independently, which implicated that an adult cell could be reprogrammed to its "embryonic status" and then develops to a full functional creature.

"iPS cells are truly a revolution," said Whitelaw. Since then scientists have developed many types of cells from iPS cells, e.g. heart cells, blood cells, cornea cells and nerve cells. But though researchers all around the world tried hard, no one had yet reported a full functional mammal from iPS cells.

In that sense, Xiao Xiao declared the victory of the revolution as two Chinese groups reported "mice made from induced stem cells" online in Nature and in Cell Stem Cell respectively on July 23.

Whitelaw said, "The world must now believe that iPS cells can be truly pluripotent."

The Chinese group of Qi Zhou and Fanyi Zeng reported 27 live births including Xiao Xiao in one of the two papers. Though some died after just two days and some displayed physical abnormalities, a number of mice have passed one of the most fundamental tests of health: all 12 mice that were mated produced offspring, and the offspring showed no abnormalities. The team said it now has hundreds of second-generation and more than 100 third-generation mice.

"The true test of pluripotency is the ability to derive an entire fully functional animal from the pluripotent cell. This animal must develop and grow then age. It must be able to reproduce and this is exactly what Qi Zhou and Fanyi Zeng have shown in their paper," Whitelaw extended his special appreciation on that.

Though Dolly was created by the cloning technology of nuclear transfer, while Xiao Xiao was by introducing iPS cells into an embryo, the resulting animals in both cases are clones, Whitelaw said.

"Yes, Xiao Xiao received the torch lit by Dolly," he commented while reviewing the history of clone.

About practical implication of Xiao Xiao, Whitelaw said it showed us the prospect to translate iPS technology into other animal species such as livestock.

Whitelaw highly praised the work of Chinese scientists.

"The two Chinese groups in achieving this success have shown persistence and dedication to the task. They have achieved what other groups all around the world have not managed yet. They deserve the credit for this achievement," Whitelaw said.

Source: Xinhua