TOKYO -- Woolly mammoths could roam the earth again someday thanks to research reported Monday, where cell nuclei from one of the long-extinct animals showed biological activity when transplanted into mouse cells.

Bone marrow and muscle tissue were extracted from the remains of a mammoth named Yuka that had been frozen in Siberian permafrost for 28,000 years in the study, published online in the journal Scientific Reports. Genomic DNA was compared against that of elephants, and the researchers confirmed that Yuka's DNA overlapped with the DNA and proteins specific to mammoths.

The team injected cell nuclei from the muscle tissue into mouse egg cells and observed the forming of structures that appear just before cell division starts. The researchers also found possible signs of repair to damaged mammoth DNA.

This marks a "significant step toward bringing mammoths back from the dead," said researcher Kei Miyamoto, one of the study's authors.

"We want to move our study forward to the stage of cell division," said Miyamoto, who acknowledged that "we still have a long way to go" before the Ice Age species can return.

The team from Kindai University, in greater Osaka, is collaborating with a Russian institution on the work using a cloning technology called somatic cell nuclear transfer.