Discovering Biology in a Digital World

Sure, this demonstration is still a long way from cloning an elephant or related species. Even cat and dog cloning are fairly recent advances and far from techniques that DIYer's can practice in their kitchens.

Why haven't people been able to clone animals from frozen tissues before?

Other cloning techniques have required intact, healthy cells. But when cells are frozen, ice crystals form and damage the membranes. The cells don't stay intact and they're certainly not living or healthy. Cells can be stored frozen and stay alive, but this requires including some kind of substance in the media like glycerol or polyvinylpyrrolidone, to protect the membranes from damage.

According to the paper:

Thus, obtaining suitable cells for nuclear transfer from naturally frozen tissues is extremely difficult, if not impossible.

So what exactly did the researchers do?

They got the dead mice out of the freezer, extracted the nuclei from several different organs and then injected the nuclei directly into enucleated mouse egg cells. When the cells had divided a few times (reached the morula or blastocyst stage), they established cell lines. The nuclei from these cells were transferred again and finally, implanted into female mice.

Apparently, the nuclei from the mouse brains worked the best. Perhaps the brain cells were better protected from damage, perhaps the lipids in the brain were helpful.

I wonder what they'll try cloning next.

Reference:
S. Wakayama, H. Ohta, T. Hikichi, E. Mizutani, T. Iwaki, O. Kanagawa, T. Wakayama (2008). Production of healthy cloned mice from bodies frozen at -20 C for 16 years Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0806166105