Regeneration recipe: Pinch of pig, cell of lizard

A very special mouse
Then there’s the specially bred mouse strain that befuddled Ellen Heber-Katz a decade ago, and has since become a focus of her research.

Heber-Katz, of the Wistar Institute in Philadelphia, was using the mouse strain known as MRL in a study of autoimmune diseases. Her team punched tiny holes in the animals’ ears as markers. About three weeks later, Heber-Katz noticed a troubling thing.

“There were no ear holes,” she recalled the other day. “We ear-punched again, and they closed up and disappeared.... We were just so shocked.”

Like salamanders, the mice were growing blastemas instead of scars. They also heal damage to their hearts.

But for regrowing digits, even this mouse falls short. If a toe is cut off at some point other than the tip, the remnant produces a cell mass that looks like a small blastema, but it doesn’t grow the missing part back. (An ordinary mouse just develops a scar.)

At least, the MRL mouse “looks like it’s trying,” Heber-Katz said.

In studying the mice and salamanders, scientists will pursue several questions. What genes rev up to produce regrowth? What biochemical signals are involved? What is the role of specific cells? Can this knowledge be used to regrow a digit on a mouse?

Scientists say it’s not clear when this research might help people.

As for Spievack, the model-airplane enthusiast, he’s had enough personal experience in this area.

“I don’t plan on cutting anything more off to find out if I can grow that back,” he said.

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