Which animals can regenerate?

<p>Figure 1</p>

This ability is widespread in the animal kingdom, but its distribution is spotty. Salamanders are the best-known regenerators, but cockroaches can regrow legs, Drosophila can renew discs, deer regain antlers, and humans can regenerate fingertips, if the wound is not sutured.

What do regenerating systems have in common?

In such systems a wound forms a blastema, a recognizable clump of proliferating cells that gives rise to the new structure. The distal tip of the new structure is made first, and then the middle part is filled in.

Regenerating systems always make the correct structures. For example, says Sue Bryant of the University of California in Irvine, planarian can be cut into 280 bits; each bit can regenerate a new body that is spatially appropriate to the starter. Researchers think that regeneration is divided into at least two phases: an early one that is poorly...

What differences exist between regenerators and nonregenerators, or poor regenerators?

Researchers aren't sure, but they have some hypotheses. Some think that regenerators have weaker immune systems than nonregenerating animals, while others sense that regenerators have this ability because they don't form scars. Some researchers posit that different evolutionary pressures may explain the distribution of regenerators and their varying abilities.

Will humans regrow more than their fingertips in the future?

Many researchers think so. For example, mammalian cloning has shown that adult cells retain the ability to return to development, as likely would be required for regrowth. Furthermore, while mice do not normally regenerate their hearts, a murine strain (MRL) was recently discovered that can do so, demonstrating that mammals can be altered to improve their regenerative ability.1

What are the big, outstanding questions?

Researchers want to know what causes regenerating organisms to form a blastema, instead of forming a scar. "How does it start?" asks Steve Johnson of the University of Wisconsin. In addition, they'd love to find a Holy Grail factor that induces regrowth in nonregenerating systems.

- Mignon Fogarty

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