Although the hydra may only be known as a Greek myth, head regrowth is actually not as fantastical as it may seem.
According Greek mythology, the hydra was a nine-headed serpent slain by Hercules. What made the feat challenging was that every time Hercules cut off one of the serpent’s heads, two new heads replaced it.
In 2008, researchers Peter Reddien and Christian Petersen of the Whitehead Institute for Biomedical Research identified the gene responsible for head regrowth: Smed-βcatenin-1.1 To investigate genes’ effects on head and tail amputation, the scientists used RNA interference to “turn off” planarian flatworms’ genes one by one. When a flatworm’s genes are left unimpeded, the worm will regenerate a tail if its tail is amputated and a head if its head is amputated. When they turned off the Smed-βcatenin-1 gene, however, Reddien and Petersen discovered that a flatworm will regenerate a head at any amputation site. In fact, if the scientists made six incisions in the side of the worm’s body, the worm would regrow six new heads.
Using the same process of RNA interference, Alejandro Sanchez Alvarado and colleagues at the University of Utah demonstrated the converse effect: they could force planarian flatworms to regrow tails at every amputation or incision site by restricting expression of the βcatenin antagonist adenomatous polyposis coli. 2
Building upon these discoveries, University of Nottingham scientist Aziz Aboobaker identified the smed-prep gene3—a gene that directs flatworms to regenerate new muscle, gastro, and even brain cells from stem cells. Moreover, the smed-prep gene targets these cells to their proper locations in the worm and organizes them into functional structures (as opposed to masses of useless cells).
The human implications of this research are enticing. Engineering a person’s body to replace damaged or diseased cells, tissues, organs, or even limbs is one possibility. This would be helpful for treating diseases such as Alzheimer’s. Also, understanding normal cell regeneration is one step toward discovering what happens when stem cells malfunction during the process of cell renewal, which occurs in diseases such as leukaemia.
Watch 8-headed planarian regeneration from Peter Reddien’s lab:
1 Petersen, C., & Reddien, P. (2008). Smed- catenin-1 Is Required for Anteroposterior Blastema Polarity in Planarian Regeneration Science, 319 (5861), 327-330 DOI: 10.1126/science.1149943
2 Gurley, K., Rink, J., & Alvarado, A. (2008). -Catenin Defines Head Versus Tail Identity During Planarian Regeneration and Homeostasis Science, 319 (5861), 323-327 DOI: 10.1126/science.1150029
3 Felix DA, & Aboobaker AA (2010). The TALE class homeobox gene Smed-prep defines the anterior compartment for head regeneration. PLoS genetics, 6 (4) PMID: 20422023