Regrowing Limbs Not As Easy As It Seems

Newts and salamanders have long been a subject of study for scientists researching the possibility of regenerating limbs in humans. The ability was regarded as a universal trait that multicellular organisms shared — even humans, before our systems grew too complex to regenerate completely.

The red spotted newt can regrow tissue better than even the most advanced biotechnology labs, including the lens in its eye, heart muscle and even components of the central nervous system, which include the spinal cord and brain. Scientists hoped that this quality was present and could be somehow reawakened in humans, Nature reports, but after analyzing the newt's genome, Thomas Braun at the Max Planck Institute for Heart and Lung Research in Germany is less optimistic.

The delay in analyzing its genes lies in the sheer size of the newt's genome — ten times the size of ours — so Braun and his team inspected the RNA for expressed genes instead, called transcriptome. They looked at already-present tissue in the heart, limbs and eyes of larvae and embryos, then compared it to regenerated tissue. Of the 120,000 RNA transcripts found, 15,000 coded for proteins and 826 were unique to the newt, as well as expressed differently in primary and regenerative cells. This implies that the newt's ability evolved more recently, and is not a trait latent in humans.

“I no longer believe that there is an ancestral program that is waiting to be reawakened,” said Jeremy Brockes, a researcher from the University of London who first found that salamanders expressed proteins not found in other vertebrates, but he isn't ruling out the possibility. "I absolutely do believe it’s possible to coax mammal tissues into regenerating to a greater degree with the lessons we learn from newts.”

Elly Tanaka, at the Center for Regenerative Therapies in Dresden, Germany, says that the ability to regenerate could tie into a variety of factors, and probably does not fall into clean 'ancestral' or 'recent' categories. Regeneration could be ancient, but salamanders and newts may also have evolved with certain traits that facilitate the processes involved to a much greater extent than in other vertebrates.

Tanaka suggests that scientists should be looking at ways to use this new information in a more achievable way than growing entire limbs, such as speeding the recovery of burns, scars and organs.

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