News: Revealed - Why salamanders are never out on a limb.
- From: Ye Old One <usenet@xxxxxxxxx>
- Date: Thu, 02 Jul 2009 10:38:18 GMT
Revealed: Why salamanders are never out on a limb
http://uk.news.yahoo.com/18/20090701/tsc-revealed-why-salamanders-are-never-o-c2ff8aa.html
Wednesday, July 1 08:44 pm
AFP
Scientists on Wednesday shed light on how the salamander, one of
nature's great oddities, is able to regrow an amputated leg.
The insight may one day help researchers to replicate the achievement
among people, they hope.
All living creatures have the ability to regrow some part or parts of
their body, but the salamander tops the list for regenerative agility.
Mammals like us can regenerate skin or fuse broken bones back
together, but salamanders can replace a lost limb in a few weeks,
regrow damaged lungs, mend a severed spinal cord and even replenish
lost chunks of brain.
Until now, biologists pondering the little amphibian's trick have
generally surmised it uses "pluripotent" cells, which charge into
action at the point of amputation, called a blastema.
Pluripotent cells are spectacularly versatile cells that, like human
embryonic stem cells, are somehow coaxed by chemical signals into
differentiating into the specific tissues that make up skin, bone,
nerves, muscle and so on.
But in a paper released by the British journal Nature, scientists from
the United States and Germany say the regrowth appears to happen
through more humdrum, tissue-specific cells -- and this is good news.
The seven researchers first took axolotls (Ambystoma mexicanum), a
species native to Mexico that is widely used as a model for vertebrate
development, and genetically modified them.
They added a gene from a fluorescent jellyfish that is commonly used
as a telltale in lab experiments.
Cells that carry the gene glow a livid green under ultraviolet, thus
giving researchers an immediate indication of the cells' origin and
progression.
Using embryonic axolotls, the researchers transplanted transgenic
tissues into sites already known to develop into certain body parts,
then observed how and where the cells organised themselves as the
embryo grew.
They then worked on genetically modified axolotls, cutting away limbs
or organs from them.
They grafted that tissue onto normal axolotls, then cut away some of
it and observed what happened to the signature "green" cells as the
blastema area regenerated.
What they found was that regeneration comes not through pluripotent
cells, as thought, but through cells that keep a "memory" of their
tissue origin.
In other words, only "old" muscle cells make new muscle cells, only
"old" nerve cells make new nerve cells, only "old" skin cells make new
skin cells, and so on.
The only cells that appeared to be versatile were those that made skin
and cartilage. In some circumstances, these two cell types could swap
roles.
The findings are important because the salamander's magic appears to
derive from tissue-specific cells, which makes it somewhat closer to
mammalian processes than thought.
"I think it's more mammal-like than was ever expected," one of the
authors, Malcolm Maden, a University of Florida professor of biology,
said in a press release.
"It gives you more hope for being able to some day regenerate
individual tissues in people."
Much more work lies ahead, though, before the vision of
salamander-style regeneration can be achieved for humans who have lost
a hand or leg can be taken seriously.
In a commentary, also published by Nature, University of Utah
neurobiologist Alejandro Sanchez Alvarado hailed the work as unveiling
"a new dimension to our understanding of regeneration."
"Like all important work, it also leaves us with questions that will
probably occupy researchers for the next few years," he said.
--
Bob.
.
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