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Home > Resources > Laboratory News
Salamanders Uncover Stem Cell MysteriesJuly 13, 2010
Dr. Andrew Johnson and his team from the Univ. of Nottingham have been using a Mexican aquatic salamander called an axolotl to study the evolution and genetics of stem cells -- research that supports the development of regenerative medicine to treat the consequences of disease and injury using stem cell therapies.
The team has found that there are extraordinary similarities in the development of axolotls and mammals that provide unique opportunities to study the properties of embryonic stem cells and germ cells. These findings are underpinned by a novel theory of evolution that unifies the diversity of mechanisms in animal developmental into a single conceptual framework.
Johnson says: "We've produced evidence that pluripotency -- the ability of an embryonic stem cell to become absolutely any kind of cell -- is actually very ancient in evolutionary terms. In fact, pluripotent cells probably exist in the embryos of the simple animals from which amphibians evolved. Axolotls, unlike many of the frogs, fish, flies and worms that are used in the lab, have pluripotent cells in their embryos that are the equivalent to those found in embryos from mammals, in that they can produce germ cells."
Axolotls are salamanders that retained primitive characteristics of the first amphibians, the animals descended from fish that moved onto land about 385 million years ago. These early amphibians were the ancestors of every land dwelling vertebrate, including humans. This places axolotls in a perfect position to understand how vertebrates evolved on land.
Johnson discovered that the genetic mechanisms controlling the development of salamander embryos were not changed as amphibian embryos evolved into those of reptiles and then, later, mammals. This finding explains why salamanders look so much like lizards, and since mammals evolved directly from reptiles it makes sense that the genetic mechanisms controlling embryo development remain largely unchanged from axolotls to humans. Axolotl embryos are therefore far more similar to those of humans than the more commonly studied embryos of frogs and fish that most development researchers use.
Through work to explore why frogs might have lost pluripotency, Johnson and colleagues developed a new theory of evolution. This theory says that a key driver of vertebrate evolution is the relationship of the germ cells, which become sperm and egg, and the rest of the body, called the soma.
The embryos of most lab animals, including frogs but not mice, contain material called germ plasm, and germ plasm has the role of instructing cells to become the primordial germ cells which go on to become sperm and egg. But axolotls are different; Dr Johnson's team found that their embryos actually don't contain germ plasm and instead they use a system very similar to mice and humans. Axolotls produce their primordial germs cells from pluripotent cells -- similar to embryonic stem cells -- by a process called induction.
"Within our new theory of evolution pluripotency came first and so germ plasm would have to have evolved independently several times in species within the branches of the tree, for example in frogs and many fish," says Johnson.
Johnson and his colleagues suggest that the evolution of germ plasm liberates the soma of an organism to evolve more rapidly, simply because the embryo doesn't need to induce germ cells -- they are already there because of germ plasm. As a result of this, the genetic mechanisms that control the soma are free to evolve, because they are no longer occupied with producing the signals that induce primordial germ cells from pluripotent embryonic cells.
"We think that ultimately, the germ line-soma relationship is likely to be a major contributor to the astonishing diversity of species that inhabit the earth," says Johnson.
Source: Univ. of Nottingham
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