Dr Johnson continued "We've found 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 explains why newts (salamanders) look so much like lizards (reptiles), 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.
"We recently found out that pluripotency in axolotls and mammals depends on a gene called Nanog, which frogs do not have. Therefore we think that the Nanog gene was lost from the frog genome after frogs and salamanders evolved separately from their common amphibian ancestor. This is contrary to a long-held opinion that ground-state pluripotency evolved with mammals and suggests that pluripotency could actually be one of the most ancient features of embryos. But since evolution depends on generating advantageous changes, and pluripotency seems to be a good thing we had to ask ourselves why would frogs have lost the Nanog gene, and with it pluripotency?""
Through work to explore why frogs might have lost pluripotency Dr Johnson and colleagues developed a new theory of evolution in 2003. 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.
Dr Johnson said "The reason that losing pluripotency would have been an advantage to frogs, for example, is that it has actually made it possible for them to diverge into numerous closely related species it is possible for them to make far more frequent fairly subtle chan
|Contact: Nancy Mendoza|
Biotechnology and Biological Sciences Research Council