Tales of Tails (and Trunks): Forming the Posterior Body in Vertebrate Embryos.

A major question in developmental biology is how the early embryonic axes are established. Recent studies using different model organisms and mammalian in vitro systems have revealed the surprising result that most of the early posterior embryonic body forms from a Wnt-regulated bipotential neuromesodermal progenitor population that escapes early germ layer patterning. Part of the regulatory network that drives the maintenance and differentiation of these progenitors has recently been determined, but much remains to be discovered. This review discusses some of the common features present in all vertebrates, as well as unique aspects that different species utilize to establish their anterior-posterior (A-P) axis.