The vertebrate tail: a gene playground for evolution

The tail of vertebrates, despite variations, originates from the tail bud, a post-anal extension in the embryo. Its formation involves cells from axial progenitors that also build the spinal cord and musculoskeletal structure of the trunk. The Gdf11 activity shifts these progenitors from trunk to tail bud development by altering the regulatory network that governs their growth and differentiation. Recent mouse studies suggest the tail bud regulatory network depends on the Lin28/let-7 axis and Hox13 genes. The balance between progenitor-promoting and -repressing activities of these genes might determine the adult tail's length, anatomy, and regeneration potential, which is linked to the spinal cord. Mammals lack tail regeneration because the spinal cord is removed from the embryonic tail via a Hox13-dependent mechanism. Conversely, salamanders and lizards retain a functional spinal cord, enabling tail regeneration. Molecular networks controlling tail bud development were co-opted and combined during evolution to diversify tail shapes and sizes.

• 1
  Gdf11 activity acts as a master switch, controlling the change from trunk to tail developmental modes in most vertebrates.
• 2
  The Lin28/let-7/Hox13 network operates at least in the tail bud of other mammals, influencing tail growth and differentiation.
• 3
  The absence of a neural tube in mammalian tails correlates with their lack of regeneration potential, while lizards and salamanders with spinal cords in their tails can regenerate them.