Vertebrate floor-plate specification: variations on common themes.

Situated at the ventral-most part of the vertebrate neural tube, the floor plate (FP) is an important signalling centre that controls the regional differentiation of neurons in the nervous system. It secretes guidance molecules that direct ventrally navigating axons crucial for the correct wiring of neuronal circuits. Although the function of the FP is well-conserved from fish to humans, discrepancies exists with respect to both the signalling system involved in FP induction, and the origin of the FP in various vertebrate species. Recent findings from the embryos of zebrafish, chicken and mouse provide insights that reconcile previous results and suggest common themes in vertebrate FP specification.