Abstract
The activation and transformation model of vertebrate nervous system formation posits that neural tissue is initially induced, or activated, with anterior forebrain character. Once established, a subset is then transformed into the more posterior midbrain, hindbrain, and spinal cord by signals emanating from the posterior of the embryo. This has been a predominant model in the field for decades. In the June issue of EMBO Reports, Polevoy and colleagues evaluate the role of signals thought to act as the neural transforming factors during Xenopus development, and find that while these signals are consistent with the activation transformation model during brain patterning, they do not fit the model with respect to spinal cord formation [1]. This work, along with other recent studies on the origin of the spinal cord, necessitates an updated model of vertebrate nervous system formation, where spinal cord induction and patterning is distinct from that of the brain.