Fig. 7

The dynamics of dorsal neural tube (NT) development: transition from neural crest (NC) to definitive roof plate (RP). a Before the onset of NC migration (left panel), presumptive RP progenitors (green) are located ventral to the premigratory NC (red). They progressively reposition dorsally upon the onset and progression of NC emigration (middle panel, red cells outside the NT are migrating NC) until reaching their definitive localization at the dorsal midline of the central nervous system primordium (right panel). Arrows depict the ventral to dorsal direction of cellular relocation. For details see [12, 13]. b, c At the early NC stage, BMP signaling becomes active in the dorsal NT (+), inducing a series of BMP-dependent genes such as Foxd3, and promoting cell-cycle progression and subsequent NC epithelial-to-mesenchymal transitions (EMT) and delamination. As time goes on, NC cells leave the dorsal NT while RP progenitors are exposed to BMP signaling for a longer duration, perhaps interpreted as a higher signaling level (++). This induces initial Hairy1 synthesis ventral to the progressively narrowing domain of Foxd3 (see also [12]). At the RP stage, Hairy1-expressing cells reach the dorsal midline domain and Hairy1 inhibits expression of Alk3 receptors and further responsiveness of RP cells to BMP signaling (−), which results in the inhibition of Foxd3 transcription, arrest of cell-cycle progression, and the end of cellular EMT, altogether contributing to the consolidation of the definitive RP. Given that misexpression of Foxd3 close to the RP stage inhibits Hairy1, these cross-repressive interactions may account for the spatial and temporal separation of NC and RP lineages. The arrow in c depicts a time sequence