[Forebrain regionalization mechanisms]

Where do the regions of the forebrain come from? The paradigm that has come to light in the last ten years is that of a neural plate subdivided by soluble factors which (through the formation of gradients or of a molecular framework) transmits positional information to the neural stem cells. Some of those soluble factors are Fgf8, Sonic hedgehog and proteins of the BMP family. The neural stem cells interpret positional information in terms of the expression of combinations of certain transcription factors. Such combinations would finally be responsible for the formation of specific neural lineages (cortical, thalamic, etc.) from specific neuroepithelial regions. In addition, this primary positional information can make certain regions of the neural primordium (secondary organizers) secrete new soluble factors. These would in turn give rise to new positional information, spatially more restricted, so that the whole process would repeat itself to confer detail to a certain area. This wealth of new knowledge is already helping us to understand the cause of some brain malformations, and maybe we will soon be able to apply it to the early diagnosis and the prevention of such conditions.