Neuronal development.

Biological tools that are unleashed in malignancies are employed in a controlled manner during neuronal development. By default, early embryonic cells would become neuronal stem cells, a path that is blocked by specific signaling pathways. The future nervous system only develops where this blockade is inhibited by inductive signals from the 'organizer'. Once the future brain and spinal cord regions are determined, the mitotic potential in this region must be maintained long enough to produce all cells required, but also be controlled to avoid excessive over-production of cells. Newly generated cells must then migrate to their future destination, they must know where to settle down, and they must differentiate. To shape the developing nervous system and to adapt its functionality to the postnatal environment, cell survival must be regulated, i.e. survival of some cells is supported while death of others is induced. Thus, inductive events, proliferation, cell migration, differentiation, cell survival and cell death are highly regulated during neuronal development, while these functions are de-regulated in malignancies. The molecular pathways for neuronal development mutually modulate each other and are still present in the adult nervous system. Because many of these pathways are implicated in tumors, neurons may affect these conditions.