Fig. 1

Models depicting the cancer development in non-neural and neural progenitor cells. a Tumorigenesis in non-neural cells. Normal non-neural somatic cells express lineage- or tissue-specific genes but without significant expression of neural specific genes. Some internal/external cellular changes may occasionally lead to activation/upregulation/gain-of-function of certain neural specific factors, which could cause the activation of subsequent signaling pathways required for neural specification/development. This activation of neural factors is accompanied by the suppression of lineage- or tissue-specific genes, hence, the loss of cell or lineage identity. Since the internal/external environment or regulatory mechanisms under this situation is rather imperfect for a normal neural specification/development, the cells undergo uncontrolled proliferation, migration, and even incomplete neuronal differentiation, which do not occur during normal neural specification/development. b Tumorigenesis in the nervous system. Tumors in the nervous system originate from neural progenitor cells [88], which harbor both promoting and inhibitory signals for proliferation, migration, differentiation, etc., so as to keep normal neural development in a balanced fashion. When the balance is broken, for example, by amplification of MYCN, tumorigenesis may occur