TGFB1 and central nervous system cancer: Axonal guidance signaling, amyloid processing, neuroinflammation signaling pathway, glioma invasiveness signaling, glioblastoma multiforme signaling, role of NANOG in mammalian embryonic stem cell pluripotency, TGF-β signaling, synaptogenesis signaling pathway, glioma signaling, and Huntingtion’s disease signaling