Differentiation of forebrain involves both intrinsic and extrinsic mechanisms. Intrinsic differentiation mechanisms are genetic program based. In this program, transcription factors acting within a cell trigger expression of genes specific to a particular phenotype.
Extrinsic differentiation mechanisms are environmental cues that act upon a cell to induce a particular phenotype. Such cues can be in the form of either soluble, cell matrix or cell bound molecules that are produced in one group of cells and then act on neighboring cells. These environmental influences typically result in changes in gene expression that drive adoption of a particular phenotype.
From the options below, choose ALL that represent intrinsic mechanisms in the forebrain development.