The establishment of gene expression domains along the anterior-posterior axis helps to segment the developing brain into the forebrain, midbrain (MB), hindbrain (HB) and spinal cord (SC). Signalling centres established at the boundaries between these segments secrete growth factors which pattern the adjacent nervous tissue. The Isthmic Organizer (IsO; shown in yellow) forms at the boundary of the posterior midbrain and anterior hindbrain: the IsO secretes Fgf8 and other growth factors, and is essential for defining the regions of the neural plate that will become the posterior midbrain (shown in blue) and the cerebellum (CB; green). The homeobox genes Otx2 and Gbx2 are involved in the formation of the IsO and in regulating the expression of Fgf8 by the IsO. Mutations in the CHARGE syndrome gene, CHD7, can alter Otx2, Gbx2 and Fgf8 expression, resulting in underdevelopment of a region of the cerebellum called the vermis (right).
Figure modified from Basson and Wingate, 2013