developmental sequence (class 4)

weeks 3 to 4

neural indiction and early AP and DV patterning, neural tube closure

weeks 3 to 4 prominent signals

• WNT BMP NODAL antagonists rostrally

• FGF WNT and RA caudally

• SHH begins ventralization

weeks 4 to 5

primary and secondary vesicles, local organizers, optic vesicles and early retina

weeks 4 to 5 prominent signals

FGF WNT BMP and SHH act from region-specific sources

weeks 5 to 8

rhombomeres and progenitor domains, early neurogenesis, cortical protomap

weeks 5 to 8 prominent signals

• RA and Hox programs in hind brain

• FGF WNT and BMP gradients in cortex

fetal period

growth of cortex cerebellum nuclei and tracts, circuit refinement

fetal period prominent signals

intrinsic temporal programs interact with morphogens and incoming axons