Figure 1.

Development of granule cells in relation to Purkinje cells in the amniote cerebellum. Granule cell precursors (red) are initially induced at the rhombic lip by TGFβ signals (green) from the adjacent roof plate (i). Precursors migrate tangentially over the subpial cerebellar surface and divide again within the transient EGL (ii). Proliferation is regulated by Shh secreted from underlying Purkinje cells (purple). After their last cell division, postmitotic granule cells (brown) radially migrate into a layer below Purkinje cells (iii). In the mature circuit, glutamatergic granule cells receive inputs from precerebellar neurons and project T-shaped axons (parallel fibers) into an almost cell-body-free (molecular) layer, in which they synapse on the dendrites of GABAergic Purkinje cells. Purkinje cell outputs directly and indirectly regulate the activity of the vestibular system, thalamus, and subcortical motor centers.