Granule cells, unipolar brush cells and cells of the (excitatory) cerebellar nuclei, all of which are excitatory neurons, are generated at the upper rhombic lip located at the dorsal edge of the cerebellar primordium.
The most prominent example of long distance tangential migration in the hindbrain comprises a subset of neurons that originate from the lower rhombic lip. After birth, these neurons form at least three migratory pathways, which lead to the formation of several discrete nuclei in the hindbrain.
Likewise, in the cerebellar cortex, while VZ progenitors generate only inhibitory neurons, such as Purkinje cells and Golgi cells, (31) excitatory neurons such as granule cells and unipolar brush cells are generated in a neighboring germinal zone, the upper rhombic lip. While inhibitory neurons migrate radially, granule cells and unipolar brush cells tangentially migrate beneath the pial surface or through the white matter, respectively, and then radially migrate to settle in the depth (granule cell layer) of the cerebellar cortex, (38,39) resulting in a mixture of excitatory and inhibitory neurons.
(2005) Math1 expression redefines the rhombic lip derivatives and reveals novel lineages within the brainstem and cerebellum.
(2006) Development of the deep cerebellar nuclei: transcription factors and cell migration from the rhombic lip. J.