THE CELLS AND MOLECULES THAT MAKE A CEREBELLUM

The molecular underpinnings of cerebellar development are being establ ished through the identification of naturally occurring mutated genes and the knockout of other genes. Sets of genes expressed in the region s of the mes- and metencephalon have been shown to play a crucial role in specifying the cerebellar anlage. Other genes have been shown to b e crucial to early granule cell development, migration of Purkinje and granule cells, and neuron-glia interactions. However, the process of development will ultimately be understood in terms of cellular interac tions and the roles that each cell type plays in the assembly of cereb ellar structure. One of the most important interactions is between gra nule and Purkinje cells. This relationship has been shown to be crucia l for the control of cell number, migration of neuroblasts and cell di fferentiation.