During the development of mouse cerebellum,the major types of neurons are temporally generated from progenitor cells located in the rhombic lip or ventricular zone of cerebellar primordium.Regulation of the balance between cerebellar progenitors differentiation and their maintenance for subsequent neurogenesis remains largely unknown.By using Cre/loxP-triggered gene inactivation,we found that loss of Notch function resulted in defective tectum and cerebellum development.In these mutant mice,the tectum and cerebellum were significantly reduced in size and the numbers of Purkinje cell and granular cell precursors were severely decreased at E16.5,compared with the wild-type littermates.