The Notch signaling pathway plays essential roles in both animal development and 
human disease. Regulation of Notch receptor levels in membrane compartments has 
been shown to affect signaling in a variety of contexts. Here we used 
steady-state and pulse-labeling techniques to follow Notch receptors in sensory 
organ precursor cells in Drosophila. We find that the endosomal adaptor protein 
Numb regulates levels of Notch receptor trafficking to Rab7-labeled late 
endosomes but not early endosomes. Using an assay we developed that labels 
different pools of Notch receptors as they move through the endocytic system, we 
show that Numb specifically suppresses a recycled Notch receptor subpopulation 
and that excess Notch signaling in numb mutants requires the recycling endosome 
GTPase Rab11 activity. Our data therefore suggest that Numb controls the balance 
between Notch receptor recycling and receptor targeting to late endosomes to 
regulate signaling output after asymmetric cell division in Drosophila neural 
progenitors.