, 2002, Verdi et al., 1999 and Zhong et al., 2000) and is also involved in promoting neurogenesis and differentiation ( Klein et al., 2004, Wakamatsu et al., 1999 and Zilian et al., 2001). Numb is a membrane-associated adaptor protein containing C59 wnt multiple protein-binding motifs, and numb associates with a number of other proteins. Via its specific binding to AP-2 and other endocytic proteins (such as Eps15 and EHD4), numb plays roles in regulated endocytosis of receptors, including those of the Notch, integrin, L1, and Trk families. Many of the biological effects of numb on neurodevelopment are therefore probably related to regulating endocytosis of specific

receptors (Santolini et al., 2000). Interaction of numb with integrin promotes endocytosis and directional cell migration (Nishimura and Kaibuchi, 2007). Par3-dependent phosphorylation of numb by aPKC regulates polarized localization of numb and its association with clathrin coated structures (Smith et al., 2007). Negative regulation of numb by aPKC appears to play an important

role in integrin endocytosis and integrin-based cell migration (Nishimura and Kaibuchi, 2007). Numb has also been reported to play 3-Methyladenine nmr a critical role in cerebellar granule cell polarization during migration via a distinct mechanism (Zhou et al., 2011). Numb interacts with activated TrkB and promotes TrkB endocytosis and polarization. BDNF-induced phosphorylation of numb by aPKC increases binding to TrkB and promotes chemotactic responses to BDNF. Thus, in the

context of TrkB endocytosis, phosphorylation by aPKC increases affinity of numb for its cargo. In addition to its role in mediating receptor internalization, numb has a novel function in endosomal recycling of receptors. For example, numb has been implicated in regulating the postendocytic trafficking of Notch1. In mammalian cell lines, overexpression of numb promotes trafficking and degradation of Notch 1, whereas depletion of numb facilitates recycling of Notch1. Numb mutants defective Digestive enzyme in binding to endocytic proteins such as α-adaptin, fail to promote Notch 1 degradation, suggesting numb suppresses Notch activity by regulating postendocytic sorting pathways that lead to Notch degradation (McGill et al., 2009 and McGill and McGlade, 2003). Neurons frequently show cell-type-specific responses to the same environment. One mechanism of cell-type specificity involves differential expression of adhesion and guidance receptors (Kolodkin and Tessier-Lavigne, 2011 and Stein and Tessier-Lavigne, 2001). Interestingly, neurons can have different responses even when expressing the same receptors. Subsets of cortical neurons, identified by differential expression of the transcription factors Satb2 or Ctip2 respond differentially to Sema3A cues even though both populations similarly express the Neuropilin1, L1, and plexinA4 receptors (Carcea et al., 2010).