Plays a role in the process of neurogenesis. Required throughout embryonic neurogenesis to maintain neural progenitor cells, also called radial glial cells (RGCs), by allowing their daughter cells to choose progenitor over neuronal cell fate. Not required for the proliferation of neural progenitor cells before the onset of embryonic neurogenesis. Also required postnatally in the subventricular zone (SVZ) neurogenesis by regulating SVZ neuroblasts survival and ependymal wall integrity. Negative regulator of NF-kappa-B signaling pathway. The inhibition of NF-kappa-B activation is mediated at least in part, by preventing MAP3K7IP2 to interact with polyubiquitin chains of TRAF6 and RIPK1 and by stimulating the 'Lys-48'-linked polyubiquitination and degradation of TRAF6 in cortical neurons. Interacts (via PTB domain) with MAP3K7IP2 (via C-terminal). Interacts (via C-terminal) with TRAF6 (via TRAF domains) (By similarity). Associates with EPS15 and NOTCH1. Symmetrically distributed throughout the cytoplasm in non dividing neuroblasts of the CNS. Preferentially expressed in the nervous system. In the developing neocortex, expressed in postmitotic neurons in the cortical plate but not in progenitors within the ventricular zone. Expressed in neural progenitor and neuron cells throughout the developing nervous system. Expressed in somites and throughout the neural tube from 8.5 dpc, onward. The PTB domain is necessary for the inhibition of MAP3K7IP2-mediated activation of NF-kappa-B. No visible phenotype. Mutants are viable and fertile. Mice lacking both Numb and Numbl genes die around 9.5 dpc, with severe defects in somite and vasculature formation, neuronal tube closure and axial turning. Conditional double-knockout (cdKO) mutants (Numb and Numbl genes), with expression abrogated in neural progenitor cells from 8.5 dpc (just before the onset of neurogenesis), display a loss of neural progenitor cells formation and an overexpression of neurons as neurogenesis progresses; cdKO mutants become necrotic at 12.5 dpc and die around this stage. Conditional double-knockout (cdKO) mutants (Numb and Numbl genes), with expression abrogated in neural progenitor cells from 10.5 dpc (just after the onset of neurogenesis), display a premature depletion of neural progenitor cells in the dorsal forebrain ventrical zone of the neocortex and in the hippocampal CA fields as neurogenesis progresses; cdKO mutants are viable and fertile, but showed a reduction in the thickness of the neocortex and the hippocampus and an enlargement of the lateral ventricles. Tamoxifen-inducible double-knockout (cdKO) mutants (Numb and Numbl genes), with expression abrogated postnatally in the subventricular zone (SVZ) neuroprogenitors and in ependymal cells, display a loss of SVZ neuroblasts and show a disorganized ependyma lacking both interdigitation junction between neighboring cells and increasing number of separated cells.