Numb deficiency in cerebellar Purkinje cells impairs synaptic expression of metabotropic glutamate receptor and motor coordination.

Protein Numb, first identified as a cell-fate determinant in Drosophila, has been shown to promote the development of neurites in mammals and to be cotransported with endocytic receptors in clathrin-coated vesicles in vitro. Nevertheless, its function in mature neurons has not yet been elucidated. Here we show that cerebellar Purkinje cells (PCs) express high levels of Numb during adulthood and that conditional deletion of Numb in PCs is sufficient to impair motor coordination despite maintenance of a normal cerebellar cyto-architecture. Numb proved to be critical for internalization and recycling of metabotropic glutamate 1 receptor (mGlu1) in PCs. A significant decrease of mGlu1 and an inhibition of long-term depression at the parallel fiber-PC synapse were observed in conditional Numb knockout mice. Indeed, the trafficking of mGlu1 induced by agonists was inhibited significantly in these mutants, but the expression of ionotropic glutamate receptor subunits and of mGlu1-associated proteins was not affected by the loss of Numb. Moreover, transient and persistent forms of mGlu1 plasticity were robustly induced in mutant PCs, suggesting that they do not require mGlu1 trafficking. Together, our data demonstrate that Numb is a regulator for constitutive expression and dynamic transport of mGlu1.

[The mechanism of NUMB regulate tumor proliferation].

OBJECTIVE: To study the specific mechanism of NUMB regulate tumor proliferation. METHODS: A stable cell line by knocking down NUMB in Hela was eatablished and the Western blot and qRT-PCR was applied to confirm the knocking out of NUMB. The effect on tumor proliferation in the absence of NUMB was investigated by observing tumor growth in nude mice. The effect on the cell cycle in the absence of NUMB was detected by flow cytometry and Brdu assay. Finally, differential expression profiles of various cell cycle regulatory proteins was detected by using Western blot analysis. RESULTS: Western blot and qRT-PCR results indicated that NUMB was specifically and efficiently knocked down in the Hela stable cell line. Tumor growth experiments demonstrated that NUMB depletion significantly promoted the tumor proliferation. Flow cytometry and Brdu assay indicated that NUMB depletion significantly promoted the G1/S transition and enhanced the cell proliferation. Western blot results demonstrated that Cyclin-E protein level was increased in NUMB depletion cell, whereas expression of P27 protein was decreased. CONCLUSION: NUMB might be involved in cell cycle process by regulating Cyclin-E and P27 protein level and thereby has an effect on tumor proliferation.

[Numb expression in colon cancer and its significance].

OBJECTIVE: To investigate the expression pattern of Numb, a membrane associated protein, in colon cancer and its biological significance. METHODS: Routine immunohistochemistry staining was used to detect the expression of Numb in tissue microarray with 60 cases of colon cancer tissue and 20 normal colon tissue. The clinical data was analyzed. The expression of Numb in SW480, SW620 cell lines were evaluated by immunostaining and Western blot. RESULTS: The positive expression rate of Numb in cytoplasm decreased in poorly differentiated tumor tissue than normal tissue and well and moderately differentiated colon cancer (P < 0.05), and the expression intensity was correlated with the differentiation state of cancer tissue. Westen blot results showed that colon cancer cell line SW480, compared with SW620 has a higher protein expression (P < 0.05). A punctate distribution of Numb in cytoplasm in colon cancer cell under confocal immunofluorescence was observed. A increased expression density in SW480 cell line was noticed when compared with that in SW620 cell line (P < 0.05). CONCLUSION: Numb may has an important regulation in the process of tumor progression and play a protective role against tumor development.

Numb and Numbl are required for maintenance of cadherin-based adhesion and polarity of neural progenitors.

The polarity and adhesion of radial glial cells (RGCs), which function as progenitors and migrational guides for neurons, are critical for morphogenesis of the cerebral cortex. These characteristics largely depend on cadherin-based adherens junctions, which anchor apical end-feet of adjacent RGCs to each other at the ventricular surface. Here, we show that mouse numb and numb-like are required for maintaining radial glial adherens junctions. Numb accumulates in the apical end-feet, where it localizes to adherens junction-associated vesicles and interacts with cadherins. Numb and Numbl inactivation in RGCs decreases proper basolateral insertion of cadherins and disrupts adherens junctions and polarity, leading to progenitor dispersion and disorganized cortical lamination. Conversely, overexpression of Numb prolongs RGC polarization, in a cadherin-dependent manner, beyond the normal neurogenic period. Thus, by regulating RGC adhesion and polarity, Numb and Numbl are required for the tissue architecture of neurogenic niches and the cerebral cortex.

Inactivation of Numb and Numblike in embryonic dorsal forebrain impairs neurogenesis and disrupts cortical morphogenesis.

Numb and Numblike, conserved homologs of Drosophila Numb, have been implicated in cortical neurogenesis; however, analysis of their involvement in later stages of cortical development has been hampered by early lethality of double mutants in previous studies. Using Emx1(IREScre) to induce more restricted inactivation of Numb in the dorsal forebrain of numblike null mice beginning at E9.5, we have generated viable double mutants that displayed striking brain defects. It was thus possible to examine neurogenesis during the later peak phase (E12.5-E16.5). Loss of Numb and Numblike in dorsal forebrain resulted in neural progenitor hyperproliferation, delayed cell cycle exit, impaired neuronal differentiation, and concomitant defects in cortical morphogenesis. These findings reveal novel and essential function of Numb and Numblike during the peak period of cortical neurogenesis. Further, these double mutant mice provide an unprecedented viable animal model for severe brain malformations due to defects in neural progenitor cells.