Mutations in the () gene cause human intellectual disability, one of the most common cognitive disorders. However, the molecular mechanisms of -related intellectual disability remain poorly understood. We investigated the role of in synaptic function and animal behavior using male mouse and models. knock-out (KO) mice showed normal brain and spine morphology as well as intact synaptic plasticity; however, they also exhibited decreases in synaptic transmission and presynaptic release probability exclusively in excitatory synapses. Presynaptic function was impaired not only by loss of CRBN expression, but also by expression of pathogenic CRBN mutants (human R419X mutant and G552X mutant). We found that the BK channel blockers paxilline and iberiotoxin reversed this decrease in presynaptic release probability in KO mice. In addition, paxilline treatment also restored normal cognitive behavior in KO mice. These results strongly suggest that increased BK channel activity is the pathological mechanism of intellectual disability in mutations. (), a well known target of the immunomodulatory drug thalidomide, was originally identified as a gene that causes human intellectual disability when mutated. However, the molecular mechanisms of CRBN-related intellectual disability remain poorly understood. Based on the idea that synaptic abnormalities are the most common factor in cognitive dysfunction, we monitored the synaptic structure and function of knock-out (KO) animals to identify the molecular mechanisms of intellectual disability. Here, we found that KO animals showed cognitive deficits caused by enhanced BK channel activity and reduced presynaptic glutamate release. Our findings suggest a physiological pathomechanism of the intellectual disability-related gene and will contribute to the development of therapeutic strategies for-related intellectual disability.
During brain development, dynamic changes in neuronal membranes perform critical roles in neuronal morphogenesis and migration to create functional neural circuits. Among the proteins that induce membrane dynamics, cell adhesion molecules are important in neuronal membrane plasticity. Here, we report that V-set and transmembrane domain-containing protein 5 (Vstm5), a cell-adhesion-like molecule belonging to the Ig superfamily, was found in mouse brain. Knock-down of Vstm5 in cultured hippocampal neurons markedly reduced the complexity of dendritic structures, as well as the number of dendritic filopodia. Vstm5 also regulates neuronal morphology by promoting dendritic protrusions that later develop into dendritic spines. Using electroporation in utero, we found that Vstm5 overexpression delayed neuronal migration andinducedmultiplebranchesinleadingprocessesduringcorticogenesis.TheseresultsindicatethatVstm5isanewcell-adhesion-likemolecule and is critically involved in synaptogenesis and corticogenesis by promoting neuronal membrane dynamics.
a b s t r a c t BK Ca channels are palmitoylated at a cluster of cysteine residues within the cytosolic linker connecting the 1st and 2nd transmembrane domains, and this lipid modification affects their surface expression. To verify the effects of palmitoylation on the diffusional dynamics of BK Ca channels, we investigated their lateral movement. Compared to wild-type channels, the movement of mutant palmitoylation-deficient channels was much less confined and close to random. The diffusion of the mutant channel was also much faster than that of the wild type. Thus, the lateral movement of BK Ca channels is greatly influenced by palmitoylation.
V-set and transmembrane domain-containing protein 5 (Vstm5), a newly characterized small membrane glycoprotein, can induce membrane protrusions in various cells. Vstm5 can modulate both the position and complexity of central neurons by altering their membrane morphology and dynamics. In this study, we investigated the significance of glycosylation in the expression and function of Vstm5. Four N-linked glycosylation sites (Asn43, Asn87, Asn101, and Asn108) are predicted to be located in the extracellular N-terminus of mouse Vstm5. Although all four sites were glycosylated, their functional roles may not be identical. N-glycosylation at multiple sites affects differentially the function of Vstm5. Glycosylation at individual sites not only played essential roles in surface expression of Vstm5 but also in the formation of neuronal dendritic filopodia. These results indicate that N-linked glycosylation at multiple sites plays important roles by differentially influencing the expression, targeting, and biological activity of Vstm5.
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