Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor.

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.

A Synthetic Approach to Dimetalated Arenes Using Flow Microreactors and the Switchable Application to Chemoselective Cross-Coupling Reactions.

In spite of their potential utility, the chemistry of dimetalated arenes is still in its infancy because they are extremely difficult to synthesize. We report a novel method of synthesizing arenes bearing a boryl group and a metallic substituent, such as boryl, silyl, stannyl, or zincyl groups, in an integrated flow microreactor based on the generation and reactions of aryllithiums bearing a trialkyl borate moiety. The bimetallic arenes showed a remarkable chemoselectivity in palladium-catalyzed cross-coupling reactions. The selectivity was switched by the selection of the metal species that constitutes the dimetalated arenes as well as appropriate catalysts.

A Novel Approach to Functionalization of Aryl Azides through the Generation and Reaction of Organolithium Species Bearing Masked Azides in Flow Microreactors.

A novel straightforward method for aryl azides having functional groups based on generation and reactions of aryllithiums bearing a triazene group from polybromoarenes using flow microreactor systems was achieved. The present approach will serve as a powerful method in organolithium chemistry and open a new possibility in the synthesis of polyfunctional organic azides.

Tumor suppressor protein CYLD regulates morphogenesis of dendrites and spines.

Cylindromatosis tumor suppressor protein (CYLD) was initially identified as a tumor suppressor deubiquitylating protein in familial cylindromatosis patients. Proteomic analyses using rodent brain samples revealed enrichment of CYLD in purified postsynaptic density fractions. Here, we report that CYLD regulates dendritic growth and postsynaptic differentiation in mouse hippocampal neurons. CYLD showed diffuse localization in rapidly growing dendrites, but was gradually concentrated in spines. Overexpression and knockdown of CYLD in the early stage of cultured neurons demonstrated that CYLD positively regulated dendritic growth. Phenotypes in dendritic morphogenesis induced by CYLD overexpression and knockdown could be reversed by manipulation of the critical acetylation site of α-tubulin, suggesting tubulin acetylation is a downstream pathway of CYLD-dependent dendritic growth. Overexpression and knockdown of CYLD in the later stage of cultured neurons revealed that CYLD promoted formation of postsynaptic spines. Influence of CYLD on spines was not affected by co-expression of acetylation mutant forms of α-tubulin, indicating that CYLD regulates dendritic growth and spine formation through different molecular mechanisms. Analyses with the truncated and mutated forms of CYLD demonstrated that the first microtubule-binding domain of CYLD was critical for spine formation. These results suggest important roles of CYLD in sequential promotion of dendritic growth and postsynaptic spine maturation.

Regulation of {alpha}-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor trafficking through PKA phosphorylation of the Glu receptor 1 subunit.

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors mediate the majority of excitatory synaptic transmission in the brain. Recent studies have shown that activation of PKA regulates the membrane trafficking of the AMPA receptor Glu receptor 1 (GluR1) subunit, but the role of direct phosphorylation of GluR1 in regulating receptor redistribution is not clear. Here we show that phosphorylation of the GluR1 subunit on serine 845 by PKA is required for PKA-induced increases in AMPA receptor cell-surface expression because it promotes receptor insertion and decreases receptor endocytosis. Furthermore, dephosphorylation of GluR1 serine 845 triggers NMDA-induced AMPA receptor internalization. These findings strongly suggest that dynamic changes in direct phosphorylation of GluR1 by PKA are crucial in the modulation of AMPA receptor trafficking and synaptic plasticity.

S-nitrosylation of N-ethylmaleimide sensitive factor mediates surface expression of AMPA receptors.

Postsynaptic AMPA receptor (AMPAR) trafficking mediates some forms of synaptic plasticity that are modulated by NMDA receptor (NMDAR) activation and N-ethylmaleimide sensitive factor (NSF). We report that NSF is physiologically S-nitrosylated by endogenous, neuronally derived nitric oxide (NO). S-nitrosylation of NSF augments its binding to the AMPAR GluR2 subunit. Surface insertion of GluR2 in response to activation of synaptic NMDARs requires endogenous NO, acting selectively upon the binding of NSF to GluR2. Thus, AMPAR recycling elicited by NMDA neurotransmission is mediated by a cascade involving NMDA activation of neuronal NO synthase to form NO, leading to S-nitrosylation of NSF which is thereby activated, enabling it to bind to GluR2 and promote the receptor's surface expression.

Imaging of receptor trafficking by using alpha-bungarotoxin-binding-site-tagged receptors.

alpha-Amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptors mediate excitatory synaptic transmission and are dynamically regulated during synaptic plasticity in the CNS. The membrane trafficking of AMPA receptors to synapses is critical for the regulation of the efficacy of excitatory synaptic transmission. Direct imaging of AMPA receptors in various cell compartments is important to dissecting the regulation of distinct steps in receptor membrane trafficking. In this study, we have developed an approach for the imaging of receptor trafficking with subunits tagged with a 13-aa alpha-bungarotoxin (BTX)-binding site (BBS). The small polypeptide neurotoxin BTX has been used for decades to study the nicotinic acetylcholine receptor. Similar high-affinity ligands are rarely available for most receptors. Engineering the BBS tag into receptor subunits allowed the high-affinity binding of fluorescent, radioactive, and biotinylated BTX to the tagged receptor subunits. By using this approach, the total receptor expression, surface expression, internalization, and insertion of receptors into the plasma membrane could be visualized and quantified in fixed or live cells including cultured neurons. The BBS tag is a flexible approach for labeling membrane proteins and studying their dynamic trafficking.

MuSC is involved in regulating axonal fasciculation of mouse primary vestibular afferents.

Regulation of axonal fasciculation plays an important role in the precise patterning of neural circuits. Selective fasciculation contributes to the sorting of different types of axons and prevents the misrouting of axons. However, axons must defasciculate once they reach the target area. To study the regulation of fasciculation, we focused on the primary vestibulo-cerebellar afferents (PVAs), which show a dramatic change from fasciculated axon bundles to defasciculated individual axons at their target region, the cerebellar primordium. To understand how fasciculation and defasciculation are regulated in this system, we investigated the roles of murine SC1-related protein (MuSC), a molecule belonging to the immunoglobulin superfamily. We show: (i) by comparing 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) labelling and anti-MuSC immunohistochemistry, that downregulation of MuSC in PVAs during development is concomitant with the defasciculation of PVA axons; (ii) in a binding assay with cells expressing MuSC, that MuSC has cell-adhesive activity via a homophilic binding mechanism, and this activity is increased by multimerization; and (iii) that MuSC also displays neurite outgrowth-promoting activity in vestibular ganglion cultures. These findings suggest that MuSC is involved in axonal fasciculation and its downregulation may help to initiate the defasciculation of PVAs.