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Protein coating material is important in many technological fields. The interaction between carbon nanomaterial and protein is especially interesting since it makes the development of novel hybrid materials possible. Functional Bacterial Amyloid (FuBA) is promising as a coating material because of its desirable features such as well-defined molecular structure, robustness against harsh conditions, and easily engineerable functionality. Here, we report the systematic assembly of the functional amyloid protein, CsgA from Escherichia coli (E. coli) on graphite. We characterize the assemblies using Scanning Tunnelling Microscopy (STM) and show that CsgA forms assemblies according to systematic patterns, dictated by the graphite lattice. In addition, we show that graphite flakes induce the fibrillization of CsgA, in vitro, suggesting a surface-induced conformational change of CsgA facilitated by the graphite lattice. Using coarse-grained molecular dynamics simulations, we model the adhesion and lamellar formation of a CsgA-derived peptide and conclude that peptides are adsorbed both as monomers and smaller aggregates leading initially to unordered graphite-bound aggregates which are followed by rearrangement into lamellar structures. Finally, we show that CsgA-derived peptides can be immobilized in very systematic assemblies and their molecular orientation can be tuned using a small chaperone-like molecule. Our findings have implications for the development of FuBA-based biosensors, catalysts, and other technologies requiring well-defined protein assemblies on graphite.

The emergence of exquisitely organized axonal projections is one of the greatest wonders of nervous system development. In addition to growing along stereotyped directions, axons join one another as they extend. It is well known that axonal growth cones recognize cell surface guidance cues on axons and either grow along the axons or away from the axons. However, it is less well understood whether and how the growth cones communicate with each other and, if so, what do these interactions mean. Recent studies from our lab provided direct evidence that the growth cones do interact with each other during axon pathfinding. And this interaction is regulated by highly regulated protein-protein interactions among components of the planar cell polarity pathway. The disruption of these interactions lead to guidance defects and disorganization of axons. We propose that this local inter-growth cone PCP-like signaling mechanism reinforces and increases the sensitivity of the growth cone response to shallow Wnt gradients to turn in a precise and organized fashion.

Directional and positional information is essential for the diverse neuronal morphology and connectivity during development. The direction of axon growth is critical for building the correct networks among neurons, sometimes from far away. Neuronal synapses are asymmetric cell-cell junctions with distinct presynaptic and postsynaptic structures to convey neural activity in a directional fashion. Recent studies show that some of the key asymmetry is mediated by highly conversed cell polarity signaling pathways. These pathways, planar cell polarity and apical-basal polarity, are not required for the global axon-dendrite polarity. Therefore, the apparent distinct types of morphological asymmetry in the nervous system, growth cone turning and synaptic junctions, are mediated by similar cell polarity signaling mechanisms widely used in cellular and tissue morphogenesis.

Summary Normal synapse formation is fundamental to brain function. We show here that an apical-basal polarity (A-BP) protein, Lgl1, is present in the postsynaptic density and negatively regulates glutamatergic synapse numbers by antagonizing the atypical protein kinase Cs (aPKCs). A planar cell polarity protein, Vangl2, which inhibits synapse formation, was decreased in synaptosome fractions of cultured cortical neurons from Lgl1 knockout embryos. Conditional knockout of Lgl1 in pyramidal neurons led to reduction of AMPA/NMDA ratio and impaired plasticity. Lgl1 is frequently deleted in Smith-Magenis syndrome (SMS). Lgl1 conditional knockout led to increased locomotion, impaired novel object recognition and social interaction. Lgl1+/− animals also showed increased synapse numbers, defects in open field and social interaction, as well as stereotyped repetitive behavior. Social interaction in Lgl1+/− could be rescued by NMDA antagonists. Our findings reveal a role of apical-basal polarity proteins in glutamatergic synapse development and function and also suggest a potential treatment for SMS patients with Lgl1 deletion., Graphical Abstract, Highlights • Lgl1 regulates glutamatergic synapse numbers by inhibiting aPKC • Lgl1 cKO leads to reduced AMPA/NMDA ratio in development and adulthood • Lgl1 conditional knockout impairs novel object cognition and social interaction • Social interaction deficits can be rescued by NMDA receptor blockade, Biological Sciences; Cell Biology; Cellular Neuroscience; Neuroscience

Implantable neural probes constitute an essential tool for neuronal activity recordings in basic neuroscience and also hold great promise for the development of neuroprosthesis to restore lost motor or sensory functions of the body. However, conventional neural probes are susceptible to biofouling because of their physicochemical mismatch with neural tissues, resulting in signal degradation in chronic studies. Here, we describe an ultraflexible neural probe (uFNP) with anti-fouling zwitterionic peptide modification for long-term stable neural activity recordings. The anti-fouling zwitterionic peptide consists of two parts: negatively charged glutamic acid (E) and positively charged lysine (K) formed EKEKEK (EK) head to create a hydration layer that resists protein adsorption on the microelectrodes, and a fragment of laminin formed IKVAV tail to increase the adhesion of the microelectrodes to neuronal cells. We demonstrate that EK-IKVAV modified uFNPs can allow for stable neuronal activity recordings over 16 weeks. Immunohistological studies confirm that EK-IKVAV functionalized uFNPs could induce greatly reduced neuronal cell loss. Collectively, these results suggest that the anti-fouling zwitterionic peptide functionalization of uFNPs provide a promising route to construct biocompatible and stable neural interfaces.

GABAergic interneurons have many important functions in cortical circuitry, a reflection of their diversity as a cell population. However, the developmental origins of this diversity are poorly understood. Here, we identify a rostral-caudal gradient of Wnt-responsiveness that delineates the specification of the two main interneuron subclasses. Caudallysituated medial ganglionic eminence (MGE) progenitors receive high levels of Wnt signaling and give rise to somatostatin (SST)-expressing cortical interneurons. Parvalbumin (PV)-expressing basket cells, by contrast, originate mostly from the rostral MGE where Wnt signaling is attenuated. Interestingly, rather than canonical signaling through beta-catenin, Wnt signaling transmitted via the non-canonical receptor, Ryk regulates interneuron cell-fate specification in vivo and in vitro. Indeed, gain-of-function of Ryk intracellular domain signaling regulates SST and PV fate in a dose-dependent manner, suggesting Ryk signaling acts in a graded fashion. These data reveal a complex and important role for non-canonical Wnt-Ryk signaling in establishing the correct ratios of mature cortical interneuron subtypes.

Many studies in the past decade have revealed the role and mechanisms of Wnt signaling in axon guidance during development and the reinduction of Wnt signaling in adult central nervous system axons upon traumatic injury, which has profound influences on axon regeneration. With 19 Wnts and 14 known receptors (10 Frizzleds (Fzds), Ryk, Ror1/2 and PTK7), the Wnt family signaling proteins contribute significantly to the wiring specificity of the complex brain and spinal cord circuitry. Subsequent investigation into the signaling mechanisms showed that conserved cell polarity pathways mediate growth cone steering. These cell polarity pathways may unveil general principles of growth cone guidance. The reappeared Wnt signaling system after spinal cord injury limits the regrowth of both descending and ascending motor and sensory axons. Therefore, the knowledge of Wnt signaling mechanisms learned from axon development can be applied to axon repair in adulthood.

Commissural axons cross the nervous system midline sural axons acquire high-level expression of Robo and, and then turn to grow alongside it, neither recrossing consequently, become highly responsive to the Slit renor projecting back into ventral regions. In Drosophila, pellent, explaining why they can no longer recross. This the midline repellent Slit prevents recrossing: axons model is consistent with the results of extensive genetic cross once because they are initially unresponsive to analysis. For example, commissural axons that lack Slit, becoming responsive only upon crossing. We Robo function (in robo mutants) can cross the midline show that commissural axons in mammals similarly multiple times, whereas in comm mutants, commissural acquire responsiveness to a midline repellent activity axons express high levels of Robo protein on their surupon crossing. Remarkably, they also become respon- faces as soon as they are initiated and fail to cross the midline (Seeger et al., 1993; Kidd et al., 1998b). Thus, sive to a repellent activity from ventral spinal cord

SummaryAlthough a growing body of evidence supports that Wnt-Frizzled signaling controls axon guidance from vertebrates to worms, whether and how this is mediated by planar cell polarity (PCP) signaling remain elusive. We show here that the core PCP components are required for Wnt5a-stimulated outgrowth and anterior-posterior guidance of commissural axons. Dishevelled1 can inhibit PCP signaling by increasing hyperphosphorylation of Frizzled3 and preventing its internalization. Vangl2 antagonizes that by reducing Frizzled3 phosphorylation and promotes its internalization. In commissural axon growth cones, Vangl2 is predominantly localized on the plasma membrane and is highly enriched on the tips of the filopodia as well as in patches of membrane where new filopodia emerge. Taken together, we propose that the antagonistic functions of Vangl2 and Dvl1 (over Frizzled3 hyperphosphorylation and endocytosis) allow sharpening of PCP signaling locally on the tips of the filopodia to sense directional cues, Wnts, eventually causing turning of growth cones.

Identification of methionine aminopeptidase-2 (MetAP-2) as the molecular target of the antiangiogenic compound TNP-470 has sparked interest in N-terminal Met excision's (NME) role in endothelial cell biology. In this regard, we recently demonstrated that MetAP-2 inhibition suppresses Wnt planar cell polarity (PCP) signaling and that endothelial cells depend on this pathway for normal function. Despite this advance, the substrate(s) whose activity is altered upon MetAP-2 inhibition, resulting in loss of Wnt PCP signaling, is not known. Here we identify the small G protein Rab37 as a MetAP-2-specific substrate that accumulates in the presence of TNP-470. A functional role for aberrant Rab37 accumulation in TNP-470's mode of action is demonstrated using a Rab37 point mutant that is resistant to NME, because expression of this mutant phenocopies the effects of MetAP-2 inhibition on Wnt PCP signaling-dependent processes.