Molecular mechanisms of axon guidance

MYC regulation of the miR-92-Robo1 axis in Slit-mediated commissural axon guidance

In the developing spinal cord, translational repression of Robo1 expression by microRNA-92 (miR-92) in precrossing commissural axons (CAs) inhibits Slit/Robo1-mediated repulsion facilitating commissural axon projection and midline crossing; however, the regulatory mechanisms governing miR-92 expression in the developing commissural neurons are currently lacking. Here, we propose that the transcription factor MYC regulates miR-92 expression in the developing spinal cord (of either sex) to control Robo1 levels in precrossing CAs, modulating Slit/Robo1-mediated repulsion and midline crossing. MYC, miR-92, and Robo1 are differentially expressed in the developing chicken spinal cord. MYC binds to the promoter region upstream of the gga-miR-92 gene in vitro. MYC knockdown dramatically decreases miR-92 expression and increases chicken Robo1 (cRobo1) levels. In contrast, overexpression of MYC significantly induces miR-92 expression and reduces cRobo1 levels. MYC knockdown or overexpression results in significant inhibition or induction of miR-92 activity in the developing chicken spinal cord, respectively. Disruption of the MYC-dependent regulation of the miR-92-cRobo1 axis affects Slit2-mediated CA growth cone collapse in vitro and impairs CA projection and midline crossing in vivo. These results elucidate the role of the MYC-miR-92-cRobo1 axis in Slit2/Robo1-mediated CA repulsion and midline crossing.

Topographic Axes of Wiring Space Converge to Genetic Topography in Shaping the Human Cortical Layout

Genetic information is involved in the gradual emergence of cortical areas since the neural tube begins to form, shaping the heterogeneous functions of neural circuits in the human brain. Informed by invasive tract-tracing measurements, the cortex exhibits marked interareal variation in connectivity profiles, revealing the heterogeneity across cortical areas. However, it remains unclear about the organizing principles possibly shared by genetics and cortical wiring to manifest the spatial heterogeneity across the cortex. Instead of considering a complex one-to-one mapping between genetic coding and interareal connectivity, we hypothesized the existence of a more efficient way that the organizing principles are embedded in genetic profiles to underpin the cortical wiring space. Leveraging vertex-wise tractography in diffusion-weighted MRI, we derived the global connectopies (GCs) in both female and male to reliably index the organizing principles of interareal connectivity variation in a low-dimensional space, which captured three dominant topographic patterns along the dorsoventral, rostrocaudal, and mediolateral axes of the cortex. More importantly, we demonstrated that the GCs converge with the gradients of a vertex-by-vertex genetic correlation matrix on the phenotype of cortical morphology and the cortex-wide spatiomolecular gradients. By diving into the genetic profiles, we found that the critical role of genes scaffolding the GCs was related to brain morphogenesis and enriched in radial glial cells before birth and excitatory neurons after birth. Taken together, our findings demonstrated the existence of a genetically determined space that encodes the interareal connectivity variation, which may give new insights into the links between cortical connections and arealization.

Understanding the role of nerves in head and neck cancers - a review

Worldwide, head and neck cancers (HNCs) account for approximately 900,000 cases and 500,000 deaths annually, with their incidence continuing to rise. Carcinogenesis is a complex, multidimensional molecular process leading to cancer development, and in recent years, the role of nerves in the pathogenesis of various malignancies has been increasingly recognized. Thanks to the abundant innervation of the head and neck region, peripheral nervous system has gained considerable interest for its possible role in the development and progression of HNCs. Intratumoral parasympathetic, sympathetic, and sensory nerve fibers are emerging as key players and potential targets for novel anti-cancer and pain-relieving medications in different tumors, including HNCs. This review explores nerve-cancer interactions, including perineural invasion (PNI), cancer-related axonogenesis, neurogenesis, and nerve reprogramming, with an emphasis on their molecular mechanisms, mediators and clinical implications. PNI, an adverse histopathologic feature, has been widely investigated in HNCs. However, its prognostic value remains debated due to inconsistent results when classified dichotomously (present/absent). Emerging evidence suggests that quantitative and qualitative descriptions of PNI may better reflect its clinical usefulness. The review also examines therapies targeting nerve-cancer crosstalk and highlights the influence of HPV status on tumor innervation. By synthesizing current knowledge, challenges, and future perspectives, this review offers insights into the molecular basis of nerve involvement in HNCs and the potential for novel therapeutic approaches.

A generative model of the connectome with dynamic axon growth

Connectome generative models, otherwise known as generative network models, provide insight into the wiring principles underpinning brain network organization. While these models can approximate numerous statistical properties of empirical networks, they typically fail to explicitly characterize an important contributor to brain organization-axonal growth. Emulating the chemoaffinity-guided axonal growth, we provide a novel generative model in which axons dynamically steer the direction of propagation based on distance-dependent chemoattractive forces acting on their growth cones. This simple dynamic growth mechanism, despite being solely geometry-dependent, is shown to generate axonal fiber bundles with brain-like geometry and features of complex network architecture consistent with the human brain, including lognormally distributed connectivity weights, scale-free nodal degrees, small-worldness, and modularity. We demonstrate that our model parameters can be fitted to individual connectomes, enabling connectome dimensionality reduction and comparison of parameters between groups. Our work offers an opportunity to bridge studies of axon guidance and connectome development, providing new avenues for understanding neural development from a computational perspective.

Semaphorin heterodimerization in cis regulates membrane targeting and neocortical wiring

Disruption of neocortical circuitry and architecture in humans causes numerous neurodevelopmental disorders. Neocortical cytoarchitecture is orchestrated by various transcription factors such as Satb2 that control target genes during strict time windows. In humans, mutations of SATB2 cause SATB2 Associated Syndrome (SAS), a multisymptomatic syndrome involving epilepsy, intellectual disability, speech delay, and craniofacial defects. Here we show that Satb2 controls neuronal migration and callosal axonal outgrowth during murine neocortical development by inducing the expression of the GPI-anchored protein, Semaphorin 7A (Sema7A). We find that Sema7A exerts this biological activity by heterodimerizing in cis with the transmembrane semaphorin, Sema4D. We could also observe that heterodimerization with Sema7A promotes targeting of Sema4D to the plasma membrane in vitro. Finally, we report an epilepsy-associated de novo mutation in Sema4D (Q497P) that inhibits normal glycosylation and plasma membrane localization of Sema4D-associated complexes. These results suggest that neuronal use of semaphorins during neocortical development is heteromeric, and a greater signaling complexity exists than was previously thought.

Assessment of clinical and histopathological characteristics in COVID-19-associated mucormycosis (CAM) patients correlating with outcome: A hospital-based cross-sectional study

Background

The second wave of the COVID-19 pandemic led to a very dreaded complication of mucormycosis. Immunosuppressive action of the COVID-19 virus, co-morbidities, for example, diabetes mellitus (DM), hypertension, use of steroids, and humidified oxygen, are among the important factors that make the patients susceptible to developing mucormycosis.

Objective

The present study was conducted to identify and understand all the significant histological changes including the type and extent of tissue involvement, the pattern of inflammation, the volume of fungal hyphae, hemorrhage, etc., in patients with COVID-19 associated mucormycosis (CAM) and correlate with clinical outcome.

Method

It was a retrospective cross-sectional observational study involving all the patients of CAM, who underwent debridement or biopsy over a period of 5 months, from April 01, 2021, to August 31, 2021. CAM was classified based on the radiological evaluation, clinical features, and organs involved. Different demographic, clinical, laboratory, and histologic parameters were recorded. The variables were assessed for their association with poor clinical outcomes using multiple logistic regression. P < 0.05 was considered statistically significant.

Results

A total of 146 patients were included in the study with a mean age of 49.4 years and 71.2% were male. Sino-naso-palatal was the most common type of CAM (32.9%), while sino-naso-cerebral was the least common (14.3%). DM was present in 54.1% of patients, out of which 26.6% were recently diagnosed. The death occurred in 21.9% of patients. Maximum mortality was observed in CAM of sino-naso-cerebral involvement (42.9%). Total leucocyte count (TLC) [OR = 0.87; 95%CI: 0.76-0.97; P = 0.02] and C-reactive protein (CRP) [OR = 0.97; 95%CI: 0.96-0.99; P = 0.008] were significantly associated with poor outcomes. Other factors, that is, high prothrombin time, DM, ferritin, and the involvement of muscle, skin, and cartilage, were also associated with poor clinical outcomes but were not statistically significant. Similarly, high fungal volume and the presence of thrombosis were also associated with poor outcomes but were not statistically significant.

Conclusion

CAM more commonly affects males with co-morbidities. TLC and CRP were significantly associated with poor outcomes. Histologically, the involvement of skin, muscle, and cartilage and the presence of excessive fungal hyphae and thrombosis were also associated with poor outcomes.

Semaphorin3C identified as mediator of neuroinflammation and microglia polarization after spinal cord injury

Excessive neuroinflammation after spinal cord injury (SCI) is a major hurdle during nerve repair. Although proinflammatory macrophage/microglia-mediated neuroinflammation plays important roles, the underlying mechanism that triggers neuroinflammation and aggravating factors remain unclear. The present study identified a proinflammatory role of semaphorin3C (SEMA3C) in immunoregulation after SCI. SEMA3C expression level peaked 7 days post-injury (dpi) and decreased by 14 dpi. In vivo and in vitro studies revealed that macrophages/microglia expressed SEMA3C in the local microenvironment, which induced neuroinflammation and conversion of proinflammatory macrophage/microglia. Mechanistic experiments revealed that RAGE/NF-κB was downstream target of SEMA3C. Inhibiting SEMA3C-mediated RAGE signaling considerably suppressed proinflammatory cytokine production, reversed polarization of macrophages/microglia shortly after SCI. In addition, inhibition of SEMA3C-mediated RAGE signaling suggested that the SEMA3C/RAGE axis is a feasible target to preserve axons from neuroinflammation. Taken together, our study provides the first experimental evidence of an immunoregulatory role for SEMA3C in SCI via an autocrine mechanism.

Hippocampal circAnk3 Deficiency Causes Anxiety-like Behaviors and Social Deficits by Regulating the miR-7080-3p/IQGAP1 Pathway in Mice

BACKGROUND

Circular RNAs are highly enriched in the synapses of the mammalian brain and play important roles in neurological function by acting as molecular sponges of microRNAs. circAnk3 is derived from the 11th intron of the ankyrin-3 gene, Ank3, a strong genetic risk factor for neuropsychiatric disorders; however, the function of circAnk3 remains elusive. In this study, we investigated the function of circAnk3 and its downstream regulatory network for target genes in the hippocampus of mice.

METHODS

The DNA sequence from which circAnk3 is generated was modified using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/Cas9) technology, and neurobehavioral tests (anxiety and depression-like behaviors, social behaviors) were performed in circAnk3+/- mice. A series of molecular and biochemical assays were used to investigate the function of circAnk3 as a microRNA sponge and its downstream regulatory network for target genes.

RESULTS

circAnk3+/- mice exhibited both anxiety-like behaviors and social deficits. circAnk3 was predominantly located in the cytoplasm of neuronal cells and functioned as a miR-7080-3p sponge to regulate the expression of Iqgap1. Inhibition of miR-7080-3p or restoration of Iqgap1 in the hippocampus ameliorated the behavioral deficits of circAnk3+/- mice. Furthermore, circAnk3 deficiency decreased the expression of the NMDA receptor subunit GluN2a and impaired the structural plasticity of dendritic synapses in the hippocampus.

CONCLUSIONS

Our results reveal an important role of the circAnk3/miR-7080-3p/IQGAP1 axis in maintaining the structural plasticity of hippocampal synapses. circAnk3 might offer new insights into the involvement of circular RNAs in neuropsychiatric disorders.

The FLRT3-UNC5B checkpoint pathway inhibits T cell-based cancer immunotherapies

Cancers exploit coinhibitory receptors on T cells to escape tumor immunity, and targeting such mechanisms has shown remarkable clinical benefit, but in a limited subset of patients. We hypothesized that cancer cells mimic noncanonical mechanisms of early development such as axon guidance pathways to evade T cell immunity. Using gain-of-function genetic screens, we profiled axon guidance proteins on human T cells and their cognate ligands and identified fibronectin leucine-rich transmembrane protein 3 (FLRT3) as a ligand that inhibits T cell activity. We demonstrated that FLRT3 inhibits T cells through UNC5B, an axon guidance receptor that is up-regulated on activated human T cells. FLRT3 expressed in human cancers favored tumor growth and inhibited CAR-T and BiTE + T cell killing and infiltration in humanized cancer models. An FLRT3 monoclonal antibody that blocked FLRT3-UNC5B interactions reversed these effects in an immune-dependent manner. This study supports the concept that axon guidance proteins mimic T cell checkpoints and can be targeted for cancer immunotherapy.

A generative model of the connectome with dynamic axon growth

Connectome generative models, otherwise known as generative network models, provide insight into the wiring principles underpinning brain network organization. While these models can approximate numerous statistical properties of empirical networks, they typically fail to explicitly characterize an important contributor to brain organization - axonal growth. Emulating the chemoaffinity guided axonal growth, we provide a novel generative model in which axons dynamically steer the direction of propagation based on distance-dependent chemoattractive forces acting on their growth cones. This simple dynamic growth mechanism, despite being solely geometry-dependent, is shown to generate axonal fiber bundles with brain-like geometry and features of complex network architecture consistent with the human brain, including lognormally distributed connectivity weights, scale-free nodal degrees, small-worldness, and modularity. We demonstrate that our model parameters can be fitted to individual connectomes, enabling connectome dimensionality reduction and comparison of parameters between groups. Our work offers an opportunity to bridge studies of axon guidance and connectome development, providing new avenues for understanding neural development from a computational perspective.

The potential of graphene coatings as neural interfaces

Recent advances in nanotechnology design and fabrication have shaped the landscape for the development of ideal cell interfaces based on biomaterials. A holistic evaluation of the requirements for a cell interface is a highly complex task. Biocompatibility is a crucial requirement which is affected by the interface's properties, including elemental composition, morphology, and surface chemistry. This review explores the current state-of-the-art on graphene coatings produced by chemical vapor deposition (CVD) and applied as neural interfaces, detailing the key properties required to design an interface capable of physiologically interacting with neural cells. The interfaces are classified into substrates and scaffolds to differentiate the planar and three-dimensional environments where the cells can adhere and proliferate. The role of specific features such as mechanical properties, porosity and wettability are investigated. We further report on the specific brain-interface applications where CVD graphene paved the way to revolutionary advances in biomedicine. Future studies on the long-term effects of graphene-based materials in vivo will unlock even more potentially disruptive neuro-applications.

Morphological and transcriptomic analyses of embryonic development of red-eared slider Trachemys scripta elegans

Embryology provides an understanding of individual's origin and developmental patterns. Turtles are among the oldest living reptiles and have unique body structure. However, the morphogenesis and mechanisms of turtles are not fully understood. In this study, we focused on the embryonic development of red-eared slider (Trachemys scripta elegans) which widely distributes in the world. At an incubation temperature of 28 °C, the turtle eggs had a 61-day incubation cycle, and the entire embryonic development process was divided into 27 stages and 3 phases according to variations in age, body size, and morphological characteristics. The early phase of embryonic development (the first 12 stages) were characterized by embryo growth, and the appearance of internal organ precursors. The middle phase (stages 13-20) involved prominent heart division at stage 13 and the appearance of carapace and plastron at stages 14 and 17, respectively. In the later phase (stages 21-27), the hatchlings formed, and the carapace and plastron thickened. Transcriptome analysis of embryos showed enrichment of the differential genes in pathways related to development, metabolism, disease, and cellular processes. The Kyoto Encyclopedia of Genes and Genomes enrichment (KEGG) analysis implied the crucial regulatory role of the axon guidance pathway. Real-time fluorescence quantitative PCR indicated upregulated expression of wnt5a and bmp7 in stages 7 and 16 compared to that in stage 12. This study revealed the development process of red-eared slider embryo and the dynamics of the signaling pathway affecting its development, which supplemented the theory of embryo development, and provided new ideas for the molecular mechanism of turtle embryo development.

Developmental delays in cortical auditory temporal processing in a mouse model of Fragile X syndrome

BACKGROUND

Autism spectrum disorders (ASD) encompass a wide array of debilitating symptoms, including sensory dysfunction and delayed language development. Auditory temporal processing is crucial for speech perception and language development. Abnormal development of temporal processing may account for the language impairments associated with ASD. Very little is known about the development of temporal processing in any animal model of ASD.

METHODS

In the current study, we quantify auditory temporal processing throughout development in the Fmr1 knock-out (KO) mouse model of Fragile X Syndrome (FXS), a leading genetic cause of intellectual disability and ASD-associated behaviors. Using epidural electrodes in awake and freely moving wildtype (WT) and KO mice, we recorded auditory event related potentials (ERP) and auditory temporal processing with a gap-in-noise auditory steady state response (gap-ASSR) paradigm. Mice were recorded at three different ages in a cross sectional design: postnatal (p)21, p30 and p60. Recordings were obtained from both auditory and frontal cortices. The gap-ASSR requires underlying neural generators to synchronize responses to gaps of different widths embedded in noise, providing an objective measure of temporal processing across genotypes and age groups.

RESULTS

We present evidence that the frontal, but not auditory, cortex shows significant temporal processing deficits at p21 and p30, with poor ability to phase lock to rapid gaps in noise. Temporal processing was similar in both genotypes in adult mice. ERP amplitudes were larger in Fmr1 KO mice in both auditory and frontal cortex, consistent with ERP data in humans with FXS.

CONCLUSIONS

These data indicate cortical region-specific delays in temporal processing development in Fmr1 KO mice. Developmental delays in the ability of frontal cortex to follow rapid changes in sounds may shape language delays in FXS, and more broadly in ASD.

Colonization of peripheral ganglia by herpes simplex virus type 1 and 2

Herpes simplex virus type 1 (HSV-1) and 2 (HSV-2) infect and establish latency in neurons of the peripheral nervous system to persist lifelong in the host and to cause recurrent disease. During primary infection, HSV replicates in epithelial cells in the mucosa and skin and then infects neurites, highly dynamic structures that grow or retract in the presence of attracting or repelling cues, respectively. Following retrograde transport in neurites, HSV establishes latency in the neuronal nucleus. Viral and cellular proteins participate in the chromatinization of the HSV genome that regulates gene expression, persistence, and reactivation. HSV-2 modulates neurite outgrowth during primary infection and upon reactivation, probably to facilitate infection and survival of neurons. Whether HSV-1 modulates neurite outgrowth and the underlying mechanism is currently under investigation. This review deals with HSV-1 and HSV-2 colonization of peripheral neurons, with a focus on the modulation of neurite outgrowth by these viruses.

Perineural Invasion Predicts Local Recurrence and Poor Survival in Laryngeal Cancer

(1) Background: Perineural invasion (PNI) in head and neck cancer is associated with a poor prognosis; however, the effect of PNI on the prognosis of laryngeal cancer remains under debate. This retrospective study aimed to investigate the effect of PNI in fresh or salvaged larynges on survival in patients who had undergone laryngectomy for squamous cell carcinoma. (2) Methods: This study enrolled 240 patients diagnosed with laryngeal cancer who had undergone open surgery at Seoul St. Mary's Hospital, Korea. The effects of PNI, other histopathologic factors, and treatment history on survival and recurrence patterns were assessed. (3) Results: PNI was observed in 30 of 240 patients (12.5%). PNI (HR: 3.05; 95% CI: 1.90-4.88; p = 0.01) was a significant predictor of poor 5-year disease-free survival. In fresh cases, preepiglottic invasion (HR: 2.37; 95% CI: 1.45-3.88; p = 0.01) and PNI (HR: 2.96; 95% CI: 1.62-2.96; p = 0.01) were negative prognostic factors for 5-year disease-free survival. In the salvage group, however, only PNI (HR: 2.74; 95% CI: 1.26-5.92; p = 0.01) was a significant predictor of disease-free survival. Further, PNI significantly influenced high local recurrence (HR: 5.02, 95% CI: 1.28-9.66; p = 0.02). (4) Conclusions: Independent of treatment history, PNI is a prognostic factor for poor survival and local recurrence in laryngeal cancer.

The Impact of Nicotine along with Oral Contraceptive Exposure on Brain Fatty Acid Metabolism in Female Rats

Smoking-derived nicotine (N) and oral contraceptive (OC) synergistically exacerbate ischemic brain damage in females, and the underlying mechanisms remain elusive. In a previous study, we showed that N + OC exposure altered brain glucose metabolism in females. Since lipid metabolism complements glycolysis, the current study aims to examine the metabolic fingerprint of fatty acids in the brain of female rats exposed to N+/-OC. Adolescent and adult Sprague-Dawley female rats were randomly (n = 8 per group) exposed to either saline or N (4.5 mg/kg) +/-OC (combined OC or placebo delivered via oral gavage) for 16-21 days. Following exposure, brain tissue was harvested for unbiased metabolomic analysis (performed by Metabolon Inc., Morrisville, NC, USA) and the metabolomic profile changes were complemented with Western blot analysis of key enzymes in the lipid pathway. Metabolomic data showed significant accumulation of fatty acids and phosphatidylcholine (PC) metabolites in the brain. Adolescent, more so than adult females, exposed to N + OC showed significant increases in carnitine-conjugated fatty acid metabolites compared to saline control animals. These changes in fatty acyl carnitines were accompanied by an increase in a subset of free fatty acids, suggesting elevated fatty acid β-oxidation in the mitochondria to meet energy demand. In support, β-hydroxybutyrate was significantly lower in N + OC exposure groups in adolescent animals, implying a complete shunting of acetyl CoA for energy production via the TCA cycle. The reported changes in fatty acids and PC metabolism due to N + OC could inhibit post-translational palmitoylation of membrane proteins and synaptic vesicle formation, respectively, thus exacerbating ischemic brain damage in female rats.

lron-11 guides axons in the ventral nerve cord of Caenorhabditis elegans

For the nervous system to develop properly, neurons must connect in a precise way to form functional networks. This requires that outgrowing neuronal processes (axons) navigate to their target areas, where they establish proper synaptic connections. The molecular basis of this navigation process is not firmly understood. A candidate family containing putative receptors acting in various aspects of neuronal development including axon navigation are transmembrane proteins of the extracellular Leucine-Rich Repeat family (eLRRs). We systematically tested members of this family in C. elegans for a role in axon navigation in the ventral nerve cord (VNC). We found that lron-11 mutants showed VNC navigation defects in several classes of neurons, including a pioneer neuron and various classes of interneurons and motoneurons. This suggests that while most members of the lron-family do not seem to have a role in axon navigation in the VNC, lron-11 is likely to be a receptor required for correct navigation of axons in the VNC of C. elegans.

Vangl as a Master Scaffold for Wnt/Planar Cell Polarity Signaling in Development and Disease

The establishment of polarity within tissues and dynamic cellular morphogenetic events are features common to both developing and adult tissues, and breakdown of these programs is associated with diverse human diseases. Wnt/Planar cell polarity (Wnt/PCP) signaling, a branch of non-canonical Wnt signaling, is critical to the establishment and maintenance of polarity in epithelial tissues as well as cell motility events critical to proper embryonic development. In epithelial tissues, Wnt/PCP-mediated planar polarity relies upon the asymmetric distribution of core proteins to establish polarity, but the requirement for this distribution in Wnt/PCP-mediated cell motility remains unclear. However, in both polarized tissues and migratory cells, the Wnt/PCP-specific transmembrane protein Vangl is required and appears to serve as a scaffold upon which the core pathway components as well as positive and negative regulators of Wnt/PCP signaling assemble. The current literature suggests that the multiple interaction domains of Vangl allow for the binding of diverse signaling partners for the establishment of context- and tissue-specific complexes. In this review we discuss the role of Vangl as a master scaffold for Wnt/PCP signaling in epithelial tissue polarity and cellular motility events in developing and adult tissues, and address how these programs are dysregulated in human disease.

Mathematical models of neuronal growth

The establishment of a functioning neuronal network is a crucial step in neural development. During this process, neurons extend neurites-axons and dendrites-to meet other neurons and interconnect. Therefore, these neurites need to migrate, grow, branch and find the correct path to their target by processing sensory cues from their environment. These processes rely on many coupled biophysical effects including elasticity, viscosity, growth, active forces, chemical signaling, adhesion and cellular transport. Mathematical models offer a direct way to test hypotheses and understand the underlying mechanisms responsible for neuron development. Here, we critically review the main models of neurite growth and morphogenesis from a mathematical viewpoint. We present different models for growth, guidance and morphogenesis, with a particular emphasis on mechanics and mechanisms, and on simple mathematical models that can be partially treated analytically.

Fzd3 Expression Within Inner Ear Afferent Neurons Is Necessary for Central Pathfinding

During development the afferent neurons of the inner ear make precise wiring decisions in the hindbrain reflective of their topographic distribution in the periphery. This is critical for the formation of sensory maps capable of faithfully processing both auditory and vestibular input. Disorganized central projections of inner ear afferents in Fzd3 null mice indicate Wnt/PCP signaling is involved in this process and ear transplantation in Xenopus indicates that Fzd3 is necessary in the ear but not the hindbrain for proper afferent navigation. However, it remains unclear in which cell type of the inner ear Fzd3 expression is influencing the guidance of inner ear afferents to their proper synaptic targets in the hindbrain. We utilized Atoh1-cre and Neurod1-cre mouse lines to conditionally knockout Fzd3 within the mechanosensory hair cells of the organ of Corti and within the inner ear afferents, respectively. Following conditional deletion of Fzd3 within the hair cells, the central topographic distribution of inner ear afferents was maintained with no gross morphological defects. In contrast, conditional deletion of Fzd3 within inner ear afferents leads to central pathfinding defects of both cochlear and vestibular afferents. Here, we show that Fzd3 is acting in a cell autonomous manner within inner ear afferents to regulate central pathfinding within the hindbrain.

Intrinsic positional memory guides target-specific axon regeneration in the zebrafish vagus nerve

Regeneration after peripheral nerve damage requires that axons re-grow to the correct target tissues in a process called target-specific regeneration. Although much is known about the mechanisms that promote axon re-growth, re-growing axons often fail to reach the correct targets, resulting in impaired nerve function. We know very little about how axons achieve target-specific regeneration, particularly in branched nerves that require distinct targeting decisions at branch points. The zebrafish vagus motor nerve is a branched nerve with a well-defined topographic organization. Here, we track regeneration of individual vagus axons after whole-nerve laser severing and find a robust capacity for target-specific, functional re-growth. We then develop a new single-cell chimera injury model for precise manipulation of axon-environment interactions and find that (1) the guidance mechanism used during regeneration is distinct from the nerve's developmental guidance mechanism, (2) target selection is specified by neurons' intrinsic memory of their position within the brain, and (3) targeting to a branch requires its pre-existing innervation. This work establishes the zebrafish vagus nerve as a tractable regeneration model and reveals the mechanistic basis of target-specific regeneration.

Molecular Mechanisms Underlying Motor Axon Guidance in Drosophila

Decoding the molecular mechanisms underlying axon guidance is key to precise understanding of how complex neural circuits form during neural development. Although substantial progress has been made over the last three decades in identifying numerous axon guidance molecules and their functional roles, little is known about how these guidance molecules collaborate to steer growth cones to their correct targets. Recent studies in Drosophila point to the importance of the combinatorial action of guidance molecules, and further show that selective fasciculation and defasciculation at specific choice points serve as a fundamental strategy for motor axon guidance. Here, I discuss how attractive and repulsive guidance cues cooperate to ensure the recognition of specific choice points that are inextricably linked to selective fasciculation and defasciculation, and correct pathfinding decision-making.

Compartmentalized Neuronal Cultures

The culturing of neurons results in formation of the layer of neurons with random extensive overlapping outgrowth. To understand specific roles of somas, axons, and dendrites in complex function of neurons and to identify molecular mechanisms of biological processes in these cellular compartments, various methods were developed. We utilized AXon Investigation System (AXIS™) manufactured by Millipore. This device provides an opportunity to orient neuronal outgrowth and spatially isolate neuronal processes from neuronal bodies. AXIS device is a slide-mounted microfluidic system, which consists of four wells. Two of the wells are connected by a channel on each side of the device. Channels are connected by microgrooves (approximately 120). The size of microgrooves (10μm in width and 5μm in height) does not permit passage of cell through while allowing extension of neurites. The microfluidic design also allows for an establishment of a hydrostatic gradient when the volume in one chamber is greater than that in the other (Park et al., Nat Protoc 1:2128-2136, 2006). This feature allows for studying of the effect of specific compounds on selected compartments of neurons.

Cerebral mucormycosis: neuroimaging findings and histopathological correlation

INTRODUCTION

Mucormycosis are infections caused by molds of the order Mucorales. These opportunistic infections are rare, difficult to diagnose, and have a poor prognosis. We aimed to describe common radiographic patterns that may help to diagnose cerebral mucormycosis and search for histopathological correlations with imaging data.

METHODS

We studied the radiological findings (CT and MRI) of 18 patients with cerebral mucormycosis and four patients' histopathological findings.

RESULTS

All patients were immunocompromised and/or diabetic. The type of lesions depended on the infection's dissemination pathway. Hematogenous dissemination lesions were most frequently abscesses (59 lesions), cortical, cortical-subcortical, or in the basal ganglia, with a halo aspect on DWI for lesions larger than 1.6 cm. Only seven lesions were enhanced after contrast injection, with different presentations depending on patients' immune status. Ischemia and hemorrhagic areas were also seen. Vascular lesions were represented by stenosis and thrombosis. Direct posterior extension lesions were bi-fronto basal hypodensities on CT and restricted diffusion without enhancement on MRI. A particular extension, perineural spread, was seen along the trigeminal nerve. Histopathological analysis found endovascular lesions with destruction of vessel walls by Mucorales, microbleeds around vessels, as well as acute and chronic inflammation.

CONCLUSIONS

MRI is the critical exam for cerebral mucormycosis. Weak ring enhancement and reduced halo diffusion suggest the diagnosis of fungal infections. Involvement of the frontal lobes should raise suspicion of mucormycosis (along with aspergillosis). The perineural spread can be considered a more specific extension pathway of mucormycosis.

Understanding, engineering, and modulating the growth of neural networks: An interdisciplinary approach

A deeper understanding of the brain and its function remains one of the most significant scientific challenges. It not only is required to find cures for a plethora of brain-related diseases and injuries but also opens up possibilities for achieving technological wonders, such as brain-machine interface and highly energy-efficient computing devices. Central to the brain's function is its basic functioning unit (i.e., the neuron). There has been a tremendous effort to understand the underlying mechanisms of neuronal growth on both biochemical and biophysical levels. In the past decade, this increased understanding has led to the possibility of controlling and modulating neuronal growth in vitro through external chemical and physical methods. We provide a detailed overview of the most fundamental aspects of neuronal growth and discuss how researchers are using interdisciplinary ideas to engineer neuronal networks in vitro. We first discuss the biochemical and biophysical mechanisms of neuronal growth as we stress the fact that the biochemical or biophysical processes during neuronal growth are not independent of each other but, rather, are complementary. Next, we discuss how utilizing these fundamental mechanisms can enable control over neuronal growth for advanced neuroengineering and biomedical applications. At the end of this review, we discuss some of the open questions and our perspectives on the challenges and possibilities related to controlling and engineering the growth of neuronal networks, specifically in relation to the materials, substrates, model systems, modulation techniques, data science, and artificial intelligence.

Advances in Proteomics Allow Insights Into Neuronal Proteomes

Protein–protein interaction networks and signaling complexes are essential for normal brain function and are often dysregulated in neurological disorders. Nevertheless, unraveling neuron- and synapse-specific proteins interaction networks has remained a technical challenge. New techniques, however, have allowed for high-resolution and high-throughput analyses, enabling quantification and characterization of various neuronal protein populations. Over the last decade, mass spectrometry (MS) has surfaced as the primary method for analyzing multiple protein samples in tandem, allowing for the precise quantification of proteomic data. Moreover, the development of sophisticated protein-labeling techniques has given MS a high temporal and spatial resolution, facilitating the analysis of various neuronal substructures, cell types, and subcellular compartments. Recent studies have leveraged these novel techniques to reveal the proteomic underpinnings of well-characterized neuronal processes, such as axon guidance, long-term potentiation, and homeostatic plasticity. Translational MS studies have facilitated a better understanding of complex neurological disorders, such as Alzheimer’s disease (AD), Schizophrenia (SCZ), and Autism Spectrum Disorder (ASD). Proteomic investigation of these diseases has not only given researchers new insight into disease mechanisms but has also been used to validate disease models and identify new targets for research.

MAOA promotes prostate cancer cell perineural invasion through SEMA3C/PlexinA2/NRP1-cMET signaling

Perineural invasion (PNI), a pathologic feature defined as cancer cell invasion in, around, and through nerves, is an indicator of poor prognosis and survival in prostate cancer (PC). Despite widespread recognition of the clinical significance of PNI, the molecular mechanisms are largely unknown. Here, we report that monoamine oxidase A (MAOA) is a clinically and functionally important mediator of PNI in PC. MAOA promotes PNI of PC cells in vitro and tumor innervation in an orthotopic xenograft model. Mechanistically, MAOA activates SEMA3C in a Twist1-dependent transcriptional manner, which in turn stimulates cMET to facilitate PNI via autocrine or paracrine interaction with coactivated PlexinA2 and NRP1. Furthermore, MAOA inhibitor treatment effectively reduces PNI of PC cells in vitro and tumor-infiltrating nerve fiber density along with suppressed xenograft tumor growth and progression in mice. Collectively, these findings characterize the contribution of MAOA to the pathogenesis of PNI and provide a rationale for using MAOA inhibitors as a targeted treatment for PNI in PC.

Soft hydrogel promotes dorsal root ganglion by upregulating gene expression of Ntn4 and Unc5B

Mechanical property is an important factor of cellular microenvironment for neural tissue regeneration. In this study, polyacrylamide (PAM) hydrogels with systematically varying elastic modulus were prepared using in situ radical polymerization. We found that the hydrogel was biocompatible, and the length of dorsal root ganglion (DRG)'s axon and cell density were optimal on the hydrogels with elastic modulus of 5.1 kPa (among hydrogels with elastic modulus between 3.6 kPa and 16.5 kPa). These DRGs also exhibited highest gene and protein expression of proliferation marker Epha4, Ntn4, Sema3D and differentiation marker Unc5B. Our study revealed the mechanism of how material stiffness affects DRG proliferation and differentiation. It will also provide theoretical basis and evidence for the design and development of nerve graft with better repair performance.

Transcriptome Comparison Reveals Key Components of Nuptial Plumage Coloration in Crested Ibis

Nuptial plumage coloration is critical in the mating choice of the crested ibis. This species has a characteristic nuptial plumage that develops from the application of a black sticky substance, secreted by a patch of skin in the throat and neck region. We aimed to identify the genes regulating its coloring, by comparing skin transcriptomes between ibises during the breeding and nonbreeding seasons. In breeding season skins, key eumelanin synthesis genes, TYR, DCT, and TYRP1 were upregulated. Tyrosine metabolism, which is closely related to melanin synthesis, was also upregulated, as were transporter proteins belonging to multiple SLC families, which might act during melanosome transportation to keratinocytes. These results indicate that eumelanin is likely an important component of the black substance. In addition, we observed upregulation in lipid metabolism in breeding season skins. We suggest that the lipids contribute to an oil base, which imbues the black substance with water insolubility and enhances its adhesion to feather surfaces. In nonbreeding season skins, we observed upregulation in cell adhesion molecules, which play critical roles in cell interactions. A number of molecules involved in innervation and angiogenesis were upregulated, indicating an ongoing expansion of nerves and blood vessels in sampled skins. Feather β keratin, a basic component of avian feather filament, was also upregulated. These results are consistent with feather regeneration in the black skin of nonbreeding season ibises. Our results provide the first molecular evidence indicating that eumelanin is the key component of ibis coloration.

Slit neuronal secretion coordinates optic lobe morphogenesis in Drosophila

The complexity of the nervous system requires the coordination of multiple cellular processes during development. Among them, we find boundary formation, axon guidance, cell migration and cell segregation. Understanding how different cell populations such as glial cells, developing neurons and neural stem cells contribute to the formation of boundaries and morphogenesis in the nervous system is a critical question in neurobiology. Slit is an evolutionary conserved protein essential for the development of the nervous system. For signaling, Slit has to bind to its cognate receptor Robo, a single-pass transmembrane protein. Although the Slit/Robo signaling pathway is well known for its involvement in axon guidance, it has also been associated to boundary formation in the Drosophila visual system. In the optic lobe, Slit is expressed in glial cells, positioned at the boundaries between developing neuropils, and in neurons of the medulla ganglia. Although it has been assumed that glial cells provide Slit to the system, the contribution of the neuronal expression has not been tested. Here, we show that, contrary to what was previously thought, Slit protein provided by medulla neurons is also required for boundary formation and morphogenesis of the optic lobe. Furthermore, tissue specific rescue using modified versions of Slit demonstrates that this protein acts at long range and does not require processing by extracellular proteases. Our data shed new light on our understanding of the cellular mechanisms involved in Slit function in the fly visual system morphogenesis.

TRPC5 regulates axonal outgrowth in developing retinal ganglion cells

The TRPC5 ion channel is activated upon depletion of intracellular calcium stores, as well as by various stimuli such as nitric oxide (NO), membrane stretch, and cold temperatures. TRPC5 is abundantly expressed in the central nervous system where it has important neuronal functions. In the chick retina, TRPC5 expression was shown to be restricted to amacrine cells (ACs) and Müller glial cells, although its expression was also observed in the ganglion cell layer (GCL) in displaced ACs, as determined by their characteristic cell morphology. However, it is possible that this expression analysis alone might be insufficient to fully understand the expression of TRPC5 in retinal ganglion cells (RGCs). Hence, we analyzed TRPC5 expression by in situ hybridization and immunostaining in the developing mouse retina, and for the first time identified that developing and mature RGCs strongly express TRPC5. The expression begins at E14.5, and is restricted to ACs and RGCs. It was reported that TRPC5 negatively regulates axonal outgrowth in hippocampal neurons. We thus hypothesized that TRPC5 might have similar functions in RGCs since they extend very long axons toward the brain, and this characteristic significantly differs from other retinal cell types. To elucidate its possible involvement in axonal outgrowth, we inhibited TRPC5 activity in developing RGCs which significantly increased RGC axon length. In contrast, overexpression of TRPC5 inhibited axonal outgrowth in developing RGCs. These results indicate that TRPC5 is an important negative regulator of RGC axonal outgrowth. Since TRPC5 is a mechanosensor, it might function to sense abnormal intraocular pressure changes, and could contribute to the death of RGCs in diseases such as glaucoma. In this case, excessive Ca²⁺ entry through TRPC5 might induce dendritic and axonal remodeling, which could lead to cell death, as our findings clearly indicate that TRPC5 is an important regulator of neurite remodeling.

Organoid and Assembloid Technologies for Investigating Cellular Crosstalk in Human Brain Development and Disease

The biology of the human brain, and in particular the dynamic interactions between the numerous cell types and regions of the central nervous system, has been difficult to study due to limited access to functional brain tissue. Technologies to derive brain organoids and assembloids from human pluripotent stem cells are increasingly utilized to model, in progressively complex preparations, the crosstalk between cell types in development and disease. Here, we review the use of these human cellular models to study cell-cell interactions among progenitors, neurons, astrocytes, oligodendrocytes, cancer cells, and non-central nervous system cell types, as well as efforts to study connectivity between brain regions following controlled assembly of organoids. Ultimately, the promise of these patient-derived preparations is to uncover previously inaccessible features of brain function that emerge from complex cell-cell interactions and to improve our mechanistic understanding of neuropsychiatric disorders.

Single-Cell RNA-seq Reveals Profound Alterations in Mechanosensitive Dorsal Root Ganglion Neurons with Vitamin E Deficiency

Ninety percent of Americans consume less than the estimated average requirements of dietary vitamin E (vitE). Severe vitE deficiency due to genetic mutations in the tocopherol transfer protein (TTPA) in humans results in ataxia with vitE deficiency (AVED), with proprioceptive deficits and somatosensory degeneration arising from dorsal root ganglia neurons (DRGNs). Single-cell RNA-sequencing of DRGNs was performed in Ttpa-/- mice, an established model of AVED. In stark contrast to expected changes in proprioceptive neurons, Ttpa-/- DRGNs showed marked upregulation of voltage-gated Ca2+ and K+ channels in mechanosensitive, tyrosine-hydroxylase positive (TH+) DRGNs. The ensuing significant conductance changes resulted in reduced excitability in mechanosensitive Ttpa-/- DRGNs. A highly supplemented vitE diet (600 mg dl-α-tocopheryl acetate/kg diet) prevented the cellular and molecular alterations and improved mechanosensation. VitE deficiency profoundly alters the molecular signature and functional properties of mechanosensitive TH+ DRGN, representing an intriguing shift of the prevailing paradigm from proprioception to mechanical sensation.

Functions of 'A disintegrin and metalloproteases (ADAMs)' in the mammalian nervous system

'A disintegrin and metalloproteases' (ADAMs) are a family of transmembrane proteins with diverse functions in multicellular organisms. About half of the ADAMs are active metalloproteases and cleave numerous cell surface proteins, including growth factors, receptors, cytokines and cell adhesion proteins. The other ADAMs have no catalytic activity and function as adhesion proteins or receptors. Some ADAMs are ubiquitously expressed, others are expressed tissue specifically. This review highlights functions of ADAMs in the mammalian nervous system, including their links to diseases. The non-proteolytic ADAM11, ADAM22 and ADAM23 have key functions in neural development, myelination and synaptic transmission and are linked to epilepsy. Among the proteolytic ADAMs, ADAM10 is the best characterized one due to its substrates Notch and amyloid precursor protein, where cleavage is required for nervous system development or linked to Alzheimer's disease (AD), respectively. Recent work demonstrates that ADAM10 has additional substrates and functions in the nervous system and its substrate selectivity may be regulated by tetraspanins. New roles for other proteolytic ADAMs in the nervous system are also emerging. For example, ADAM8 and ADAM17 are involved in neuroinflammation. ADAM17 additionally regulates neurite outgrowth and myelination and its activity is controlled by iRhoms. ADAM19 and ADAM21 function in regenerative processes upon neuronal injury. Several ADAMs, including ADAM9, ADAM10, ADAM15 and ADAM30, are potential drug targets for AD. Taken together, this review summarizes recent progress concerning substrates and functions of ADAMs in the nervous system and their use as drug targets for neurological and psychiatric diseases.

Dysregulation of Neuronal Genes by Fetal-Neonatal Iron Deficiency Anemia Is Associated with Altered DNA Methylation in the Rat Hippocampus

Early-life iron deficiency results in long-term abnormalities in cognitive function and affective behavior in adulthood. In preclinical models, these effects have been associated with long-term dysregulation of key neuronal genes. While limited evidence suggests histone methylation as an epigenetic mechanism underlying gene dysregulation, the role of DNA methylation remains unknown. To determine whether DNA methylation is a potential mechanism by which early-life iron deficiency induces gene dysregulation, we performed whole genome bisulfite sequencing to identify loci with altered DNA methylation in the postnatal day (P) 15 iron-deficient (ID) rat hippocampus, a time point at which the highest level of hippocampal iron deficiency is concurrent with peak iron demand for axonal and dendritic growth. We identified 229 differentially methylated loci and they were mapped within 108 genes. Among them, 63 and 45 genes showed significantly increased and decreased DNA methylation in the P15 ID hippocampus, respectively. To establish a correlation between differentially methylated loci and gene dysregulation, the methylome data were compared to our published P15 hippocampal transcriptome. Both datasets showed alteration of similar functional networks regulating nervous system development and cell-to-cell signaling that are critical for learning and behavior. Collectively, the present findings support a role for DNA methylation in neural gene dysregulation following early-life iron deficiency.

NR4A3 fusion proteins trigger an axon guidance switch that marks the difference between EWSR1 and TAF15 translocated extraskeletal myxoid chondrosarcomas

Extraskeletal myxoid chondrosarcoma (EMC) is a rare sarcoma histotype with uncertain differentiation. EMC is hallmarked by the rearrangement of the NR4A3 gene, which in most cases fuses with EWSR1 or TAF15. TAF15‐translocated EMC seem to feature a more aggressive course compared to EWSR1‐positive EMCs, but whether the type of NR4A3 chimera impinges upon EMC biology is still largely undefined. To gain insights on this issue, a series of EMC samples (7 EWSR1‐NR4A3 and 5 TAF15‐NR4A3) were transcriptionally profiled. Our study unveiled that the two EMC variants display a distinct transcriptional profile and that the axon guidance pathway is a major discriminant. In particular, class 4–6 semaphorins and axonal guidance cues endowed with pro‐tumorigenic activity were more expressed in TAF15‐NR4A3 tumors; vice versa, class 3 semaphorins, considered to convey growth inhibitory signals, were more abundant in EWSR1‐NR4A3 EMC. Intriguingly, the dichotomy in axon guidance signaling observed in the two tumor variants was recapitulated in in vitro cell models engineered to ectopically express EWSR1‐NR4A3 or TAF15‐NR4A3. Moreover, TAF15‐NR4A3 cells displayed a more pronounced tumorigenic potential, as assessed by anchorage‐independent growth. Overall, our results indicate that the type of NR4A3 chimera dictates an axon guidance switch and impacts on tumor cell biology. These findings may provide a framework for interpretation of the different clinical–pathological features of the two EMC variants and lay down the bases for the development of novel patient stratification criteria and therapeutic approaches. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Regulators of Rho GTPases in the Nervous System: Molecular Implication in Axon Guidance and Neurological Disorders

One of the fundamental steps during development of the nervous system is the formation of proper connections between neurons and their target cells-a process called neural wiring, failure of which causes neurological disorders ranging from autism to Down's syndrome. Axons navigate through the complex environment of a developing embryo toward their targets, which can be far away from their cell bodies. Successful implementation of neuronal wiring, which is crucial for fulfillment of all behavioral functions, is achieved through an intimate interplay between axon guidance and neural activity. In this review, our focus will be on axon pathfinding and the implication of some of its downstream molecular components in neurological disorders. More precisely, we will talk about axon guidance and the molecules implicated in this process. After, we will briefly review the Rho family of small GTPases, their regulators, and their involvement in downstream signaling pathways of the axon guidance cues/receptor complexes. We will then proceed to the final and main part of this review, where we will thoroughly comment on the implication of the regulators for Rho GTPases-GEFs (Guanine nucleotide Exchange Factors) and GAPs (GTPase-activating Proteins)-in neurological diseases and disorders.

Harnessing stem cells and biomaterials to promote neural repair

With the limited capacity for self-repair in the adult CNS, efforts to stimulate quiescent stem cell populations within discrete brain regions, as well as harness the potential of stem cell transplants, offer significant hope for neural repair. These new cells are capable of providing trophic cues to support residual host populations and/or replace those cells lost to the primary insult. However, issues with low-level adult neurogenesis, cell survival, directed differentiation and inadequate reinnervation of host tissue have impeded the full potential of these therapeutic approaches and their clinical advancement. Biomaterials offer novel approaches to stimulate endogenous neurogenesis, as well as for the delivery and support of neural progenitor transplants, providing a tissue-appropriate physical and trophic milieu for the newly integrating cells. In this review, we will discuss the various approaches by which bioengineered scaffolds may improve stem cell-based therapies for repair of the CNS.

Neurointegrity and neurophysiology: astrocyte, glutamate, and carbon monoxide interactions

Astrocyte contributions to brain function and prevention of neuropathologies are as extensive as that of neurons. Astroglial regulation of glutamate, a primary neurotransmitter, is through uptake, release through vesicular and non-vesicular pathways, and catabolism to intermediates. Homeostasis by astrocytes is considered to be of primary importance in determining normal central nervous system health and central nervous system physiology - glutamate is central to dynamic physiologic changes and central nervous system stability. Gasotransmitters may affect diverse glutamate interactions positively or negatively. The effect of carbon monoxide, an intrinsic central nervous system gasotransmitter, in the complex astrocyte homeostasis of glutamate may offer insights to normal brain development, protection, and its use as a neuromodulator and neurotherapeutic. In this article, we will review the effects of carbon monoxide on astrocyte homeostasis of glutamate.

A perspective on SOAL, a stochastic model of neuronal outgrowth

A functional nervous system requires neuronal connections to be made in a highly detailed and stereotypic manner. During development, neurons extend processes that can branch, travel in different directions, and form elaborate patterns. These patterns are essential for forming proper connections. Patterns of outgrowth are produced by complex molecular events that cause a fluid membrane to move. The collective impact of dynamic fluctuating events at the microscale cause the patterns of outgrowth observed at the macroscale. Patterning is genetically controlled, but the effects genes have on membrane movement and patterning are not well understood. To better understand how genes control outgrowth patterns, I propose a statistically-oriented asymmetric localization (SOAL) model. This model is based on the theory that receptor-mediated outgrowth activity is stochastically oriented and when the system is at equilibrium there is an equal probability of outgrowth being oriented in any direction. This concept allows a statistical mechanics approach that can correlate the microscale events of outgrowth to the observed macroscale patterns. Proof-of-concept experiments suggest this approach can be used to study the effect genes have on outgrowth patterns. The SOAL model also provides a new theoretical framework for conceptualizing guidance. According to the model, outgrowth activity becomes asymmetrically localized to the neuron's surface in a statistically dependent manner. Extracellular cues regulate the probability of outgrowth along the surface and the orientation of outgrowth fluctuates across the surface over time. This creates a directional bias that allows the growth cone to navigate in reference to the composition of extracellular cues.

Axonal Guidance Signaling Pathway Is Suppressed in Human Nasal Polyps

Background Dysfunctional innervation might contribute to the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP), but the state of the axonal outgrowth signaling in CRSwNP is unknown. The purpose of this study was to explore the axonal outgrowth pathway-related protein expression in CRSwNP. Methods Institutional review board approved study in which tissue proteomes were compared between control and CRSwNP patients (n = 10/group) using an aptamer-based proteomic array and confirmed by whole transcriptomic analysis. Results Compared with controls, proteins associated with axonal guidance signaling pathway such as beta-nerve growth factor, semaphorin 3A, Ras-related C3 botulinum toxin substrate 1, Bcl-2, protein kinase C delta type, and Fyn were significantly decreased in patients with CRSwNP (fold change [FC] = -1.17, P = .002; FC = -1.09, P < .001; FC = -1.33, P < .001; FC = -1.31, P < .001; FC = -1.31, P = .004; and FC = -1.20, P = 0.012, respectively). In contrast, reticulon-4 receptor, an inhibitory factor, was significantly increased in patients with CRSwNP (FC = 1.25, P < .001). Furthermore, neuronal growth-associated proteins such as ciliary neurotrophic factor receptor subunit alpha, neuronal growth regulator 1, neuronal cell adhesion molecule, neural cell adhesion molecule L1, platelet-derived growth factor subunit A, and netrin-4 were all significantly decreased in patients with CRSwNP (FC = -1.25, P < .001; FC = -1.27, P = .002; FC = -1.65, P = .013; FC = -4.20, P < .001; FC = -1.28, P < .001; and FC = -2.31, P < .001, respectively). In contrast, tissue eosinophil count ( P < .001) and allergic inflammation factors such as IgE, periostin, and galectin-10 were all significantly increased in patients with CRSwNP (FC = 12.28, P < .001; FC = 3.95, P < .001; and FC = 2.44, P < .001, respectively). Furthermore, the log FC of the studied proteins expression significantly and positively correlated with log FC of their mRNA expression ( P < .001, r = .88). Conclusions Axonal guidance signaling and neural growth factors pathways proteins are significantly suppressed in eosinophilic CRSwNP.

Disturbed phospholipid metabolism in serine biosynthesis defects revealed by metabolomic profiling

Serine biosynthesis defects are autosomal recessive metabolic disorders resulting from the deficiency of any of the three enzymes involved in de novo serine biosynthesis, specifically phosphoglycerate dehydrogenase (PGDH), phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP). In this study, we performed metabolomic profiling on 4 children with serine biosynthesis defects; 3 with PGDH deficiency and 1 with PSAT deficiency. The evaluations were performed at baseline and with serine and glycine supplementation. Metabolomic profiling performed at baseline showed low phospholipid species, including glycerophosphocholine, glycerophosphoethanolamine, and sphingomyelin. All children had low serine and glycine as expected. Low glycerophosphocholine compounds were found in 4 children, low glycerophosphoethanolamine compounds in 3 children, and low sphingomyelin species in 2 children. Metabolic profiling with serine and glycine supplementation showed normalization of most of the low phospholipid compounds in the 4 children. Phospholipids are the major component of plasma and intracellular membranes, and phosphatidylcholine is the most abundant phospholipid of all mammalian cell types and subcellular organelles. Phosphatidylcholine is of particular importance for the nervous system, where it is essential for neuronal differentiation. The observed low phosphatidylcholine species in children with serine biosynthesis defects that improved after serine supplementation, supports the role of serine as a significant precursor for phosphatidylcholine. The vital role that phosphatidylcholine has during neuronal differentiation and the pronounced neurological manifestations in serine biosynthesis defects suggest that phosphatidylcholine deficiency occurring secondary to serine deficiency may have a significant contribution to the development of the neurological manifestations in individuals with serine biosynthesis defects.

Hierarchical Design of Tissue Regenerative Constructs

The worldwide shortage of organs fosters significant advancements in regenerative therapies. Tissue engineering and regeneration aim to supply or repair organs or tissues by combining material scaffolds, biochemical signals, and cells. The greatest challenge entails the creation of a suitable implantable or injectable 3D macroenvironment and microenvironment to allow for ex vivo or in vivo cell-induced tissue formation. This review gives an overview of the essential components of tissue regenerating scaffolds, ranging from the molecular to the macroscopic scale in a hierarchical manner. Further, this review elaborates about recent pivotal technologies, such as photopatterning, electrospinning, 3D bioprinting, or the assembly of micrometer-scale building blocks, which enable the incorporation of local heterogeneities, similar to most native extracellular matrices. These methods are applied to mimic a vast number of different tissues, including cartilage, bone, nerves, muscle, heart, and blood vessels. Despite the tremendous progress that has been made in the last decade, it remains a hurdle to build biomaterial constructs in vitro or in vivo with a native-like structure and architecture, including spatiotemporal control of biofunctional domains and mechanical properties. New chemistries and assembly methods in water will be crucial to develop therapies that are clinically translatable and can evolve into organized and functional tissues.

Differential Expression Patterns of Eph Receptors and Ephrin Ligands in Human Cancers

Eph receptors constitute the largest family of receptor tyrosine kinases, which are activated by ephrin ligands that either are anchored to the membrane or contain a transmembrane domain. These molecules play important roles in the development of multicellular organisms, and the physiological functions of these receptor-ligand pairs have been extensively documented in axon guidance, neuronal development, vascular patterning, and inflammation during tissue injury. The recognition that aberrant regulation and expression of these molecules lead to alterations in proliferative, migratory, and invasive potential of a variety of human cancers has made them potential targets for cancer therapeutics. We present here the involvement of Eph receptors and ephrin ligands in lung carcinoma, breast carcinoma, prostate carcinoma, colorectal carcinoma, glioblastoma, and medulloblastoma. The aberrations in their abundances are described in the context of multiple signaling pathways, and differential expression is suggested as the mechanism underlying tumorigenesis.

The protocadherin alpha cluster is required for axon extension and myelination in the developing central nervous system

In adult mammals, axon regeneration after central nervous system injury is very poor, resulting in persistent functional loss. Enhancing the ability of axonal outgrowth may be a potential treatment strategy because mature neurons of the adult central nervous system may retain the intrinsic ability to regrow axons after injury. The protocadherin (Pcdh) clusters are thought to function in neuronal morphogenesis and in the assembly of neural circuitry in the brain. We cultured primary hippocampal neurons from E17.5 Pcdhα deletion (del-α) mouse embryos. After culture for 1 day, axon length was obviously shorter in del-α neurons compared with wild-type neurons. RNA sequencing of hippocampal E17.5 RNA showed that expression levels of BDNF, Fmod, Nrp2, OGN, and Sema3d, which are associated with axon extension, were significantly down-regulated in the absence of the Pcdhα gene cluster. Using transmission electron microscopy, the ratio of myelinated nerve fibers in the axons of del-α hippocampal neurons was significantly decreased; myelin sheaths of P21 Pcdhα-del mice showed lamellar disorder, discrete appearance, and vacuoles. These results indicate that the Pcdhα cluster can promote the growth and myelination of axons in the neurodevelopmental stage.

Identifying the dynamics of actin and tubulin polymerization in iPSCs and in iPSC-derived neurons

The development of the nervous system requires cytoskeleton-mediated processes coordinating self-renewal, migration, and differentiation of neurons. It is not surprising that many neurodevelopmental problems and neurodegenerative disorders are caused by deficiencies in cytoskeleton-related genes. For this reason, we focus on the cytoskeletal dynamics in proliferating iPSCs and in iPSC-derived neurons to better characterize the underpinnings of cytoskeletal organization looking at actin and tubulin repolymerization studies using the cell permeable probes SiR-Actin and SiR-Tubulin. During neurogenesis, each neuron extends an axon in a complex and changing environment to reach its final target. The dynamic behavior of the growth cone and its capacity to respond to multiple spatial information allows it to find its correct target. We decided to characterize various parameters of the actin filaments and microtubules. Our results suggest that a rapid re-organization of the cytoskeleton occurs 45 minutes after treatments with de-polymerizing agents in iPSCs and 60 minutes in iPSC-derived neurons in both actin filaments and microtubules. The quantitative data confirm that the actin filaments have a primary role in the re-organization of the cytoskeleton soon after de-polymerization, while microtubules have a major function following cytoskeletal stabilization. In conclusion, we investigate the possibility that de-polymerization of the actin filaments may have an impact on microtubules organization and that de-polymerization of the microtubules may affect the stability of the actin filaments. Our results suggest that a reciprocal influence of the actin filaments occurs over the microtubules and vice versa in both in iPSCs and iPSC-derived neurons.

Systems genetic analysis of brown adipose tissue function

Brown adipose tissue (BAT) has been suggested to play an important role in lipid and glucose metabolism in rodents and possibly also in humans. In the current study, we used genetic and correlation analyses in the BXH/HXB recombinant inbred (RI) strains, derived from Brown Norway (BN) and spontaneously hypertensive rats (SHR), to identify genetic determinants of BAT function. Linkage analyses revealed a quantitative trait locus (QTL) associated with interscapular BAT mass on chromosome 4 and two closely linked QTLs associated with glucose oxidation and glucose incorporation into BAT lipids on chromosome 2. Using weighted gene coexpression network analysis (WGCNA) we identified 1,147 gene coexpression modules in the BAT from BXH/HXB rats and mapped their module eigengene QTLs. Through an unsupervised analysis, we identified modules related to BAT relative mass and function. The Coral4.1 coexpression module is associated with BAT relative mass (includes Cd36 highly connected gene), and the Darkseagreen coexpression module is associated with glucose incorporation into BAT lipids (includes Hiat1, Fmo5, and Sort1 highly connected transcripts). Because multiple statistical criteria were used to identify candidate modules, significance thresholds for individual tests were not adjusted for multiple comparisons across modules. In summary, a systems genetic analysis using genomic and quantitative transcriptomic and physiological information has produced confirmation of several known genetic factors and significant insight into novel genetic components functioning in BAT and possibly contributing to traits characteristic of the metabolic syndrome.

Cerium oxide nanoparticles inhibit differentiation of neural stem cells

Cerium oxide nanoparticles (nanoceria) display antioxidant properties and have shown cytoprotective effects both in vitro and in vivo. Here, we explored the effects of nanoceria on neural progenitor cells using the C17.2 murine cell line as a model. First, we assessed the effects of nanoceria versus samarium (Sm) doped nanoceria on cell viability in the presence of the prooxidant, DMNQ. Both particles were taken up by cells and nanoceria, but not Sm-doped nanoceria, elicited a temporary cytoprotective effect upon exposure to DMNQ. Next, we employed RNA sequencing to explore the transcriptional responses induced by nanoceria or Sm-doped nanoceria during neuronal differentiation. Detailed computational analyses showed that nanoceria altered pathways and networks relevant for neuronal development, leading us to hypothesize that nanoceria inhibits neuronal differentiation, and that nanoceria and Sm-doped nanoceria both interfere with cytoskeletal organization. We confirmed that nanoceria reduced neuron specific β3-tubulin expression, a marker of neuronal differentiation, and GFAP, a neuroglial marker. Furthermore, using super-resolution microscopy approaches, we could show that both particles interfered with cytoskeletal organization and altered the structure of neural growth cones. Taken together, these results reveal that nanoceria may impact on neuronal differentiation, suggesting that nanoceria could pose a developmental neurotoxicity hazard.

Regulation of Drosophila Brain Wiring by Neuropil Interactions via a Slit-Robo-RPTP Signaling Complex

The axonal wiring molecule Slit and its Round-About (Robo) receptors are conserved regulators of nerve cord patterning. Robo receptors also contribute to wiring brain circuits. Whether molecular mechanisms regulating these signals are modified to fit more complex brain wiring processes is unclear. We investigated the role of Slit and Robo receptors in wiring Drosophila higher-order brain circuits and identified differences in the cellular and molecular mechanisms of Robo/Slit function. First, we find that signaling by Robo receptors in the brain is regulated by the Receptor Protein Tyrosine Phosphatase RPTP69d. RPTP69d increases membrane availability of Robo3 without affecting its phosphorylation state. Second, we detect no midline localization of Slit during brain development. Instead, Slit is enriched in the mushroom body, a neuronal structure covering large areas of the brain. Thus, a divergent molecular mechanism regulates neuronal circuit wiring in the Drosophila brain, partly in response to signals from the mushroom body.

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In the Drosophila brain, mushroom bodies are a source of the Slit guidance cue

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Slit regulates axon growth in the vicinity of mushroom bodies via Robo receptors

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The phosphatase RPTP69D regulates Robo signaling in the brain

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RPTP69D regulates Robo3 membrane presentation independent of its enzymatic activity

Modeling Human Neurological and Neurodegenerative Diseases: From Induced Pluripotent Stem Cells to Neuronal Differentiation and Its Applications in Neurotrauma

With the help of several inducing factors, somatic cells can be reprogrammed to become induced pluripotent stem cell (iPSCs) lines. The success is in obtaining iPSCs almost identical to embryonic stem cells (ESCs), therefore various approaches have been tested and ultimately several ones have succeeded. The importance of these cells is in how they serve as models to unveil the molecular pathways and mechanisms underlying several human diseases, and also in its potential roles in the development of regenerative medicine. They further aid in the development of regenerative medicine, autologous cell therapy and drug or toxicity screening. Here, we provide a comprehensive overview of the recent development in the field of iPSCs research, specifically for modeling human neurological and neurodegenerative diseases, and its applications in neurotrauma. These are mainly characterized by progressive functional or structural neuronal loss rendering them extremely challenging to manage. Many of these diseases, including Parkinson's disease (PD), Huntington's disease (HD), Amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) have been explored in vitro. The main purpose is to generate patient-specific iPS cell lines from the somatic cells that carry mutations or genetic instabilities for the aim of studying their differentiation potential and behavior. This new technology will pave the way for future development in the field of stem cell research anticipating its use in clinical settings and in regenerative medicine in order to treat various human diseases, including neurological and neurodegenerative diseases.