Morphological Polarity Research Articles

Draft Genome Sequence of the Phototropic Cyanobacterium Rivularia sp. Strain IAM M-261

ABSTRACTRivularia sp. strain IAM M-261 is a filamentous cyanobacterium with tapering morphology and basal-apical polarity. The apical filament of this cyanobacterium exhibits positive phototropism toward visible light. To elucidate the molecular basis for this phototropism, we determined the draft genome sequence of this strain.

A Loss of Nuclear-Cytoskeletal Interactions in Vascular Smooth Muscle Cell Differentiation Induced by a Micro-Grooved Collagen Substrate Enabling the Modeling of an In Vivo Cell Arrangement.

Vascular smooth muscle cells (VSMCs) remodel vascular walls actively owing to mechanical cues and dedifferentiate to the synthetic phenotype from contractile phenotype in pathological conditions. It is crucial to clarify the mechanisms behind the VSMC phenotypic transition for elucidating their role in the vascular adaptation and repair and for designing engineered tissues. We recently developed novel micro-grooved collagen substrates with “wavy wrinkle” grooves to induce cell–substrate adhesion, morphological polarization, and a tissue-like cell arrangement with cytoskeletal rearrangements similar to those in vascular tissue in vivo. We found that cultivation with this micro-grooved collagen significantly induced VSMC contractile differentiation. Nonetheless, the detailed mechanism underlying the promotion of such VSMC differentiation by micro-grooved collagen has not been clarified yet. Here, we investigated the detailed mechanism of the cell arrangement into a tissue and contractile-differentiation improvement by our micro-grooved collagen substrates in terms of nuclear–cytoskeletal interactions that possibly affect the nuclear mechanotransduction involved in the activation of transcription factors. We found that VSMCs on micro-grooved collagen manifested significant cell arrangement into a tissue and nucleus slimming with a volume reduction in response to the remodeling of the actin cytoskeleton, with consequent inhibition of nuclear shuttling of a transcriptional coactivator, Yes-associated protein (YAP), and improved contractile differentiation. Furthermore, VSMC nuclei rarely deformed during macroscopic cell stretching and featured a loss of nesprin-1–mediated nuclear–cytoskeletal interactions. These results indicate that our micro-grooved collagen induces a cell alignment mimicking in vivo VSMC tissue and promotes contractile differentiation. In such processes of contractile differentiation, mechanical interaction between the nucleus and actin cytoskeleton may diminish to prevent a nuclear disturbance from the excess mechanical stress that might be essential for maintaining vascular functions.

The Origin of Parity Violation in Polarized Dust Emission and Implications for Cosmic Birefringence

Abstract Recent measurements of Galactic polarized dust emission have found a nonzero TB signal, a correlation between the total intensity and the B-mode polarization component. We present evidence that this parity-odd signal is driven by the relative geometry of the magnetic field and the filamentary interstellar medium in projection. Using neutral hydrogen morphology and Planck polarization data, we find that the angle between intensity structures and the plane-of-sky magnetic field orientation is predictive of the signs of Galactic TB and EB. Our results suggest that magnetically misaligned filamentary dust structures introduce nonzero TB and EB correlations in the dust polarization, and that the intrinsic dust EB can be predicted from measurements of dust TB and TE over the same sky mask. We predict correlations between TE, TB, EB, and EE/BB, and confirm our predictions using synthetic dust polarization maps from magnetohydrodynamic simulations. We introduce and measure a scale-dependent effective magnetic misalignment angle, ψ ℓ dust ∼ 5 ° for 100 ≲ ℓ ≲ 500, and predict a positive intrinsic dust EB with amplitude D ℓ EB ≲ 2.5 μ K CMB 2 for the same multipole range at 353 GHz over our sky mask. Both the sign and amplitude of the Galactic EB signal can change with the sky area considered. Our results imply that searches for parity violation in the cosmic microwave background must account for the nonzero Galactic EB and TB signals, necessitating revision of existing analyses of the evidence for cosmic birefringence.

Inherited apicobasal polarity defines the key features of axon-dendrite polarity in a sensory neuron

Neurons are highly polarized cells with morphologically and functionally distinct dendritic and axonal processes. The molecular mechanisms that establish axon-dendrite polarity invivo are poorly understood. Here, we describe the initial polarization of posterior deirid (PDE), a ciliated mechanosensory neuron, during development invivo through 4D live imaging with endogenously tagged proteins. PDE inherits and maintains apicobasal polarity from its epithelial precursor. Its apical domain is directly transformed into the ciliated dendritic tip through apical constriction, which is followed by axonal outgrowth from the opposite basal side of the cell. The apical Par complex and junctional proteins persistently localize at the developing dendritic domain throughout this transition. Consistent with their instructive role in axon-dendrite polarization, conditional depletion of the Par complex and junctional proteins results in robust defects in dendrite and axon formation. During apical constriction, a microtubule-organizing center (MTOC) containing the microtubule nucleator γ-tubulin ring complex (γ-TuRC) forms along the apical junction between PDE and its sister cell in a manner dependent on the Par complex and junctional proteins. This junctional MTOC patterns neuronal microtubule polarity and facilitate the dynein-dependent recruitment of the basal body for ciliogenesis. When non-ciliated neurons are genetically manipulated to obtain ciliated neuronal fate, inherited apicobasal polarity is required for generating ciliated dendritic tips. We propose that inherited apicobasal polarity, together with apical cell-cell interactions drive the morphological and cytoskeletal polarity in early neuronal differentiation.

Cannabinoid receptor 2 deficiency enhances isoflurane-induced spatial cognitive impairment in adult mice by affecting neuroinflammation, neurogenesis and neuroplasticity.

Isoflurane (Iso) is a commonly used inhalational anesthetic and is associated with the incidence of postoperative cognitive dysfunction (POCD). Cannabinoid receptor 2 (CB2R) was previously reported to have a promising neuroprotective function in cases of POCD, but the specific mechanisms have remained to be fully explored. The aim of the present study was to investigate the effect of CB2R deficiency on spatial cognitive performance in adult mice exposed to Iso. A total of 20 adult CB2R knockout (KO) and 20 wild-type (WT) mice were exposed to Iso (1.4% in oxygen for 4 h) or 100% oxygen. The Morris water maze (MWZ) test was performed 10 days after Iso exposure. Immunofluorescence staining and reverse transcription-quantitative PCR were performed to assess the expression of microglial marker ionized calcium-binding adaptor molecule-1 (Iba1) and the mRNA expression levels of microglial phenotype markers (M1: Interleukin-6, tumor necrosis factor-α, inducible nitric oxide synthase; M2: Chitinase-3 like protein) in the hippocampus. Changes in hippocampal neurogenesis and neuroplasticity were assessed by 5-bromodeoxyuridine (BrdU) immunostaining and Golgi staining. Compared with control mice, WT Iso-exposed mice had impaired spatial performance in the MWZ test. Furthermore, hippocampal Iba1 immunoreactivity and the number of microglial branches were notably increased in Iso-exposed WT mice. This was paralleled by significant upregulation of M1-associated markers and downregulation of M2-associated markers in the hippocampus. An obviously reduced number of BrdU+ neurons and decreased spine density were observed in WT Iso-exposed mice compared with control mice. Of note, CB2R deficiency exacerbated the spatial cognition impairment induced by Iso in the MWZ test. The alterations in the activation, morphology and M1 polarization of microglia, the number of BrdU+ neurons and spine density were more pronounced in CB2R-deficient Iso-exposed KO mice than in WT Iso-exposed mice. These results suggested that CB2R has a crucial role in Iso-induced cognitive impairment, which may be related to changes in hippocampal neuroinflammation, neurogenesis and neuroplasticity.

RAB1A Regulates Glioma Cellular Proliferation and Invasion Via the mTOR Signaling Pathway and Epithelial–Mesenchymal Transition

Aim: We aimed at investigating the mechanism of RAB1A proliferation and invasion in gliomas. Materials & methods: Genome-wide expression profile data and immunohistochemistry were analyzed to assess RAB1A expression in gliomas. The Transwell assay, wound healing assay, brain slice coculture model, cellular fluorescenceand intracranial xenograft model of nude mice were used to determine the proliferation and invasion of glioma cells. Results & conclusion: RAB1A was highly expressed in gliomas compared with normal brain tissue. The overall survival time of gliomapatients with high RAB1A expressionwas significantly shortened. RAB1A regulated the activity of RAC1 by inhibiting the mTOR signaling pathway, affecting actin polymerization, cell morphology and cell polarity. RAB1A downregulation inhibited the epithelial-mesenchymal transition, proliferation andinvasion of glioma cells.

Furry is required for cell movements during gastrulation and functionally interacts with NDR1

Gastrulation is a key event in animal embryogenesis during which germ layer precursors are rearranged and the embryonic axes are established. Cell polarization is essential during gastrulation, driving asymmetric cell division, cell movements, and cell shape changes. The furry (fry) gene encodes an evolutionarily conserved protein with a wide variety of cellular functions, including cell polarization and morphogenesis in invertebrates. However, little is known about its function in vertebrate development. Here, we show that in Xenopus, Fry plays a role in morphogenetic processes during gastrulation, in addition to its previously described function in the regulation of dorsal mesoderm gene expression. Using morpholino knock-down, we demonstrate a distinct role for Fry in blastopore closure and dorsal axis elongation. Loss of Fry function drastically affects the movement and morphological polarization of cells during gastrulation and disrupts dorsal mesoderm convergent extension, responsible for head-to-tail elongation. Finally, we evaluate a functional interaction between Fry and NDR1 kinase, providing evidence of an evolutionarily conserved complex required for morphogenesis.

ORAI2 Promotes Gastric Cancer Tumorigenicity and Metastasis through PI3K/Akt Signaling and MAPK-Dependent Focal Adhesion Disassembly.

The ubiquitous second messenger Ca2+ has long been recognized as a key regulator in cell migration. Locally confined Ca2+, in particular, is essential for building front-to-rear Ca2+ gradient, which serves to maintain the morphologic polarity required in directionally migrating cells. However, little is known about the source of the Ca2+ and the mechanism by which they crosstalk between different signaling pathways in cancer cells. Here, we report that calcium release-activated calcium modulator 2 (ORAI2), a poorly characterized store-operated calcium (SOC) channel subunit, predominantly upregulated in the lymph node metastasis of gastric cancer, supports cell proliferation and migration. Clinical data reveal that a high frequency of ORAI2-positive cells in gastric cancer tissues significantly correlated with poor differentiation, invasion, lymph node metastasis, and worse prognosis. Gain- and loss-of-function showed that ORAI2 promotes cell motility, tumor formation, and metastasis in both gastric cancer cell lines and mice. Mechanistically, ORAI2 mediated SOC activity and regulated tumorigenic properties through the activation of the PI3K/Akt signaling pathways. Moreover, ORAI2 enhanced the metastatic ability of gastric cancer cells by inducing FAK-mediated MAPK/ERK activation and promoted focal adhesion disassembly at rear-edge of the cell. Collectively, our results demonstrate that ORAI2 is a novel gene that plays an important role in the tumorigenicity and metastasis of gastric cancer. SIGNIFICANCE: These findings describe the critical role of ORAI2 in gastric cancer cell migration and tumor metastasis and uncover the translational potential to advance drug discovery along the ORAI2 signaling pathway.

Combined kinesin-1 and kinesin-3 activity drives axonal trafficking of TrkB receptors in Rab6 carriers.

SummaryNeurons depend on proper localization of neurotrophic receptors in their distal processes for their function. The Trk family of neurotrophin receptors controls neuronal survival, differentiation, and remodeling and are well known to function as retrograde signal carriers transported from the distal axon toward the cell body. However, the mechanism driving anterograde trafficking of Trk receptors into the axon is not well established. We used microfluidic compartmental devices and inducible secretion assay to systematically investigate the retrograde and anterograde trafficking routes of TrkB receptor along the axon in rat hippocampal neurons. We show that newly synthesized TrkB receptors traffic through the secretory pathway and are directly delivered into axon. We found that these TrkB carriers associate and are regulated by Rab6. Furthermore, the combined activity of kinesin-1 and kinesin-3 is needed for the formation of axon-bound TrkB secretory carriers and their effective entry and processive anterograde transport beyond the proximal axon.

The Transmembrane Adaptor Protein LIME Is Essential for Chemokine-Mediated Migration of Effector T Cells to Inflammatiory Sites.

Lck-interacting transmembrane adaptor 1 (LIME) has been previously identified as a raft-associated transmembrane protein expressed predominantly in T and B lymphocytes. Although LIME is shown to transduce the immunoreceptor signaling and immunological synapse formation via its tyrosine phosphorylation by Lck, a Src-family kinase, the in vivo function of LIME has remained elusive in the previous studies. Here we report that LIME is preferentially expressed in effector T cells and mediates chemokine-mediated T cell migration. Interestingly, in LIME-/- mice, while T cell receptor stimulation-dependent proliferation, differentiation to effector T cells, cytotoxic T lymphocyte (CTL) function and regulatory T lymphocyte (Treg) function were normal, only T cell-mediated inflammatory response was significantly defective. The reduced inflammation was accompanied by the impaired infiltration of leukocytes and T cells to the inflammatory sites of LIME-/- mice. More specifically, the absence of LIME in effector T cells resulted in the reduced migration and defective morphological polarization in response to inflammatory chemokines such as CCL5 and CXCL10. Consistently, LIME-/- effector T cells were found to be defective in chemokine-mediated activation of Rac1 and Rap1, and dysregulated phosphorylation of Pyk2 and Cas. Taken together, the present findings show that LIME is a critical regulator of inflammatory chemokine-mediated signaling and the subsequent migration of effector T cells to inflammatory sites.

Green and Digital Economy for Sustainable Development of Urban Areas

The article proposes an original typology of Sustainable Development Goals (SDGs) 2030, which makes it possible to formulate methods and criteria for sustainable urban development (SDG-11) via other SDGs. Due to digitalization, all ten branches of the green economy can give breakthrough effects in ensuring the sustainable development of urbanized areas. Although the elements of the green economy are historically organic to Russian urbanization, it is not possible to solve the main problem of sustainable development of Russia’s modern spatial development on the existing technological basis: the growing contradictions between the trends of hyperconcentration of the population and the economy in a small (for Russia’s size) number of megacities and, in parallel, their critical deconcentration on the periphery. The consistent implementation of the capabilities of the technological mode based on integration of the digital and green economies creates opportunities for significantly increased productivity in the infrastructural and industrial sectors of cities and development of the knowledge and experience economies in them, at the same time improving the quality of the urban environment and urban life and ensuring sustainable development. A consistent and balanced multiscale spatiotemporal and functional polarization of urbanized areas is an adequate form for implementing this technological mode, which makes it possible, by deepening the geographical division of labor and coordinating the turnover of material, natural, and human capital, to solve problems of sustainable spatial development for Russia by harmonizing its ecological, economic, and social components. The principles of spatiotemporal, morphological, and functional polarization are manifested at various territorial levels. With the development of the set of indicators and expansion of the statistical base for analyzing the green economy, the dissemination of smart city technologies and management of the life cycle for land use, a constructive-geographical, project-based approach in urban planning and ensuring the sustainable development of cities and urban agglomerations in Russia will become as common as the prevailing research approach.

Activity-Dependent Mitochondrial Plasticity and Mitoproteome are Dysregulated in Fragile X Syndrome

Homeostatic plasticity is necessary for the construction and maintenance of functional neuronal networks and becomes disrupted in certain neurodevelopmental disorders. Principal molecular mechanisms required for or modified by homeostatic plasticity are not well understood. We recently reported that homeostatic plasticity induced by activity deprivation is dysregulated in cortical neurons from Fragile X Mental Retardation protein (FMRP) knockout mice (Bulow et al. 2019). These findings suggested to us that proteins responsive to both activity deprivation and modulated by FMRP expression would be robust putative pathways necessary for or modified by homeostatic plasticity. Here, we used unbiased quantitative mass spectrometry to quantify steady-state proteome changes following chronic activity deprivation in wild type and Fmr1-/y cortical neurons. We found that most proteome hits responsive to both activity deprivation and the Fmr1-/y genotype were annotated to mitochondria. Surprisingly, we observed that Fmr1-/y neurons showed exaggerated changes in the expression of mitochondrial proteins following activity deprivation. We identified significant, but compartment specific, changes in the mitochondrial morphology and membrane polarization in dendrites and axons of wild type neurons following activity deprivation. However, these compartmentalized changes were already present in Fmr1-/y neurons at baseline and remained insensitive to activity deprivation. Our findings suggest that mitochondria are required and modified during the induction, establishment or maintenance of homeostatic plasticity. Loss of FMRP exaggerates changes in the mitoproteome during activity deprivation, but Fmr1-/y neurons fail to appropriately regulate mitochondrial morphology and function in an activity dependent and compartmentalized manner. We propose that abnormal compartmentalized mitochondrial plasticity contributes to neurodevelopmental disorders.

Elucidation of the desalination mechanism of solvent extraction method through molecular modeling studies

Desalination by solvent extraction is a simple and cost-effective technology to replace current ones. Although desalination solvents are continually developed, there is still a lack of understanding of the mechanism. In this study, we elucidate the solvent extraction desalination mechanism at the atomic level using molecular dynamics(MD) simulations. Three organic solvents octylamine(8A), dibutylamine(DBA), and 2-ethylhexylamine(EHA), which all have the same chemical composition but the amine group at different positions, were used. We simulated the desalination process from the brine-and-organic-solvents-mixing step to the brine-separation step. The MD simulations showed that DBA and EHA formed planar clusters while 8A formed gel clusters. By analyzing MD trajectories, we identified two types of water recovery mechanism, in which DBA and EHA clusters selectively absorb water and 8A traps brine by forming a gel structure. The polar interactions between water molecules and solvents are important driving forces for the absorption of water. To explain the desalination performances of DBA and EHA, morphological characteristics and surface polarity of the clusters were measured. It was found that a higher surface polarity facilitates more water absorption. Partial recovery of the salt ions was attributed to the surface polarity of the organic solvent clusters.

Mechanochemical symmetry breaking during morphogenesis of lateral-line sensory organs.

Actively regulated symmetry breaking, which is ubiquitous in biological cells, underlies phenomena such as directed cellular movement and morphological polarization. Here we investigate how an organ-level polarity pattern emerges through symmetry breaking at the cellular level during the formation of a mechanosensory organ. Combining theory, genetic perturbations, and in vivo imaging, we study the development and regeneration of the fluid-motion sensors in the zebrafish’s lateral line. We find that two interacting symmetry-breaking events — one mediated by biochemical signaling and the other by cellular mechanics — give rise to precise rotations of cell pairs, which produce a mirror-symmetric polarity pattern in the receptor organ.

Noncanonical Wnt planar cell polarity signaling in lung development and disease.

The planar cell polarity (PCP) signaling pathway is a potent developmental regulator of directional cell behaviors such as migration, asymmetric division and morphological polarization that are critical for shaping the body axis and the complex three-dimensional architecture of tissues and organs. PCP is considered a noncanonical Wnt pathway due to the involvement of Wnt ligands and Frizzled family receptors in the absence of the beta-catenin driven gene expression observed in the canonical Wnt cascade. At the heart of the PCP mechanism are protein complexes capable of generating molecular asymmetries within cells along a tissue-wide axis that are translated into polarized actin and microtubule cytoskeletal dynamics. PCP has emerged as an important regulator of developmental, homeostatic and disease processes in the respiratory system. It acts along other signaling pathways to create the elaborately branched structure of the lung by controlling the directional protrusive movements of cells during branching morphogenesis. PCP operates in the airway epithelium to establish and maintain the orientation of respiratory cilia along the airway axis for anatomically directed mucociliary clearance. It also regulates the establishment of the pulmonary vasculature. In adult tissues, PCP dysfunction has been linked to a variety of chronic lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary arterial hypertension, stemming chiefly from the breakdown of proper tissue structure and function and aberrant cell migration during regenerative wound healing. A better understanding of these (impaired) PCP mechanisms is needed to fully harness the therapeutic opportunities of targeting PCP in chronic lung diseases.

Зеленая и цифровая экономика как инструмент устойчивого развития урбанизированных территорий

The article proposes an original typology of the Sustainable Development Goals (SDGs) 2030, which allows formulating through other SDGs methods and criteria for sustainable development of cities (SDG-11). Due to digitalization, all of the 10 branches of the green economy can give breakthrough effects in ensuring the sustainable development of urbanized territories. Although elements of the green economy are historically organic to Russian urbanization, it is not possible to solve the main problem of sustainable development of Russian modern spatial development—the growing contradictions between the trends of hyperconcentration of population and economy in a small (for the size of Russia) number of megacities and their critical deconcentration on the periphery—on the existing technological basis. Nevertheless, the consistent implementation of technological capabilities based on the integration of digital and green economies creates opportunities for significant productivity growth in infrastructure and production sectors of cities and development of knowledge economy and experience economy, while improving the quality of the urban environment and the quality of urban life and achieving sustainable development. A consistent and balanced multi-scale spatial-temporal and functional polarization of urbanized territories is an adequate form of implementation of this technological order. It allows on the basis of deepening the geographical labor division and coordination of the turnover of material, natural and human capital to solve the problems of sustainable spatial development of Russia by harmonizing its environmental, economic and social components. The principles of spatial-temporal, morphological and functional polarization are manifested in various spatial levels. With the development of indicators’ set and the expansion of the statistical base for the analysis of the green economy, the spread of smart city technologies and lifecycle management of land use, the constructive-geographical, project approach in urban planning, in ensuring the sustainable development of cities and agglomerations in Russia will become as familiar as the prevailing research approach.

Promoting the microwave absorption characteristics in the X band using core-shell structures of Cu metal particles/PPy and hexaferrite/PPy

Abstract Multifunctional microwave absorber materials exhibit promising characteristics, since they combine the diverse properties of their components. More precisely, by precipitating polypyrrole (PPy) on a mixture soundly chosen of copper and two different hexaferrites, the dielectric, plasmonic and ferrimagnetic properties can be combined in a beneficial way to tune the absorption characteristics. Beyond the multifunctionality of this absorber, several properties may emerge from intrinsic factors, such as: morphology and/or interfacial polarization linked to the core-shell structure. The absorber has been structurally characterized by XRD, FTIR and UV–vis spectroscopy. The magnetic properties and the microwave reflection loss (RL) have been investigated using a VSM and VNA, respectively. The results indicate that the presence of copper metal boosts the reflection loss of the absorber, widen the bandwidth and shifts the matching frequency towards higher values. The core-shell structure formed by coating PPy on the copper and hexaferrites mixture enhances the RL and lower both absorber thickness and loading percentage required to achieve comparable absorption performance to that of an absorber prepared by simple mixture of the components. The current optimized absorber exhibits a minimum RL of −22 dB at a matching frequency around 10.8 GHz and a thickness of 2 mm. The bandwidth under −10 dB covers all the X band starting from 9.6 GHz and continues into the Ku band.

Upregulation of fascin-1 is involved in HIF-1α-dependent invasion and migration of hypopharyngeal squamous cell carcinoma.

Fascin-1 is an actin-bundling protein, which specifically interacts with F-actin to form parallel actin bundles, and participates in the regulation of cell adhesion, interactions and migration. However, the expression and regulatory mechanisms of fascin-1 in hypopharyngeal squamous cell carcinoma (HSCC) remain poorly understood. The present study investigated the effects and underlying molecular mechanism of fascin-1 on the invasion and metastasis of HSCC. The results demonstrated that fascin-1 was overexpressed and correlated with lymph node metastasis and tumor-node-metastasis stage in HSCC tissues. Further in vitro study revealed that fascin-1 promoted cell morphology polarization to increase the motility of FaDu cells. In addition, fascin-1 significantly promoted the migration and invasion of FaDu cells. At the molecular level, fascin-1 promoted cell invasion and migration by upregulating matrix metalloproteinase-2 (MMP-2) expression in FaDu cells. Immunohistochemical analysis revealed that a correlation existed between hypoxia inducible factor (HIF)-1α and fascin-1 expression in the HSCC tissues. Furthermore, the results from a cobalt chloride-induced hypoxia model demonstrated that fascin-1 may be upregulated by HIF-1α in FaDu cells. Further analysis revealed that fascin-1 knockdown significantly decreased the invasion of cells under hypoxia and partially reversed hypoxia-induced MMP-2 expression under hypoxia in FaDu cells. In conclusion, fascin-1 was upregulated by HIF-1α, and promoted the invasion and migration of HSCC cells; therefore, fascin-1 may provide a potential target for the treatment of invasion and metastasis in HSCC.

A Model of Hereditary Sensory and Autonomic Neuropathy Type 1 Reveals a Role of Glycosphingolipids in Neuronal Polarity.

Hereditary sensory and autonomic neuropathy Type 1 (HSAN1) is a rare autosomal dominantly inherited neuropathy, clinically characterized by a loss of distal peripheral sensory and motoneuronal function. Mutations in subunits of serine palmitoyltransferase (SPT) have been linked to the majority of HSAN1 cases. SPTs catalyze the condensation of l-serine with palmitoyl-CoA, the first committed and rate-limiting step in de novo sphingolipid biosynthesis. Despite extensive investigation, the molecular pathogenesis of HSAN1 remains controversial. Here, we established a Caenorhabditis elegans (C. elegans) model of HSAN1 by generating a sptl-1(c363g) mutation, encoding SPTL-1(C121W) and equivalent to human SPTLC1C133W, at the C. elegans genomic locus through CRISPR. The sptl-1(c363g) homozygous mutants exhibited the same larval lethality and epithelial polarity defect as observed in sptl-1(RNAi) animals, suggesting a loss-of-function effect of the SPTL-1(C121W) mutation. sptl-1(c363g)/+ heterozygous mutants displayed sensory dysfunction with concomitant neuronal morphology and axon-dendrite polarity defects, demonstrating that the C. elegans model recapitulates characteristics of the human disease. sptl-1(c363g)-derived neuronal defects were copied in animals with defective sphingolipid biosynthetic enzymes downstream of SPTL-1, including ceramide glucosyltransferases, suggesting that SPTLC1C133W contributes to the HSAN1 pathogenesis by limiting the production of complex sphingolipids, including glucosylceramide. Overexpression of SPTL-1(C121W) led to similar epithelial and neuronal defects and to reduced levels of complex sphingolipids, specifically glucosylceramide, consistent with a dominant-negative effect of SPTL-1(C121W) that is mediated by loss of this downstream product. Genetic interactions between SPTL-1(C121W) and components of directional trafficking in neurons suggest that the neuronal polarity phenotype could be caused by glycosphingolipid-dependent defects in polarized vesicular trafficking.SIGNIFICANCE STATEMENT The symptoms of inherited metabolic diseases are often attributed to the accumulation of toxic intermediates or byproducts, no matter whether the disease-causing enzyme participates in a biosynthetic or a degradation pathway. By showing that the phenotypes observed in a C. elegans model of HSAN1 disease could be caused by loss of a downstream product (glucosylceramide) rather than the accumulation of a toxic byproduct, our work provides new insights into the origins of the symptoms of inherited metabolic diseases while expanding the repertoire of sphingolipid functions, specifically, of glucosylceramides. These findings not only have their most immediate relevance for neuroprotective treatments for HSAN1, they may also have implications for a much broader range of neurologic conditions.

P2Y1 Purinergic Receptor Modulate Axon Initial Segment Initial Development.

Morphological and functional polarization of neurons depends on the generation and maintenance of the axon initial segment (AIS). This axonal domain maintains axonal properties but is also the place where the action potential (AP) is generated. All these functions require the AIS, a complex structure that is not fully understood. An integrated structure of voltage-gated ion channels, specific cytoskeleton architecture, as well as, scaffold proteins contributes to these functions. Among them, ankyrinG plays a crucial role to maintain ion channels and membrane proteins. However, it is still elusive how the AIS performs its complex structural and functional regulation. Recent studies reveal that AIS is dynamically regulated in molecular composition, length and location in response to neuronal activity. Some mechanisms acting on AIS plasticity have been uncovered recently, including Ca2+, calpain or calmodulin-mediated modulation, as well as post-translational modifications of cytoskeleton proteins and actin-associated proteins. Neurons are able to respond to different kind of physiological and pathological stimuli from development to maturity by adapting their AIS composition, position and length. This raises the question of which are the neuronal receptors that contribute to the modulation of AIS plasticity. Previous studies have shown that purinergic receptor P2X7 activation is detrimental to AIS maintenance. During initial axonal elongation, P2X7 is coordinated with P2Y1, another purinergic receptor that is essential for proper axon elongation. In this study, we focus on the role of P2Y1 receptor on AIS development and maintenance. Our results show that P2Y1 receptor activity and expression are necessary during AIS initial development, while has no role once AIS maturity is achieved. P2Y1 inhibition or suppression results in a decrease in ankyrinG, βIV-spectrin and voltage-gated sodium channels accumulation that can be rescued by actin stabilization or the modulation of actin-binding proteins at the AIS. Moreover, P2X7 or calpain inhibition also rescues ankyrinG decrease. Hence, a dynamic balance of P2Y1 and P2X7 receptors expression and function during AIS assembly and maturation may represent a fine regulatory mechanism in response to physiological or pathological extracellular purines concentration.