Localization of glutamate receptors to distal dendrites depends on subunit composition and the kinesin motor protein KIF17

KIF17 Modulates Epileptic Seizures and Membrane Expression of the NMDA Receptor Subunit NR2B

Epilepsy is a common and severe brain disease affecting >65 million people worldwide. Recent studies have shown that kinesin superfamily motor protein 17 (KIF17) is expressed in neurons and is involved in regulating the dendrite-targeted transport of N-methyl-D-aspartate receptor subtype 2B (NR2B). However, the effect of KIF17 on epileptic seizures remains to be explored. We found that KIF17 was mainly expressed in neurons and that its expression was increased in epileptic brain tissue. In the kainic acid (KA)-induced epilepsy mouse model, KIF17 overexpression increased the severity of epileptic activity, whereas KIF17 knockdown had the opposite effect. In electrophysiological tests, KIF17 regulated excitatory synaptic transmission, potentially due to KIF17-mediated NR2B membrane expression. In addition, this report provides the first demonstration that KIF17 is modified by SUMOylation (SUMO, small ubiquitin-like modifier), which plays a vital role in the stabilization and maintenance of KIF17 in epilepsy.

The potential function of KIF17 in large yellow croaker (Larimichthys crocea) spermatid remodeling: molecular characterization and expression pattern during spermiogenesis

KIF17, which belongs to the kinesin-2 protein family, plays an indispensable role in mammalian spermiogenesis. However, the role of KIF17 in fish spermatid remodeling during spermiogenesis remains poorly understood. Therefore, we aimed to study the role of KIF17 in spermatid remodeling during Larimichthys crocea (L. crocea) spermiogenesis. The kif17 cDNA sequence, 3247 bp in length, was cloned from L. crocea testis, which consisted of a 347-bp 5'-untranslated region (UTR), 413-bp 3' -UTR, and 2487-bp open reading frame. Bioinformatic analyses revealed that KIF17 obtained from L. crocea (Lc-KIF17) exhibited a high sequence identity compared with those from other teleosts and possessed the structural features of other kinesin-2 proteins. Based on structural similarity, we speculate that the role of Lc-KIF17 may be similar to that of KIF17 in other animals. Lc-kif17 mRNA was diffusely expressed in L. crocea tissues and was highly expressed in the testis, especially at stage IV testicular development. Immunofluorescence analysis revealed that Lc-KIF17 signals colocalized with β-tubulin signals and migrated from the perinuclear cytoplasm to the side of the nucleus where the tail forms during spermiogenesis. These findings revealed that KIF17 may be involved in L. crocea spermiogenesis. In particular, KIF17 may participate in spermatid remodeling by interacting with perinuclear microtubules during L. crocea spermiogenesis. Collectively, this study contributes to an improved understanding of the mechanism underlying L. crocea spermiogenesis and provides a basis for further research on L. crocea reproduction and development.

Understanding how kinesin motor proteins regulate postsynaptic function in neuron

The Kinesin superfamily proteins (KIFs) are major molecular motors that transport diverse set of cargoes along microtubules to both the axon and dendrite of a neuron. Much of our knowledge about kinesin function is obtained from studies on axonal transport. Emerging evidence reveals how specific kinesin motor proteins carry cargoes to dendrites, including proteins, mRNAs and organelles that are crucial for synapse development and plasticity. In this review, we will summarize the major kinesin motors and their associated cargoes that have been characterized to regulate postsynaptic function in neuron. We will also discuss how specific kinesins are selectively involved in the development of excitatory and inhibitory postsynaptic compartments, their regulation by post-translational modifications (PTM), as well as their roles beyond conventional transport carrier.

ATF4 selectively regulates heat nociception and contributes to kinesin-mediated TRPM3 trafficking

Effective treatments for patients suffering from heat hypersensitivity are lacking, mostly due to our limited understanding of the pathogenic mechanisms underlying this disorder. In the nervous system, activating transcription factor 4 (ATF4) is involved in the regulation of synaptic plasticity and memory formation. Here, we show that ATF4 plays an important role in heat nociception. Indeed, loss of ATF4 in mouse dorsal root ganglion (DRG) neurons selectively impairs heat sensitivity. Mechanistically, we show that ATF4 interacts with transient receptor potential cation channel subfamily M member-3 (TRPM3) and mediates the membrane trafficking of TRPM3 in DRG neurons in response to heat. Loss of ATF4 also significantly decreases the current and KIF17-mediated trafficking of TRPM3, suggesting that the KIF17/ATF4/TRPM3 complex is required for the neuronal response to heat stimuli. Our findings unveil the non-transcriptional role of ATF4 in the response to heat stimuli in DRG neurons.

Spatial control of membrane traffic in neuronal dendrites

Neuronal dendrites are highly branched and specialized compartments with distinct structures and secretory organelles (e.g., spines, Golgi outposts), and a unique cytoskeletal organization that includes microtubules of mixed polarity. Dendritic membranes are enriched with proteins, which specialize in the formation and function of the post-synaptic membrane of the neuronal synapse. How these proteins partition preferentially in dendrites, and how they traffic in a manner that is spatiotemporally accurate and regulated by synaptic activity are long-standing questions of neuronal cell biology. Recent studies have shed new insights into the spatial control of dendritic membrane traffic, revealing new classes of proteins (e.g., septins) and cytoskeleton-based mechanisms with dendrite-specific functions. Here, we review these advances by revisiting the fundamental mechanisms that control membrane traffic at the levels of protein sorting and motor-driven transport on microtubules and actin filaments. Overall, dendrites possess unique mechanisms for the spatial control of membrane traffic, which might have specialized and co-evolved with their highly arborized morphology.

A novel function for the ER retention signals in the C-terminus of kainate receptor subunit, GluK5

Classically, endoplasmic reticulum (ER) retention signals in secreted integral membrane proteins impose the requirement to assemble with other cognate subunits to form functional assemblies before they can exit the ER. We report that GluK5 has two ER retention signals in its cytoplasmic C-terminus: an arginine-based signal and a di-leucine motif previously thought to be an endocytic motif. GluK5 assembles with GluK2, but surprisingly GluK2 association does little to block the ER retention signals. We find instead that the ER retention signals are blocked by two proteins involved in intracellular trafficking, SAP97 and CASK. We show that SAP97, in the presence of CASK and the receptor complex, assumes an extended conformation. In the extended conformation, SAP97 makes its SH3 and GuK domains available to bind and sterically mask the ER retention signals in the GluK5 C-terminus. SAP97 and CASK are also necessary for sorting receptor cargoes into the local dendritic secretory pathway in neurons. We show that the ER retention signals of GluK5 play a vital role in sorting the receptor complex in the local dendritic secretory pathway in neurons. These data suggest a new role for ER retention signals in trafficking integral membrane proteins in neurons. SIGNIFICANCE: We present evidence that the ER retention signals in the kainate receptors containing GluK5 impose a requirement for sorting into local dendritic secretory pathways in neurons, as opposed to traversing the somatic Golgi apparatus. There are two ER retention signals in the C-terminus of GluK5. We show that both are blocked by physical association with SAP97 and CASK. The SH3 and GuK domains of SAP97, in the presence of CASK, bind directly to each ER retention signal and form a complex. These results support an entirely new function for ER retention signals in the C-termini of neuronal receptors, such as NMDA and kainate receptors, and define a mechanism for selective entry of receptors into local secretory pathways.

Mechanisms regulating dendritic arbor patterning

The nervous system is populated by diverse types of neurons, each of which has dendritic trees with strikingly different morphologies. These neuron-specific morphologies determine how dendritic trees integrate thousands of synaptic inputs to generate different firing properties. To ensure proper neuronal function and connectivity, it is necessary that dendrite patterns are precisely controlled and coordinated with synaptic activity. Here, we summarize the molecular and cellular mechanisms that regulate the formation of cell type-specific dendrite patterns during development. We focus on different aspects of vertebrate dendrite patterning that are particularly important in determining the neuronal function; such as the shape, branching, orientation and size of the arbors as well as the development of dendritic spine protrusions that receive excitatory inputs and compartmentalize postsynaptic responses. Additionally, we briefly comment on the implications of aberrant dendritic morphology for nervous system disease.

Intraflagellar transport velocity is governed by the number of active KIF17 and KIF3AB motors and their motility properties under load

Homodimeric KIF17 and heterotrimeric KIF3AB are processive, kinesin-2 family motors that act jointly to carry out anterograde intraflagellar transport (IFT), ferrying cargo along microtubules (MTs) toward the tips of cilia. How IFT trains attain speeds that exceed the unloaded rate of the slower, KIF3AB motor remains unknown. By characterizing the motility properties of kinesin-2 motors as a function of load we find that the increase in KIF3AB velocity, elicited by forward loads from KIF17 motors, cannot alone account for the speed of IFT trains in vivo. Instead, higher IFT velocities arise from an increased likelihood that KIF3AB motors dissociate from the MT, resulting in transport by KIF17 motors alone, unencumbered by opposition from KIF3AB. The rate of transport is therefore set by an equilibrium between a faster state, where only KIF17 motors move the train, and a slower state, where at least one KIF3AB motor on the train remains active in transport. The more frequently the faster state is accessed, the higher the overall velocity of the IFT train. We conclude that IFT velocity is governed by (i) the absolute numbers of each motor type on a given train, (ii) how prone KIF3AB is to dissociation from MTs relative to KIF17, and (iii) how prone both motors are to dissociation relative to binding MTs.

Nanoparticulate TiO2 -mediated inhibition of the Wnt signaling pathway causes dendritic development disorder in cultured rat hippocampal neurons

Titanium dioxide nanoparticles (TiO₂ NPs) are increasingly used in daily life, in industry, and in environmental clearing, but their potential neurodevelopmental toxicity has been highly debated. In this study, we explored whether TiO₂ NPs inhibited development of dendritic morphology and identified possible molecular mechanisms associated with this inhibition in primary cultured rat hippocampal neurons. Results showed that TiO₂ NPs decreased neurite length, the number of branches and the spine density, and impaired mitochondrial function in the developing neurons. Furthermore, TiO₂ NPs significantly reduced the expression of several proteins involved in canonical Wnt3a/β-catenin signaling including Wnt3a, β-catenin, p-GSK-3β, and CyclinD1 and conversely, elevated GSK-3β expression. In addition to altering expression of proteins involved in canonical Wnt3a/β-catenin signaling, TiO₂ NPs decreased expression of proteins invovled in non-canonical Wnt signaling, including, MKLP1, CRMP3, ErbB4, and KIF17. Taken together, these results indicate that suppression of dendritic development caused by TiO₂ NPs is associated with inhibition of activation of the Wnt/β-catenin pathway or non-canonical Wnt pathway-induced expression of microtubule cytoskeletal components in the developing neurons. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2139-2149, 2017.

Three-Step Model for Polarized Sorting of KIF17 into Dendrites

Kinesin and dynein motors drive bidirectional cargo transport along microtubules and have a critical role in polarized cargo trafficking in neurons [1, 2]. The kinesin-2 family protein KIF17 is a dendrite-specific motor protein and has been shown to interact with several dendritic cargoes [3-7]. However, the mechanism underlying the dendritic targeting of KIF17 remains poorly understood [8-11]. Using live-cell imaging combined with inducible trafficking assays to directly probe KIF17 motor activity in living neurons, we found that the polarized sorting of KIF17 to dendrites is regulated in multiple steps. First, cargo binding of KIF17 relieves autoinhibition and initiates microtubule-based cargo transport. Second, KIF17 does not autonomously target dendrites, but enters the axon where the actin cytoskeleton at the axon initial segment (AIS) prevents KIF17 vesicles from moving further into the axon. Third, dynein-based motor activity is able to redirect KIF17-coupled cargoes into dendrites. We propose a three-step model for polarized targeting of KIF17, in which the collective function of multiple motor teams is required for proper dendritic sorting.

Tc1 mouse model of trisomy-21 dissociates properties of short- and long-term recognition memory

The present study examined memory function in Tc1 mice, a transchromosomic model of Down syndrome (DS). Tc1 mice demonstrated an unusual delay-dependent deficit in recognition memory. More specifically, Tc1 mice showed intact immediate (30sec), impaired short-term (10-min) and intact long-term (24-h) memory for objects. A similar pattern was observed for olfactory stimuli, confirming the generality of the pattern across sensory modalities. The specificity of the behavioural deficits in Tc1 mice was confirmed using APP overexpressing mice that showed the opposite pattern of object memory deficits. In contrast to object memory, Tc1 mice showed no deficit in either immediate or long-term memory for object-in-place information. Similarly, Tc1 mice showed no deficit in short-term memory for object-location information. The latter result indicates that Tc1 mice were able to detect and react to spatial novelty at the same delay interval that was sensitive to an object novelty recognition impairment. These results demonstrate (1) that novelty detection per se and (2) the encoding of visuo-spatial information was not disrupted in adult Tc1 mice. The authors conclude that the task specific nature of the short-term recognition memory deficit suggests that the trisomy of genes on human chromosome 21 in Tc1 mice impacts on (perirhinal) cortical systems supporting short-term object and olfactory recognition memory.

Septin 9 interacts with kinesin KIF17 and interferes with the mechanism of NMDA receptor cargo binding and transport

Kinesin motor interactions with cargo and their regulation are not well understood. Septin 9 (SEPT9) interacts directly with kinesin KIF17 and interferes with binding of the cargo adaptor/scaffold mLin-10/Mint1, which links the NMDA receptor subunit 2B (NR2B) to KIF17. SEPT9 down-regulates NR2B transport without affecting the motile properties of KIF17.

Intracellular transport involves the regulation of microtubule motor interactions with cargo, but the underlying mechanisms are not well understood. Septins are membrane- and microtubule-binding proteins that assemble into filamentous, scaffold-like structures. Septins are implicated in microtubule-dependent transport, but their roles are unknown. Here we describe a novel interaction between KIF17, a kinesin 2 family motor, and septin 9 (SEPT9). We show that SEPT9 associates directly with the C-terminal tail of KIF17 and interacts preferentially with the extended cargo-binding conformation of KIF17. In developing rat hippocampal neurons, SEPT9 partially colocalizes and comigrates with KIF17. We show that SEPT9 interacts with the KIF17 tail domain that associates with mLin-10/Mint1, a cargo adaptor/scaffold protein, which underlies the mechanism of KIF17 binding to the NMDA receptor subunit 2B (NR2B). Significantly, SEPT9 interferes with binding of the PDZ1 domain of mLin-10/Mint1 to KIF17 and thereby down-regulates NR2B transport into the dendrites of hippocampal neurons. Measurements of KIF17 motility in live neurons show that SEPT9 does not affect the microtubule-dependent motility of KIF17. These results provide the first evidence of an interaction between septins and a nonmitotic kinesin and suggest that SEPT9 modulates the interactions of KIF17 with membrane cargo.

Diversifying the secretory routes in neurons

Nervous system homeostasis and synaptic function need dedicated mechanisms to locally regulate the molecular composition of the neuronal plasma membrane and allow the development, maintenance and plastic modification of the neuronal morphology. The cytoskeleton and intracellular trafficking lies at the core of all these processes. In most mammalian cells, the Golgi apparatus (GA) is at the center of the biosynthetic pathway, located in the proximity of the microtubule-organizing center. In addition to this central localization, the somatic GA in neurons is complemented by satellite Golgi outposts (GOPs) in dendrites, which are essential for dendritic morphogenesis and are emerging like local stations of membranes trafficking to synapses. Largely, GOPs participation in post-ER trafficking has been determined by imaging the transport of the exogenous protein VSVG. Here we review the diversity of neuronal cargoes that traffic through GOPs and the assortment of different biosynthetic routes to synapses. We also analyze the recent advances in understanding the role of cytoskeleton and Golgi matrix proteins in the biogenesis of GOPs and how the diversity of secretory routes can be generated.

Whole-exome sequencing reveals a novel frameshift mutation in the FAM161A gene causing autosomal recessive retinitis pigmentosa in the Indian population

Retinitis pigmentosa (RP) is a heterogenous group of inherited retinal degenerations caused by mutations in at least 50 genes. To identify genetic mutations underlying autosomal recessive RP (arRP), we performed whole-exome sequencing study on two consanguineous marriage Indian families (RP-252 and RP-182) and 100 sporadic RP patients. Here we reported novel mutation in FAM161A in RP-252 and RP-182 with two patients affected with RP in each family. The FAM161A gene was identified as the causative gene for RP28, an autosomal recessive form of RP. By whole-exome sequencing we identified several homozygous genomic regions, one of which included the recently identified FAM161A gene mutated in RP28-linked arRP. Sequencing analysis revealed the presence of a novel homozygous frameshift mutation p.R592FsX2 in both patients of family RP-252 and family RP-182. In 100 sporadic Indian RP patients, this novel homozygous frameshift mutation p.R592FsX2 was identified in one sporadic patient ARRP-S-I-46 by whole-exome sequencing and validated by Sanger sequencing. Meanwhile, this homozygous frameshift mutation was absent in 1000 ethnicity-matched control samples screened by direct Sanger sequencing. In conclusion, we identified a novel homozygous frameshift mutations of RP28-linked RP gene FAM161A in Indian population.

Kinesin family 17 (osmotic avoidance abnormal-3) is dispensable for photoreceptor morphology and function

In Caenorhabditis elegans, homodimeric [kinesin family (KIF) 17, osmotic avoidance abnormal-3 (OSM-3)] and heterotrimeric (KIF3) kinesin-2 motors are required to establish sensory cilia by intraflagellar transport (IFT) where KIF3 and KIF17 cooperate to build the axoneme core and KIF17 builds the distal segments. However, the function of KIF17 in vertebrates is unresolved. We expressed full-length and motorless KIF17 constructs in mouse rod photoreceptors using adeno-associated virus in Xenopus laevis rod photoreceptors using a transgene and in ciliated IMCD3 cells. We found that tagged KIF17 localized along the rod outer segment axoneme when expressed in mouse and X. laevis photoreceptors, whereas KIF3A was restricted to the proximal axoneme. Motorless KIF3A and KIF17 mutants caused photoreceptor degeneration, likely through dominant negative effects on IFT. KIF17 mutant lacking the motor domain translocated to nuclei after exposure of a C-terminal nuclear localization signal. Germ-line deletion of Kif17 in mouse did not affect photoreceptor function. A rod-specific Kif3/Kif17 double knockout mouse demonstrated that KIF17 and KIF3 do not act synergistically and did not prevent rhodopsin trafficking to rod outer segments. In summary, the nematode model of KIF3/KIF17 cooperation apparently does not apply to mouse photoreceptors in which the photosensory cilium is built exclusively by KIF3.

Adolescent nicotine induces persisting changes in development of neural connectivity

Adolescent nicotine induces persisting changes in development of neural connectivity. A large number of brain changes occur during adolescence as the CNS matures. These changes suggest that the adolescent brain may still be susceptible to developmental alterations by substances which impact its growth. Here we review recent studies on adolescent nicotine which show that the adolescent brain is differentially sensitive to nicotine-induced alterations in dendritic elaboration, in several brain areas associated with processing reinforcement and emotion, specifically including nucleus accumbens, medial prefrontal cortex, basolateral amygdala, bed nucleus of the stria terminalis, and dentate gyrus. Both sensitivity to nicotine, and specific areas responding to nicotine, differ between adolescent and adult rats, and dendritic changes in response to adolescent nicotine persist into adulthood. Areas sensitive to, and not sensitive to, structural remodeling induced by adolescent nicotine suggest that the remodeling generally corresponds to the extended amygdala. Evidence suggests that dendritic remodeling is accompanied by persisting changes in synaptic connectivity. Modeling, electrophysiological, neurochemical, and behavioral data are consistent with the implication of our anatomical studies showing that adolescent nicotine induces persisting changes in neural connectivity. Emerging data thus suggest that early adolescence is a period when nicotine consumption, presumably mediated by nicotine-elicited changes in patterns of synaptic activity, can sculpt late brain development, with consequent effects on synaptic interconnection patterns and behavior regulation. Adolescent nicotine may induce a more addiction-prone phenotype, and the structures altered by nicotine also subserve some emotional and cognitive functions, which may also be altered. We suggest that dendritic elaboration and associated changes are mediated by activity-dependent synaptogenesis, acting in part through D1DR receptors, in a network activated by nicotine. The adolescent nicotine effects reviewed here suggest that modification of late CNS development constitutes a hazard of adolescent nicotine use.

Functions of kinesin superfamily proteins in neuroreceptor trafficking

Synaptic plasticity is widely regarded as the cellular basis of learning and memory. Understanding the molecular mechanism of synaptic plasticity has been one of center pieces of neuroscience research for more than three decades. It has been well known that the trafficking of α-amino-3-hydroxy-5-methylisoxazoloe-4-propionic acid- (AMPA-) type, N-methyl-D-aspartate- (NMDA-) type glutamate receptors to and from synapses is a key molecular event underlying many forms of synaptic plasticity. Kainate receptors are another type of glutamate receptors playing important roles in synaptic transmission. In addition, GABA receptors also play important roles in modulating the synaptic plasticity. Kinesin superfamily proteins (also known as KIFs) transport various cargos in both anterograde and retrograde directions through the interaction with different adaptor proteins. Recent studies indicate that KIFs regulate the trafficking of NMDA receptors, AMPA receptors, kainate receptors, and GABA receptors and thus play important roles in neuronal activity. Here we review the essential functions of KIFs in the trafficking of neuroreceptor and synaptic plasticity.

Synapse assembly and neurodevelopmental disorders

In this review we examine the current understanding of how genetic deficits associated with neurodevelopmental disorders may impact synapse assembly. We then go on to discuss how the critical periods for these genetic deficits will shape the nature of future clinical interventions.

Trafficking of kainate receptors

Ionotropic glutamate receptors (iGluRs) mediate the vast majority of excitatory neurotransmission in the central nervous system of vertebrates. In the protein family of iGluRs, kainate receptors (KARs) comprise the probably least well understood receptor class. Although KARs act as key players in the regulation of synaptic network activity, many properties and functions of these proteins remain elusive until now. Especially the precise pre-, extra-, and postsynaptic localization of KARs plays a critical role for neuronal function, as an unbalanced localization of KARs would ultimately lead to dysregulated neuronal excitability. Recently, important advances in the understanding of the regulation of surface expression, function, and agonist-dependent endocytosis of KARs have been achieved. Post-translational modifications like PKC-mediated phosphorylation and SUMOylation have been reported to critically influence surface expression and endocytosis, while newly discovered auxiliary proteins were shown to shape the functional properties of KARs.

Synaptic control of secretory trafficking in dendrites

Localized signaling in neuronal dendrites requires tight spatial control of membrane composition. Upon initial synthesis, nascent secretory cargo in dendrites exits the endoplasmic reticulum (ER) from local zones of ER complexity that are spatially coupled to post-ER compartments. Although newly synthesized membrane proteins can be processed locally, the mechanisms that control the spatial range of secretory cargo transport in dendritic segments are unknown. Here, we monitored the dynamics of nascent membrane proteins in dendritic post-ER compartments under regimes of low or increased neuronal activity. In response to activity blockade, post-ER carriers are highly mobile and are transported over long distances. Conversely, increasing synaptic activity dramatically restricts the spatial scale of post-ER trafficking along dendrites. This activity-induced confinement of secretory cargo requires site-specific phosphorylation of the kinesin motor KIF17 by Ca²⁺/calmodulin-dependent protein kinases (CaMK). Thus, the length scales of early secretory trafficking in dendrites are tuned by activity-dependent regulation of microtubule-dependent transport.

Spatial gene's (Tbata) implication in neurite outgrowth and dendrite patterning in hippocampal neurons

The unique architecture of neurons requires the establishment and maintenance of polarity, which relies in part on microtubule-based kinesin motor transport to deliver essential cargo into axons and dendrites. In developing neurons, kinesin trafficking is essential for delivering organelles and molecules that are crucial for elongation and guidance of the growing axonal and dendritic termini. In mature neurons, kinesin cargo delivery is essential for neuron dynamic physiological functions which are critical in brain development. In this work, we followed Spatial (Tbata) gene expression during primary hippocampal neuron development and showed that it is highly expressed during dendrite formation. Spatial protein exhibits a somatodendritic distribution and we show that the kinesin motor Kif17, among other dendrite specific kinesins, is crucial for Spatial localization to dendrites of hippocampal neurons. Furthermore, Spatial down regulation in primary hippocampal cells revealed a role for Spatial in maintaining neurons' polarity by ensuring proper neurite outgrowth. This polarity is specified by intrinsic and extracellular signals that allow neurons to determine axon and dendrite fate during development. Neurotrophic factors, such as the Nerve Growth Factor (NGF), are candidate extracellular polarity-regulating cues which are proposed to accelerate neuronal polarization by enhancing dendrite growth. Here, we show that NGF treatment increases Spatial expression in hippocampal neurons. Altogether, these data suggest that Spatial, in response to NGF and through its transport by Kif17, is crucial for neuronal polarization and can be a key regulator of neurite outgrowth.

MAPping out distribution routes for kinesin couriers

In the crowded environment of eukaryotic cells, diffusion is an inefficient distribution mechanism for cellular components. Long-distance active transport is required and is performed by molecular motors including kinesins. Furthermore, in highly polarised, compartmentalised and plastic cells such as neurons, regulatory mechanisms are required to ensure appropriate spatio-temporal delivery of neuronal components. The kinesin machinery has diversified into a large number of kinesin motor proteins as well as adaptor proteins that are associated with subsets of cargo. However, many mechanisms contribute to the correct delivery of these cargos to their target domains. One mechanism is through motor recognition of sub-domain-specific microtubule (MT) tracks, sign-posted by different tubulin isoforms, tubulin post-translational modifications, tubulin GTPase activity and MT-associated proteins (MAPs). With neurons as a model system, a critical review of these regulatory mechanisms is presented here, with a particular focus on the emerging contribution of compartmentalised MAPs. Overall, we conclude that - especially for axonal cargo - alterations to the MT track can influence transport, although in vivo, it is likely that multiple track-based effects act synergistically to ensure accurate cargo distribution.

The retinitis pigmentosa 28 protein FAM161A is a novel ciliary protein involved in intermolecular protein interaction and microtubule association

Loss-of-function mutations in the gene encoding FAM161A were recently discovered as the cause for RP28, an autosomal recessive form of retinitis pigmentosa. To initiate the characterization of the cellular role of FAM161A in the retina, we focused on its subcellular localization and conducted in vitro studies to identify FAM161A-interacting proteins and associated cellular structures. Immunohistochemistry revealed the presence of mouse FAM161A in the photoreceptor inner segments, the synaptic regions of the outer and inner plexiform layers and the ganglion cells. In mouse and human retinal sections from unfixed eyes, FAM161A localized to the ciliary region linking photoreceptor outer and inner segments. High-resolution immunofluorescence and immunoelectron microscopy mapped FAM161A to the connecting cilium, the basal body region and the adjacent centriole. Ectopic FAM161A was found in the centrosome and concentrated at the base of primary cilia in cultured cells. In addition, overexpressed FAM161A was clearly associated with microtubules during interphase and mitosis. The presence of FAM161A increased microtubule acetylation and stabilization. We further show that the evolutionarily conserved UPF0564 domain of FAM161A is crucial for its binding to microtubules and mediates homo- and heterotypic FAM161A and FAM161B interaction. In conclusion, our study shows that FAM161A is a microtubule-associated ciliary protein presumably involved in microtubule stabilization to maintain the microtubule tracks and/or in transport processes along microtubules in photoreceptors and other retinal cell types.

The kinesin superfamily protein KIF17: one protein with many functions

Kinesins are ATP-dependent molecular motors that carry cargos along microtubules, generally in an anterograde direction. They are classified into 14 distinct families with varying structural and functional characteristics. KIF17 is a member of the kinesin-2 family that is plus end-directed. It is a homodimer with a pair of head motor domains that bind microtubules, a coiled-coil stalk, and a tail domain that binds cargos. In neurons, KIF17 transports N-methyl-D-aspartate receptor NR2B subunit, kainate receptor GluR5, and potassium Kv4.2 channels from cell bodies exclusively to dendrites. These cargos are necessary for synaptic transmission, learning, memory, and other functions. KIF17's interaction with NXF2 enables the transport of mRNA bidirectionally in dendrites. KIF17 or its homolog OSM-3 also mediates intraflagellar transport of cargos to the distal tips of flagella or cilia, thereby aiding in ciliogenesis. In many invertebrate and vertebrate sensory cells, KIF17 delivers cargos that contribute to chemosensory perception and signal transduction. In vertebrate photoreceptors, KIF17 is necessary for outer segment development and disc morphogenesis. In the testis, KIF17 (KIF17b) mediates microtubule-independent delivery of ACT from the nucleus to the cytoplasm and microtubule-dependent transport of Spatial-ε, both are presumably involved in spermatogenesis. KIF17 is also implicated in epithelial polarity and morphogenesis, placental transport and development, and the development of specific brain regions. The transcriptional regulation of KIF17 has recently been found to be mediated by nuclear respiratory factor 1 (NRF-1), which also regulates NR2B as well as energy metabolism in neurons. Dysfunctions of KIF17 are linked to a number of pathologies.

Expression of GluK1c underlies the developmental switch in presynaptic kainate receptor function

Kainate-type glutamate receptors (KARs) regulate synaptic transmission and neuronal excitability via multiple mechanisms, depending on their subunit composition. Presynaptic KARs tonically depress glutamatergic transmission during restricted period of synapse development; however, the molecular basis behind this effect is unknown. Here, we show that the developmental and cell-type specific expression pattern of a KAR subunit splice variant, GluK1c, corresponds to the immature-type KAR activity in the hippocampus. GluK1c localizes to dendritic contact sites at distal axons, the distal targeting being promoted by heteromerization with the subunit GluK4. Presynaptic expression of GluK1c strongly suppresses glutamatergic transmission in cell-pairs in vitro and mimics the immature-type KAR activity at CA3-CA1 synapses in vivo, at a developmental stage when the endogenous expression is already downregulated. These data support a central role for GluK1c in mediating tonic inhibition of glutamate release and the consequent effects on excitability and activity-dependent fine-tuning of the developing hippocampal circuitry.

Endocytosis of the glutamate receptor subunit GluK3 controls polarized trafficking

Kainate receptors (KARs) are widely expressed in the brain and are present at both presynaptic and postsynaptic sites. GluK3-containing KARs are thought to compose presynaptic autoreceptors that facilitate hippocampal mossy fiber synaptic transmission. Here we identify molecular mechanisms that underlie the polarized trafficking of KARs composed of the GluK3b splice variant. Endocytosis followed by degradation is driven by a dileucine motif on the cytoplasmic C-terminal domain of GluK3b in heterologous cells, in cultured hippocampal neurons, and in dentate granule cells from organotypic slice cultures. The internalization of GluK3b is clathrin and dynamin2 dependent. GluK3b is differentially endocytosed in dendrites as compared to the axons. These data suggest that the polarized trafficking of KARs in neurons could be controlled by the regulation of receptor endocytosis.

Synaptic targeting and functional modulation of GluK1 kainate receptors by the auxiliary neuropilin and tolloid-like (NETO) proteins

Auxiliary proteins modify the biophysical function and pharmacological properties of ionotropic glutamate receptors and likely are important components of receptor signaling complexes in vivo. The neuropilin and tolloid-like proteins (NETO) 1 and NETO2, two closely related CUB domain-containing integral membrane proteins, were identified recently as auxiliary proteins that slowed GluK2a kainate receptor current kinetics without impacting receptor membrane localization. Here we demonstrate that NETO2 profoundly slows the desensitization rate of GluK1 kainate receptors, promotes plasma membrane localization of transfected receptors in heterologous cells and rat hippocampal neurons, and targets GluK1-containing receptors to synapses. Conversely, the closely related protein NETO1 increases the rate of GluK1 receptor desensitization. Incorporation of NETO proteins into kainate receptor-signaling complexes therefore extends the temporal range of receptor gating by over an order of magnitude. The presence of these auxiliary proteins could underlie some of the unusual aspects of kainate receptor function in the mammalian CNS.

Bioinformatic analyses identifies novel protein-coding pharmacogenomic markers associated with paclitaxel sensitivity in NCI60 cancer cell lines

BACKGROUND

Paclitaxel is a microtubule-stabilizing drug that has been commonly used in treating cancer. Due to genetic heterogeneity within patient populations, therapeutic response rates often vary. Here we used the NCI60 panel to identify SNPs associated with paclitaxel sensitivity. Using the panel's GI50 response data available from Developmental Therapeutics Program, cell lines were categorized as either sensitive or resistant. PLINK software was used to perform a genome-wide association analysis of the cellular response to paclitaxel with the panel's SNP-genotype data on the Affymetrix 125 k SNP array. FastSNP software helped predict each SNP's potential impact on their gene product. mRNA expression differences between sensitive and resistant cell lines was examined using data from BioGPS. Using Haploview software, we investigated for haplotypes that were more strongly associated with the cellular response to paclitaxel. Ingenuity Pathway Analysis software helped us understand how our identified genes may alter the cellular response to paclitaxel.

RESULTS

43 SNPs were found significantly associated (FDR<0.005) with paclitaxel response, with 10 belonging to protein-coding genes (CFTR, ROBO1, PTPRD, BTBD12, DCT, SNTG1, SGCD, LPHN2, GRIK1, ZNF607). SNPs in GRIK1, DCT, SGCD and CFTR were predicted to be intronic enhancers, altering gene expression, while SNPs in ZNF607 and BTBD12 cause conservative missense mutations. mRNA expression analysis supported these findings as GRIK1, DCT, SNTG1, SGCD and CFTR showed significantly (p<0.05) increased expression among sensitive cell lines. Haplotypes found in GRIK1, SGCD, ROBO1, LPHN2, and PTPRD were more strongly associated with response than their individual SNPs.

CONCLUSIONS

Our study has taken advantage of available genotypic data and its integration with drug response data obtained from the NCI60 panel. We identified 10 SNPs located within protein-coding genes that were not previously shown to be associated with paclitaxel response. As only five genes showed differential mRNA expression, the remainder would not have been detected solely based on expression data. The identified haplotypes highlight the role of utilizing SNP combinations within genomic loci of interest to improve the risk determination associated with drug response. These genetic variants represent promising biomarkers for predicting paclitaxel response and may play a significant role in the cellular response to paclitaxel.

Expression of kinesin superfamily genes in cultured hippocampal neurons

The nature of the different kinesin family members that function in a single, specific neuron type has not been systematically investigated. Here, we used quantitative real-time PCR to analyze the developmental expression patterns of kinesin family genes in cultured mouse hippocampal neurons, a highly homogeneous population of nerve cells. For purposes of comparison, we also determined the set of kinesins expressed in embryonic and adult hippocampal tissue. Twenty kinesins are expressed at moderate-to-high levels in mature hippocampal cultures. These include 9 plus-end directed kinesins from the Kinesin-1, -2, and -3 families that are known to mediate organelle transport and 6 other members of the Kinesin-3 and -4 families that are candidate organelle motors. Hippocampal cultures express high levels of a Kinesin-13, which regulates microtubule depolymerization, and moderate-to-high levels of Kinesin-9 and -14 family members, whose functions are not understood. Twelve additional kinesins, including 10 known mitotic kinesins, are expressed at moderate levels in embryonic hippocampus but at very low levels in mature cultures and the adult hippocampus. Collectively, our findings suggest that kinesins subserve diverse functions within a single type of neuron.

De novo truncating mutation in Kinesin 17 associated with schizophrenia

BACKGROUND

Schizophrenia (SCZ) is one of the most disabling psychiatric disorders. It is thought to be due to a complex interplay between polygenic and various environmental risk factors, although recent reports on genomic copy number variations suggest that a fraction of the cases could result from variably penetrant de novo variants. The gene encoding the synaptic motor protein kinesin 17 (KIF17) involved in glutamatergic synapse is a candidate gene for SCZ.

METHODS

As part of our Synapse to Disease project, we resequenced KIF17 in a cohort of individuals with sporadic SCZ (188 subjects). Additional populations included autism spectrum disorder (142 subjects), nonsyndromic mental retardation (95 subjects), and control subjects (568 subjects). Functional validation of the human mutation was done in developing zebrafish.

RESULTS

Here we report the identification of a de novo nonsense truncating mutation in one patient with SCZ, in kinesin 17, a synaptic motor protein. No de novo or truncating KIF17 mutations were found in the additional samples. We further validated the pathogenic nature of this mutation by knocking down its expression in zebrafish embryos, which resulted in a developmental defect.

CONCLUSIONS

Together our findings suggest that disruption of KIF17, although rare, could result in a schizophrenia phenotype and emphasize the possible involvement of rare de novo mutations in this disorder.

Expression of the NR2B-NMDA receptor trafficking complex in prefrontal cortex from a group of elderly patients with schizophrenia

Dysregulated glutamate neurotransmission has been implicated in the pathophysiology of schizophrenia. In particular, hypofunction of the NMDA glutamate receptor has been proposed to play an important role in mediating cognitive deficits in patients. The two NMDA receptor subunits, NR2A and NR2B, are distinctly regulated during development and are associated with different intracellular pathways and functions, which suggest that these receptors play separate roles in the control of higher cognitive functions such as learning and memory. Trafficking of the NR2B subunit-containing receptor is regulated by a microtubule-associated trafficking complex consisting of the KIF17, APBA1, CASK, and mLin7 proteins. Several studies have demonstrated an integrated functional regulation of this trafficking complex with NR2B receptor subunit expression, which in turn has been linked to higher cognitive functions. In the present work, we investigated whether expression of this NR2B-associated trafficking complex might be abnormal in schizophrenia. We analyzed the expression of KIF17, APBA1, CASK, mLin7A and mLin7C in postmortem brain from patients with schizophrenia a comparison group. Analysis of transcripts for all of these proteins revealed particularly prominent expression in cortical layer III and layer IV, which overlapped with NR2B but not NR2A transcripts. We found altered expression of transcripts for the CASK, ABPA1, and mLin7 molecules and the CASK, mLin7 proteins, suggesting that NR2B-containing NMDA receptor transport could be selectively compromised in schizophrenia, and that these changes likely involve altered NR2B function in a subset of cortical neurons.

Intraflagellar transport molecules in ciliary and nonciliary cells of the retina

The assembly and maintenance of cilia require intraflagellar transport (IFT), a process mediated by molecular motors and IFT particles. Although IFT is a focus of current intense research, the spatial distribution of individual IFT proteins remains elusive. In this study, we analyzed the subcellular localization of IFT proteins in retinal cells by high resolution immunofluorescence and immunoelectron microscopy. We report that IFT proteins are differentially localized in subcompartments of photoreceptor cilia and in defined periciliary target domains for cytoplasmic transport, where they are associated with transport vesicles. IFT20 is not in the IFT core complex in photoreceptor cilia but accompanies Golgi-based sorting and vesicle trafficking of ciliary cargo. Moreover, we identify a nonciliary IFT system containing a subset of IFT proteins in dendrites of retinal neurons. Collectively, we provide evidence to implicate the differential composition of IFT systems in cells with and without primary cilia, thereby supporting new functions for IFT beyond its well-established role in cilia.

Mixed microtubules steer dynein-driven cargo transport into dendrites

BACKGROUND

To establish and maintain their polarized morphology, neurons employ active transport driven by molecular motors to sort cargo between axons and dendrites. However, the basic traffic rules governing polarized transport on neuronal microtubule arrays are unclear.

RESULTS

Here we show that the microtubule minus-end-directed motor dynein is required for the polarized targeting of dendrite-specific cargo, such as AMPA receptors. To directly examine how dynein motors contribute to polarized dendritic transport, we established a trafficking assay in hippocampal neurons to selectively probe specific motor protein activity. This revealed that, unlike kinesins, dynein motors drive cargo selectively into dendrites, governed by their mixed microtubule array. Moreover, axon-specific cargos, such as presynaptic vesicle protein synaptophysin, are redirected to dendrites by coupling to dynein motors. Quantitative modeling demonstrated that bidirectional dynein-driven transport on mixed microtubules provides an efficient mechanism to establish a stable density of continuously renewing vesicles in dendrites.

CONCLUSIONS

These results demonstrate a powerful approach to study specific motor protein activity inside living cells and imply a key role for dynein in dendritic transport. We propose that dynein establishes the initial sorting of dendritic cargo and additional motor proteins assist in subsequent delivery.

The microtubule interacting drug candidate NAP protects against kainic acid toxicity in a rat model of epilepsy

NAP (NAPVSIPQ, generic name, davunetide), a neuroprotective peptide in clinical development for neuroprotection against Alzheimer's disease and other neurodegenerative indications, has been recently shown to provide protection against kainic acid excitotoxicity in hippocampal neuronal cultures. In vivo, kainic acid toxicity models status epilepticus that is associated with hippocampal cell death. Kainic acid toxicity has been previously suggested to involve the microtubule cytoskeleton and NAP is a microtubule-interacting drug candidate. In the current study, kainic acid-treated rats showed epileptic seizures and neuronal death. Injection of NAP into the dentate gyrus partially protected against kainic acid-induced CA3 neuron death. Microarray analysis (composed of > 31 000 probe sets, analyzing over 30 000 transcripts and variants from over 25 000 well-substantiated rat genes) in the kainic acid-injured rat brain revealed multiple changes in gene expression, which were prevented, in part, by NAP treatment. Selected transcripts were further verified by reverse transcription coupled with quantitative real-time polymerase chain reaction. Importantly, among the transcripts regulated by NAP were key genes associated with proconvulsant properties and with long-lasting changes that underlie the epileptic state, including activin A receptor (associated with apoptosis), neurotensin (associated with proper neurotransmission) and the Wolfram syndrome 1 homolog (human, associated with neurodegeneration). These data suggest that NAP may provide neuroprotection in one of the most serious neurological conditions, epilepsy.

Kinesin superfamily motor proteins and intracellular transport

Intracellular transport is fundamental for cellular function, survival and morphogenesis. Kinesin superfamily proteins (also known as KIFs) are important molecular motors that directionally transport various cargos, including membranous organelles, protein complexes and mRNAs. The mechanisms by which different kinesins recognize and bind to specific cargos, as well as how kinesins unload cargo and determine the direction of transport, have now been identified. Furthermore, recent molecular genetic experiments have uncovered important and unexpected roles for kinesins in the regulation of such physiological processes as higher brain function, tumour suppression and developmental patterning. These findings open exciting new areas of kinesin research.

The presence of kinesin superfamily motor proteins KIFC1 and KIF17 in normal and pathological human placenta

Kinesin superfamily proteins (KIFs) are motor proteins that participate in chromosomal and spindle movements during mitosis and meiosis, and transport membranous organelles and macromolecules fundamental for cellular functions. Although the roles of KIFs in axonal and dendritic transports have been studied extensively, their role in intracellular transport in general is less well known. The diversity of kinesins suggests that each kinesin may have a specific function. Therefore, in this study we aimed to investigate the presence and cellular localization of KIFC1 and KIF17 in normal and pathological human placentas. First-trimester (22-56 days) and normal, preeclamptic (PE), and diabetic-term placental tissues were obtained and further studied by immunohistochemistry (IHC) and Western blot methods. KIFC1 was mainly localized to the syncytiotrophoblast both in early and term placental samples. However, a stronger immunoreactivity was observed both in PE and diabetic placentas compared to normal-term placentas. KIF17 was most intensively localized in developing vascular endothelium in early pregnancy. Even though KIF17 was moderately stained in the endothelium of villi from normal human-term placentas, stronger immunoreactivity was observed in all types of villi of both PE and diabetic placentas. Western blotting of tissue extracts confirmed the IHC results. Here, we demonstrate the presence of KIFC1 and KIF17 in human placenta for the first time. The intense expression of KIFC1 in syncytiotrophoblast and KIF17 in vascular endothelium suggests that both the proteins might be important in a cargo-transport system. An increased expression pattern of both KIFC1 and KIF17 in PE and diabetes might suggest that these proteins may be involved in complex trophoblast functions and placental pathologies. Further studies will clarify the physiological role of KIFs in human placental transport and development.

Calcium-permeable presynaptic kainate receptors involved in excitatory short-term facilitation onto somatostatin interneurons during natural stimulus patterns

Schaffer collateral synapses in hippocampus show target-cell specific short-term plasticity. Using GFP-expressing Inhibitory Neuron (GIN) transgenic mice that express enhanced green fluorescent protein (EGFP) in a subset of somatostatin-containing interneurons (SOM interneurons), we previously showed that Schaffer collateral synapses onto SOM interneurons in stratum (S.) radiatum have unusually large (up to 6-fold) paired-pulse facilitation. This results from a low initial release probability and the enhancement of facilitation by synaptic activation of presynaptic kainate receptors. Here we further investigate the properties of these kainate receptors and examine their effects on short-term facilitation during physiologically derived stimulation patterns, using excitatory postsynaptic currents recorded in S. radiatum interneurons during Schaffer collateral stimulation in acute slices from juvenile GIN mice. We find that GluR5 and GluR6 antagonists decrease short-term facilitation at Schaffer collateral synapses onto SOM interneurons with no additive effects, suggesting that the presynaptic kainate receptors are heteromers containing both GluR5 and GluR6 subunits. The calcium-permeable receptor antagonist 1-napthyl acetyl spermine (NASPM) both mimics and occludes the effect of the kainate receptor antagonists, indicating that the presynaptic kainate receptors are calcium permeable. Furthermore, Schaffer collateral synapses onto SOM interneurons show up to 11-fold short-term facilitation during physiologically derived stimulus patterns, in contrast to other interneurons that have less than 1.5-fold facilitation. Blocking the kainate receptors reduces facilitation in SOM interneurons by approximately 50% during the physiologically derived patterns and reduces the dynamic range. Activation of calcium-permeable kainate receptors containing GluR5/GluR6 causes a dramatic increase in short-term facilitation during physiologically derived stimulus patterns, a mechanism likely to be important in regulating the strength of Schaffer collateral synapses onto SOM interneurons in vivo.

Expression, transport, and axonal sorting of neuronal CCL21 in large dense-core vesicles

Neurons are highly polarized cells, and neuron-neuron communication is based on directed transport and release of neurotransmitters, neuropeptides, and neurotrophins. Directed communication may also be attributed to neuron-microglia signaling, since neuronal damage can induce a microglia reaction at specific sites only. However, the mechanism underlying this site-specific microglia reaction is not yet understood. Neuronal CCL21 is a microglia-activating chemokine, which in brain is solely found in endangered neurons and is therefore a candidate for neuron-microglia signaling. Here we present that neuronal CCL21 is sorted into large dense-core vesicles, the secretory granules of the regulated release pathway of neurons. Live-cell imaging studies show preferential sorting of CCL21-containing vesicles into axons, indicating its directed transport. Thus, mouse neurons express and transport a microglia activating factor very similar to signaling molecules used in neuron-neuron communication. These data show for the first time the directed transport of a microglia activating factor in neurons and corroborate the function of neuronal CCL21 in directed neuron-microglia communication.

Molecular determinants of kainate receptor trafficking

Glutamate receptors of the kainate subtype are ionotropic receptors that play a key role in the modulation of neuronal network activity. The role of kainate receptors depends on their precise membrane and subcellular localization in presynaptic, extrasynaptic and postsynaptic domains. These receptors are composed of the combination of five subunits, three of them having several splice variants. The subunits and splice variants show great divergence in their C-terminal cytoplasmic tail domains, which have been implicated in intracellular trafficking of homomeric and heteromeric receptors. Differential trafficking of kainate receptors to specific neuronal compartments likely relies on interactions between the different kainate receptor subunits with distinct subsets of protein partners that interact with C-terminal domains. These C-terminal domains have also been implicated in the degradation of kainate receptors. Finally, the phosphorylation of the C-terminal domain regulates receptor trafficking and function. This review summarizes our knowledge on the regulation of membrane delivery and trafficking of kainate receptors implicating C-terminal domains of the different isoforms and focuses on the identification and characterization of the function of interacting partners.

The homodimeric kinesin, Kif17, is essential for vertebrate photoreceptor sensory outer segment development

Sensory cilia and intraflagellar transport (IFT), a pathway essential for ciliogenesis, play important roles in embryonic development and cell differentiation. In vertebrate photoreceptors IFT is required for the early development of ciliated sensory outer segments (OS), an elaborate organelle that sequesters the many proteins comprising the phototransduction machinery. As in other cilia and flagella, heterotrimeric members of the kinesin 2 family have been implicated as the anterograde IFT motor in OS. However, in Caenorhabditis elegans, OSM-3, a homodimeric kinesin 2 motor, plays an essential role in some, but not all sensory cilia. Kif17, a vertebrate OSM-3 homologue, is known for its role in dendritic trafficking in neurons, but a function in ciliogenesis has not been determined. We show that in zebrafish Kif17 is widely expressed in the nervous system and retina. In photoreceptors Kif17 co-localizes with IFT proteins within the OS, and co-immunoprecipitates with IFT proteins. Knockdown of Kif17 has little if any effect in early embryogenesis, including the formation of motile sensory cilia in the pronephros. However, OS formation and targeting of the visual pigment protein is severely disrupted. Our analysis shows that Kif17 is essential for photoreceptor OS development, and suggests that Kif17 plays a cell type specific role in vertebrate ciliogenesis.