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Abstract Motor proteins, encoded by Kinesin superfamily (KIF) genes, are critical for brain development and plasticity. Increasing studies reported KIF’s roles in neurodevelopmental disorders. Here, a 6 years and 3 months‐old Chinese boy with markedly symptomatic epilepsy, intellectual disability, brain atrophy, and psychomotor retardation was investigated. His parents and younger sister were phenotypically normal and had no disease‐related family history. Whole exome sequencing identified a novel heterozygous in‐frame deletion (c.265_267delTCA) in exon 3 of the KIF5C in the proband, resulting in the removal of evolutionarily highly conserved p.Ser90, located in its ATP‐binding domain. Sanger sequencing excluded the proband's parents and family members from harboring this variant. The activity of ATP hydrolysis in vitro was significantly reduced as predicted. Immunofluorescence studies showed wild‐type KIF5C was widely distributed throughout the cytoplasm, while mutant KIF5C was colocalized with microtubules. The live‐cell imaging of the cargo‐trafficking assay revealed that mutant KIF5C lost the peroxisome‐transporting ability. Drosophila models also confirmed p.Ser90del's essential role in nervous system development. This study emphasized the importance of the KIF5C gene in intracellular cargo‐transport as well as germline variants that lead to neurodevelopmental disorders and might enable clinicians for timely and accurate diagnosis and disease management in the future.

Abstract Mice with the C3H background show greater behavioral propensity for schizophrenia, including lower prepulse inhibition (PPI), than C57BL/6 (B6) mice. To characterize as‐yet‐unknown pathophysiologies of schizophrenia, we undertook proteomics analysis of the brain in these strains, and detected elevated levels of Mpst, a hydrogen sulfide (H2S)/polysulfide‐producing enzyme, and greater sulfide deposition in C3H than B6 mice. Mpst‐deficient mice exhibited improved PPI with reduced storage sulfide levels, while Mpst‐transgenic (Tg) mice showed deteriorated PPI, suggesting that “sulfide stress” may be linked to PPI impairment. Analysis of human samples demonstrated that the H2S/polysulfides production system is upregulated in schizophrenia. Mechanistically, the Mpst‐Tg brain revealed dampened energy metabolism, while maternal immune activation model mice showed upregulation of genes for H2S/polysulfides production along with typical antioxidative genes, partly via epigenetic modifications. These results suggest that inflammatory/oxidative insults in early brain development result in upregulated H2S/polysulfides production as an antioxidative response, which in turn cause deficits in bioenergetic processes. Collectively, this study presents a novel aspect of the neurodevelopmental theory for schizophrenia, unraveling a role of excess H2S/polysulfides production.

Summary: In schizophrenia (SCZ), neurons in the brain tend to undergo gross morphological changes, but the related molecular mechanism remains largely elusive. Using Kif3b+/− mice as a model with SCZ-like behaviors, we found that a high-betaine diet can significantly alleviate schizophrenic traits related to neuronal morphogenesis and behaviors. According to a deficiency in the transport of collapsin response mediator protein 2 (CRMP2) by the KIF3 motor, we identified a significant reduction in lamellipodial dynamics in developing Kif3b+/− neurons as a cause of neurite hyperbranching. Betaine administration significantly decreases CRMP2 carbonylation, which enhances the F-actin bundling needed for proper lamellipodial dynamics and microtubule exclusion and may thus functionally compensate for KIF3 deficiency. Because the KIF3 expression levels tend to be downregulated in the human prefrontal cortex of the postmortem brains of SCZ patients, this mechanism may partly participate in human SCZ pathogenesis, which we hypothesize could be alleviated by betaine administration.

Summary: Kinesin superfamily proteins (KIFs) are molecular motors that typically alter the subcellular localization of their cargos. However, the atypical kinesin KIF26A does not serve as a motor but can bind microtubules and affect cellular signaling cascades. Here, we show that KIF26A maintains intracellular calcium homeostasis and negatively regulates nociceptive sensation. Kif26a−/− mice exhibit intense and prolonged nociceptive responses. In their primary sensory neurons, excessive inhibitory phosphorylation of plasma membrane Ca2+ ATPase (PMCA) mediated by focal adhesion kinase (FAK) rendered the Ca transients resistant to termination, and the peripheral axonal outgrowth was significantly enhanced. Upstream, KIF26A is directly associated with a FERM domain of FAK and antagonizes FAK function in integrin-Src family kinase (SFK)-FAK signaling, possibly through steric hindrance and localization to cytoplasmic microtubules. : Wang et al. establish a mouse model of pain by deleting the Kif26a gene, which encodes an atypical kinesin. The nociceptive response of this model is abnormally prolonged. KIF26A sequesters FAK onto cytoplasmic microtubules and facilitates Ca pump activity, which leads to prolonged pain response. Keywords: kinesin, KIF26A, integrin, focal adhesion kinase, plasma membrane Ca ATPase, Ca homeostasis, sensory neurons, nociceptive response, prolonged pain, mouse model

Summary: Fear extinction is a component of cognitive flexibility that is relevant for important psychiatric diseases, but its molecular mechanism is still largely elusive. We established mice lacking the kinesin-4 motor KIF21B as a model for fear extinction defects. Postsynaptic NMDAR-dependent long-term depression (LTD) is specifically impaired in knockouts. NMDAR-mediated LTD-causing stimuli induce dynamic association of KIF21B with the Rac1GEF subunit engulfment and cell motility protein 1 (ELMO1), leading to ELMO1 translocation out of dendritic spines and its sequestration in endosomes. This process may essentially terminate transient activation of Rac1, shrink spines, facilitate AMPAR endocytosis, and reduce postsynaptic strength, thereby forming a mechanistic link to LTD expression. Antagonizing ELMO1/Dock Rac1GEF activity by the administration of 4-[3′-(2″-chlorophenyl)-2′-propen-1′-ylidene]-1-phenyl-3,5-pyrazolidinedione (CPYPP) significantly reverses the knockout phenotype. Therefore, we propose that KIF21B-mediated Rac1 inactivation is a key molecular event in NMDAR-dependent LTD expression underlying cognitive flexibility in fear extinction. : Morikawa et al. establish a mouse model lacking NMDAR-mediated cognitive flexibility by deleting the Kif21b kinesin gene. The mouse is impaired in terminating a Rac1 activity cycle by ELMO1 sequestration for LTD expression and treatable by the Rac1GEF inhibitor CPYPP. These findings have implications for further study of cognitive flexibility. Keywords: kinesin, KIF21B, ELMO1, cognitive flexibility, fear extinction, synaptic plasticity, LTD, NMDAR-mediated LTD, Rac1 activity cycle, CPYPP

Microtubules (MTs) are dynamic structures that are fundamental for cell morphogenesis and motility. MT-associated motors work efficiently to perform their functions. Unlike other motile kinesins, KIF2 catalytically depolymerizes MTs from the peeled protofilament end during ATP hydrolysis. However, the detailed mechanism by which KIF2 drives processive MT depolymerization remains unknown. To elucidate the catalytic mechanism, the transitional KIF2-tubulin complex during MT depolymerization was analyzed through multiple methods, including atomic force microscopy, size-exclusion chromatography, multi-angle light scattering, small-angle X-ray scattering, analytical ultracentrifugation, and mass spectrometry. The analyses outlined the conformation in which one KIF2core domain binds tightly to two tubulin dimers in the middle pre-hydrolysis state during ATP hydrolysis, a process critical for catalytic MT depolymerization. The X-ray crystallographic structure of the KIF2core domain displays the activated conformation that sustains the large KIF2-tubulin 1:2 complex.

Summary: Acute kidney injury (AKI) is characterized by mitochondrial dysfunction and activation of the innate immune system. The cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway detects cytosolic DNA and induces innate immunity. Here, we investigate the role of mitochondrial damage and subsequent activation of the cGAS-STING pathway using a genetically engineered animal model of cisplatin-induced AKI and cultured tubular cells. Cisplatin induced mtDNA leakage into the cytosol—probably through BCL-2-like protein 4 (BAX) pores in the mitochondrial outer membrane—in tubules, with subsequent activation of the cGAS-STING pathway, thereby triggering inflammation and AKI progression, which is improved in STING-deficient mice. STING knockdown in cultured tubular cells ameliorates inflammatory responses induced by cisplatin. mtDNA depletion and repletion studies support tubular inflammatory responses via the cGAS-STING signal activation by cytosolic mtDNA. Therefore, we conclude that mitochondrial dysfunction and subsequent activation of the mtDNA-cGAS-STING pathway is a critical regulator of kidney injury. : Acute kidney injury (AKI) is associated with tubular inflammation and mitochondrial dysfunction. Maekawa et al. reveal that tubular mitochondrial damage leads to mtDNA leakage into the cytosol, probably via BAX pores on the mitochondria, activating cGAS-STING signaling and subsequent tubular inflammation in cisplatin-induced AKI. Suppression of the STING ameliorates tubular inflammation and progression of AKI. Keywords: acute kidney injury, tubular cells, mitochondrial DNA, inflammation, cGAS-STING pathway, cisplatin nephrotoxicity

Summary: The axon initial segment (AIS) is a compartment that serves as a molecular barrier to achieve axon-dendrite differentiation. Distribution of specific proteins during early neuronal development has been proposed to be critical for AIS construction. However, it remains unknown how these proteins are specifically targeted to the proximal axon within this limited time period. Here, we reveal spatiotemporal regulation driven by the microtubule (MT)-based motor KIF3A/B/KAP3 that transports TRIM46, influenced by a specific MARK2 phosphorylation cascade. In the proximal part of the future axon under low MARK2 activity, the KIF3/KAP3 motor recognizes TRIM46 as cargo and transports it to the future AIS. In contrast, in the somatodendritic area under high MARK2 activity, KAP3 phosphorylated at serine 60 by MARK2 cannot bind with TRIM46 and be transported. This spatiotemporal regulation between KIF3/KAP3 and TRIM46 under specific MARK2 activity underlies the specific transport needed for axonal differentiation. : Ichinose et al. demonstrate that the KIF3/KAP3/TRIM46 protein complex spatiotemporally facilitates axonal differentiation. Unphosphorylated KAP3 can bind to TRIM46 and transport it to the axon initial segment (AIS) during neuronal polarization. This mechanism is facilitated by a biased distribution of MARK2 at the somatodendritic site. Keywords: kinesin, KIF3, kifap3, axonal transport, axon initial segment, axon differentiation, TRIM46, Par1b/MARK2

Kinesin motor proteins transport intracellular cargoes throughout cells by hydrolyzing ATP and moving along microtubule tracks. Intramolecular autoinhibitory interactions have been shown for several kinesins in vitro; however, the physiological significance of autoinhibition remains poorly understood. Here, we identified four mutations in the stalk region and motor domain of the synaptic vesicle (SV) kinesin UNC-104/KIF1A that specifically disrupt autoinhibition. These mutations augment both microtubule and cargo vesicle binding in vitro. In vivo, these mutations cause excessive activation of UNC-104, leading to decreased synaptic density, smaller synapses, and ectopic localization of SVs in the dendrite. We also show that the SV-bound small GTPase ARL-8 activates UNC-104 by unlocking the autoinhibition. These results demonstrate that the autoinhibitory mechanism is used to regulate the distribution of transport cargoes and is important for synaptogenesis in vivo.

Kinesin super family protein 2A (KIF2A), an ATP-dependent microtubule (MT) destabilizer, regulates cell migration, axon elongation, and pruning in the developing nervous system. KIF2A mutations have recently been identified in patients with malformed cortical development. However, postnatal KIF2A is continuously expressed in the hippocampus, in which new neurons are generated throughout an individual's life in established neuronal circuits. In this study, we investigated KIF2A function in the postnatal hippocampus by using tamoxifen-inducible Kif2a conditional knockout (Kif2a-cKO) mice. Despite exhibiting no significant defects in neuronal proliferation or migration, Kif2a-cKO mice showed signs of an epileptic hippocampus. In addition to mossy fiber sprouting, the Kif2a-cKO dentate granule cells (DGCs) showed dendro-axonal conversion, leading to the growth of many aberrant overextended dendrites that eventually developed axonal properties. These results suggested that postnatal KIF2A is a key length regulator of DGC developing neurites and is involved in the establishment of precise postnatal hippocampal wiring.

Neurons exhibit dynamic structural changes in response to extracellular stimuli. Microtubules (MTs) provide rapid and dramatic cytoskeletal changes within the structural framework. However, the molecular mechanisms and signaling networks underlying MT dynamics remain unknown. Here, we have applied a comprehensive and quantitative phospho-analysis of the MT destabilizer KIF2A to elucidate the regulatory mechanisms of MT dynamics within neurons in response to extracellular signals. Interestingly, we identified two different sets of KIF2A phosphorylation profiles that accelerate (A-type) and brake (B-type) the MT depolymerization activity of KIF2A. Brain-derived neurotrophic factor (BDNF) stimulates PAK1 and CDK5 kinases, which decrease the MT depolymerizing activity of KIF2A through B-type phosphorylation, resulting in enhanced outgrowth of neural processes. In contrast, lysophosphatidic acid (LPA) induces ROCK2 kinase, which suppresses neurite outgrowth from round cells via A-type phosphorylation. We propose that these two mutually exclusive forms of KIF2A phosphorylation differentially regulate neuronal morphogenesis during development.

Extensive axonal pruning and neuronal cell death are critical events for the development of the nervous system. Like neuronal cell death, axonal elimination occurs in discrete steps; however, the regulators of these processes remain mostly elusive. Here, we identify the kinesin superfamily protein 2A (KIF2A) as a key executor of microtubule disassembly and axonal breakdown during axonal pruning. Knockdown of Kif2a, but not other microtubule depolymerization or severing proteins, protects axonal microtubules from disassembly upon trophic deprivation. We further confirmed and extended this result to demonstrate that the entire degeneration process is delayed in neurons from the Kif2a knockout mice. Finally, we show that the Kif2a-null mice exhibit normal sensory axon patterning early during development, but abnormal target hyperinnervation later on, as they compete for limited skin-derived trophic support. Overall, these findings reveal a central regulatory mechanism of axonal pruning during development.

Molecular motors are fundamental to neuronal morphogenesis and function. However, the extent to which molecular motors are involved in higher brain functions remains largely unknown. In this study, we show that mice deficient in the kinesin family motor protein KIF13A (Kif13a−/− mice) exhibit elevated anxiety-related behavioral phenotypes, probably because of a reduction in 5HT1A receptor (5HT1AR) transport. The cell-surface expression level of the 5HT1AR was reduced in KIF13A-knockdown neuroblastoma cells and Kif13a−/− hippocampal neurons. Biochemical analysis showed that the forkhead-associated (FHA) domain of KIF13A and an intracellular loop of the 5HT1AR are the interface between the motor and cargo vesicles. A minimotor consisting of the motor and FHA domains is able to transport 5HT1AR-carrying organelles in in vitro reconstitution assays. Collectively, our results suggest a role for this molecular motor in anxiety control.

The kinesin-8 motor, KIF19A, accumulates at cilia tips and controls cilium length. Defective KIF19A leads to hydrocephalus and female infertility because of abnormally elongated cilia. Uniquely among kinesins, KIF19A possesses the dual functions of motility along ciliary microtubules and depolymerization of microtubules. To elucidate the molecular mechanisms of these functions we solved the crystal structure of its motor domain and determined its cryo-electron microscopy structure complexed with a microtubule. The features of KIF19A that enable its dual function are clustered on its microtubule-binding side. Unexpectedly, a destabilized switch II coordinates with a destabilized L8 to enable KIF19A to adjust to both straight and curved microtubule protofilaments. The basic clusters of L2 and L12 tether the microtubule. The long L2 with a characteristic acidic-hydrophobic-basic sequence effectively stabilizes the curved conformation of microtubule ends. Hence, KIF19A utilizes multiple strategies to accomplish the dual functions of motility and microtubule depolymerization by ATP hydrolysis.

The heavy chain of rat brain cytoplasmic dynein, composed of four putative nucleotide-finding consensus sequences GX4GK(T/S) in the middle one third region, and inferred protein sequence are analogous to the sea urchin flagellar beta-dynein by 27.0% and to Dictyostelium cytoplasmic dynein by 53.5%. The N-terminal one third of the heavy chain of rat brain cytoplasmic dynein resembles the Dictyostelium cytoplasmic dynein by 43.8% and has a low resemblance of 19.4% to the sea urchin flagellar dynein. The inference shows that the N-terminal regions are different between sea urchin and Dictyostelium dyneins and that the C-terminal two-thirds of the dyneins function in the microtubule-dependent motility action.

The mechanism of MT depolymerization by KIF-Ms is explored by solving the crystal structure of the minimal functional domain of mouse KIF2C, a member of KIF-M, in two different nucleotide states. The mutational analysis to support the structural implications is presented and a structural model for the mechanism for MT depolymerization by KIF-M is proposed.

Microtubule-associated protein 1A (MAP1A) is a member of the major non-motor microtubule-binding proteins. It has been suggested that MAP1A tethers NMDA receptors (NRs) to the cytoskeleton by binding with proteins postsynaptic density (PSD)-93 and PSD-95, although the function of MAP1A in vivo remains elusive. The present study demonstrates that mouse MAP1A plays an essential role in maintaining synaptic plasticity through an analysis of MAP1A knock-out mice. The mice exhibited learning disabilities, which correlated with decreased long-term potentiation and long-term depression in the hippocampal neurons, as well as a concomitant reduction in the extent of NR-dependent EPSCs. Surface expression of NR2A and NR2B subunits also decreased. Enhanced activity-dependent degradation of PSD-93 and reduced transport of NR2A/2B in dendrites was likely responsible for altered receptor function in neurons lacking MAP1A. These data suggest that tethering of NR2A/2B with the cytoskeleton through MAP1A is fundamental for synaptic function. [ABSTRACT FROM AUTHOR]

Epilepsy is a common neurological disease worldwide, and one of its causes is genetic abnormalities. Here, we identified a point mutation in KIF4A, a member of kinesin superfamily molecular motors, in patients with neurological disorders such as epilepsy, developmental delay, and intellectual disability. KIF4 is involved in the poly (ADP-ribose) polymerase (PARP) signaling pathway, and the mutation (R728Q) strengthened its affinity with PARP1 through elongation of the KIF4 coiled--coil domain. Behavioral tests showed that KIF4-mutant mice exhibited mild developmental delay with lower seizure threshold. Further experiments revealed that the KIF4 mutation caused aberrant morphology in dendrites and spines of hippocampal pyramidal neurons through PARP1-TrkB-KCC2 pathway. Furthermore, supplementing NAD, which activates PARP1, could modulate the TrkB-KCC2 pathway and rescue the seizure susceptibility phenotype of the mutant mice. Therefore, these findings indicate that KIF4 is engaged in a fundamental mechanism regulating seizure susceptibility and could be a potential target for epilepsy treatment. [ABSTRACT FROM AUTHOR]

Multifunctional low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) recognizes and internalizes a large number of diverse ligands, including LDL and factor VIII. However, little is known about the regulation of LRP1 endocytosis. Here, we show that a microtubule-based motor protein, KIF13B, in an unexpected and unconventional function, enhances caveolin-dependent endocytosis of LRP1. KIF13B was highly expressed in the liver and was localized on the sinusoidal plasma membrane of hepatocytes. KIF13B knockout (KO) mice showed elevated levels of serum cholesterol and factor VIII, and KO MEFs showed decreased uptake of LDL. Exogenous KIF13B, initially localized on the plasma membrane with caveolae, was translocated to the vesicles in the cytoplasm with LRP1 and caveolin-1. KIF13B bound to hDLGl and utrophin, which, in turn, bound to LRP1 and caveolae, respectively. These linkages were required for the KIF13B-enhanced endocytosis of LRP1. Thus, we propose that KIF13B, working as a scaffold, recruits LRP1 to caveolae via LRP1-hDLGl-KIF13B-utrophin-caveolae linkage and enhances the endocytosis of LRP1. [ABSTRACT FROM AUTHOR]

Kinesin-1, the founding member of the kinesin superfamily of proteins, is known to use only a subset of microtubules for transport in living cells. This biased use of microtubules is proposed as the guidance cue for polarized transport in neurons, but the underlying mechanisms are still poorly understood. Here, we report that kinesin-1 binding changes the microtubule lattice and promotes further kinesin-1 binding. This high-affinity state requires the binding of kinesin-1 in the nucleotidefree state. Microtubules return to the initial low-affinity state by washing out the binding kinesin-1 or by the binding of non-hydrolyzable ATP analogue AMP PNP to kinesin-1. X-ray fiber diffraction, fluorescence speckle microscopy, and secondharmonic generation microscopy, as well as cryo-EM, collectively demonstrated that the binding of nucleotide-free kinesin-1 to GDP microtubules changes the conformation of the GDP microtubule to a conformation resembling the GTP microtubule. [ABSTRACT FROM AUTHOR]

KIF1Bβ is a kinesin-3 family anterograde motor protein essential for neuronal development, viability, and function. KIF1Bβ mutations have previously been reported in a limited number of pedigrees of Charcot-Marie-Tooth disease type 2A (CMT2A) neuropathy. However, the gene responsible for CMT2A is still controversial, and the mechanism of pathogenesis remains elusive. In this study, we show that the receptor tyrosine kinase IGF1R is a new direct binding partner of KIF1Bβ, and its binding and transport is specifically impaired by the Y1087C mutation of KIF1Bβ, which we detected in hereditary neuropathic patients. The axonal outgrowth and IGF-I signaling of Kif1b-/- neurons were significantly impaired, consistent with decreased surface IGF1R expression. The complementary capacity of KIF1Bβ-Y1087C of these phenotypes was significantly impaired, but the binding capacity to synaptic vesicle precursors was not affected. These data have supported the relevance of KIF1Bβ in IGF1R transport, which may give new clue to the neuropathic pathogenesis. [ABSTRACT FROM AUTHOR]