Cytoplasmic dynein nomenclature

The function of the cytoplasmic dynein light chain PTKM23 in the transport of PTSMAD2 during spermatogenesis in Portunus trituberculatus†

Cytoplasmic dynein participates in transport functions and is essential in spermatogenesis. KM23 belongs to the dynein light chain family. The TGFβ signaling pathway is indispensable in spermatogenesis, and Smad2 is an important member of this pathway. We cloned PTKM23 and PTSMAD2 from Portunus trituberculatus and measured their expression during spermatogenesis. PTKM23 may be related to cell division, acrosome formation, and nuclear remodeling, and PTSMAD2 may participate in regulating the expression of genes related to spermatogenesis. We assessed the localization of PTKM23 with PTDHC and α-tubulin, and the results suggested that PTKM23 functions in intracellular transport during spermatogenesis. We knocked down PTKM23 in vivo, and the expression of p53, B-CATAENIN and CYCLIN B decreased significantly, further suggesting a role of PTKM23 in transport and cell division. The localization of PTDIC with α-tubulin and that of PTSMAD2 with PTDHC changed after PTKM23 knockdown. We transfected PTKM23 and PTSMAD2 into HEK-293 T cells and verified their colocalization. These results indicate that PTKM23 is involved in the assembly of cytoplasmic dynein and microtubules during spermatogenesis and that PTKM23 mediates the participation of cytoplasmic dynein in the transport of PTSMAD2 during spermatogenesis.

The BICD2 dynein cargo adaptor binds to the HPV16 L2 capsid protein and promotes HPV infection

During entry, human papillomavirus (HPV) traffics from the endosome to the trans Golgi network (TGN) and Golgi and then the nucleus to cause infection. Although dynein is thought to play a role in HPV infection, how this host motor recruits the virus to support infection and which entry step(s) requires dynein are unclear. Here we show that the dynein cargo adaptor BICD2 binds to the HPV L2 capsid protein during entry, recruiting HPV to dynein for transport of the virus along the endosome-TGN/Golgi axis to promote infection. In the absence of BICD2 function, HPV accumulates in the endosome and TGN and infection is inhibited. Cell-based and in vitro binding studies identified a short segment near the C-terminus of L2 that can directly interact with BICD2. Our results reveal the molecular basis by which the dynein motor captures HPV to promote infection and identify this virus as a novel cargo of the BICD2 dynein adaptor.

DYNLT1 promotes mitochondrial metabolism to fuel breast cancer development by inhibiting ubiquitination degradation of VDAC1

BACKGROUND

Mitochondrial metabolism has been proposed as an attractive target for breast cancer therapy. The discovery of new mechanisms underlying mitochondrial dysfunction will facilitate the development of new metabolic inhibitors to improve the clinical treatment of breast cancer patients. DYNLT1 (Dynein Light Chain Tctex-Type 1) is a key component of the motor complex that transports cellular cargo along microtubules in the cell, but whether and how DYNLT1 affects mitochondrial metabolism and breast cancer has not been reported.

METHODS

The expression levels of DYNLT1 were analyzed in clinical samples and a panel of cell lines. The role of DYNLT1 in breast cancer development was investigated using in vivo mouse models and in vitro cell assays, including CCK-8, plate cloning and transwell assay. The role of DYNLT1 in regulating mitochondrial metabolism in breast cancer development is examined by measuring mitochondrial membrane potential and ATP levels. To investigate the underlying molecular mechanism, many methods, including but not limited to Co-IP and ubiquitination assay were used.

RESULTS

First, we found that DYNLT1 was upregulated in breast tumors, especially in ER + and TNBC subtypes. DYNLT1 promotes the proliferation, migration, invasion and mitochondrial metabolism in breast cancer cells in vitro and breast tumor development in vivo. DYNLT1 colocalizes with voltage-dependent anion channel 1 (VDAC1) on mitochondria to regulate key metabolic and energy functions. Mechanistically, DYNLT1 stabilizes the voltage-dependent anion channel 1 (VDAC1) by hindering E3 ligase Parkin-mediated VDAC1 ubiquitination and degradation.

CONCLUSION

Our data demonstrate that DYNLT1 promotes mitochondrial metabolism to fuel breast cancer development by inhibiting Parkin-mediated ubiquitination degradation of VDAC1. This study suggests that mitochondrial metabolism can be exploited by targeting the DYNLT1-Parkin-VDAC1 axis to improve the ability of metabolic inhibitors to suppress cancers with limited treatment options, such as triple-negative breast cancer (TNBC).

Pain sensitivity related to gamma oscillation of parvalbumin interneuron in primary somatosensory cortex in Dync1i1-/- mice

Cytoplasmic dynein is an important intracellular motor protein that plays an important role in neuronal growth, axonal polarity formation, dendritic differentiation, and dendritic spine development among others. The intermediate chain of dynein, encoded by Dync1i1, plays a vital role in the dynein complex. Therefore, we assessed the behavioral and related neuronal activities in mice with dync1i1 gene knockout. Neuronal activities in primary somatosensory cortex were recorded by in vivo electrophysiology and manipulated by optogenetic and chemogenetics. Nociception of mechanical, thermal, and cold pain in Dync1i1^-/- mice were impaired. The activities of parvalbumin (PV) interneurons and gamma oscillation in primary somatosensory were also impaired when exposed to mechanical nociceptive stimulation. This neuronal dysfunction was rescued by optogenetic activation of PV neurons in Dync1i1^-/- mice, and mimicked by suppressing PV neurons using chemogenetics in WT mice. Impaired pain sensations in Dync1i1^-/- mice were correlated with impaired gamma oscillations due to a loss of interneurons, especially the PV type. This genotype-driven approach revealed an association between impaired pain sensation and cytoplasmic dynein complex.

The meiotic LINC complex component KASH5 is an activating adaptor for cytoplasmic dynein

Cytoplasmic dynein-driven movement of chromosomes during prophase I of mammalian meiosis is essential for synapsis and genetic exchange. Dynein connects to chromosome telomeres via KASH5 and SUN1 or SUN2, which together span the nuclear envelope. Here, we show that KASH5 promotes dynein motility in vitro, and cytosolic KASH5 inhibits dynein's interphase functions. KASH5 interacts with a dynein light intermediate chain (DYNC1LI1 or DYNC1LI2) via a conserved helix in the LIC C-terminal, and this region is also needed for dynein's recruitment to other cellular membranes. KASH5's N-terminal EF-hands are essential as the interaction with dynein is disrupted by mutation of key calcium-binding residues, although it is not regulated by cellular calcium levels. Dynein can be recruited to KASH5 at the nuclear envelope independently of dynactin, while LIS1 is essential for dynactin incorporation into the KASH5-dynein complex. Altogether, we show that the transmembrane protein KASH5 is an activating adaptor for dynein and shed light on the hierarchy of assembly of KASH5-dynein-dynactin complexes.

Dynein intermediate chains DYCI-1 and WDR-60 have specific functions in Caenorhabditis elegans

Dynein is a microtubule-dependent motor protein required for cell division, retrograde intracellular transport, and intraflagellar transport (IFT). Dynein 1 and dynein 2 serve as molecular motors in the cytoplasm and cilia, respectively. Each dynein consists of multiple subunits. Although the components of dynein 1 and dynein 2 are different and specific in most species, a previous study has suggested that dynein intermediate chain subunit DYCI-1 is shared by both dynein 1 and 2 in Caenorhabditis elegans (C. elegans). Here, we show that C. elegans has two dynein intermediate chains-DYCI-1 and WDR-60-and their functions are different. Mutational analysis showed that dyci-1 is essential for the retrograde axonal transport of synaptic vesicles. In the same mutant allele, IFT is not affected at all. Instead, wdr-60 is essential for IFT. Thus, we suggest that dynein 1 and dynein 2 have specific intermediate chains in C. elegans as in other organisms.

A Pseudorabies Virus Serine/Threonine Kinase, US3, Promotes Retrograde Transport in Axons via Akt/mToRC1

Infection of peripheral axons by alpha herpesviruses (AHVs) is a critical stage in establishing a lifelong infection in the host. Upon entering the cytoplasm of axons, AHV nucleocapsids and associated inner-tegument proteins must engage the cellular retrograde transport machinery to promote the long-distance movement of virion components to the nucleus. The current model outlining this process is incomplete, and further investigation is required to discover all viral and cellular determinants involved as well as the temporality of the events. Using a modified trichamber system, we have discovered a novel role of the pseudorabies virus (PRV) serine/threonine kinase US3 in promoting efficient retrograde transport of nucleocapsids. We discovered that transporting nucleocapsids move at similar velocities in both the presence and absence of a functional US3 kinase; however, fewer nucleocapsids are moving when US3 is absent, and they move for shorter periods of time before stopping, suggesting that US3 is required for efficient nucleocapsid engagement with the retrograde transport machinery. This led to fewer nucleocapsids reaching the cell bodies to produce a productive infection 12 h later. Furthermore, US3 was responsible for the induction of local translation in axons as early as 1 h postinfection (hpi) through the stimulation of a phosphatidylinositol 3-kinase (PI3K)/Akt-mToRC1 pathway. These data describe a novel role for US3 in the induction of local translation in axons during AHV infection, a critical step in transport of nucleocapsids to the cell body. IMPORTANCE Neurons are highly polarized cells with axons that can reach centimeters in length. Communication between axons at the periphery and the distant cell body is a relatively slow process involving the active transport of chemical messengers. There is a need for axons to respond rapidly to extracellular stimuli. Translation of repressed mRNAs present within the axon occurs to enable rapid, localized responses independently of the cell body. AHVs have evolved a way to hijack local translation in the axons to promote their transport to the nucleus. We have determined the cellular mechanism and viral components involved in the induction of axonal translation. The US3 serine/threonine kinase of PRV activates Akt-mToRC1 signaling pathways early during infection to promote axonal translation. When US3 is not present, the number of moving nucleocapsids and their processivity are reduced, suggesting that US3 activity is required for efficient engagement of nucleocapsids with the retrograde transport machinery.

Consensus nomenclature for dyneins and associated assembly factors

Dyneins are highly complex, multicomponent, microtubule-based molecular motors. These enzymes are responsible for numerous motile behaviors in cytoplasm, mediate retrograde intraflagellar transport (IFT), and power ciliary and flagellar motility. Variants in multiple genes encoding dyneins, outer dynein arm (ODA) docking complex subunits, and cytoplasmic factors involved in axonemal dynein preassembly (DNAAFs) are associated with human ciliopathies and are of clinical interest. Therefore, clear communication within this field is particularly important. Standardizing gene nomenclature, and basing it on orthology where possible, facilitates discussion and genetic comparison across species. Here, we discuss how the human gene nomenclature for dyneins, ODA docking complex subunits, and DNAAFs has been updated to be more functionally informative and consistent with that of the unicellular green alga Chlamydomonas reinhardtii, a key model organism for studying dyneins and ciliary function. We also detail additional nomenclature updates for vertebrate-specific genes that encode dynein chains and other proteins involved in dynein complex assembly.

Miro1 provides neuroprotection via the mitochondrial trafficking pathway in a rat model of traumatic brain injury

The outer mitochondrial membrane protein mitochondrial Rho-GTPase 1 (Miro1) is known to be involved in the regulation of mitochondrial transport required for neuronal protection. Previous reports established that disruption of Miro1-dependent mitochondrial movement could result in nervous system diseases such as Parkinson's disease and Alzheimer's disease. This study was designed to explore the expression and mechanisms of Miro1 in secondary brain injury after traumatic brain injury (TBI). A total of 115 male Sprague Dawley rats were used in the weight-drop TBI rat model, and Miro1 in vivo knockdown was performed 24 h before TBI modeling by treatment with Miro1 short-interfering RNA. Real-time polymerase chain reaction, western blot, immunofluorescence, adenosine triphosphate (ATP) level assay, neuronal apoptosis, brain water content measurement, and neurological score analyses were carried out. Our results showed that the mRNA and protein levels of Miro1 were increased after TBI and co-localized with neurons and astrocytes in the peri-injury cortex. Moreover, Miro1 knockdown further exacerbated neuronal apoptosis, brain edema, and neurological deficits at 48 h after TBI, accompanied by impaired mitochondrial transport, reduction of mitochondria number and energy deficiency. Additionally, the apoptosis-related factors Bax upregulation and Bcl-2 downregulation as Miro1 knockdown after TBI implied that antiapoptotic effects on neuroprotection of Miro1, which were verified by the Fluoro-Jade C (FJC) staining and TUNEL staining. In conclusion, these findings suggest that Miro1 probably plays a neuroprotective role against secondary brain injury through the mitochondria trafficking pathway, suggesting that enhancing Miro1 might be a new strategy for the treatment of TBI.

Phosphorylation and Pin1 binding to the LIC1 subunit selectively regulate mitotic dynein functions

The dynein motor performs multiple functions in mitosis by engaging with a wide cargo spectrum. One way to regulate dynein's cargo-binding selectivity is through the C-terminal domain (CTD) of its light intermediate chain 1 subunit (LIC1), which binds directly with cargo adaptors. Here we show that mitotic phosphorylation of LIC1-CTD at its three cdk1 sites is required for proper mitotic progression, for dynein loading onto prometaphase kinetochores, and for spindle assembly checkpoint inactivation in human cells. Mitotic LIC1-CTD phosphorylation also engages the prolyl isomerase Pin1 predominantly to Hook2-dynein-Nde1-Lis1 complexes, but not to dynein-spindly-dynactin complexes. LIC1-CTD dephosphorylation abrogates dynein-Pin1 binding, promotes prophase centrosome-nuclear envelope detachment, and impairs metaphase chromosome congression and mitotic Golgi fragmentation, without affecting interphase membrane transport. Phosphomutation of a conserved LIC1-CTD SP site in zebrafish leads to early developmental defects. Our work reveals that LIC1-CTD phosphorylation differentially regulates distinct mitotic dynein pools and suggests the evolutionary conservation of this phosphoregulation.

Insights into the Regulation of Ciliary Disassembly

The primary cilium, an antenna-like structure that protrudes out from the cell surface, is present in most cell types. It is a microtubule-based organelle that serves as a mega-signaling center and is important for sensing biochemical and mechanical signals to carry out various cellular processes such as proliferation, migration, differentiation, and many others. At any given time, cilia length is determined by a dynamic balance of cilia assembly and disassembly processes. Abnormally short or long cilia can cause a plethora of human diseases commonly referred to as ciliopathies, including, but not limited to, skeletal malformations, obesity, autosomal dominant polycystic kidney disease, retinal degeneration, and bardet-biedl syndrome. While the process of cilia assembly is studied extensively, the process of cilia disassembly and its biological role(s) are less well understood. This review discusses current knowledge on ciliary disassembly and how different cellular processes and molecular signals converge to carry out this process. This information will help us understand how the process of ciliary disassembly is regulated, identify the key steps that need further investigation, and possibly design therapeutic targets for a subset of ciliopathies that are causally linked to defective ciliary disassembly.

Neurogenomic divergence during speciation by reinforcement of mating behaviors in chorus frogs (Pseudacris)

BACKGROUND

Species interactions can promote mating behavior divergence, particularly when these interactions are costly due to maladaptive hybridization. Selection against hybridization can indirectly cause evolution of reproductive isolation within species, a process termed cascade reinforcement. This process can drive incipient speciation by generating divergent selection pressures among populations that interact with different species assemblages. Theoretical and empirical studies indicate that divergent selection on gene expression networks has the potential to increase reproductive isolation among populations. After identifying candidate synaptic transmission genes derived from neurophysiological studies in anurans, we test for divergence of gene expression in a system undergoing cascade reinforcement, the Upland Chorus Frog (Pseudacris feriarum).

RESULTS

Our analyses identified seven candidate synaptic transmission genes that have diverged between ancestral and reinforced populations of P. feriarum, including five that encode synaptic vesicle proteins. Our gene correlation network analyses revealed four genetic modules that have diverged between these populations, two possessing a significant concentration of neurotransmission enrichment terms: one for synaptic membrane components and the other for metabolism of the neurotransmitter nitric oxide. We also ascertained that a greater number of genes have diverged in expression by geography than by sex. Moreover, we found that more genes have diverged within females as compared to males between populations. Conversely, we observed no difference in the number of differentially-expressed genes within the ancestral compared to the reinforced population between the sexes.

CONCLUSIONS

This work is consistent with the idea that divergent selection on mating behaviors via cascade reinforcement contributed to evolution of gene expression in P. feriarum. Although our study design does not allow us to fully rule out the influence of environment and demography, the fact that more genes diverged in females than males points to a role for cascade reinforcement. Our discoveries of divergent candidate genes and gene networks related to neurotransmission support the idea that neural mechanisms of acoustic mating behaviors have diverged between populations, and agree with previous neurophysiological studies in frogs. Increasing support for this hypothesis, however, will require additional experiments under common garden conditions. Our work points to the importance of future replicated and tissue-specific studies to elucidate the relative contribution of gene expression divergence to the evolution of reproductive isolation during incipient speciation.

Rotavirus viroplasm biogenesis involves microtubule-based dynein transport mediated by an interaction between NSP2 and dynein intermediate chain

Rotaviruses are the causative agents of severe and dehydrating gastroenteritis in children, piglets, and many other young animals. They replicate their genomes and assemble double-layered particles in cytoplasmic electron-dense inclusion bodies called 'viroplasms'. The formation of viroplasms is reportedly associated with the stability of microtubules. Although material transport is an important function of microtubules, whether and how microtubule-based transport influences the formation of viroplasms is still unclear. Here, we demonstrate that the small viroplasms move and fuse in living cells. We show that microtubule-based dynein transport affects rotavirus infection, viroplasm formation, and the assembly of transient enveloped particles (TEPs) and triple-layered particles (TLPs). The dynein intermediate chain (DIC) is shown to localize in the viroplasm and to interact directly with non-structural protein 2 (NSP2), indicating that DIC is responsible for connecting the viroplasm to dynein. The WD40 repeat domain of DIC regulates the interaction between DIC and NSP2, and the knockdown of DIC inhibited rotaviral infection, viroplasm formation, and the assembly of TEPs and TLPs. Our findings show that rotavirus viroplasms hijack dynein transport for fusion events, required for maximal assembly of infectious viral progeny. This study provides novel insights into the intracellular transport of viroplasms, which is involved in their biogenesis. Importance Because the viroplasm is the viral factory for rotavirus replication, viroplasm formation undoubtedly determines the effective production of progeny rotavirus. Therefore, understanding the virus-host interactions involved in the biogenesis of the viroplasm is critical for the future development of prophylactic and therapeutic strategies. Previous studies have reported that the formation of viroplasms is associated with the stability of microtubules, whereas little is known about its specific mechanism. Here, we demonstrate that rotavirus viroplasm formation takes advantage of microtubule-based dynein transport mediated by an interaction between NSP2 and DIC. These findings provide new insight into the intracellular transport of viroplasms.

Structure and Mechanics of Dynein Motors

Dyneins make up a family of AAA+ motors that move toward the minus end of microtubules. Cytoplasmic dynein is responsible for transporting intracellular cargos in interphase cells and mediating spindle assembly and chromosome positioning during cell division. Other dynein isoforms transport cargos in cilia and power ciliary beating. Dyneins were the least studied of the cytoskeletal motors due to challenges in the reconstitution of active dynein complexes in vitro and the scarcity of high-resolution methods for in-depth structural and biophysical characterization of these motors. These challenges have been recently addressed, and there have been major advances in our understanding of the activation, mechanism, and regulation of dyneins. This review synthesizes the results of structural and biophysical studies for each class of dynein motors. We highlight several outstanding questions about the regulation of bidirectional transport along microtubules and the mechanisms that sustain self-coordinated oscillations within motile cilia.

Cellular and Viral Determinants of HSV-1 Entry and Intracellular Transport towards Nucleus of Infected Cells

HSV-1 employs cellular motor proteins and modulates kinase pathways to facilitate intracellular virion capsid transport. Previously, we and others have shown that the Akt inhibitor miltefosine inhibited virus entry. Herein, we show that the protein kinase C inhibitors staurosporine (STS) and gouml inhibited HSV-1 entry into Vero cells, and that miltefosine prevents HSV-1 capsid transport toward the nucleus. We have reported that the HSV-1 UL37 tegument protein interacts with the dynein motor complex during virus entry and virion egress, while others have shown that the UL37/UL36 protein complex binds dynein and kinesin causing a saltatory movement of capsids in neuronal axons. Co-immoprecipitation experiments confirmed previous findings from our laboratory that the UL37 protein interacted with the dynein intermediate chain (DIC) at early times post infection. This UL37-DIC interaction was concurrent with DIC phosphorylation in infected, but not mock-infected cells. Miltefosine inhibited dynein phosphorylation when added before, but not after virus entry. Inhibition of motor accessory protein dynactins (DCTN2, DCTN3), the adaptor proteins EB1 and the Bicaudal D homolog 2 (BICD2) expression using lentiviruses expressing specific shRNAs, inhibited intracellular transport of virion capsids toward the nucleus of human neuroblastoma (SK-N-SH) cells. Co-immunoprecipitation experiments revealed that the major capsid protein Vp5 interacted with dynactins (DCTN1/p150 and DCTN4/p62) and the end-binding protein (EB1) at early times post infection. These results show that Akt and kinase C are involved in virus entry and intracellular transport of virion capsids, but not in dynein activation via phosphorylation. Importantly, both the UL37 and Vp5 viral proteins are involved in dynein-dependent transport of virion capsids to the nuclei of infected cells.Importance. Herpes simplex virus type-1 enter either via fusion at the plasma membranes or endocytosis depositing the virion capsids into the cytoplasm of infected cells. The viral capsids utilize the dynein motor complex to move toward the nuclei of infected cells using the microtubular network. This work shows that inhibitors of the Akt kinase and kinase C inhibit not only viral entry into cells but also virion capsid transport toward the nucleus. In addition, the work reveals that the virion protein ICP5 (VP5) interacts with the dynein cofactor dynactin, while the UL37 protein interacts with the dynein intermediate chain (DIC). Importantly, neither Akt nor Kinase C was found to be responsible for phosphorylation/activation of dynein indicating that other cellular or viral kinases may be involved.

Microtubule motors in centrosome homeostasis: A target for cancer therapy?

Cancer is a grievous concern to human health, owing to a massive heterogeneity in its cause and impact. Dysregulation (numerical, positional and/or structural) of centrosomes is one of the notable factors among those that promote onset and progression of cancers. In a normal dividing cell, a pair of centrosomes forms two poles, thereby governing the formation of a bipolar spindle assembly. A large number of cancer cells, however, harbor supernumerary centrosomes, which mimic the bipolar arrangement in normal cells by centrosome clustering (CC) into two opposite poles, thus developing a pseudo-bipolar spindle assembly. Manipulation of centrosome homeostasis is the paramount pre-requisite for the evasive strategy of CC in cancers. Out of the varied factors that uphold centrosome integrity, microtubule motors (MiMos) play a critical role. Categorized as dyneins and kinesins, MiMos are involved in cohesion of centrosomes, and also facilitate the maintenance of the numerical, positional and structural integrity of centrosomes. Herein, we elucidate the decisive mechanisms undertaken by MiMos to mediate centrosome homeostasis, and how dysregulation of the same might lead to CC in cancer cells. Understanding the impact of MiMos on CC might open up avenues toward a credible therapeutic target against diverse cancers.

Cargo-Mediated Activation of Cytoplasmic Dynein in vivo

Cytoplasmic dynein-1 is a minus-end-directed microtubule motor that transports a variety of cargoes including early endosomes, late endosomes and other organelles. In many cell types, dynein accumulates at the microtubule plus end, where it interacts with its cargo to be moved toward the minus end. Dynein binds to its various cargoes via the dynactin complex and specific cargo adapters. Dynactin and some of the coiled-coil-domain-containing cargo adapters not only link dynein to cargo but also activate dynein motility, which implies that dynein is activated by its cellular cargo. Structural studies indicate that a dynein dimer switches between the autoinhibited phi state and an open state; and the binding of dynactin and a cargo adapter to the dynein tails causes the dynein motor domains to have a parallel configuration, allowing dynein to walk processively along a microtubule. Recently, the dynein regulator LIS1 has been shown to be required for dynein activation in vivo, and its mechanism of action involves preventing dynein from switching back to the autoinhibited state. In this review, we will discuss our current understanding of dynein activation and point out the gaps of knowledge on the spatial regulation of dynein in live cells. In addition, we will emphasize the importance of studying a complete set of dynein regulators for a better understanding of dynein regulation in vivo.

Microtubule Retrograde Motors and Their Role in Retroviral Transport

Following entry into the host cell, retroviruses generate a dsDNA copy of their genomes via reverse transcription, and this viral DNA is subsequently integrated into the chromosomal DNA of the host cell. Before integration can occur, however, retroviral DNA must be transported to the nucleus as part of a ‘preintegration complex’ (PIC). Transporting the PIC through the crowded environment of the cytoplasm is challenging, and retroviruses have evolved different mechanisms to accomplish this feat. Within a eukaryotic cell, microtubules act as the roads, while the microtubule-associated proteins dynein and kinesin are the vehicles that viruses exploit to achieve retrograde and anterograde trafficking. This review will examine the various mechanisms retroviruses have evolved in order to achieve retrograde trafficking, confirming that each retrovirus has its own strategy to functionally subvert microtubule associated proteins.

Role of Dynein and Dynactin (DCTN-1) in Neurodegenerative Diseases

The pathophysiology and concept of degeneration in central nervous system is very complex and overwhelming at times. There is a complex mechanism which exists among different molecules in the cytoplasm of cell bodies of neurons, antegrade and retrograde axonal transport of cargoes and accumulation of certain substances and proteins which can influence the excitatory neurotransmitter like glutamate initiating the process of neurodegeneration. Neurons have extensive processes and communication between those processes and the cell body is crucial to neuronal function, viability and survival over time with progression of age. Researchers believe neurons are uniquely dependent on microtubule-based cargo transport. There is enough evidence to support that deficits in retrograde axonal transport contribute to pathogenesis in multiple neurodegenerative diseases. Cytoplasmic dynein and its regulation by Dynactin (DCTN1) is the major molecular motor cargo involved in autophagy, mitosis and neuronal cell survival. Mutation in dynactin gene located in 2p13.1,is indeed studied very extensively and is considered to be involved directly or indirectly to various conditions like Perry syndrome, familial and sporadic Amyotrophic lateral sclerosis, Hereditary spastic paraplegia, Spinocerebellar Ataxia (SCA-5), Huntingtons disease, Alzheimers disease, Charcot marie tooth disease, Hereditary motor neuropathy 7B, prion disease, parkinsons disease, malformation of cortical development, polymicrogyria to name a few with exception of Multiple Sclerosis (MS).

Interaction of human dynein light chain 1 (DYNLL1) with enterochelin esterase (Salmonella typhimurium) and protective antigen (Bacillus anthraci) might be the potential cause of human infection

The cytoplasmic dynein light chain 1 (DYNLL1) is an important constituent of motor proteins complex. In human it is encoded by DYNLL1 gene. It is involved in cargo transport functions and interacts with many viral proteins with the help of short linear consensus motif sequence (K/R) XTQT. Viral proteins bind to DYNLL1 through its consensus short linear motif (SLiM) sequence to reach the target site in the cell and cause different infections in the host. It is still unknown if bacterial proteins also contain the same conserved SLiMs sequence through which they bind to this motor protein and cause infections. So, it is important to investigate the role of DYNLL1 in human bacterial infections. The interaction partner proteins of DYNLL1 against conserved viral motif sequences were predicted through PDBSum. Pairwise sequence alignment, between viral motif sequence and that of predicted proteins, was performed to identify conserved region in predicted interaction partners. Docking between the DYNLL1 and new pathogenic interaction partners was performed, by using PatchDock, to explore the protein-protein binding quality. Interactions of docked complexes were visualized by DimPlot. Three pathogenic bacterial proteins i.e., enterochelin esterase (3MGA), protective antigen (3J9C) and putative lipoprotein (4KT3) were selected as candidate interaction partners of DYNLL1. The putative lipoprotein (4KT3) showed low quality binding with DYNLL1. So, enterochelin esterase (3MGA) and protective antigen (3J9C) were speculated to be involved in human bacterial infections by using DYNLL1 to reach their target sites.

The Carboxyl Terminus of Tegument Protein pUL21 Contributes to Pseudorabies Virus Neuroinvasion

Following its entry into cells, pseudorabies virus (PRV) utilizes microtubules to deliver its nucleocapsid to the nucleus. Previous studies have shown that PRV VP1/2 is an effector of dynein-mediated capsid transport. However, the mechanism of PRV for recruiting microtubule motor proteins for successful neuroinvasion and neurovirulence is not well understood. Here, we provide evidence that PRV pUL21 is an inner tegument protein. We tested its interaction with the cytoplasmic light chains using a bimolecular fluorescence complementation (BiFC) assay and observed that PRV pUL21 interacts with Roadblock-1. This interaction was confirmed by coimmunoprecipitation (co-IP) assays. We also determined the efficiency of retrograde and anterograde axonal transport of PRV strains in explanted neurons using a microfluidic chamber system and investigated pUL21's contribution to PRV neuroinvasion in vivo Further data showed that the carboxyl terminus of pUL21 is essential for its interaction with Roadblock-1, and this domain contributes to PRV retrograde axonal transport in vitro and in vivo Our findings suggest that the carboxyl terminus of pUL21 contributes to PRV neuroinvasion.IMPORTANCE Herpesviruses are a group of DNA viruses that infect both humans and animals. Alphaherpesviruses are distinguished by their ability to establish latent infection in peripheral neurons. After entering neurons, the herpesvirus capsid interacts with cellular motor proteins and undergoes retrograde transport on axon microtubules. This elaborate process is vital to the herpesvirus lifecycle, but the underlying mechanism remains poorly understood. Here, we determined that pUL21 is an inner tegument protein of pseudorabies virus (PRV) and that it interacts with the cytoplasmic dynein light chain Roadblock-1. We also observed that pUL21 promotes retrograde transport of PRV in neuronal cells. Furthermore, our findings confirm that pUL21 contributes to PRV neuroinvasion in vivo Importantly, the carboxyl terminus of pUL21 is responsible for interaction with Roadblock-1, and this domain contributes to PRV neuroinvasion. This study offers fresh insights into alphaherpesvirus neuroinvasion and the interaction between virus and host during PRV infection.

The dynein adaptor Hook2 plays essential roles in mitotic progression and cytokinesis

Hook proteins are evolutionarily conserved dynein adaptors that promote assembly of highly processive dynein-dynactin motor complexes. Mammals express three Hook paralogs, namely Hook1, Hook2, and Hook3, that have distinct subcellular localizations and expectedly, distinct cellular functions. Here we demonstrate that Hook2 binds to and promotes dynein-dynactin assembly specifically during mitosis. During the late G2 phase, Hook2 mediates dynein-dynactin localization at the nuclear envelope (NE), which is required for centrosome anchoring to the NE. Independent of its binding to dynein, Hook2 regulates microtubule nucleation at the centrosome; accordingly, Hook2-depleted cells have reduced astral microtubules and spindle positioning defects. Besides the centrosome, Hook2 localizes to and recruits dynactin and dynein to the central spindle. Dynactin-dependent targeting of centralspindlin complex to the midzone is abrogated upon Hook2 depletion; accordingly, Hook2 depletion results in cytokinesis failure. We find that the zebrafish Hook2 homologue promotes dynein-dynactin association and was essential for zebrafish early development. Together, these results suggest that Hook2 mediates assembly of the dynein-dynactin complex and regulates mitotic progression and cytokinesis.

Neospora caninum cytoplasmic dynein LC8 light chain 2 (NcDYNLL2) is differentially produced by pathogenically distinct isolates and regulates the host immune response

Neospora caninum is the causative agent of bovine neosporosis. A N. caninum cytoplasmic dynein LC8 light chain (NcDYNLL) protein was characterized in this study. Cytoplasmic dyneins, including DYNLLs, belong to the microtubule minus-end-directed motor proteins and are involved in many cellular processes. Previous microarray studies revealed that NcDYNLL was downregulated in the non-pathogenic clone, Ncts-8, when compared with the wild-type NC1 isolate. The present study showed that DYNLLs from different species are highly conserved (>85% identity), and the NcDYNLL belongs to the DYNLL2 family. NcDYNLL2 and Toxoplasma gondii DYNLL2 have identical amino acid sequences, although they are slightly divergent at the genetic level (89% identity). NcDYNLL2 was cloned and expressed in Escherichia coli and purified. NcDYNLL2 was identified in soluble and insoluble fractions of tachyzoite lysate. As expected, soluble NcDYNLL2 was lower in the Ncts-8 lysate when compared with that of NC1 isolate. NcDYNLL2 release by the tachyzoites was low; however, it was increased when tachyzoites were treated with either calcium ionophore or ethanol. The data indicate that NcDYNLL2 may be actively secreted at low levels, but the secretion was upregulated by agents that also augment microneme protein secretions. Immunostaining of NcDYNLL2 in isolated and intracellular Neospora tachyzoites showed a diffuse distribution pattern. Furthermore, rNcDYNLL2 was internalized by the host immune cells and stimulated tumour necrosis factor-α) and interleukin-12 (IL-12) production by murine dendritic cells. Taken together, these results suggest that NcDYNLL2 is a secretory protein that cross-regulates host immunity.

NDE1 positively regulates oligodendrocyte morphological differentiation

Oligodendrocytes, the myelin-forming cells in the central nervous system (CNS), undergo morphological differentiation characterized by elaborated branched processes to enwrap neuronal axons. However, the basic molecular mechanisms underlying oligodendrocyte morphogenesis remain unknown. Herein, we describe the essential roles of Nuclear Distribution E Homolog 1 (NDE1), a dynein cofactor, in oligodendrocyte morphological differentiation. In the mouse corpus callosum, Nde1 mRNA expression was detected in oligodendrocyte lineage cells at the postnatal stage. In vitro analysis revealed that downregulation of NDE1 by siRNA impaired the outgrowth and extensive branching of oligodendrocyte processes and led to a decrease in the expression of myelin-related markers, namely, CNPase and MBP. In myelinating co-cultures with dorsal root ganglion (DRG) neurons, NDE1-knockdown oligodendrocyte precursor cells (OPCs) failed to develop into MBP-positive oligodendrocytes with multiple processes contacting DRG axons. Immunoprecipitation studies showed that NDE1 interacts with the dynein intermediate chain (DIC) in oligodendrocytes, and an overexpressed DIC-binding region of NDE1 exerted effects on oligodendrocyte morphogenesis that were similar to those following NDE1 knockdown. Furthermore, NDE1-knockdown-impaired oligodendrocyte process formation was rescued by siRNA-resistant wild-type NDE1 but not by DIC-binding region-deficient NDE1 overexpression. These results suggest that NDE1 plays a crucial role in oligodendrocyte morphological differentiation via interaction with dynein.

Nanoparticles engineered to bind cellular motors for efficient delivery

Background

Dynein is a cytoskeletal molecular motor protein that transports cellular cargoes along microtubules. Biomimetic synthetic peptides designed to bind dynein have been shown to acquire dynamic properties such as cell accumulation and active intra- and inter-cellular motion through cell-to-cell contacts and projections to distant cells. On the basis of these properties dynein-binding peptides could be used to functionalize nanoparticles for drug delivery applications.

Results

Here, we show that gold nanoparticles modified with dynein-binding delivery sequences become mobile, powered by molecular motor proteins. Modified nanoparticles showed dynamic properties, such as travelling the cytosol, crossing intracellular barriers and shuttling the nuclear membrane. Furthermore, nanoparticles were transported from one cell to another through cell-to-cell contacts and quickly spread to distant cells through cell projections.

Conclusions

The capacity of these motor-bound nanoparticles to spread to many cells and increasing cellular retention, thus avoiding losses and allowing lower dosage, could make them candidate carriers for drug delivery.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0354-1) contains supplementary material, which is available to authorized users.

Desmosomal cadherin association with Tctex-1 and cortactin-Arp2/3 drives perijunctional actin polymerization to promote keratinocyte delamination

The epidermis is a multi-layered epithelium that serves as a barrier against water loss and environmental insults. Its morphogenesis occurs through a tightly regulated program of biochemical and architectural changes during which basal cells commit to differentiate and move towards the skin's surface. Here, we reveal an unexpected role for the vertebrate cadherin desmoglein 1 (Dsg1) in remodeling the actin cytoskeleton to promote the transit of basal cells into the suprabasal layer through a process of delamination, one mechanism of epidermal stratification. Actin remodeling requires the interaction of Dsg1 with the dynein light chain, Tctex-1 and the actin scaffolding protein, cortactin. We demonstrate that Tctex-1 ensures the correct membrane compartmentalization of Dsg1-containing desmosomes, allowing cortactin/Arp2/3-dependent perijunctional actin polymerization and decreasing tension at E-cadherin junctions to promote keratinocyte delamination. Moreover, Dsg1 is sufficient to enable simple epithelial cells to exit a monolayer to form a second layer, highlighting its morphogenetic potential.

Structure based function-annotation of hypothetical protein MGG_01005 from Magnaporthe oryzae reveals it is the dynein light chain orthologue of dynlt1/3

Magnaporthe oryzae is a model fungal plant pathogen employed for studying plant-fungi interactions. Whole genome sequencing and bioinformatics analyses revealed that this fungal pathogen has more than 12,000 protein-coding genes with 65% of the genes remaining functionally un-annotated. Here, we determine the structure of the hypothetical protein, MGG_01005 and show that it is the Magnaporthe oryzae Dynein light chain Tctex-type 1 (dynlt1/3), demonstrated by its structural similarity to other orthologous dynlt1 proteins and its conserved interaction with the N-terminus of the Magnaporthe oryzae dynein intermediate chain, MoDyn1I2. In addition, we present the structure of the MGG_01005-MoDyn1I2 complex together with mutagenesis studies that reveals a di-histidine motif interaction with a glutamate residue in the dynein intermediate chain within a conserved molecular interface. These results demonstrate the utility of structure-based annotation and validate it as a viable approach for the molecular assignment of hypothetic proteins from phyto-pathogenic fungi.

Nuclear movement in fungi

Nuclear movement within a cell occurs in a variety of eukaryotic organisms including yeasts and filamentous fungi. Fungal molecular genetic studies identified the minus-end-directed microtubule motor cytoplasmic dynein as a critical protein for nuclear movement or orientation of the mitotic spindle contained in the nucleus. Studies in the budding yeast first indicated that dynein anchored at the cortex via its anchoring protein Num1 exerts pulling force on an astral microtubule to orient the anaphase spindle across the mother-daughter axis before nuclear division. Prior to anaphase, myosin V interacts with the plus end of an astral microtubule via Kar9-Bim1/EB1 and pulls the plus end along the actin cables to move the nucleus/spindle close to the bud neck. In addition, pushing or pulling forces generated from cortex-linked polymerization or depolymerization of microtubules drive nuclear movements in yeasts and possibly also in filamentous fungi. In filamentous fungi, multiple nuclei within a hyphal segment undergo dynein-dependent back-and-forth movements and their positioning is also influenced by cytoplasmic streaming toward the hyphal tip. In addition, nuclear movement occurs at various stages of fungal development and fungal infection of plant tissues. This review discusses our current understanding on the mechanisms of nuclear movement in fungal organisms, the importance of nuclear positioning and the regulatory strategies that ensure the proper positioning of nucleus/spindle.

Retroviruses and microtubule-associated motor proteins

Retroviruses are obligate intracellular parasites of eukaryotic cells. After reverse transcription, the viral DNA contained in the preintegration complex is delivered to the nucleus of the host cell, where it integrates. Before reaching the nucleus, the incoming particle and the preintegration complex must travel throughout the cytoplasm. Likewise, the newly synthesized viral proteins and viral particles must transit the cytoplasm during exit. The cytoplasm is a crowded environment, and simple diffusion is difficult. Therefore, viruses have evolved to utilize the cellular mechanisms of movement through the cytoplasm, where microtubules are the roads, and the ATP-dependent motors dynein and kinesin are the vehicles for retrograde and anterograde trafficking. This review will focus on how different retroviruses (Mazon-Pfizer monkey virus, prototype foamy virus, bovine immunodeficiency virus, human immunodeficiency virus type 1, and murine leukemia virus) have subjugated the microtubule-associated motor proteins for viral replication. Although there have been advances in our understanding of how retroviruses move along microtubules, the strategies are different among them. Thus, a better understanding of the mechanisms used by each retrovirus to functionally subvert microtubule motor proteins will provide important clues in the design of new antiretroviral drugs that can specifically disrupt intracellular viral trafficking.

Regulation of dynein-dynactin-driven vesicular transport

Most of the long-range intracellular movements of vesicles, organelles and other cargoes are driven by microtubule (MT)-based molecular motors. Cytoplasmic dynein, a multisubunit protein complex, with the aid of dynactin, drives transport of a wide variety of cargoes towards the minus end of MTs. In this article, I review our current understanding of the mechanisms underlying spatiotemporal regulation of dynein-dynactin-driven vesicular transport with a special emphasis on the many steps of directional movement along MT tracks. These include the recruitment of dynein to MT plus ends, the activation and processivity of dynein, and cargo recognition and release by the motor complex at the target membrane. Furthermore, I summarize the most recent findings about the fine control mechanisms for intracellular transport via the interaction between the dynein-dynactin motor complex and its vesicular cargoes.

The Light Intermediate Chain 2 Subpopulation of Dynein Regulates Mitotic Spindle Orientation

Cytoplasmic dynein 1 is a multi-protein intracellular motor essential for mediating several mitotic functions, including the establishment of proper spindle orientation. The functional relevance and mechanistic distinctions between two discrete dynein subpopulations distinguished only by Light Intermediate Chain (LIC) homologues, LIC1 and LIC2 is unknown during mitosis. Here, we identify LIC2-dynein as the major mediator of proper spindle orientation and uncover its underlying molecular mechanism. Cortically localized dynein, essential for maintaining correct spindle orientation, consists majorly of LIC2-dynein, which interacts with cortical 14-3-3 ε- ζ and Par3, conserved proteins required for orienting the spindle. LIC2-dynein is also responsible for the majority of dynein-mediated asymmetric poleward transport of NuMA, helping focus microtubule minus ends. In addition, LIC2-dynein dominates in equatorially aligning chromosomes at metaphase and in regulating mitotic spindle length. Key mitotic functions of LIC2 were remarkably conserved in and essential for early embryonic divisions and development in zebrafish. Thus LIC2-dynein exclusively engages with two major cortical pathways to govern spindle orientation. Overall, we identify a novel selectivity of molecular interactions between the two LICs in mitosis as the underlying basis for their uneven distribution of labour in ensuring proper spindle orientation.

Fine-Tuning Motile Cilia and Flagella: Evolution of the Dynein Motor Proteins from Plants to Humans at High Resolution

The flagellum is a key innovation linked to eukaryogenesis. It provides motility by regulated cycles of bending and bend propagation, which are thought to be controlled by a complex arrangement of seven distinct dyneins in repeated patterns of outer- (OAD) and inner-arm dynein (IAD) complexes. Electron tomography showed high similarity of this axonemal repeat pattern across ciliates, algae, and animals, but the diversity of dynein sequences across the eukaryotes has not yet comprehensively been resolved and correlated with structural data. To shed light on the evolution of the axoneme I performed an exhaustive analysis of dyneins using the available sequenced genome data. Evidence from motor domain phylogeny allowed expanding the current set of nine dynein subtypes by eight additional isoforms with, however, restricted taxonomic distributions. I confirmed the presence of the nine dyneins in all eukaryotic super-groups indicating their origin predating the last eukaryotic common ancestor. The comparison of the N-terminal tail domains revealed a most likely axonemal dynein origin of the new classes, a group of chimeric dyneins in plants/algae and Stramenopiles, and the unique domain architecture and origin of the outermost OADs present in green algae and ciliates but not animals. The correlation of sequence and structural data suggests the single-headed class-8 and class-9 dyneins to localize to the distal end of the axonemal repeat and the class-7 dyneins filling the region up to the proximal heterodimeric IAD. Tracing dynein gene duplications across the eukaryotes indicated ongoing diversification and fine-tuning of flagellar functions in extant taxa and species.

Mechanisms of ciliogenesis suppression in dividing cells

The primary cilium is a non-motile and microtubule-enriched protrusion ensheathed by plasma membrane. Primary cilia function as mechano/chemosensors and signaling hubs and their disorders predispose to a wide spectrum of human diseases. Most types of cells assemble their primary cilia in response to cellular quiescence, whereas they start to retract the primary cilia upon cell-cycle reentry. The retardation of ciliary resorption process has been shown to delay cell-cycle progression to the S or M phase after cell-cycle reentry. Apart from this conventional concept of ciliary disassembly linked to cell-cycle reentry, recent studies have led to a novel concept, suggesting that cells can suppress primary cilia assembly during cell proliferation. Accumulating evidence has also demonstrated the importance of Aurora-A (a protein originally identified as one of mitotic kinases) not only in ciliary resorption after cell-cycle reentry but also in the suppression of ciliogenesis in proliferating cells, whereas Aurora-A activators are clearly distinct in both phenomena. Here, we summarize the current knowledge of how cycling cells suppress ciliogenesis and compare it with mechanisms underlying ciliary resorption after cell-cycle reentry. We also discuss a reciprocal relationship between primary cilia and cell proliferation.

Cellular model of neuronal atrophy induced by DYNC1I1 deficiency reveals protective roles of RAS-RAF-MEK signaling

Neuronal atrophy is a common pathological feature occurred in aging and neurodegenerative diseases. A variety of abnormalities including motor protein malfunction and mitochondrial dysfunction contribute to the loss of neuronal architecture; however, less is known about the intracellular signaling pathways that can protect against or delay this pathogenic process. Here, we show that the DYNC1I1 deficiency, a neuron-specific dynein intermediate chain, causes neuronal atrophy in primary hippocampal neurons. With this cellular model, we are able to find that activation of RAS-RAF-MEK signaling protects against neuronal atrophy induced by DYNC1I1 deficiency, which relies on MEK-dependent autophagy in neuron. Moreover, we further reveal that BRAF also protects against neuronal atrophy induced by mitochondrial impairment. These findings demonstrate protective roles of the RAS-RAF-MEK axis against neuronal atrophy, and imply a new therapeutic target for clinical intervention.

Molecular Basis for the Protein Recognition Specificity of the Dynein Light Chain DYNLT1/Tctex1: CHARACTERIZATION OF THE INTERACTION WITH ACTIVIN RECEPTOR IIB

It has been suggested that DYNLT1, a dynein light chain known to bind to various cellular and viral proteins, can function both as a molecular clamp and as a microtubule-cargo adapter. Recent data have shown that the DYNLT1 homodimer binds to two dynein intermediate chains to subsequently link cargo proteins such as the guanine nucleotide exchange factor Lfc or the small GTPases RagA and Rab3D. Although over 20 DYNLT1-interacting proteins have been reported, the exact sequence requirements that enable their association to the canonical binding groove or to the secondary site within the DYNLT1 surface are unknown. We describe herein the sequence recognition properties of the hydrophobic groove of DYNLT1 known to accommodate dynein intermediate chain. Using a pepscan approach, we have substituted each amino acid within the interacting peptide for all 20 natural amino acids and identified novel binding sequences. Our data led us to propose activin receptor IIB as a novel DYNLT1 ligand and suggest that DYNLT1 functions as a molecular dimerization engine bringing together two receptor monomers in the cytoplasmic side of the membrane. In addition, we provide evidence regarding a dual binding mode adopted by certain interacting partners such as Lfc or the parathyroid hormone receptor. Finally, we have used NMR spectroscopy to obtain the solution structure of human DYNLT1 forming a complex with dynein intermediate chain of ∼74 kDa; it is the first mammalian structure available.

Dynein Light Intermediate Chain 2 Facilitates the Metaphase to Anaphase Transition by Inactivating the Spindle Assembly Checkpoint

The multi-functional molecular motor cytoplasmic dynein performs diverse essential roles during mitosis. The mechanistic importance of the dynein Light Intermediate Chain homologs, LIC1 and LIC2 is unappreciated, especially in the context of mitosis. LIC1 and LIC2 are believed to exist in distinct cytoplasmic dynein complexes as obligate subunits. LIC1 had earlier been reported to be required for metaphase to anaphase progression by inactivating the kinetochore-microtubule attachment-sensing arm of the spindle assembly checkpoint (SAC). However, the functional importance of LIC2 during mitosis remains elusive. Here we report prominent novel roles for the LIC2 subunit of cytoplasmic dynein in regulating the spindle assembly checkpoint. LIC2 depletion in mammalian cells led to prolonged metaphase arrest in the presence of an active SAC and also to stretched kinetochores, thus implicating it in SAC inactivation. Quantitative fluorescence microscopy of SAC components revealed accumulation of both attachment- and tension-sensing checkpoint proteins at metaphase kinetochores upon LIC2 depletion. These observations support a stronger and more diverse role in checkpoint inactivation for LIC2 in comparison to its close homolog LIC1. Our study uncovers a novel functional hierarchy during mitotic checkpoint inactivation between the closely related but homologous LIC subunits of cytoplasmic dynein. These subtle functional distinctions between dynein subpopulations could be exploited to study specific aspects of the spindle assembly checkpoint, which is a key mediator of fidelity in eukaryotic cell division.

Axonal Transport and Neurodegeneration: How Marine Drugs Can Be Used for the Development of Therapeutics

Unlike virtually any other cells in the human body, neurons are tasked with the unique problem of transporting important factors from sites of synthesis at the cell bodies, across enormous distances, along narrow-caliber projections, to distally located nerve terminals in order to maintain cell viability. As a result, axonal transport is a highly regulated process whereby necessary cargoes of all types are packaged and shipped from one end of the neuron to the other. Interruptions in this finely tuned transport have been linked to many neurodegenerative disorders including Alzheimer's (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) suggesting that this pathway is likely perturbed early in disease progression. Therefore, developing therapeutics targeted at modifying transport defects could potentially avert disease progression. In this review, we examine a variety of potential compounds identified from marine aquatic species that affect the axonal transport pathway. These compounds have been shown to function in microtubule (MT) assembly and maintenance, motor protein control, and in the regulation of protein degradation pathways, such as the autophagy-lysosome processes, which are defective in many degenerative diseases. Therefore, marine compounds have great potential in developing effective treatment strategies aimed at early defects which, over time, will restore transport and prevent cell death.

Dync1h1 Mutation Causes Proprioceptive Sensory Neuron Loss and Impaired Retrograde Axonal Transport of Dorsal Root Ganglion Neurons

BACKGROUND AND PURPOSE

Sprawling (Swl) is a radiation-induced mutation which has been identified to have a nine base pair deletion in dynein heavy chain 1 (DYNC1H1: encoded by a single gene Dync1h1). This study is to investigate the phenotype and the underlying mechanism of the Dync1h1 mutant.

METHODS AND RESULTS

To display the phenotype of Swl mutant mice, we examined the embryos of homozygous (Swl/Swl) and heterozygous (Swl/+) mice and their postnatal dorsal root ganglion (DRG) of surviving Swl/+ mice. The Swl/+ mice could survive for a normal life span, while Swl/Swl could only survive till embryonic (E) 8.5 days. Excessive apoptosis of Swl/+ DRG neurons was revealed during E11.5-E15.5 days, and the peak rate was at E13.5 days. In vitro study of mutated DRG neurons showed impaired retrograde transport of dynein-driven nerve growth factor (NGF). Mitochondria, another dynein-driven cargo, demonstrated much slower retrograde transport velocity in Swl/+ neurons than in wild-type (WT) neurons. Nevertheless, the Swl, Loa, and Cra mutations did not affect homodimerization of DYNC1H1.

CONCLUSION

The Swl/Swl mutation of Dync1h1 gene led to embryonic mal-development and lethality, whereas the Swl/+ DRG neurons demonstrated deficient retrograde transport in dynein-driven cargos and excessive apoptosis during mid- to late-developmental stages. The underlying mechanism of the mutation may not be due to impaired homodimerization of DYNC1H1.

Transcriptomic Analysis of Trout Gill Ionocytes in Fresh Water and Sea Water Using Laser Capture Microdissection Combined with Microarray Analysis

Fish gills represent a complex organ composed of several cell types that perform multiple physiological functions. Among these cells, ionocytes are implicated in the maintenance of ion homeostasis. However, because the ionocyte represents only a small percent of whole gill tissue, its specific transcriptome can be overlooked among the numerous cell types included in the gill. The objective of this study is to better understand ionocyte functions by comparing the RNA expression of this cell type in freshwater and seawater acclimated rainbow trout. To realize this objective, ionocytes were captured from gill cryosections using laser capture microdissection after immunohistochemistry. Then, transcriptome analyses were performed on an Agilent trout oligonucleotide microarray. Gene expression analysis identified 108 unique annotated genes differentially expressed between freshwater and seawater ionocytes, with a fold change higher than 3. Most of these genes were up-regulated in freshwater cells. Interestingly, several genes implicated in ion transport, extracellular matrix and structural cellular proteins appeared up-regulated in freshwater ionocytes. Among them, several ion transporters, such as CIC2, SLC26A6, and NBC, were validated by qPCR and/or in situ hybridization. The latter technique allowed us to localize the transcripts of these ion transporters in only ionocytes and more particularly in the freshwater cells. Genes involved in metabolism and also several genes implicated in transcriptional regulation, cell signaling and the cell cycle were also enhanced in freshwater ionocytes. In conclusion, laser capture microdissection combined with microarray analysis allowed for the determination of the transcriptional signature of scarce cells in fish gills, such as ionocytes, and aided characterization of the transcriptome of these cells in freshwater and seawater acclimated trout.

DYNLT (Tctex-1) forms a tripartite complex with dynein intermediate chain and RagA, hence linking this small GTPase to the dynein motor

It has been suggested that DYNLT, a dynein light chain known to bind to various cellular and viral proteins, can function as a microtubule-cargo adaptor. Recent data showed that DYNLT links the small GTPase Rab3D to microtubules and, for this to occur, the DYNLT homodimer needs to display a binding site for dynein intermediate chain together with a binding site for the small GTPase. We have analysed in detail how RagA, another small GTPase, associates to DYNLT. After narrowing down the binding site of RagA to DYNLT we could identify that a β strand, part of the RagA G3 box involved in nucleotide binding, mediates this association. Interestingly, we show that both microtubule-associated DYNLT and cytoplasmic DYNLT are equally able to bind to the small GTPases Rab3D and RagA. Using NMR spectroscopy, we analysed the binding of dynein intermediate chain and RagA to mammalian DYNLT. Our experiments identify residues of DYNLT affected by dynein intermediate chain binding and residues affected by RagA binding, hence distinguishing the docking site for each of them. In summary, our results shed light on the mechanisms adopted by DYNLT when binding to protein cargoes that become transported alongside microtubules bound to the dynein motor.

N-acetyl-D-glucosamine kinase interacts with dynein light-chain roadblock type 1 at Golgi outposts in neuronal dendritic branch points

N-acetylglucosamine kinase (GlcNAc kinase or NAGK) is a ubiquitously expressed enzyme in mammalian cells. Recent studies have shown that NAGK has an essential structural, non-enzymatic role in the upregulation of dendritogenesis. In this study, we conducted yeast two-hybrid screening to search for NAGK-binding proteins and found a specific interaction between NAGK and dynein light-chain roadblock type 1 (DYNLRB1). Immunocytochemistry (ICC) on hippocampal neurons using antibodies against NAGK and DYNLRB1 or dynein heavy chain showed some colocalization, which was increased by treating the live cells with a crosslinker. A proximity ligation assay (PLA) of NAGK-dynein followed by tubulin ICC showed the localization of PLA signals on microtubule fibers at dendritic branch points. NAGK-dynein PLA combined with Golgi ICC showed the colocalization of PLA signals with somal Golgi facing the apical dendrite and with Golgi outposts in dendritic branch points and distensions. NAGK-Golgi PLA followed by tubulin or DYNLRB1 ICC showed that PLA signals colocalize with DYNLRB1 at dendritic branch points and at somal Golgi, indicating a tripartite interaction between NAGK, dynein and Golgi. Finally, the ectopic introduction of a small peptide derived from the C-terminal amino acids 74–96 of DYNLRB1 resulted in the stunting of hippocampal neuron dendrites in culture. Our data indicate that the NAGK-dynein-Golgi tripartite interaction at dendritic branch points functions to regulate dendritic growth and/or branching.

Somatic CRISPR-Cas9-induced mutations reveal roles of embryonically essential dynein chains in Caenorhabditis elegans cilia

CRISPR–Cas9-induced mutations in intraflagellar transport (IFT) motors reveal that IFT-specific dynein and cytoplasmic dynein have unique compositions but share components and regulatory mechanisms.

Cilium formation and maintenance require intraflagellar transport (IFT). Although much is known about kinesin-2–driven anterograde IFT, the composition and regulation of retrograde IFT-specific dynein remain elusive. Components of cytoplasmic dynein may participate in IFT; however, their essential roles in cell division preclude functional studies in postmitotic cilia. Here, we report that inducible expression of the clustered regularly interspaced short palindromic repeats (CRISPR)–Cas9 system in Caenorhabditis elegans generated conditional mutations in IFT motors and particles, recapitulating ciliary defects in their null mutants. Using this method to bypass the embryonic requirement, we show the following: the dynein intermediate chain, light chain LC8, and lissencephaly-1 regulate retrograde IFT; the dynein light intermediate chain functions in dendrites and indirectly contributes to ciliogenesis; and the Tctex and Roadblock light chains are dispensable for cilium assembly. Furthermore, we demonstrate that these components undergo biphasic IFT with distinct transport frequencies and turnaround behaviors. Together, our results suggest that IFT–dynein and cytoplasmic dynein have unique compositions but also share components and regulatory mechanisms.

Regulation of processive motion and microtubule localization of cytoplasmic dynein

The cytoplasmic dynein complex is the major minus-end-directed microtubule motor. Although its directionality is evolutionary well conserved, differences exist among cytoplasmic dyneins from different species in their stepping behaviour, maximum velocity and force production. Recent experiments also suggest differences in processivity regulation. In the present article, we give an overview of dynein's motile properties, with a special emphasis on processivity and its regulation. Furthermore, we summarize recent findings of different pathways for microtubule plus-end loading of dynein. The present review highlights how distinct functions in different cell types or organisms appear to require different mechanochemical dynein properties and localization pathways.

Distinct functional roles of cytoplasmic dynein defined by the intermediate chain isoforms

The motor protein, cytoplasmic dynein is responsible for the movement of a variety of cargoes toward microtubule minus ends in cells. Little is understood about how dynein is regulated to specifically transport its various cargoes. In vertebrates, the dynein motor domain (DYNC1H) is encoded by a single gene; while there are two genes for the five smaller subunits that comprise the cargo binding domain of the dynein complex. The isoforms of the intermediate chain (DYNC1I) provide a good model system with which to study the roles the different isoforms of the cargo domain subunits have in designating specific dynein functions. The intermediate chains (DYNC1I) play a key scaffold role in the dynein complex. In neurons, dynein complexes with different intermediate chain isoforms have distinct roles, including cargo binding and transport. Some of the phospho-isoforms of the intermediate chain also specify binding to specific cargo. These data support the model that cytoplasmic dynein can be specifically regulated through the different isoforms of the subunits.

Cilia/Ift protein and motor -related bone diseases and mouse models

Primary cilia are essential cellular organelles projecting from the cell surface to sense and transduce developmental signaling. They are tiny but have complicated structures containing microtubule (MT)-based internal structures (the axoneme) and mother centriole formed basal body. Intraflagellar transport (Ift) operated by Ift proteins and motors are indispensable for cilia formation and function. Mutations in Ift proteins or Ift motors cause various human diseases, some of which have severe bone defects. Over the last few decades, major advances have occurred in understanding the roles of these proteins and cilia in bone development and remodeling by examining cilia/Ift protein-related human diseases and establishing mouse transgenic models. In this review, we describe current advances in the understanding of the cilia/Ift structure and function. We further summarize cilia/Ift-related human diseases and current mouse models with an emphasis on bone-related phenotypes, cilia morphology, and signaling pathways.

Function and regulation of primary cilia and intraflagellar transport proteins in the skeleton

Primary cilia are microtubule-based organelles that project from the cell surface to enable transduction of various developmental signaling pathways. The process of intraflagellar transport (IFT) is crucial for the building and maintenance of primary cilia. Ciliary dysfunction has been found in a range of disorders called ciliopathies, some of which display severe skeletal dysplasias. In recent years, interest has grown in uncovering the function of primary cilia/IFT proteins in bone development, mechanotransduction, and cellular regulation. We summarize recent advances in understanding the function of cilia and IFT proteins in the regulation of cell differentiation in osteoblasts, osteocytes, chondrocytes, and mesenchymal stem cells (MSCs). We also discuss the mechanosensory function of cilia and IFT proteins in bone cells, cilia orientation, and other functions of cilia in chondrocytes.