Lis1 Has Two Opposing Modes of Regulating Cytoplasmic Dynein

Isoform-specific phosphorylation of axonemal dynein heavy chains

Axonemal dyneins power ciliary motility and phosphorylation of key intermediate and light chain components affects the regulation and properties of these motors in very distantly related organisms. It is also known that many axonemal dynein heavy chains are subject to this posttranslational modification although this has been little studied. Here we examine axonemal dynein heavy chains from a broad range of ciliated eukaryotes and identify phosphorylated sites embedded within various kinase recognition motifs such as those for protein kinase A, protein kinase C, and casein kinase II. Mapping these sites onto discrete heavy chain types reveals class-specific locations apparently mediated by different kinases. For example, we find that all Chlamydomonas α heavy chain phosphorylation sites are in an extended loop derived from AAA5 that arches over the coiled-coil buttress which in turn interacts with the microtubule-binding stalk. In contrast, most sites in the monomeric inner arm dyneins occur very close to the N-terminus and may be involved in assembly processes. In Chlamydomonas, the two cilia (termed cis and trans) exhibit different intrinsic beat frequencies and we identify cilium-specific phosphorylation patterns on both the α heavy chain and outer arm docking complex consistent with differential regulation of these motors in the two organelles.

The Power of Three: Dynactin associates with three dyneins under load for greater force production

Cytoplasmic dynein is an essential microtubule motor protein that powers organelle transport and mitotic spindle assembly. Its activity depends on dynein-dynactin-cargo adaptor complexes, such as dynein-dynactin-BicD2 (DDB), which typically function with two dynein motors. We show that mechanical tension recruits a third dynein motor via an auxiliary BicD adaptor binding the light intermediate chain of the third dynein, stabilizing multi-dynein assemblies and enhancing force generation. Lis1 prevents dynein from transitioning into a force-limiting phi-like conformation, allowing single-dynein DDB to sustain forces up to ~4.5 pN, whereas force generation often ends at ~2.5 pN without Lis1. Complexes with two or three dyneins generate ~7 pN and ~9 pN, respectively, consistent with a staggered motor arrangement that enhances collective output. Under load, DDB primarily takes ~8 nm steps, challenging existing dynein coordination models. These findings reveal adaptive mechanisms that enable robust intracellular transport under varying mechanical demands.

A nucleotide code governs Lis1's ability to relieve dynein autoinhibition

Dynein-1 is a microtubule motor responsible for the transport of cytoplasmic cargoes. Activation of motility requires it first overcome an autoinhibited state prior to its assembly with dynactin and a cargo adaptor. Studies suggest that Lis1 may relieve dynein's autoinhibited state. However, evidence for this mechanism is lacking. We first set out to determine the rules governing dynein-Lis1 binding, which reveals that their binding affinity is regulated by the nucleotide-bound states of each of three nucleotide-binding pockets within the dynein motor domain. We also find that distinct nucleotide 'codes' coordinate dynein-Lis1 binding stoichiometry by impacting binding affinity at two different sites within the dynein motor domain. Electron microscopy reveals that a 1 Lis1:1 dynein complex directly promotes an open, uninhibited conformational state of dynein, whereas a 2:1 complex resembles the autoinhibited state. Cryo-EM analysis reveals the structural basis for Lis1 opening dynein relies on interactions with the linker domain.

Cryo-EM visualizes multiple steps of dynein's activation pathway

Cytoplasmic dynein-1 (dynein) is an essential molecular motor controlled in part by autoinhibition. We recently identified a structure of partially autoinhibited dynein bound to Lis1, a key dynein regulator mutated in the neurodevelopmental disease lissencephaly. This structure provides an intermediate state in dynein's activation pathway; however, other structural information is needed to fully explain Lis1 function in dynein activation. Here, we used cryo-EM and samples incubated with ATP for different times to reveal novel conformations that we propose represent intermediate states in the dynein's activation pathway. We solved sixteen high-resolution structures, including seven distinct dynein and dynein-Lis1 structures from the same sample. Our data also support a model in which Lis1 relieves dynein autoinhibition by increasing its basal ATP hydrolysis rate and promoting conformations compatible with complex assembly and motility. Together, this analysis advances our understanding of dynein activation and the contribution of Lis1 to this process.

Patient-specific mutation of Dync1h1 in mice causes brain and behavioral deficits

AIMS

Cytoplasmic dynein heavy chain (DYNC1H1) is a multi-subunit protein complex that provides motor force for movement of cargo on microtubules and traffics them back to the soma. In humans, mutations along the DYNC1H1 gene result in intellectual disabilities, cognitive delays, and neurologic and motor deficits. The aim of the study was to generate a mouse model to a newly identified de novo heterozygous DYNC1H1 mutation, within a functional ATPase domain (c9052C > T(P3018S)), identified in a child with motor deficits, and intellectual disabilities.

RESULTS

P3018S heterozygous (HET) knockin mice are viable; homozygotes are lethal. Metabolic and EchoMRI™ testing show that HET mice have a higher metabolic rate, are more active, and have less body fat compared to wildtype mice. Neurobehavioral studies show that HET mice perform worse when traversing elevated balance beams, and on the negative geotaxis test. Immunofluorescent staining shows neuronal migration abnormalities in the dorsal and lateral neocortex with heterotopia in layer I. Neuron-subtype specific transcription factors CUX1 and CTGF identified neurons from layers II/III and VI respectively in cortical layer I, and abnormal pyramidal neurons with MAP2+ dendrites projecting downward from the pial surface.

CONCLUSION

The HET mice are a good model for the motor deficits seen in the child, and highlights the importance of cytoplasmic dynein in the maintenance of cortical function and dendritic orientation relative to the pial surface. Our results are discussed in the context of other dynein mutant mice and in relation to clinical presentation in humans with DYNC1H1 mutations.

From Entry to the Nucleus: How Retroviruses Commute

Once inside host cells, retroviruses generate a double-stranded DNA copy of their RNA genomes via reverse transcription inside a viral core, and this viral DNA is subsequently integrated into the genome of the host cell. Before integration can occur, the core must cross the cell cortex, be transported through the cytoplasm, and enter the nucleus. Retroviruses have evolved different mechanisms to accomplish this journey. This review examines the various mechanisms retroviruses, especially HIV-1, have evolved to commute throughout the cell. Retroviruses cross the cell cortex while modulating actin dynamics and use microtubules as roads while connecting with microtubule-associated proteins and motors to reach the nucleus. Although a clearer picture exists for HIV-1 compared with other retroviruses, there is still much to learn about how retroviruses accomplish their commute.

Cryptococcus neoformans Slu7 ensures nuclear positioning during mitotic progression through RNA splicing

The position of the nucleus before it divides during mitosis is variable in different budding yeasts. Studies in the pathogenic intron-rich fungus Cryptococcus neoformans reveal that the nucleus moves entirely into the daughter bud before its division. Here, we report functions of a zinc finger motif containing spliceosome protein C. neoformans Slu7 (CnSlu7) in cell cycle progression. The budding yeast and fission yeast homologs of Slu7 have predominant roles for intron 3' splice site definition during pre-mRNA splicing. Using a conditional knockdown strategy, we show CnSlu7 is an essential factor for viability and is required for efficient cell cycle progression with major role during mitosis. Aberrant nuclear migration, including improper positioning of the nucleus as well as the spindle, were frequently observed in cells depleted of CnSlu7. However, cell cycle delays observed due to Slu7 depletion did not activate the Mad2-dependent spindle assembly checkpoint (SAC). Mining of the global transcriptome changes in the Slu7 knockdown strain identified downregulation of transcripts encoding several cell cycle regulators and cytoskeletal factors for nuclear migration, and the splicing of specific introns of these genes was CnSlu7 dependent. To test the importance of splicing activity of CnSlu7 on nuclear migration, we complemented Slu7 knockdown cells with an intron less PAC1 minigene and demonstrated that the nuclear migration defects were significantly rescued. These findings show that CnSlu7 regulates the functions of diverse cell cycle regulators and cytoskeletal components, ensuring timely cell cycle transitions and nuclear division during mitosis.

Lis1 slows force-induced detachment of cytoplasmic dynein from microtubules

Lis1 is a key cofactor for the assembly of active cytoplasmic dynein complexes that transport cargo along microtubules. Lis1 binds to the AAA+ ring and stalk of dynein and slows dynein motility, but the underlying mechanism has remained unclear. Using single-molecule imaging and optical trapping assays, we investigated how Lis1 binding affects the motility and force generation of yeast dynein in vitro. We showed that Lis1 slows motility by binding to the AAA+ ring of dynein, not by serving as a roadblock or tethering dynein to microtubules. Lis1 binding also does not affect force generation, but it induces prolonged stalls and reduces the asymmetry in the force-induced detachment of dynein from microtubules. The mutagenesis of the Lis1-binding sites on the dynein stalk partially recovers this asymmetry but does not restore dynein velocity. These results suggest that Lis1-stalk interaction slows the detachment of dynein from microtubules by interfering with the stalk sliding mechanism.

Molecular mechanism of dynein-dynactin complex assembly by LIS1

Cytoplasmic dynein is a microtubule motor vital for cellular organization and division. It functions as a ~4-megadalton complex containing its cofactor dynactin and a cargo-specific coiled-coil adaptor. However, how dynein and dynactin recognize diverse adaptors, how they interact with each other during complex formation, and the role of critical regulators such as lissencephaly-1 (LIS1) protein (LIS1) remain unclear. In this study, we determined the cryo-electron microscopy structure of dynein-dynactin on microtubules with LIS1 and the lysosomal adaptor JIP3. This structure reveals the molecular basis of interactions occurring during dynein activation. We show how JIP3 activates dynein despite its atypical architecture. Unexpectedly, LIS1 binds dynactin's p150 subunit, tethering it along the length of dynein. Our data suggest that LIS1 and p150 constrain dynein-dynactin to ensure efficient complex formation.

Nde1 promotes Lis1-mediated activation of dynein

Cytoplasmic dynein drives the motility and force generation functions towards the microtubule minus end. The assembly of dynein with dynactin and a cargo adaptor in an active transport complex is facilitated by Lis1 and Nde1/Ndel1. Recent studies proposed that Lis1 relieves dynein from its autoinhibited conformation, but the physiological function of Nde1/Ndel1 remains elusive. Here, we investigate how human Nde1 and Lis1 regulate the assembly and subsequent motility of mammalian dynein using in vitro reconstitution and single molecule imaging. We find that Nde1 recruits Lis1 to autoinhibited dynein and promotes Lis1-mediated assembly of dynein-dynactin adaptor complexes. Nde1 can compete with the α2 subunit of platelet activator factor acetylhydrolase 1B (PAF-AH1B) for the binding of Lis1, which suggests that Nde1 may disrupt PAF-AH1B recruitment of Lis1 as a noncatalytic subunit, thus promoting Lis1 binding to dynein. Before the initiation of motility, the association of dynactin with dynein triggers the dissociation of Nde1 from dynein by competing against Nde1 binding to the dynein intermediate chain. Our results provide a mechanistic explanation for how Nde1 and Lis1 synergistically activate the dynein transport machinery.

Nde1 Promotes Lis1-Mediated Activation of Dynein

Cytoplasmic dynein is the primary motor that drives the motility and force generation functions towards the microtubule minus end. The activation of dynein motility requires its assembly with dynactin and a cargo adaptor. This process is facilitated by two dynein-associated factors, Lis1 and Nde1/Ndel1. Recent studies proposed that Lis1 rescues dynein from its autoinhibited conformation, but the physiological function of Nde1/Ndel1 remains elusive. Here, we investigated how human Nde1 and Lis1 regulate the assembly and subsequent motility of the mammalian dynein/dynactin complex using in vitro reconstitution and single molecule imaging. We found that Nde1 promotes the assembly of active dynein complexes in two distinct ways. Nde1 competes with the α2 subunit of platelet activator factor acetylhydrolase (PAF-AH) 1B, which recruits Lis1 as a noncatalytic subunit and prevents its binding to dynein. Second, Nde1 recruits Lis1 to autoinhibited dynein and promotes Lis1-mediated assembly of dynein-dynactin-adaptor complexes. However, excess Nde1 inhibits dynein, presumably by competing against dynactin to bind the dynein intermediate chain. The association of dynactin with dynein triggers Nde1 dissociation before the initiation of dynein motility. Our results provide a mechanistic explanation for how Nde1 and Lis1 synergistically activate the dynein transport machinery.

Lis1 relieves cytoplasmic dynein-1 autoinhibition by acting as a molecular wedge

Cytoplasmic dynein-1 transports intracellular cargo towards microtubule minus ends. Dynein is autoinhibited and undergoes conformational changes to form an active complex that consists of one or two dynein dimers, the dynactin complex, and activating adapter(s). The Lissencephaly 1 gene, LIS1, is genetically linked to the dynein pathway from fungi to mammals and is mutated in people with the neurodevelopmental disease lissencephaly. Lis1 is required for active dynein complexes to form, but how it enables this is unclear. Here, we present a structure of two yeast dynein motor domains with two Lis1 dimers wedged in-between. The contact sites between dynein and Lis1 in this structure, termed 'Chi,' are required for Lis1's regulation of dynein in Saccharomyces cerevisiae in vivo and the formation of active human dynein-dynactin-activating adapter complexes in vitro. We propose that this structure represents an intermediate in dynein's activation pathway, revealing how Lis1 relieves dynein's autoinhibited state.

Microtubule-binding-induced allostery triggers LIS1 dissociation from dynein prior to cargo transport

The lissencephaly-related protein LIS1 is a critical regulator of cytoplasmic dynein that governs motor function and intracellular localization (for example, to microtubule plus-ends). Although LIS1 binding is required for dynein activity, its unbinding prior to initiation of cargo transport is equally important, since preventing dissociation leads to dynein dysfunction. To understand whether and how dynein-LIS1 binding is modulated, we engineered dynein mutants locked in a microtubule-bound (MT-B) or microtubule-unbound (MT-U) state. Whereas the MT-B mutant exhibits low LIS1 affinity, the MT-U mutant binds LIS1 with high affinity, and as a consequence remains almost irreversibly associated with microtubule plus-ends. We find that a monomeric motor domain is sufficient to exhibit these opposing LIS1 affinities, and that this is evolutionarily conserved between yeast and humans. Three cryo-EM structures of human dynein with and without LIS1 reveal microtubule-binding induced conformational changes responsible for this regulation. Our work reveals key biochemical and structural insight into LIS1-mediated dynein activation.

LIS1 RNA-binding orchestrates the mechanosensitive properties of embryonic stem cells in AGO2-dependent and independent ways

Lissencephaly-1 (LIS1) is associated with neurodevelopmental diseases and is known to regulate the molecular motor cytoplasmic dynein activity. Here we show that LIS1 is essential for the viability of mouse embryonic stem cells (mESCs), and it governs the physical properties of these cells. LIS1 dosage substantially affects gene expression, and we uncovered an unexpected interaction of LIS1 with RNA and RNA-binding proteins, most prominently the Argonaute complex. We demonstrate that LIS1 overexpression partially rescued the extracellular matrix (ECM) expression and mechanosensitive genes conferring stiffness to Argonaute null mESCs. Collectively, our data transforms the current perspective on the roles of LIS1 in post-transcriptional regulation underlying development and mechanosensitive processes.

Structures of human dynein in complex with the lissencephaly 1 protein, LIS1

The lissencephaly 1 protein, LIS1, is mutated in type-1 lissencephaly and is a key regulator of cytoplasmic dynein-1. At a molecular level, current models propose that LIS1 activates dynein by relieving its autoinhibited form. Previously we reported a 3.1 Å structure of yeast dynein bound to Pac1, the yeast homologue of LIS1, which revealed the details of their interactions (Gillies et al., 2022). Based on this structure, we made mutations that disrupted these interactions and showed that they were required for dynein's function in vivo in yeast. We also used our yeast dynein-Pac1 structure to design mutations in human dynein to probe the role of LIS1 in promoting the assembly of active dynein complexes. These mutations had relatively mild effects on dynein activation, suggesting that there may be differences in how dynein and Pac1/LIS1 interact between yeast and humans. Here, we report cryo-EM structures of human dynein-LIS1 complexes. Our new structures reveal the differences between the yeast and human systems, provide a blueprint to disrupt the human dynein-LIS1 interactions more accurately, and map type-1 lissencephaly disease mutations, as well as mutations in dynein linked to malformations of cortical development/intellectual disability, in the context of the dynein-LIS1 complex.

Doublecortin and JIP3 are neural-specific counteracting regulators of dynein-mediated retrograde trafficking

Mutations in the microtubule (MT)-binding protein doublecortin (DCX) or in the MT-based molecular motor dynein result in lissencephaly. However, a functional link between DCX and dynein has not been defined. Here, we demonstrate that DCX negatively regulates dynein-mediated retrograde transport in neurons from Dcx-/y or Dcx-/y;Dclk1-/- mice by reducing dynein's association with MTs and disrupting the composition of the dynein motor complex. Previous work showed an increased binding of the adaptor protein C-Jun-amino-terminal kinase-interacting protein 3 (JIP3) to dynein in the absence of DCX. Using purified components, we demonstrate that JIP3 forms an active motor complex with dynein and its cofactor dynactin with two dyneins per complex. DCX competes with the binding of the second dynein, resulting in a velocity reduction of the complex. We conclude that DCX negatively regulates dynein-mediated retrograde transport through two critical interactions by regulating dynein binding to MTs and regulating the composition of the dynein motor complex.

Structure of dynein-dynactin on microtubules shows tandem adaptor binding

Cytoplasmic dynein is a microtubule motor that is activated by its cofactor dynactin and a coiled-coil cargo adaptor1-3. Up to two dynein dimers can be recruited per dynactin, and interactions between them affect their combined motile behaviour4-6. Different coiled-coil adaptors are linked to different cargos7,8, and some share motifs known to contact sites on dynein and dynactin4,9-13. There is limited structural information on how the resulting complex interacts with microtubules and how adaptors are recruited. Here we develop a cryo-electron microscopy processing pipeline to solve the high-resolution structure of dynein-dynactin and the adaptor BICDR1 bound to microtubules. This reveals the asymmetric interactions between neighbouring dynein motor domains and how they relate to motile behaviour. We found that two adaptors occupy the complex. Both adaptors make similar interactions with the dyneins but diverge in their contacts with each other and dynactin. Our structure has implications for the stability and stoichiometry of motor recruitment by cargos.

LIS1 interacts with CLIP170 to promote tumor growth and metastasis via the Cdc42 signaling pathway in salivary gland adenoid cystic carcinoma

Salivary gland adenoid cystic carcinoma (SACC) is one of the most common malignant tumors, with high aggressive potential in the oral and maxillofacial regions. Lissencephaly 1 (LIS1) is a microtubule-organizing center-associated protein that regulates the polymerization and stability of microtubules by mediating the motor function of dynein. Recent studies have suggested that LIS1 plays a potential role in the malignant development of tumors, such as in mitosis and migration. However, the role of LIS1 in SACC development and its related molecular mechanisms remain unclear. Thus, the effects of LIS1 on the proliferation, apoptosis, invasion and metastasis of SACC were studied, in vivo and in vitro. The results of immunohistochemical staining showed that LIS1 was highly expressed in SACC tissues, and its expression level was associated with malignant progression. In vitro, the results of CCK-8, TUNEL, wound healing and Transwell assays demonstrated that LIS1 promotes proliferation, inhibits apoptosis, and enhances the migration and invasion of SACC-LM cells. In vivo, knockdown of LIS1 effectively suppressed the growth of subcutaneous tumors in a mouse xenograft and distant metastasis of tumor cells in the metastasis model. The co-immunoprecipitation, immunofluorescence and western blot results also revealed that LIS1 binds to cytoplasmic linker protein 170 (CLIP170) to form a protein complex (LIS1/CLIP170), which activates the cell division control protein 42 homolog (Cdc42) signaling pathway to modulate the proliferation and anti-apoptosis of tumor cells, and enhanced invasion and metastasis by regulating the formation of invadopodia and the expression of MMPs in SACC-LM cells. Therefore, the present study demonstrated that LIS1 is a cancer promoter in SACC, and the molecular mechanism of the LIS1/CLIP170/Cdc42 signaling pathway is involved in the malignant progression, which offers a promising strategy for targeted therapy of SACC.

Nde1 and Ndel1: Outstanding Mysteries in Dynein-Mediated Transport

Cytoplasmic dynein-1 (dynein) is the primary microtubule minus-end directed molecular motor in most eukaryotes. As such, dynein has a broad array of functions that range from driving retrograde-directed cargo trafficking to forming and focusing the mitotic spindle. Dynein does not function in isolation. Instead, a network of regulatory proteins mediate dynein’s interaction with cargo and modulate dynein’s ability to engage with and move on the microtubule track. A flurry of research over the past decade has revealed the function and mechanism of many of dynein’s regulators, including Lis1, dynactin, and a family of proteins called activating adaptors. However, the mechanistic details of two of dynein’s important binding partners, the paralogs Nde1 and Ndel1, have remained elusive. While genetic studies have firmly established Nde1/Ndel1 as players in the dynein transport pathway, the nature of how they regulate dynein activity is unknown. In this review, we will compare Ndel1 and Nde1 with a focus on discerning if the proteins are functionally redundant, outline the data that places Nde1/Ndel1 in the dynein transport pathway, and explore the literature supporting and opposing the predominant hypothesis about Nde1/Ndel1’s molecular effect on dynein activity.

Structural basis for cytoplasmic dynein-1 regulation by Lis1

The lissencephaly 1 gene, LIS1, is mutated in patients with the neurodevelopmental disease lissencephaly. The Lis1 protein is conserved from fungi to mammals and is a key regulator of cytoplasmic dynein-1, the major minus-end-directed microtubule motor in many eukaryotes. Lis1 is the only dynein regulator known to bind directly to dynein's motor domain, and by doing so alters dynein's mechanochemistry. Lis1 is required for the formation of fully active dynein complexes, which also contain essential cofactors: dynactin and an activating adaptor. Here, we report the first high-resolution structure of the yeast dynein-Lis1 complex. Our 3.1 Å structure reveals, in molecular detail, the major contacts between dynein and Lis1 and between Lis1's ß-propellers. Structure-guided mutations in Lis1 and dynein show that these contacts are required for Lis1's ability to form fully active human dynein complexes and to regulate yeast dynein's mechanochemistry and in vivo function.

Nde1 is a Rab9 effector for loading late endosomes to cytoplasmic dynein motor complex

Rab9 is mainly located on late endosomes and required for their intracellular transport to trans-Golgi network (TGN). The cytoplasmic dynein motor, together with its regulatory proteins Nde1/Ndel1 and Lis1, controls intracellular retrograde transport of membranous organelles along the microtubule network. How late endosomes are tethered to the microtubule-based motor dynein for their retrograde transport remains unclear. Here, we demonstrate that the guanosine triphosphate (GTP)-bound Rab9A/B specifically uses Nde1/Ndel1 as an effector to interact with the dynein motor complex. We determined the crystal structure of Rab9A-GTP in complex with the Rab9-binding region of Nde1. The functional roles of key residues involved in the Rab9A-Nde1 interaction are verified using biochemical and cell biology assays. Rab9A mutants unable to bind to Nde1 also failed to associate with dynein, Lis1, and dynactin. Therefore, Nde1 is a Rab9 effector that tethers Rab9-associated late endosomes to the dynein motor for their retrograde transport to the TGN.

Dynein activation in vivo is regulated by the nucleotide states of its AAA3 domain

Cytoplasmic dynein is activated by the dynactin complex, cargo adapters and LIS1 (Lissencephaly 1). How this process is regulated in vivo remains unclear. The dynein motor ring contains six AAA+ (ATPases associated with diverse cellular activities) domains. Here, we used the filamentous fungus Aspergillus nidulans to examine whether ATP hydrolysis at AAA3 regulates dynein activation in the context of other regulators. In fungal hyphae, early endosomes undergo dynein-mediated movement away from the microtubule plus ends near the hyphal tip. Dynein normally accumulates at the microtubule plus ends. The early endosomal adaptor Hook protein, together with dynactin, drives dynein activation to cause its relocation to the microtubule minus ends. This activation process depends on LIS1, but LIS1 tends to dissociate from dynein after its activation. In this study, we found that dynein containing a mutation-blocking ATP hydrolysis at AAA3 can undergo LIS1-independent activation, consistent with our genetic data that the same mutation suppresses the growth defect of the A. nidulans LIS1-deletion mutant. Our data also suggest that blocking AAA3 ATP hydrolysis allows dynein activation by dynactin without the early endosomal adaptor. As a consequence, dynein accumulates at microtubule minus ends whereas early endosomes stay near the plus ends. Dynein containing a mutation-blocking ATP binding at AAA3 largely depends on LIS1 for activation, but this mutation abnormally prevents LIS1 dissociation upon dynein activation. Together, our data suggest that the AAA3 ATPase cycle regulates the coordination between dynein activation and cargo binding as well as the dynamic dynein-LIS1 interaction.

Mitochondrial adaptor TRAK2 activates and functionally links opposing kinesin and dynein motors

Mitochondria are transported along microtubules by opposing kinesin and dynein motors. Kinesin-1 and dynein-dynactin are linked to mitochondria by TRAK proteins, but it is unclear how TRAKs coordinate these motors. We used single-molecule imaging of cell lysates to show that TRAK2 robustly activates kinesin-1 for transport toward the microtubule plus-end. TRAK2 is also a novel dynein activating adaptor that utilizes a conserved coiled-coil motif to interact with dynein to promote motility toward the microtubule minus-end. However, dynein-mediated TRAK2 transport is minimal unless the dynein-binding protein LIS1 is present at a sufficient level. Using co-immunoprecipitation and co-localization experiments, we demonstrate that TRAK2 forms a complex containing both kinesin-1 and dynein-dynactin. These motors are functionally linked by TRAK2 as knockdown of either kinesin-1 or dynein-dynactin reduces the initiation of TRAK2 transport toward either microtubule end. We propose that TRAK2 coordinates kinesin-1 and dynein-dynactin as an interdependent motor complex, providing integrated control of opposing motors for the proper transport of mitochondria.

Self-repair protects microtubules from destruction by molecular motors

Microtubule instability stems from the low energy of tubulin dimer interactions, which sets the growing polymer close to its disassembly conditions. Molecular motors use ATP hydrolysis to produce mechanical work and move on microtubules. This raises the possibility that the mechanical work produced by walking motors can break dimer interactions and trigger microtubule disassembly. We tested this hypothesis by studying the interplay between microtubules and moving molecular motors in vitro. Our results show that molecular motors can remove tubulin dimers from the lattice and rapidly destroy microtubules. We also found that dimer removal by motors was compensated for by the insertion of free tubulin dimers into the microtubule lattice. This self-repair mechanism allows microtubules to survive the damage induced by molecular motors as they move along their tracks. Our study reveals the existence of coupling between the motion of molecular motors and the renewal of the microtubule lattice.

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.

Targeting allostery in the Dynein motor domain with small molecule inhibitors

Cytoplasmic dyneins are AAA (ATPase associated with diverse cellular activities) motor proteins responsible for microtubule minus-end-directed intracellular transport. Dynein's unusually large size, four distinct nucleotide-binding sites, and conformational dynamics pose challenges for the design of potent and selective chemical inhibitors. Here we use structural approaches to develop a model for the inhibition of a well-characterized S. cerevisiae dynein construct by pyrazolo-pyrimidinone-based compounds. These data, along with functional assays of dynein motility and mutagenesis studies, suggest that the compounds inhibit dynein by engaging the regulatory ATPase sites in the AAA3 and AAA4 domains, and not by interacting with dynein's main catalytic site in the AAA1 domain. A double Walker B mutation of the AAA3 and AAA4 sites substantially reduces enzyme activity, suggesting that targeting these regulatory domains is sufficient to inhibit dynein. Our findings reveal how chemical inhibitors can be designed to disrupt allosteric communication across dynein's AAA domains.

Roles of the multivalent dynein adaptors BicD2 and RILP in neurons

Cytoplasmic dynein is responsible for all forms of retrograde transport in neurons and other cells. Work over several years has led to the identification of a class of coiled-coil domain containing "adaptor" proteins that are responsible for expanding dynein's range of cargo interactions, as well as regulating dynein motor behavior. This brief review focuses first on the BicD family of adaptor proteins, which clearly serve to expand the number of dynein cargo interactions. RILP, another adaptor protein, also interacts with multiple proteins. Surprisingly, this is to mediate a series of steps within a common pathway, higher eukaryotic autophagy. These distinct features have important implications for understanding the full range of dynein adaptor functions.

Dynamic multimerization of Dab2-Myosin VI complexes regulates cargo processivity while minimizing cortical actin reorganization

Myosin VI ensembles on endocytic cargo facilitate directed transport through a dense cortical actin network. Myosin VI is recruited to clathrin-coated endosomes via the cargo adaptor Dab2. Canonically, it has been assumed that the interactions between a motor and its cargo adaptor are stable. However, it has been demonstrated that the force generated by multiple stably attached motors disrupts local cytoskeletal architecture, potentially compromising transport. In this study, we demonstrate that dynamic multimerization of myosin VI-Dab2 complexes facilitates cargo processivity without significant reorganization of cortical actin networks. Specifically, we find that Dab2 myosin interacting region (MIR) binds myosin VI with a moderate affinity (184 nM) and single-molecule kinetic measurements demonstrate a high rate of turnover (1 s⁻¹) of the Dab2 MIR–myosin VI interaction. Single-molecule motility shows that saturating Dab2-MIR concentration (2 μM) promotes myosin VI homodimerization and processivity with run lengths comparable with constitutive myosin VI dimers. Cargo-mimetic DNA origami scaffolds patterned with Dab2 MIR-myosin VI complexes are weakly processive, displaying sparse motility on single actin filaments and “stop-and-go” motion on a cellular actin network. On a minimal actin cortex assembled on lipid bilayers, unregulated processive movement by either constitutive myosin V or VI dimers results in actin remodeling and foci formation. In contrast, Dab2 MIR–myosin VI interactions preserve the integrity of a minimal cortical actin network. Taken together, our study demonstrates the importance of dynamic motor–cargo association in enabling cargo transportation without disrupting cytoskeletal organization.

N-Acetyl-D-Glucosamine Kinase Interacts with NudC and Lis1 in Dynein Motor Complex and Promotes Cell Migration

Recently, we showed that N-acetylglucosamine kinase (NAGK), an enzyme of amino sugar metabolism, interacts with dynein light chain roadblock type 1 (DYNLRB1) and promotes the functions of dynein motor. Here, we report that NAGK interacts with nuclear distribution protein C (NudC) and lissencephaly 1 (Lis1) in the dynein complex. Yeast two-hybrid assays, pull-down assays, immunocytochemistry, and proximity ligation assays revealed NAGK-NudC-Lis1-dynein complexes around nuclei, at the leading poles of migrating HEK293T cells, and at the tips of migratory processes of cultured rat neuroblast cells. The exogenous expression of red fluorescent protein (RFP)-tagged NAGK accelerated HEK293T cell migration during in vitro wound-healing assays and of neurons during in vitro neurosphere migration and in utero electroporation assays, whereas NAGK knockdown by short hairpin RNA (shRNA) delayed migration. Finally, a small NAGK peptide derived from the NudC interacting domain in in silico molecular docking analysis retarded the migrations of HEK293T and SH-SY5Y cells. These data indicate a functional interaction between NAGK and dynein-NudC-Lis1 complex at the nuclear envelope is required for the regulation of cell migration.

The regulatory function of the AAA4 ATPase domain of cytoplasmic dynein

Cytoplasmic dynein is the primary motor for microtubule minus-end-directed transport and is indispensable to eukaryotic cells. Although each motor domain of dynein contains three active AAA+ ATPases (AAA1, 3, and 4), only the functions of AAA1 and 3 are known. Here, we use single-molecule fluorescence and optical tweezers studies to elucidate the role of AAA4 in dynein's mechanochemical cycle. We demonstrate that AAA4 controls the priming stroke of the motion-generating linker, which connects the dimerizing tail of the motor to the AAA+ ring. Before ATP binds to AAA4, dynein remains incapable of generating motion. However, when AAA4 is bound to ATP, the gating of AAA1 by AAA3 prevails and dynein motion can occur. Thus, AAA1, 3, and 4 work together to regulate dynein function. Our work elucidates an essential role for AAA4 in dynein's stepping cycle and underscores the complexity and crosstalk among the motor's multiple AAA+ domains.

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.

Arsenic trioxide disturbs the LIS1/NDEL1/dynein microtubule dynamic complex by disrupting the CLIP170 zinc finger in head and neck cancer

Cancer mortality is mainly caused by metastasis, which requires dynamic remodeling of cytoskeletal components such as microtubules. Targeting microtubules presents a promising antimetastatic strategy that could prevent cancer spreading and recurrence. It is known that arsenic trioxide (ATO) is able to inhibit the migration and invasion of solid malignant tumors, but its exact molecular mechanism remains unclear. Here, we report a novel molecular target and antimetastatic mechanism of ATO in head and neck squamous cell carcinoma (HNSCC). We found that cytoplasmic linker protein 170 (CLIP170) was overexpressed in HNSCC tissues and cells compared to normal controls. ATO at non-cytotoxic level (1 μM) inhibited the migration and invasion of HNSCC cells by displacing zinc in the zinc finger motif of CLIP170, which is a key protein that controls microtubule dynamics. The antimetastatic effects of ATO were equivalent to those of siRNA-mediated CLIP170 knockdown. Furthermore, ATO dysregulated microtubule polymerization via the CLIP170/LIS1/NDEL1/dynein signaling pathway in Cal27 cells as a functional consequence of CLIP170 zinc finger disruption. The effect was partially reversed by zinc supplementation. Taken together, these findings reveal that CLIP170 is a novel molecular target of ATO and demonstrate the capability and underlying mechanisms of ATO as a potential antimetastatic agent for HNSCC treatment.

New insights into the mechanism of dynein motor regulation by lissencephaly-1

Lissencephaly (‘smooth brain’) is a severe brain disease associated with numerous symptoms, including cognitive impairment, and shortened lifespan. The main causative gene of this disease – lissencephaly-1 (LIS1) – has been a focus of intense scrutiny since its first identification almost 30 years ago. LIS1 is a critical regulator of the microtubule motor cytoplasmic dynein, which transports numerous cargoes throughout the cell, and is a key effector of nuclear and neuronal transport during brain development. Here, we review the role of LIS1 in cellular dynein function and discuss recent key findings that have revealed a new mechanism by which this molecule influences dynein-mediated transport. In addition to reconciling prior observations with this new model for LIS1 function, we also discuss phylogenetic data that suggest that LIS1 may have coevolved with an autoinhibitory mode of cytoplasmic dynein regulation.

Lis1 co-localizes with actin in the phagocytic cup and regulates phagocytosis

Phagocytosis, the ingestion of solid particles by cells is essential for nutrient uptake, innate immune response, antigen presentation and organelle homeostasis. Here we show that Lissencephaly-1 (Lis1), a well-known regulator of the microtubule motor dynein, co-localizes with actin at the phagocytic cup in the early stages of phagocytosis. Both knockdown and overexpression of Lis1 perturb phagocytosis, suggesting that Lis1 levels may be regulated during particle engulfment to facilitate remodeling of actin filaments within the phagocytic cup. This requirement of Lis1 is replicated in mouse macrophage cells as well as in the amoeba Dictyostelium, indicating an evolutionarily conserved role for Lis1 in phagocytosis. In support of these findings, Dictyostelium cells overexpressing Lis1 show defects in migration possibly caused by dysregulated actin. Taken together, Lis1 localizes to the phagocytic cup and influences the actin cytoskeleton in a manner that appears important for the uptake of solid particles into cells.

CENP-F stabilizes kinetochore-microtubule attachments and limits dynein stripping of corona cargoes

Accurate chromosome segregation demands efficient capture of microtubules by kinetochores and their conversion to stable bioriented attachments that can congress and then segregate chromosomes. An early event is the shedding of the outermost fibrous corona layer of the kinetochore following microtubule attachment. Centromere protein F (CENP-F) is part of the corona, contains two microtubule-binding domains, and physically associates with dynein motor regulators. Here, we have combined CRISPR gene editing and engineered separation-of-function mutants to define how CENP-F contributes to kinetochore function. We show that the two microtubule-binding domains make distinct contributions to attachment stability and force transduction but are dispensable for chromosome congression. We further identify a specialized domain that functions to limit the dynein-mediated stripping of corona cargoes through a direct interaction with Nde1. This antagonistic activity is crucial for maintaining the required corona composition and ensuring efficient kinetochore biorientation.

Activation and Regulation of Cytoplasmic Dynein

Cytoplasmic dynein is an AAA+ motor that drives the transport of many intracellular cargoes towards the minus end of microtubules (MTs). Previous in vitro studies characterized isolated dynein as an exceptionally weak motor that moves slowly and diffuses on an MT. Recent studies altered this view by demonstrating that dynein remains in an autoinhibited conformation on its own, and processive motility is activated when it forms a ternary complex with dynactin and a cargo adaptor. This complex assembles more efficiently in the presence of Lis1, providing an explanation for why Lis1 is a required cofactor for most cytoplasmic dynein-driven processes in cells. This review describes how dynein motility is activated and regulated by cargo adaptors and accessory proteins.

LIS1 promotes the formation of activated cytoplasmic dynein-1 complexes

Cytoplasmic dynein-1 is a molecular motor that drives nearly all minus-end-directed microtubule-based transport in human cells, performing functions that range from retrograde axonal transport to mitotic spindle assembly1,2. Activated dynein complexes consist of one or two dynein dimers, the dynactin complex and an 'activating adaptor', and they show faster velocity when two dynein dimers are present3-6. Little is known about the assembly process of this massive ~4 MDa complex. Here, using purified recombinant human proteins, we uncover a role for the dynein-binding protein LIS1 in promoting the formation of activated dynein-dynactin complexes that contain two dynein dimers. Complexes activated by proteins representing three families of activating adaptors-BicD2, Hook3 and Ninl-all show enhanced motile properties in the presence of LIS1. Activated dynein complexes do not require sustained LIS1 binding for fast velocity. Using cryo-electron microscopy, we show that human LIS1 binds to dynein at two sites on the motor domain of dynein. Our research suggests that LIS1 binding at these sites functions in multiple stages of assembling the motile dynein-dynactin-activating adaptor complex.

Lis1 activates dynein motility by modulating its pairing with dynactin

Lissencephaly-1 (Lis1) is a key cofactor for dynein-mediated intracellular transport towards the minus-ends of microtubules. It remains unclear whether Lis1 serves as an inhibitor or an activator of mammalian dynein motility. Here we use single-molecule imaging and optical trapping to show that Lis1 does not directly alter the stepping and force production of individual dynein motors assembled with dynactin and a cargo adaptor. Instead, Lis1 promotes the formation of an active complex with dynactin. Lis1 also favours the recruitment of two dyneins to dynactin, resulting in increased velocity, higher force production and more effective competition against kinesin in a tug-of-war. Lis1 dissociates from motile complexes, indicating that its primary role is to orchestrate the assembly of the transport machinery. We propose that Lis1 binding releases dynein from its autoinhibited state, which provides a mechanistic explanation for why Lis1 is required for efficient transport of many dynein-associated cargos in cells.

Pac1/LIS1 stabilizes an uninhibited conformation of dynein to coordinate its localization and activity

Dynein is a microtubule motor that transports many different cargos in various cell types and contexts. How dynein is regulated to perform these activities with spatial and temporal precision remains unclear. Human dynein is regulated by autoinhibition, whereby intermolecular contacts limit motor activity. Whether this mechanism is conserved throughout evolution, whether it can be affected by extrinsic factors, and its role in regulating dynein function remain unclear. Here, we use a combination of negative stain electron microscopy, single-molecule assays, genetic, and cell biological techniques to show that autoinhibition is conserved in budding yeast, and plays a key role in coordinating in vivo dynein function. Moreover, we find that the Lissencephaly-related protein, LIS1 (Pac1 in yeast), plays an important role in regulating dynein autoinhibition. Our studies demonstrate that, rather than inhibiting dynein motility, Pac1/LIS1 promotes dynein activity by stabilizing the uninhibited conformation, which ensures appropriate dynein localization and activity in cells.

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.

What Could Go Wrong? A Practical Guide to Single-Particle Cryo-EM: From Biochemistry to Atomic Models

Cryo-electron microscopy (cryo-EM) has enjoyed explosive recent growth due to revolutionary advances in hardware and software, resulting in a steady stream of long-awaited, high-resolution structures with unprecedented atomic detail. With this comes an increased number of microscopes, cryo-EM facilities, and scientists eager to leverage the ability to determine protein structures without crystallization. However, numerous pitfalls and considerations beset the path toward high-resolution structures and are not necessarily obvious from literature surveys. Here, we detail the most common misconceptions when initiating a cryo-EM project and common technical hurdles, as well as their solutions, and we conclude with a vision for the future of this exciting field.

Microtubule-Dependent Trafficking of Alphaherpesviruses in the Nervous System: The Ins and Outs

The Alphaherpesvirinae include the neurotropic pathogens herpes simplex virus and varicella zoster virus of humans and pseudorabies virus of swine. These viruses establish lifelong latency in the nuclei of peripheral ganglia, but utilize the peripheral tissues those neurons innervate for productive replication, spread, and transmission. Delivery of virions from replicative pools to the sites of latency requires microtubule-directed retrograde axonal transport from the nerve terminus to the cell body of the sensory neuron. As a corollary, during reactivation newly assembled virions must travel along axonal microtubules in the anterograde direction to return to the nerve terminus and infect peripheral tissues, completing the cycle. Neurotropic alphaherpesviruses can therefore exploit neuronal microtubules and motors for long distance axonal transport, and alternate between periods of sustained plus end- and minus end-directed motion at different stages of their infectious cycle. This review summarizes our current understanding of the molecular details by which this is achieved.

LIS1 regulates cargo-adapter-mediated activation of dynein by overcoming its autoinhibition in vivo

Deficiency of the LIS1 protein causes lissencephaly, a brain developmental disorder. Although LIS1 binds the microtubule motor cytoplasmic dynein and has been linked to dynein function in many experimental systems, its mechanism of action remains unclear. Here, we revealed its function in cargo-adapter-mediated dynein activation in the model organism Aspergillus nidulans Specifically, we found that overexpressed cargo adapter HookA (Hook in A. nidulans) missing its cargo-binding domain (ΔC-HookA) causes dynein and its regulator dynactin to relocate from the microtubule plus ends to the minus ends, and this relocation requires LIS1 and its binding protein, NudE. Astonishingly, the requirement for LIS1 or NudE can be bypassed to a significant extent by mutations that prohibit dynein from forming an autoinhibited conformation in which the motor domains of the dynein dimer are held close together. Our results suggest a novel mechanism of LIS1 action that promotes the switch of dynein from the autoinhibited state to an open state to facilitate dynein activation.

Fighting Cancer Stem Cell Fate by Targeting LIS1 a WD40 Repeat Protein

Cancer is one of the most frequent and devastating diseases. Previous reports have shown that radio and chemo-resistant cancer stem cell (CSC) population is primarily responsible for cancer recurrences after radiotherapy and chemotherapy. Other studies demonstrated that Lissencephaly-1 (LIS1) protein, also known as platelet activating factor acetylhydrolase 1b regulatory subunit 1 (PAFAH1B1), a dynein-binding protein involved in neural stem cell division, plays a crucial role in maintaining CSC population in hematological malignancies. Moreover, one recent report demonstrated that LIS1 gene is preferentially expressed in CD133+ glioblastoma cells and may have also an important role in regulating CD133+ CSC in glioblastoma. The hypothesis of this paper is that LIS1 plays a key role in maintaining CD133+ CSC population in various solid cancers by orientating the cell division plane through an interaction with dynein and therefore controlling the stem cell fate regulatory mechanism. As CD133+ CSC population is responsible for radio- and chemo-resistance, which finally determines the cancer recurrences and metastases, identifying the molecular mechanisms which regulate the CD133+ CSC population represents a major target for cancer research. Given the structure of LIS1, which contains WD40 repeat domain, small peptide inhibitors could be used to alter its function. Therefore, the impact of confirming this hypothesis is significant because LIS1 may become an important molecular target for future adjuvant anticancer therapies directed against radio- and chemo-resistant CSC population.

Hook3 is a scaffold for the opposite-polarity microtubule-based motors cytoplasmic dynein-1 and KIF1C

The unidirectional and opposite-polarity microtubule-based motors, dynein and kinesin, drive long-distance intracellular cargo transport. Cellular observations suggest that opposite-polarity motors may be coupled. We recently identified an interaction between the cytoplasmic dynein-1 activating adaptor Hook3 and the kinesin-3 KIF1C. Here, using in vitro reconstitutions with purified components, we show that KIF1C and dynein/dynactin can exist in a complex scaffolded by Hook3. Full-length Hook3 binds to and activates dynein/dynactin motility. Hook3 also binds to a short region in the "tail" of KIF1C, but unlike dynein/dynactin, this interaction does not activate KIF1C. Hook3 scaffolding allows dynein to transport KIF1C toward the microtubule minus end, and KIF1C to transport dynein toward the microtubule plus end. In cells, KIF1C can recruit Hook3 to the cell periphery, although the cellular role of the complex containing both motors remains unknown. We propose that Hook3's ability to scaffold dynein/dynactin and KIF1C may regulate bidirectional motility, promote motor recycling, or sequester the pool of available dynein/dynactin activating adaptors.

Interplay of LIS1 and MeCP2: Interactions and Implications With the Neurodevelopmental Disorders Lissencephaly and Rett Syndrome

LIS1 is the main causative gene for lissencephaly, while MeCP2 is the main causative gene for Rett syndrome, both of which are neurodevelopmental diseases. Here we report nuclear functions for LIS1 and identify previously unrecognized physical and genetic interactions between the products of these two genes in the cell nucleus, that has implications on MeCP2 organization, neuronal gene expression and mouse behavior. Reduced LIS1 levels affect the association of MeCP2 with chromatin. Transcriptome analysis of primary cortical neurons derived from wild type, Lis1±, MeCP2−/y, or double mutants mice revealed a large overlap in the differentially expressed (DE) genes between the various mutants. Overall, our findings provide insights on molecular mechanisms involved in the neurodevelopmental disorders lissencephaly and Rett syndrome caused by dysfunction of LIS1 and MeCP2, respectively.

Dynein activators and adaptors at a glance

Cytoplasmic dynein-1 (hereafter dynein) is an essential cellular motor that drives the movement of diverse cargos along the microtubule cytoskeleton, including organelles, vesicles and RNAs. A long-standing question is how a single form of dynein can be adapted to a wide range of cellular functions in both interphase and mitosis. Recent progress has provided new insights - dynein interacts with a group of activating adaptors that provide cargo-specific and/or function-specific regulation of the motor complex. Activating adaptors such as BICD2 and Hook1 enhance the stability of the complex that dynein forms with its required activator dynactin, leading to highly processive motility toward the microtubule minus end. Furthermore, activating adaptors mediate specific interactions of the motor complex with cargos such as Rab6-positive vesicles or ribonucleoprotein particles for BICD2, and signaling endosomes for Hook1. In this Cell Science at a Glance article and accompanying poster, we highlight the conserved structural features found in dynein activators, the effects of these activators on biophysical parameters, such as motor velocity and stall force, and the specific intracellular functions they mediate.

RNA localization and transport

RNA localization serves numerous purposes from controlling development and differentiation to supporting the physiological activities of cells and organisms. After a brief introduction into the history of the study of mRNA localization I will focus on animal systems, describing in which cellular compartments and in which cell types mRNA localization was observed and studied. In recent years numerous novel localization patterns have been described, and countless mRNAs have been documented to accumulate in specific subcellular compartments. These fascinating revelations prompted speculations about the purpose of localizing all these mRNAs. In recent years experimental evidence for an unexpected variety of different functions has started to emerge. Aside from focusing on the functional aspects, I will discuss various ways of localizing mRNAs with a focus on the mechanism of active and directed transport on cytoskeletal tracks. Structural studies combined with imaging of transport and biochemical studies have contributed to the enormous recent progress, particularly in understanding how dynein/dynactin/BicD (DDB) dependent transport on microtubules works. This transport process actively localizes diverse cargo in similar ways to the minus end of microtubules and, at least in flies, also individual mRNA molecules. A sophisticated mechanism ensures that cargo loading licenses processive transport.