The Golgi apparatus controls the formation of non-centrosomal microtubule arrays important for Golgi organization, polarized transport, cell motility, and cell differentiation. Here, we show that ...CAMSAP2 stabilizes and attaches microtubule minus ends to the Golgi through a complex of AKAP450 and myomegalin. CLASPs stabilize CAMSAP2-decorated microtubules but are not required for their Golgi tethering. AKAP450 is also essential for Golgi microtubule nucleation, and myomegalin and CDK5RAP2 but not CAMSAP2 contribute to this function. In the absence of centrosomes, AKAP450- and CAMSAP2-dependent pathways of microtubule minus-end organization become dominant, and the presence of at least one of them is needed to maintain microtubule density. Strikingly, a compact Golgi can be assembled in the absence of both centrosomal and Golgi microtubules. However, CAMSAP2- and AKAP450-dependent Golgi microtubules facilitate Golgi reorientation and cell invasion in a 3D matrix. We propose that Golgi-anchored microtubules are important for polarized cell movement but not for coalescence of Golgi membranes.
•CAMSAP2 stabilizes microtubule minus ends at the Golgi•A complex of AKAP450 and myomegalin recruits CAMSAP2-bound microtubules to the Golgi•A single Golgi can be maintained in the absence of centrosome and Golgi microtubules•Golgi microtubules facilitate cell reorientation and migration in 3D matrix
Wu et al. describe how a microtubule minus-end-binding protein, CAMSAP2, acts together with Golgi-associated proteins AKAP450 and myomegalin to promote microtubule organization at the Golgi. They also show how these proteins affect cell migration and describe the redundancy between the centrosome-dependent and -independent pathways in microtubule minus-end stabilization.
In neurons, the distinct molecular composition of axons and dendrites is established through polarized targeting mechanisms, but it is currently unclear how nonpolarized cargoes, such as ...mitochondria, become uniformly distributed over these specialized neuronal compartments. Here, we show that TRAK family adaptor proteins, TRAK1 and TRAK2, which link mitochondria to microtubule-based motors, are required for axonal and dendritic mitochondrial motility and utilize different transport machineries to steer mitochondria into axons and dendrites. TRAK1 binds to both kinesin-1 and dynein/dynactin, is prominently localized in axons, and is needed for normal axon outgrowth, whereas TRAK2 predominantly interacts with dynein/dynactin, is more abundantly present in dendrites, and is required for dendritic development. These functional differences follow from their distinct conformations: TRAK2 preferentially adopts a head-to-tail interaction, which interferes with kinesin-1 binding and axonal transport. Our study demonstrates how the molecular interplay between bidirectional adaptor proteins and distinct microtubule-based motors drives polarized mitochondrial transport.
► Kinesin-1 and dynein drive mitochondrial transport to axons and dendrites ► TRAK1 binds to both kinesin-1 and dynein/dynactin and is localized in axons ► TRAK2 predominantly interacts with dynein/dynactin and is present in dendrites ► TRAK2 backfolding inhibits kinesin-1 binding and controls mitochondrial transport
van Spronsen et al. show that mitochondria utilize different machineries to steer their transport into axons and dendrites. The molecular interplay between mitochondrial adaptor protein family TRAK/Milton and distinct microtubule-based motors drives polarized mitochondrial transport.
Cytoplasmic dynein is the major microtubule minus-end-directed cellular motor. Most dynein activities require dynactin, but the mechanisms regulating cargo-dependent dynein-dynactin interaction are ...poorly understood. In this study, we focus on dynein-dynactin recruitment to cargo by the conserved motor adaptor Bicaudal D2 (BICD2). We show that dynein and dynactin depend on each other for BICD2-mediated targeting to cargo and that BICD2 N-terminus (BICD2-N) strongly promotes stable interaction between dynein and dynactin both in vitro and in vivo. Direct visualization of dynein in live cells indicates that by itself the triple BICD2-N-dynein-dynactin complex is unable to interact with either cargo or microtubules. However, tethering of BICD2-N to different membranes promotes their microtubule minus-end-directed motility. We further show that LIS1 is required for dynein-mediated transport induced by membrane tethering of BICD2-N and that LIS1 contributes to dynein accumulation at microtubule plus ends and BICD2-positive cellular structures. Our results demonstrate that dynein recruitment to cargo requires concerted action of multiple dynein cofactors.
Radial glial progenitors (RGPs) are elongated epithelial cells that give rise to neurons, glia, and adult stem cells during brain development. RGP nuclei migrate basally during G1, apically using ...cytoplasmic dynein during G2, and undergo mitosis at the ventricular surface. By live imaging of in utero electroporated rat brain, we find that two distinct G2-specific mechanisms for dynein nuclear pore recruitment are essential for apical nuclear migration. The “RanBP2-BicD2” and “Nup133-CENP-F” pathways act sequentially, with Nup133 or CENP-F RNAi arresting nuclei close to the ventricular surface in a premitotic state. Forced targeting of dynein to the nuclear envelope rescues nuclear migration and cell-cycle progression, demonstrating that apical nuclear migration is not simply correlated with cell-cycle progression from G2 to mitosis, but rather, is a required event. These results reveal that cell-cycle control of apical nuclear migration occurs by motor protein recruitment and identify a role for nucleus- and centrosome-associated forces in mitotic entry.
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•Nuclear pore recruitment of dynein in RGPs mediates G2 apical nuclear migration•Two-step dynein recruitment required for mitotic entry and neurogenesis•RNAi for late recruitment factors interferes with centrosome motility•Forced dynein recruitment restores nuclear migration and cell-cycle progression
Two pathways that target dynein to nuclear pores are required for apical nuclear migration in neural progenitors. This dynein-mediated movement of the nucleus is also required to drive entry into mitosis, indicating a role for nucleus-related forces and/or nuclear cellular environment in cell-cycle progression.
Plant cells cannot rearrange their positions; therefore, sharp tissue boundaries must be accurately programmed. Movement of the cell fate regulator SHORT-ROOT from the stele to the ground tissue has ...been associated with transferring positional information across tissue boundaries. The zinc finger BIRD protein JACKDAW has been shown to constrain SHORT-ROOT movement to a single layer, and other BIRD family proteins were postulated to counteract JACKDAW’s role in restricting SHORT-ROOT action range. Here, we report that regulation of SHORT-ROOT movement requires additional BIRD proteins whose action is critical for the establishment and maintenance of the boundary between stele and ground tissue. We show that BIRD proteins act in concert and not in opposition. The exploitation of asymmetric redundancies allows the separation of two BIRD functions: constraining SHORTROOT spread through nuclear retention and transcriptional regulation of key downstream SHORT-ROOT targets, including SCARECROW and CYCLIND6. Our data indicate that BIRD proteins promote formative divisions and tissue specification in the Arabidopsis thaliana root meristem ground tissue by tethering and regulating transcriptional competence of SHORT-ROOT complexes. As a result, a tissue boundary is not “locked in” after initial patterning like in many animal systems, but possesses considerable developmental plasticity due to continuous reliance on mobile transcription factors.
Microtubules are filamentous polymers essential for cell viability. Microtubule plus-end tracking proteins (+TIPs) associate with growing microtubule plus ends and control microtubule dynamics and ...interactions with different cellular structures during cell division, migration, and morphogenesis. EB1 and its homologs are highly conserved proteins that play an important role in the targeting of +TIPs to microtubule ends, but the underlying molecular mechanism remains elusive. By using live cell experiments and in vitro reconstitution assays, we demonstrate that a short polypeptide motif, Ser-x-Ile-Pro (SxIP), is used by numerous +TIPs, including the tumor suppressor APC, the transmembrane protein STIM1, and the kinesin MCAK, for localization to microtubule tips in an EB1-dependent manner. Structural and biochemical data reveal the molecular basis of the EB1-SxIP interaction and explain its negative regulation by phosphorylation. Our findings establish a general “microtubule tip localization signal” (MtLS) and delineate a unifying mechanism for this subcellular protein targeting process.
Regulation of microtubule dynamic instability van der Vaart, Babet; Akhmanova, Anna; Straube, Anne
Biochemical Society transactions,
10/2009, Letnik:
37, Številka:
Pt 5
Journal Article
Recenzirano
Proper regulation of MT (microtubule) dynamics is essential for various vital processes, including the segregation of chromosomes, directional cell migration and differentiation. MT assembly and ...disassembly is modulated by a complex network of intracellular factors that co-operate or antagonize each other, are highly regulated in space and time and are thus attuned to the cell cycle and differentiation processes. While we only begin to appreciate how the concerted action of MT stabilizers and destabilizers shapes different MT patterns, a clear picture of how individual factors affect the MT structure is emerging. In this paper, we review the current knowledge about proteins that modulate MT dynamic instability.
The development and homeostasis of neurons relies heavily on the selective targeting of vesicles into axon and dendrites. Microtubule-based motor proteins play an important role in polarized ...transport; however, the sorting mechanism to exclude dendritic cargo from the axon is unclear. We show that the dynein regulator NDEL1 controls somatodendritic cargo transport at the axon initial segment (AIS). NDEL1 localizes to the AIS via an interaction with the scaffold protein Ankyrin-G. Depletion of NDEL1 or its binding partner LIS1 results in both cell-wide and local defects, including the non-polarized trafficking of dendritic cargo through the AIS. We propose a model in which LIS1 is a critical mediator of local NDEL1-based dynein activation at the AIS. By localizing to the AIS, NDEL1 facilitates the reversal of somatodendritic cargos in the proximal axon.
•NDEL1 redistributes from the centrosome to the AIS during neurodevelopment•Dynein regulator NDEL1 stably binds to Ankyrin-G at the AIS•The motor protein dynein drives transport of somatodendritic cargo out of the AIS•Accumulation of NDEL1 at the AIS is necessary for efficient local cargo reversal
Polarized cargo transport ensures the sorting of vesicles specifically into the axon or dendrites. Kuijpers et al. reveal a critical role for dynein regulator NDEL1 as a gatekeeper of somatodendritic cargos at the axon initial segment.
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The cross-talk between dynamic microtubules and integrin-based adhesions to the extracellular matrix plays a crucial role in cell polarity and migration. Microtubules regulate the turnover of ...adhesion sites, and, in turn, focal adhesions promote the cortical microtubule capture and stabilization in their vicinity, but the underlying mechanism is unknown. Here, we show that cortical microtubule stabilization sites containing CLASPs, KIF21A, LL5β and liprins are recruited to focal adhesions by the adaptor protein KANK1, which directly interacts with the major adhesion component, talin. Structural studies showed that the conserved KN domain in KANK1 binds to the talin rod domain R7. Perturbation of this interaction, including a single point mutation in talin, which disrupts KANK1 binding but not the talin function in adhesion, abrogates the association of microtubule-stabilizing complexes with focal adhesions. We propose that the talin-KANK1 interaction links the two macromolecular assemblies that control cortical attachment of actin fibers and microtubules.
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