Cytoskeleton (Hoboken, N.J.)最新文献

Microtubules are highly adaptable cytoskeletal polymers whose dynamic nature supports a broad spectrum of cellular activities. Their dynamic behavior is regulated by an intricate network of factors, including tubulin isotypes and post-translational modifications. Together, these elements shape the properties of microtubules in response to both intrinsic and extrinsic cues. Within this regulatory landscape, the "tubulin code" has been proposed as a conceptual framework to explain how subtle molecular variations shape context-specific microtubule functions. Among mammalian α-tubulin isotypes, TUBA4A is characterized by the unique C-terminal tail, distinct biochemical behaviors, enriched expression in multiple tissues (e.g., in the central nervous system) and emerging roles in neurodegeneration. This review summarizes the molecular and physiological features of TUBA4A, highlights its potential contributions to normal neuronal function and neurological disorders, and offers perspectives for future studies.

Elastic tethers connect telomeres of separating chromosomes in anaphase of animal cells. Immunofluorescence staining of titin in crane-fly spermatocytes, using 4 different antibodies, shows that the giant elastic protein titin seems to be a component of mitotic tethers: titin "strands" extend between separating chromosomes, connecting their telomeres, just as tethers do. Since titin is responsible for elastic forces in myofibrils, we suggest that titin is responsible for the backwards forces exerted on chromosome arms during anaphase.

Cilia, evolutionarily conserved organelles on eukaryotic cell surfaces, depend on the intraflagellar transport (IFT) system for their assembly, maintenance, and signaling. The IFT system orchestrates bidirectional trafficking of structural components and signaling molecules through coordinated actions of protein complexes and molecular motors. IFT complexes assemble into anterograde trains at the ciliary base and undergo structural remodeling at the ciliary tip to form retrograde trains, with bidirectional motility regulated by modifications on the trains per se and the microtubule tracks. The BBSome rides with the IFT train and serves as a pivotal adaptor linking membrane cargos to the IFT train primarily for cargo exit from the cilia. Mutations in cilium-related genes from human ciliopathies contribute to the understanding of the IFT machinery. This review comprehensively delineates the molecular architecture, transport mechanisms, and regulatory networks of IFT complexes, bridging their functional dysregulation to disease phenotypes and advancing mechanistic insights.

The centrosomal protein of 44 kDa (CEP44) is essential for centriole duplication, centrosome cohesion, and spindle integrity. It localizes to the proximal end of centrioles and associates with spindle microtubules. Liquid-liquid phase separation (LLPS) is a process by which biomolecules undergo demixing into distinct liquid-like phases, facilitating the formation of cellular condensates such as the centrosome. However, whether CEP44 possesses LLPS properties remains unclear. In this study, we identified intrinsically disordered regions (IDRs) within CEP44, and droplet formation assays confirmed its capacity to form liquid droplets in vivo and in vitro. Immunoblotting detected O-GlcNAcylation of CEP44, indicating its interaction with O-GlcNAc transferase (OGT). Subsequent immunostaining demonstrated that O-GlcNAcylation promotes CEP44 droplet fusion. Post-translational modification prediction analysis suggested a potential interplay between O-GlcNAcylation and phosphorylation that may modulate the structural dynamics of CEP44. Overall, our findings reveal the LLPS capability of CEP44 and underscore the critical role of O-GlcNAcylation in regulating CEP44 droplet fusion and potentially influencing its subcellular localization.

The precise control of microtubule dynamics is essential for diverse cellular processes and is a promising target for optical regulation using photoresponsive molecules. In this study, we developed Tau-derived peptides bearing azobenzene moieties on their side chains that enabled reversible photocontrol of microtubule polymerization by binding to the inside of microtubules. Two peptide derivatives with azobenzene located at different positions were synthesized by simple on-resin Fmoc solid-phase chemistry. Confocal microscopy and competition assays confirmed that both derivatives target the Taxol-binding pocket inside microtubules. Although both cis- and trans-forms bound microtubules, only the cis-form of one derivative (cis-TMR-Azo-TP2) significantly enhanced microtubule polymerization with longer lengths compared with the corresponding trans-form (trans-TMR-Azo-TP2). Moreover, light-dependent switching of microtubule length was achieved via photoisomerization. These findings highlight azobenzene-functionalized Tau-derived peptides as a versatile platform for achieving spatiotemporal control over microtubule polymerization using optical stimuli.

The Arp2/3 complex is a key actin nucleator essential for cytoskeletal dynamics in eukaryotes. Previously believed absent in apicomplexan parasites, we recently identified an atypical Arp2/3 complex in malaria parasites consisting of five divergent subunits and a putative kinetochore-associated factor. This complex ensures proper kinetochore-spindle attachment during male gametogenesis, likely by nucleating actin at the mitotic spindle. Disruption of Arp2/3 function or actin polymerization leads to defective DNA segregation into gametes and developmental arrest of the parasite in the mosquito. Our findings reveal unexpected diversity in Arp2/3 complex composition and function, highlighting specialized adaptations in malaria parasites and expanding our understanding of the Arp2/3 complex and actin functions during mitosis. Here, we discuss some of the open questions that need to be addressed to fully understand the molecular mechanism of this unusual Arp2/3 complex and its essential role in malaria transmission.

Kinesin-1 is a dimeric motor protein that moves towards the microtubule plus-end in a hand-over-hand fashion. However, the minimal motor domain of kinesin-1 is a single head, and the mechanism by which minimal motor domains generate the force for directional movement remains poorly understood. Here, we engineered artificial tethers (polyethylene glycol, single-stranded DNA, or double-stranded DNA) within the motor domain to investigate whether tether properties such as charge, length, and stiffness affect the motility of teams of kinesin-1 monomers. Neck-linker tethered kinesin with long stiff tethers was found to decrease microtubule-gliding velocity in an in vitro gliding assay, indicating that amplified conformational changes in the neck-linker do not enhance motility. Loop-12 tethered kinesin monomers with various tethers showed consistent minus-end-directed motility, reversing the usual polarity of kinesin-1 monomers. Moreover, loop-3 tethered kinesin monomers switched their directionality depending on tether stiffness. These results indicate that the tether has the potential to influence the direction in which the minimal motor domain moves. We argue that the determinants of motility exist in the minimal motor domain, with the combination of tether properties and its attachment position altering the MT-gliding velocity and direction.

The centrosome, an evolutionarily conserved organelle in most animal cells, plays a pivotal role in fundamental processes such as cell division and ciliogenesis. Recent evidence increasingly highlights active crosstalk between the centrosome and the signaling pathways, through which cells dynamically detect and respond to diverse extracellular and intracellular cues. In this review, we summarize the roles of the centrosome in multiple signaling pathways, including Hedgehog, Wnt, and Notch that govern cellular growth, division, differentiation, and tissue homeostasis. We also explore how these interactions mold centrosomal behavior, emphasizing its function as a hub for signaling integration.

Dyneins were present in the last eukaryotic common ancestor (LECA) and play key roles in eukaryotic biology. Axonemal dyneins form the inner and outer arms that power ciliary beating, and it has long been recognized that outer arms in some organisms contain two different heavy chain motors, whereas those from other species contain a third unit that imparts enhanced motive force during ciliary beating. Previous phylogenetic analyses suggested that this third motor derived from a gene duplication event in the LECA, followed by the subsequent replacement of the N-terminal assembly domain with one formed from kelch and immunoglobulin repeats. Here I revisit the origin and organization of this dynein, combining the increased breadth of sequence information now available, AlphaFold modeling, and the recent recovery of a robustly rooted eukaryotic tree-of-life. This analysis confirms the third outer arm dynein HC arose in a common ancestor of the Diaphoretickes, with a basic N-terminal domain consisting of a β-propeller structure followed by two immunoglobulin folds. However, this region has undergone further diversification in some groups, gaining an additional full or partial β-propeller located immediately adjacent to the AAA motor domain. Thus, three variant forms of this N-terminal segment are discernable in extant eukaryotes.