Cytoskeleton (Hoboken, N.J.)最新文献

Actin, a ubiquitous and highly conserved cytoskeletal protein, plays a pivotal role in various cellular functions such as structural support, facilitating cell motility, and contributing to the dynamic processes of synaptic function. Apart from its established role in inducing morphological changes, recent developments in the field indicate an active involvement of actin in modulating both the structure and function of pre- and postsynaptic terminals. Within the presynapse, it is involved in the organization and trafficking of synaptic vesicles, contributing to neurotransmitter release. In the postsynapse, actin dynamically modulates dendritic spines, influencing the postsynaptic density organization and anchoring of neurotransmitter receptors. In addition, the dynamic interplay of actin at the synapse underscores its essential role in regulating neural communication. This review strives to offer a comprehensive overview of the recent advancements in understanding the multifaceted role of the actin cytoskeleton in synaptic functions. By emphasizing its aberrant regulation, we aim to provide valuable insights into the underlying mechanisms of Alzheimer's disease pathophysiology.

Not only for man-made architecture but also for living cells, the relationship between force and structure is a fundamental properties that governs their mechanical behaviors. However, our knowledge of the mechanical properties of intracellular structures is very limited because of the lack of direct measurement methods. We established high-force intracellular magnetic tweezers that can generate calibrated forces up to 10 nN, enabling direct force measurements of the cytoskeleton. Using this method, we show that the strain field of the microtubule and actin meshwork follow the same scaling, suggesting that the two cytoskeletal systems behave as an integrated elastic body. Furthermore, quantification of structural response of single microtubules demonstrates that microtubules are enclosed by the elastic medium of filamentous actin. Our results defining the force-structure relationship of the cytoskeleton serve as a framework to understand cellular behaviors by direct intracellular mechanical measurement.

Cytokinesis in animal and fungal cells requires the contraction of actomyosin-based contractile rings formed in the division cortex of the cell during late mitosis. However, the detailed mechanism remains incompletely understood. Here, we aim to develop a novel cell-free system by encapsulating cell extracts obtained from fission yeast cells within lipid vesicles, which subsequently leads to the formation of a contractile ring-like structure inside the vesicles. Using this system, we found that an actin ring structure formed in vesicles of a size similar to that of fission yeast cells, with the frequency of ring appearance increasing in the presence of PI(4,5)P₂ (PIP₂). In contrast, larger vesicles tended to form actin bundles, which were sometimes associated with ring structures or network-like structures. The effects of various inhibitors affecting cytoskeleton formation were investigated, revealing that actin polymerization was essential for the formation of these actin structures. Additionally, the involvement of ATP, the Schizosaccharomyces pombe PLK "Plo1," and the small GTPase Rho was suggested to play a crucial role in this process. Examination of mitotic extracts revealed the formation of actin dot structures in phosphatidylethanolamine vesicles. However, most of these structures disappeared in the presence of PIP₂, leading to the formation of actin Rings instead. Using extracts from cells expressing α-actinin Ain1 or myosin-II light chain Rlc1, both fused with fluorescent proteins, we found that these proteins colocalized with actin bundles. In summary, we have developed a new semi-in vitro system to investigate mechanisms such as cell division and cytoskeleton formation.

Single molecule tracking and super-resolution microscopy of integrin adhesion proteins and actin in developing Drosophila muscle attachment sites reveals that nanotopography triggered by Arp2/3-dependent actin protrusions promotes stable adhesion formation. The nanodomains formed during this process confine the diffusion of integrins and promote their immobilization. Spatial confinement is also applied to the motion of actin filaments, resulting in enhanced mechanical connection with the integrin adhesion complex. Fabricated nano-structured surfaces mimicking the nanotopography observed in living tissue are able to recapitulate the formation of these adhesions in isolated muscle cells and the confinement of integrin diffusion. These results emphasize the importance of geometrical regulation of tissue morphogenesis at a single molecule level.

Dyneins are huge motor protein complexes that are essential for cell motility, cell division, and intracellular transport. Dyneins are classified into three major subfamilies, namely cytoplasmic, intraflagellar-transport (IFT), and ciliary dyneins, based on their intracellular localization and functions. Recently, several near-atomic resolution structures have been reported for cytoplasmic/IFT dyneins. In contrast, the structures of ciliary dyneins, as well as their regulatory mechanisms, have yet to be fully elucidated. Here, we isolated a heterodimeric ciliary dynein (IDA-f/I1) from Chlamydomonas reinhardtii, a ciliated green alga, and studied its structure in the presence or absence of ATP by negative-stain electron microscopy and single-particle analysis. Surprisingly, a population of IDA-f adopted a distinctive compact structure, which has been scarcely reported for ciliary dyneins but is very similar to the "phi-particle" structure widely recognized as the autoinhibited/inactivated conformation for cytoplasmic/IFT dyneins. Our results suggest that the inactivation mechanism of dimeric dyneins is conserved in all three dynein subfamilies, regardless of their cellular functions, highlighting the intriguing intrinsic regulatory mechanism that may have been acquired at an early stage in the evolution of dynein motors.

We analysed here the dynamic of the kinesin-like Pavarotti (Pav) during male gametogenesis of wild-type and Sas4 mutant flies. Pav localizes to the equatorial region and the inner central spindle of late anaphase wild-type spermatogonia and displays a strong concentration at the midbody during late telophase. At metaphase of the first meiotic division, Pav shows widespread localization on the equatorial region of the spermatocytes. This unusual distribution restricts and enhances during anaphase where antiparallel cortical microtubules overlap. Additional Pav staining is also found in the inner central spindle where the microtubules overlap between the segregating chromosomes. At late telophase, Pav accumulates to the midbody and on a weak ring that surround the cytoplasmic bridges. Pav localizes in an equatorial discontinuous ring of Sas4 spermatogonia where the non-centrosomal microtubules overlap, but the motor protein is absent in the interior central spindle where the inner microtubules are lacking. However, the anastral spindles properly support cell division, suggesting that astral microtubules are dispensable for Pav localization in the Sas4 spermatogonial cell cortex. This function is presumably replaced by the antiparallel cortical microtubules extending from the acentriolar polar regions. In contrast, the majority of the meiotic spindles in Sas4 mutant testes do not progress beyond late anaphase, and only a small fraction of the primary spermatocytes experienced an abnormal division with the assembly of aberrant telophase spindles. Pav accumulates around the chromatin clusters or enhanced at the plus ends of the antiparallel non-centrosomal cortical bundles of microtubules. However, these bundles are not arranged properly in the equatorial region of the cell and cytokinesis is abnormal or fails. Therefore, the observations in Sas4 mutant testes suggest that the spermatogonial mitoses correctly occur in the absence of astral microtubules, whereas meiotic divisions fail.

The serine/threonine kinase polo-like kinase 1 (PLK1) is a master regulator of cell proliferation and contraction, but its physiological role in the lower urinary tract is unknown. We utilized transcriptomic programs of human bladder smooth muscle cells (hBSMCs), 3D bladder spheroid viability assays, and human ureterovesical junction contractility measurements to elucidate the impacts of PLK1 inhibition. This work reveals PLK1 reduction with the selective inhibitor TAK-960 (500 nM) suppresses high K+-evoked contractions of human urinary smooth muscle ex vivo while decreasing urothelial cell viability. Transcriptomic analysis of hBSMCs treated with TAK-960 shows modulation of cell cycle and contraction pathways, specifically through altered expression of Cys2/His2-type zinc finger transcription factors. In bladder spheroids, PLK1 inhibition also suppresses smooth muscle contraction protein filamin. Taken together, these findings establish PLK1 is a critical governor of urinary smooth muscle contraction and urothelial proliferation with implications for lower urinary tract disorders. Targeting PLK1 pharmacologically may therefore offer therapeutic potential to ameliorate hypercontractility and aberrant growth. Further elucidation of PLK1 signaling networks promises new insights into pathogenesis and much needed treatment advances for debilitating urinary symptoms.