Cell structure and function最新文献

For the biogenesis and maintenance of cilia, bidirectional protein trafficking within cilia is crucial, and is conducted by intraflagellar transport (IFT) trains containing the IFT-A and IFT-B complexes that are powered by dynein-2 and kinesin-II motors. We have recently shown that before the assembly of anterograde IFT trains, the IFT-A, IFT-B, and dynein-2 complexes are independently recruited to the mother centriole/basal body. The IFT-B complex, which consists of 16 subunits, can be divided into the IFT-B1 and IFT-B2 subcomplexes, and IFT-B1 can be further divided into the IFT-B1a and IFT-B1b subgroups. Here we investigated how the IFT-B complex is assembled and recruited to the mother centriole for ciliogenesis. Analyses using cells with knockouts of individual IFT-B subunits, and analyses of proteins coimmunoprecipitated with EGFP-fused IFT-B2, IFT-B1b, and IFT-B1a subunits expressed in these knockout cells demonstrated the following: (i) although IFT-B2 is dispensable for the linkage between IFT-B1b and IFT-B1a, it is essential for their localization to the mother centriole; (ii) IFT-B1b is essential both for bridging IFT-B2 and IFT-B1a, and for their localization to the mother centriole; (iii) IFT-B1a is not required for the linkage between IFT-B2 and IFT-B1b nor for their localization to the mother centriole; and (iv) all IFT-B components (IFT-B2, IFT-B1b, and IFT-B1a) are essential for ciliogenesis. Thus, although ciliogenesis is not a prerequisite for the recruitment of the IFT-B complex to the mother centriole, the linkage between IFT-B2 and IFT-B1b is crucial for the mother centriole localization of the IFT-B complex for ciliogenesis.Key words: cilia, ciliogenesis, distal appendages, IFT-B complex, mother centriole.

p53 protein, a crucial transcription factor in cellular responses to a wide variety of stress, regulates multiple target genes involved in tumor suppression, senescence induction, and metabolic functions. To characterize the context-dependent roles of p53, it is still needed to develop an experimental system that enables selective activation of p53 in cells and tissues. In this study, we developed an optogenetic tool, Opto-p53, to control p53 signaling by light. Opto-p53 was designed to trigger p53 signaling by reconstituting p53 N-terminal and C-terminal fragments with a light-inducible dimerization (LID) system. Upon light exposure, cells expressing Opto-p53 demonstrated p53 transcriptional activation, resulting in cell death and cell cycle arrest. We further enhanced the efficacy of light-induced p53 activation by introducing specific mutations into Opto-p53 fragments. Our findings unveil the capability of Opto-p53 to serve as a powerful tool for dissecting the complex roles of p53 in cellular processes, thereby contributing to the field of synthetic biology and providing general design principles for optogenetic tools using endogenous transcription factors.Key words: synthetic biology, transcriptional factor, p53, optogenetics.

Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER)-localized transmembrane protein. STING induces type I interferon and inflammatory responses against a variety of double-stranded DNA (dsDNA) viruses, which is critical for limiting their infection and replication. In certain settings where self-DNAs (genomic or mitochondrial DNA) emerge in the cytosol or when intracellular membrane traffic is impaired, STING becomes activated and triggers inflammation, which may contribute to the pathogenesis of various autoinflammatory and neurodegenerative diseases, including COPA syndrome and Parkinson's disease. The human STING gene exhibits genetic heterogeneity with R232, HAQ (R71H-G230A-R293Q), and H232 being the most common variants, along with population stratification. A very recent study has shown that HAQ, not R232 or H232, mediates complete clinical protection in the pathogenesis of COPA syndrome. These results reveal, for the first time, the distinct activities of the major variants in the context of the pathogenesis of autoinflammatory diseases. Besides these major variants, there exist minor pathogenic STING variants that cause an autoinflammatory disease called STING-associated vasculopathy with onset in infancy (SAVI). This review summarizes recent insights into human STING variants and their inflammatory activities.Key words: innate immunity, STING variants, COPA syndrome, membrane traffic, the Golgi.

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) to maintain the homeostasis of the ER. The UPR consists of the IRE1, PERK and ATF6 pathways in vertebrates. Knockout of the IRE1 and PERK pathways causes defects in liver and pancreatic β cells, respectively, in mice, whereas knockout of the ATF6 pathway causes very early embryonic lethality in mice and medaka fish, a vertebrate model organism. We previously showed that ATF6 knockout in medaka causes a defect in the development of the notochord-the notochord becomes shorter-but that transient overexpression of the ER chaperone BiP via microinjection of BiP mRNA into one-cell stage embryos of these ATF6 knockout rescues this defect. Here, we microinjected mRNA encoding various ER chaperones and found that GRP94, calreticulin and calnexin also partially rescued this defect. Thus, BiP/GRP94 and calreticulin/calnexin greatly contribute to the development of the notochord by controlling the quality of collagens and N-glycosylated proteins (such as laminin and fibrillin), respectively, which have been confirmed necessary for the formation of the notochord in zebrafish.Key words: endoplasmic reticulum, protein folding, molecular chaperone, collagen, glycoprotein.

Stimulator of interferon genes (STING) triggers the type I interferon and inflammatory responses against a variety of DNA pathogens, which is essential to limiting viral infection and replication. STING activates the downstream kinase TBK1 at the trans-Golgi network (TGN) and is degraded at lysosomes through a process called lysosomal microautophagy. Impaired STING targeting to lysosomes results in the prolonged inflammatory signal, which may be associated with a variety of neurodegenerative and autoinflammatory diseases. Thus, development of methods to quantify STING degradation helps understand the mechanism of lysosomal microautophagy and its related diseases. Here we report a quantitative method to monitor STING degradation with two luciferases, firefly luciferase (FLuc) and Nanoluciferase (NLuc). The expression plasmid is composed of FLuc, a P2A self-cleavage site, and NLuc-tagged STING. FLuc intensity reflects the total amount of translated protein, serving as an internal control, while NLuc intensity corresponds to the amount of STING. Comparison of the NLuc/FLuc ratios at different time points after STING stimulation revealed the kinetics of decay of STING levels in live cells. This method should provide a useful complement to western blotting and fluorescence-activated cell sorter (FACS) analysis presently used to monitor STING degradation.Key words: innate immunity, STING, membrane traffic, lysosomal degradation, luciferase.

Macropinocytosis, a type of large-scale endocytosis process, is induced in macrophages by extracellular stimuli, including lipopolysaccharide (LPS). In addition to uptake function, emerging evidence supports a link between macropinocytosis and LPS-induced signal transduction. Following LPS stimulation, membrane ruffles are induced to form cup-like structures known as macropinocytic cups, a necessary precursory step for macropinocytosis. We have recently shown that Akt is activated at the cups and is an upstream regulator of the Iκ-B/NF-κB pathway implicated in the production of IL-1α and IL-6. Here, we further investigated the molecular mechanisms and show that the macropinocytic cups also regulated the Ras/Mek/Erk/c-Fos pathway to modulate IL-1β expression independently of the Akt pathway. In addition, we observed that the cup-dependent Akt pathway downregulated the expression of IL-10, in which the activation of the Erk pathway was critical. Taken together, we propose that macropinocytic cups separately modulate the Akt and Erk pathways in cytokine expression.Key words: macropinocytosis, Erk, IL-1β, IL-10.

During angiogenesis, sprouting endothelial cells (ECs) migrate and eventually connect to target vessels to form new vessel branches. However, it remains unclear how these sprouting vessels migrate toward the target vessels in three-dimensional space. We performed in vivo imaging of the cerebral capillary network formation in zebrafish to investigate how sprouting tip cells migrate toward their targets. Of note, we found that tip cells reach the target vessels through two phases: a non-directional phase and a directional phase. In the non-directional phase, sprouting tip cells dynamically extend and retract their protrusions at the leading front and have less directionality in their movement. In contrast, once tip cells enter the directional phase, they migrate directly toward the anastomotic targets. Chemokine receptor Cxcr4a and its ligand Cxcl12b are important for the phase transition to the directional phase. In cxcr4a mutants, sprouting tip cells lose their directionality and tend to connect to nearby sprouting ECs, resulting in altered capillary network patterning. Furthermore, in wild-type (WT) larvae, local Ca²⁺ oscillations were detected in protrusions of tip cells, specifically in the non-directional phase, but almost disappeared in the directional phase as a result of the Cxcr4-dependent phase transition. Thus, this study provides evidence of a chemokine-induced phase transition in migrating tip cells, which is important for proper vascular network formation in the zebrafish brain.Key words: angiogenesis, directional migration, live imaging, chemokine, Ca²⁺ dynamics, zebrafish.

Cyclin-dependent kinases (CDKs) orchestrate cell cycle progression through precise temporal control of substrate phosphorylation. While traditional biochemical approaches and phosphoproteomics have provided valuable insights into CDK-mediated regulation, these methods require cell population analyses and cannot capture real-time dynamics in individual cells. The recent development of fluorescent biosensors has revolutionized our ability to monitor CDK activity in living cells with unprecedented temporal and spatial resolution. Here, we comprehensively review genetically encoded fluorescent biosensors for measuring CDK activity. The two major modes of action in CDK activity biosensors-FRET-based and translocation-based biosensors-enable researchers to select appropriate tools for their specific experimental objectives. These biosensors have revealed precise spatiotemporal CDK activity dynamics across diverse model systems, including yeast, cultured mammalian cells, worms, flies, frog egg extract, fish, and mice. Such technological advances are transforming our understanding of quantitative principles underlying cell cycle control and opening new avenues for investigating cell cycle regulation in various biological contexts.Key words: CDK, FRET, cell cycle, live imaging, biosensor.

Newly synthesized proteins destined for the secretory pathway are folded and assembled in the endoplasmic reticulum (ER) and then transported to the Golgi apparatus via COPII vesicles, which are normally 60-90 nm. COPII vesicles must accordingly be enlarged to accommodate proteins larger than 90 nm, such as long-chain collagen. Key molecules involved in this enlargement are Tango1 and Tango1-like (Tali), which are transmembrane proteins in the ER encoded by the MIA3 and MIA2 genes, respectively. Interestingly, two splicing variants are expressed from each of these two genes: Tango1L and Tango1S from the MIA3 gene, and Tali and cTAGE5 from the MIA2 gene. Here, we constructed Tango1L-knockout (KO), Tango1S-KO, Tali-KO, and cTAGE5-KO separately in medaka fish, a vertebrate model organism, and characterized them. Results showed that only Tango1L-KO conferred a lethal phenotype to medaka fish. Only Tango1L-KO medaka fish exhibited a shorter tail than wild-type (WT) fish and showed the defects in the export of type II collagen from the ER, contrary to the previous reports analyzing Tango1-KO or Tali-KO mice and the results of knockdown experiments in human cultured cells. Medaka fish may employ a simpler system than mammals for the export of large molecules from the ER.Key words: intracellular transport, COPII vesicles, enlargement, endoplasmic reticulum, Golgi apparatus.

The process of mammalian myogenesis is fundamental to understanding muscle development and holds broad relevance across multiple fields, from developmental biology to regenerative medicine. This review highlights two key aspects: myoblast proliferation and the role of cilia in this process. Myoblasts, as muscle precursor cells, must undergo tightly regulated cycles of proliferation and differentiation to ensure proper muscle growth and function. Recent research has uncovered an essential role for primary cilia, hair-like sensory organelles on the cell surface, in modulating signaling pathways crucial to myogenesis. Cilium-mediated signaling appears to regulate various stages of myogenesis, including the control of myoblast differentiation. Furthermore, primary cilia undergo multiple cycles of formation and disassembly during myogenesis, presumably enabling detailed, context-dependent regulation of their functions. In particular, the regulation of myoblast proliferation through cell cycle control by primary cilia is an important topic that requires further investigation. By examining the interactions between primary cilia and myoblasts, this review aims to provide new insights into the molecular and cellular mechanisms driving muscle development, with potential applications for understanding muscle-related diseases and advancing therapeutic strategies. Additionally, advancements in imaging and image analysis technologies have become indispensable for studying these processes at the cellular level. This review also addresses these technological advancements and current challenges.Key words: myogenesis, myoblast, proliferation, cilia, imaging.