Endoplasmic reticulum contact sites regulate the dynamics of membraneless organelles

Multi-organelle-mediated mRNA localization in neurons and links to disease

Brain function requires precise spatiotemporal regulation of the neuronal proteome. To allow adaptation of the proteome in distal outposts of neurons, mRNAs are transported into neurites for localized translation. This mRNA localization and local translation is crucial for neuron function and maintenance, and dysregulation of these processes can contribute to neurological disease. Recently, organelles have emerged as key players in regulating mRNA localization and local translation in dendrites and axons. In this review, we discuss the current evidence and open questions for this organelle-mediated mRNA localization. We highlight an emerging model in which multiple organelles create and orchestrate a subcellular microenvironment that can support precise mRNA localization and selective translation. This seems essential for maintaining organellar and neuronal function and health, as mutations in many of the involved proteins lead to various neurological disorders.

Tuning SBDs as Endoplasmic Reticulum Self-Targeting Fluorophores and Its Application for Zn2+ Tracking in ER Stress

The emerging endoplasmic recticulum (ER) crosstalk system demands a more reliable approach for ER-targeting fluorophores to explore ER-associated biochemical species and events. Providing the aromatic sulfonamides' affinity to ATP-sensitive potassium channel protein localized mainly on ER membrane, the sulfonamide fluorophore 4-amino-7-sulfamoylbenzoxadiazole (SBD) was modified to construct ER self-targeting fluorophores without any additional targeting group by alternating the N-substituent structure and numbers of its 4-amino and 7-sulfamoyl groups. The results revealed that a ClogP value over 3.0 endowed those SBDs the ER self-targetability effectively. This provides a strategy to devise an ER-targeting probe by simply modifying the 4-amino group of SBDs as a sensing moiety to make the probe CLogP over 3.0 despite the CLogP value of parent SBDs, and two ER-targeting Zn2+ probes ER-SBD-Zn1 and ER-SBD-Zn2 were obtained following this idea. Moreover, ER Zn2+ tracking with ER-SBD-Zn1 disclosed for the first time tunicamycin concentration-dependent ER Zn2+ fluctuation behavior during ER stress induction.

Condensate-membrane interactions shape membranes, tune cytoskeletal assembly, and localize mRNAs

Biomolecular condensates have emerged as essential subcellular compartments. Although condensates organize biochemistry without a delimiting membrane, condensates frequently interact with membrane surfaces in diverse cellular contexts. Condensates and membranes reciprocally modulate each other, inducing membrane shape changes, establishing domains of distinct lipid composition, and catalyzing reactions within condensates. Here I discuss recent advancements in our understanding of the condensate-membrane interface, with a focus on membrane shaping, lipid organization, cytoskeletal regulation, and mRNA transport. I conclude by suggesting research avenues that may uncover new functions for membrane-associated condensates, with emphasis on the understudied role of RNA in the condensate-membrane interface.

Large-scale purifications reveal yeast and human stress granule cores are heterogeneous particles with complex transcriptomes and proteomes

Stress granules are a conserved response of eukaryotic cells to environmental insults. These cytoplasmic ribonucleoprotein condensates have hitherto been primarily studied by microscopy, which showed previously that they comprise dense ∼200 nm cores embedded in a diffuse shell. We have developed large-scale purifications of budding yeast and mammalian (HEK293T cell) stress granule cores that do not rely on immunoprecipitation of candidate protein constituents. These unbiased preparations reveal that stress granule cores are discrete particles with variable size (average, 135 and 225 nm for yeast and human, respectively) and shape. Proteomics and transcriptomics demonstrate complex composition. The results of hybridization chain reaction fluorescence in situ hybridization (FISH) analyses in HEK293T cells are consistent with stress granule cores having heterogeneous composition, i.e., each stress granule core particle contains only a limited number of mRNA species. Biochemical purification now opens the way to mechanistic analysis of the heterogeneity and complexity of stress granules.

Changing complexity into simplicity: visualization of endoplasmic reticulum autophagy employing a self-deliver viscosity sensor by lifetime imaging

Endoplasmic reticulum autophagy (ER-phagy) is a highly specialized form of autophagy that maintains cellular homeostasis by sweeping damaged or excessive endoplasmic reticulum segments. Dysregulation of ER-phagy has profound implications for normal physiological activities and is closely associated with various diseases. Therefore, accurately visualizing ER-phagy process is imperative. Herein, we successfully developed a novel ER-targeted viscosity sensor (YKI) for conveniently and accurately visualizing ER-phagy by lifetime imaging. Compared with commercial ER Tracker Green and ER Tracker Red that required specific combination incubation reagent to stain the endoplasmic reticulum of live cell, YKI could directly target endoplasmic reticulum by the self-delivery way and without leakage, which profited from the hydrophobic interaction between the long alkyl chain of YKI and the lipid bilayer of the ER. And it could also specifically target the endoplasmic reticulum of fixed cells. Since YKI was sensitive to viscosity, it displayed short fluorescence lifetime in endoplasmic reticulum but exhibited longer fluorescence lifetime upon co-delivery with ER into lysosomes. As a consequence, YKI could achieve accurate and convenient visualization of ER-phagy alone via lifetime imaging. This work provided a powerful tool for studying ER-phagy and could promote the development of related fields.

Endoplasmic reticulum facilitates the coordinated division of Salmonella-containing vacuoles

Salmonella Typhimurium (STM) resides in a membrane-bound compartment called the Salmonella-containing vacuole (SCV) in several infected cell types where bacterial and SCV division occur synchronously to maintain a single bacterium per vacuole. However, the mechanism behind this synchronous fission is not well understood. Fission of intracellular organelles is known to be regulated by the dynamic tubular endoplasmic reticulum (ER). In this study, we evaluated the role of ER in controlling SCV division. Interestingly, Salmonella-infected cells show activation of the unfolded protein response (UPR) and expansion of ER tubules. Altering the expression of ER morphology regulators, such as reticulon-4a (Rtn4a) and CLIMP63, significantly impacted bacterial proliferation, suggesting a potential role of tubular ER in facilitating SCV division. Live-cell imaging revealed the marking of tubular ER at the center of 78% of SCV division sites. This study also explored the role of SteA (a known Salmonella effector in modulating membrane dynamics) in coordinating the SCV division. SteA resides on the SCV membranes and helps form membrane contact between SCV and ER. The colocalization of ER with SCV enclosing STMΔsteA was significantly reduced, compared with SCV of STM WT or STMΔsteA:steA. STMΔsteA shows profound defects in SCV division, resulting in multiple bacteria in a single vacuole with proliferation defects. In vivo, the STMΔsteA shows a defect in colonization in the spleen and liver and affects the initial survival rate of mice. Overall, this study suggests a coordinated role of bacterial effector SteA in promoting ER contact/association with SCVs and regulating SCV division.IMPORTANCEThis study highlights the essential role of the host endoplasmic reticulum in facilitating SCV division and maintaining a single bacterium per vacuole. The Salmonella effector SteA helps maintain the single bacterium per vacuole state. In the absence of SteA, Salmonella resides as multiple bacteria within a single large vacuole. The STMΔsteA shows reduced proliferation under in vitro conditions and exhibits colonization defects in vivo, highlighting the importance of this effector in Salmonella pathogenesis. These findings suggest that targeting SteA could provide a novel therapeutic approach to inhibit Salmonella pathogenicity.

Revisiting Endoplasmic Reticulum Homeostasis, an Expanding Frontier Between Host Plants and Pathogens

The endoplasmic reticulum (ER) serves as the primary site for protein biosynthesis and processing, with ER homeostasis being essential for the survival of plant cells. Numerous studies have underscored the pivotal role of the ER as a battleground for host-pathogen interactions. Pathogens secrete effectors to subvert the host ER and manipulate ER-mediated defense responses, fostering an infection-permissive environment for their proliferation. Plants respond to these challenges by triggering ER stress responses, including the unfolded protein response (UPR), autophagy, and cell death pathways, to combat pathogens and ensure survival. Consequently, plants are faced with a life-or-death decision, directly influencing the outcomes of pathogen infection. In this review, recent advances in manipulating host ER homeostasis by pathogens are introduced, further key counteracting strategies employed by host plants to maintain ER homeostasis during infection are summarized, and finally, several pending questions the studies involving both parties in this evolving field are proposed.

Activation of the mitochondrial unfolded protein response regulates the dynamic formation of stress granules

To rapidly adapt to harmful changes to their environment, cells activate the integrated stress response (ISR). This results in an adaptive transcriptional and translational rewiring, and the formation of biomolecular condensates named stress granules (SGs), to resolve stress. In addition to this first line of defence, the mitochondrial unfolded protein response (UPRmt) activates a specific transcriptional programme to maintain mitochondrial homeostasis. We present evidence that the SG formation and UPRmt pathways are intertwined and communicate. UPRmt induction results in eIF2α phosphorylation and the initial and transient formation of SGs, which subsequently disassemble. The induction of GADD34 (also known as PPP1R15A) during late UPRmt protects cells from prolonged stress by impairing further assembly of SGs. Furthermore, mitochondrial functions and cellular survival are enhanced during UPRmt activation when SGs are absent, suggesting that UPRmt-induced SGs have an adverse effect on mitochondrial homeostasis. These findings point to a novel crosstalk between SGs and the UPRmt that might contribute to restoring mitochondrial functions under stressful conditions.

Correlation of organelle interactions in the development of non-alcoholic fatty liver disease

Organelles, despite having distinct functions, interact with each other. Interactions between organelles typically occur at membrane contact sites (MCSs) to maintain cellular homeostasis, allowing the exchange of metabolites and other pieces of information required for normal cellular physiology. Imbalances in organelle interactions may lead to various pathological processes. Increasing evidence suggests that abnormalorganelle interactions contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the key role of organelle interactions in NAFLD has not been fully evaluated and researched. In this review, we summarize the role of organelle interactions in NAFLD and emphasize their correlation with cellular calcium homeostasis, lipid transport, and mitochondrial dynamics.

Organelle interplay in cardiovascular diseases: Mechanisms, pathogenesis, and therapeutic perspectives

Cardiovascular diseases (CVDs) are the leading cause of rising morbidity and mortality among humans worldwide; however, our approach to the pathogenesis, exploration, and management of CVDs still remains limited. As the heart consists of cardiomyocytes, cardiac fibroblasts, endothelial cells, smooth muscle cells, and several types of cells, different types of dysfunction in the interplay between organelles play an important damaging role, resulting in cardiac pathologies. The interplay between cellular organelles is intricate and vital for maintaining cellular homeostasis, as highlighted by multiple diseases linked to the dysfunction of both organelles. Many studies have revealed the potential mechanisms by which organelles communicate with each other and regulate the pathological processes of CVDs together. However, gaps remain in fully understanding the complexity of these interactions and translating these insights into therapeutic approaches. In this review, we summarized how the interplay between cellular organelles in the cardiomyocytes alters in various heart diseases. We find underexplored areas, such as the crucial signaling pathways governing organelle communication, and discuss their implications for disease future progression. Furthermore, we evaluate emerging potential medicines aimed at restoring organelle interactions. Finally, we propose future directions for researching to advance the development of novel medicines and therapies, addressing current gaps and providing a theoretical basis for improved clinical outcomes in CVDs.

ANXA11 biomolecular condensates facilitate protein-lipid phase coupling on lysosomal membranes

Phase transitions of cellular proteins and lipids play a key role in governing the organisation and coordination of intracellular biology. Recent work has raised the intriguing prospect that phase transitions in proteins and lipids can be co-regulated. Here we investigate this possibility in the ribonucleoprotein (RNP) granule-ANXA11-lysosome ensemble, where ANXA11 tethers RNP granules to lysosomal membranes to enable their co-trafficking. We show that changes to the protein phase state within this system, driven by the low complexity ANXA11 N-terminus, induces a coupled phase state change in the lipids of the underlying membrane. We identify the ANXA11 interacting proteins ALG2 and CALC as potent regulators of ANXA11-based phase coupling and demonstrate their influence on the nanomechanical properties of the ANXA11-lysosome ensemble and its capacity to engage RNP granules. The phenomenon of protein-lipid phase coupling we observe within this system serves as a potential regulatory mechanism in RNA trafficking and offers an important template to understand other examples across the cell whereby biomolecular condensates closely juxtapose organellar membranes.

Lipid packing and cholesterol content regulate membrane wetting and remodeling by biomolecular condensates

Biomolecular condensates play a central role in cellular processes by interacting with membranes driving wetting transitions and inducing mutual remodeling. While condensates are known to locally alter membrane properties such as lipid packing and hydration, it remains unclear how membrane composition and phase state in turn affect condensate affinity. Here, we show that it is not only the membrane phase itself, but rather the degree of lipid packing that determines the condensate affinity for membranes. Increasing lipid chain length, saturation, or cholesterol content, enhances lipid packing, thereby decreasing condensate interaction. This regulatory mechanism is consistent across various condensate-membrane systems, highlighting the critical role of the membrane interface. In addition, protein adsorption promotes extensive membrane remodeling, including the formation of tubes and double-membrane sheets. Our findings reveal a mechanism by which membrane composition fine-tunes condensate wetting, highlighting its potential impact on cellular functions and organelle interactions.

Crosstalk Between Phase-Separated Membraneless Condensates and Membrane-Bound Organelles in Cellular Function and Disease

Compartmentalization in eukaryotic cells allows the spatiotemporal regulation of biochemical processes, in addition to allowing specific sets of proteins to interact in a regulated as well as stochastic manner. Although membrane-bound organelles are thought to be the key players of cellular compartmentalization, membraneless biomolecular condensates such as stress granules, P bodies, and many others have recently emerged as key players that are also thought to bring order to a highly chaotic environment. Here, we have evaluated the latest studies on biomolecular condensates, specifically focusing on how they interact with membrane-bound organelles and modulate each other's functions. We also highlight the importance of this interaction in neurodegenerative and cardiovascular diseases as well as in cancer.

Rickettsia parkeri forms extensive, stable contacts with the rough endoplasmic reticulum

Upon invasion into the host cell, a subset of bacterial pathogens resides exclusively in the cytosol. While previous research revealed how they reshape the plasma membrane during invasion, subvert the immune response, and hijack cytoskeletal dynamics to promote their motility, it was unclear if these pathogens also interacted with the organelles in this crowded intracellular space. Here, we examined if the obligate intracellular pathogen Rickettsia parkeri interacts with the endoplasmic reticulum (ER), a large and dynamic organelle spread throughout the cell. Using live-cell microscopy and transmission and focused-ion-beam scanning electron microscopy, we show that R. parkeri forms extensive contacts with the rough ER that are ∼55 nm apart and cover more than half the bacterial surface. Depletion of the ER-specific tethers VAPA and VAPB reduced rickettsia-ER contacts, and VAPA and VAPB were localized around intracellular rickettsiae. Overall, our findings illuminate an interkingdom ER contact uniquely mediated by rickettsiae that mimics some characteristics of traditional host membrane contact sites.

Disruption of ER-mitochondria contact sites induces autophagy-dependent loss of P-bodies through the Ca2+-CaMKK2-AMPK pathway

P-bodies (PBs) and stress granules (SGs) are conserved, non-membranous cytoplasmic condensates of RNA-protein complexes. PBs are implicated in post-transcriptional regulation of gene expression through mRNA decay, translational repression and/or storage. Although much is known about the de novo formation of PBs and SGs involving liquid-liquid phase separation through multiple protein-protein and protein-RNA interactions, their subcellular localization and turnover mechanisms are less understood. Here, we report the presence of a subpopulation of PBs and SGs that are in proximity to ER-mitochondria contact sites (ERMCSs) in mammalian cells. Disruption of ERMCSs, achieved through depletion of ER-mitochondria tethering proteins, leads to the disappearance of PBs but not SGs. This effect can be reversed by inhibiting autophagy through both genetic and pharmacological means. Additionally, we find that the disruption of ERMCSs leads to cytosolic Ca2+-induced activation of CaMKK2 and AMP-activated protein kinase (AMPK), ultimately resulting in an autophagy-dependent decrease in PB abundance. Collectively, our findings unveil a mechanism wherein disturbances in ERMCSs induce autophagy-dependent loss of PBs via activation of the Ca2+-CaMKK2-AMPK pathway, thus potentially linking the dynamics and functions of ERMCS with post-transcriptional gene regulation.

The emerging roles of the endoplasmic reticulum in mechanosensing and mechanotransduction

Cells are continuously subjected to physical and chemical cues from the extracellular environment, and sense and respond to mechanical cues via mechanosensation and mechanotransduction. Although the role of the cytoskeleton in these processes is well known, the contribution of intracellular membranes has been long neglected. Recently, it has become evident that various organelles play active roles in both mechanosensing and mechanotransduction. In this Review, we focus on mechanosensitive roles of the endoplasmic reticulum (ER), the functions of which are crucial for maintaining cell homeostasis. We discuss the effects of mechanical stimuli on interactions between the ER, the cytoskeleton and other organelles; the role of the ER in intracellular Ca2+ signalling via mechanosensitive channels; and how the unfolded protein response and lipid homeostasis contribute to mechanosensing. The expansive structure of the ER positions it as a key intracellular communication hub, and we additionally explore how this may be leveraged to transduce mechanical signals around the cell. By synthesising current knowledge, we aim to shed light on the emerging roles of the ER in cellular mechanosensing and mechanotransduction.

Emerging of Ultrafine Membraneless Organelles as the Missing Piece of Nanostress: Mechanism of Biogenesis and Implications at Multilevels

Understanding the interaction between nanomaterials and cellular structures is crucial for nanoparticle applications in biomedicine. We have identified a subtype of stress granules, called nanomaterial-provoked stress granules (NSGs), induced by gold nanorods (AuNRs). These NSGs differ from traditional SGs in their physical properties and biological functions. Uptake of AuNRs causes reactive oxygen species accumulation and protein misfolding in the cell, leading to NSG formation. Physically, NSGs have a gel-like core and a liquid-like shell, influenced positively by HSP70 and negatively by HSP90 and the ubiquitin-proteasome system. AuNRs promote NSG assembly by interacting with G3BP1, reducing the energy needed for liquid-liquid phase separation (LLPS). NSGs impact cellular functions by affecting mRNA surveillance and activating Adenosine 5'-monophosphate (AMP)-activated protein kinase signaling, crucial for a cellular stress response. Our study highlights the role of LLPS in nanomaterial metabolism and suggests NSGs as potential targets for drug delivery strategies, advancing the field of nanomedicine.

Engineering a Novel NIR RNA-Specific Probe for Tracking Stress Granule Dynamics in Living Cells

Real-time monitoring of the dynamics of cytosolic RNA-protein condensates, termed stress granules (SGs), is vital for understanding their biological roles in stress response and related disease treatment but is challenging due to the lack of simple and accurate methods. Compared with protein visualization that requires complex transfection procedures, direct RNA labeling offers an ideal alternative for tracking SG dynamics in living cells. Here, we propose a novel molecular design strategy to construct a near-infrared RNA-specific fluorescent probe (HQBT) for tracking SGs in living cells. The positively charged probe HQBT was designed to target the negative groove of RNA, and its binding affinity to RNA was significantly improved by adjusting the position of the nitrogen atom in the molecule. Furthermore, an additional hydroxyl group was introduced to achieve near-infrared emission and enhance the RNA-binding capability. HQBT can rapidly stain RNA within 5 s in living cells and showed performance superior to the commercial SYTO RNA-Select dye in terms of photostability and selectivity. Importantly, the reversible assembly and disassembly dynamics of SGs are successfully visualized in living cells using this simple and direct RNA-selective imaging probe.

Trafficking in cancer: from gene deregulation to altered organelles and emerging biophysical properties

Intracellular trafficking supports all cell functions maintaining the exchange of material between membrane-bound organelles and the plasma membrane during endocytosis, cargo sorting, and exocytosis/secretion. Several proteins of the intracellular trafficking machinery are deregulated in diseases, particularly cancer. This complex and deadly disease stays a heavy burden for society, despite years of intense research activity. Here, we give an overview about trafficking proteins and highlight that in addition to their molecular functions, they contribute to the emergence of intracellular organelle landscapes. We review recent evidence of organelle landscape alterations in cancer. We argue that focusing on organelles, which represent the higher-order, cumulative behavior of trafficking regulators, could help to better understand, describe and fight cancer. In particular, we propose adopting a physical framework to describe the organelle landscape, with the goal of identifying the key parameters that are crucial for a stable and non-random organelle organization characteristic of healthy cells. By understanding these parameters, we may gain insights into the mechanisms that lead to a pathological organelle spatial organization, which could help explain the plasticity of cancer cells.

Fluorescence lifetime sorting reveals tunable enzyme interactions within cytoplasmic condensates

Ribonucleoprotein (RNP) condensates partition RNA and protein into multiple liquid phases. The multiphasic feature of condensate-enriched components creates experimental challenges for distinguishing membraneless condensate functions from the surrounding dilute phase. We combined fluorescence lifetime imaging microscopy (FLIM) with phasor plot filtering and segmentation to resolve condensates from the dilute phase. Condensate-specific lifetimes were used to track protein-protein interactions by measuring FLIM-Förster resonance energy transfer (FRET). We used condensate FLIM-FRET to evaluate whether mRNA decapping complex subunits can form decapping-competent interactions within P-bodies. Condensate FLIM-FRET revealed the presence of core subunit interactions within P-bodies under basal conditions and the disruption of interactions between the decapping enzyme (Dcp2) and a critical cofactor (Dcp1A) during oxidative stress. Our results show a context-dependent plasticity of the P-body interaction network, which can be rewired within minutes in response to stimuli. Together, our FLIM-based approaches provide investigators with an automated and rigorous method to uncover and track essential protein-protein interaction dynamics within RNP condensates in live cells.

The role of ER exit sites in maintaining P-body organization and integrity during Drosophila melanogaster oogenesis

Processing bodies (P-bodies) are cytoplasmic membrane-less organelles which host multiple mRNA processing events. While the fundamental principles of P-body organization are beginning to be elucidated in vitro, a nuanced understanding of how their assembly is regulated in vivo remains elusive. Here, we investigate the potential link between ER exit sites and P-bodies in Drosophila melanogaster egg chambers. Employing a combination of live and super-resolution imaging, we find that P-bodies associated with ER exit sites are larger and less mobile than cytoplasmic P-bodies, indicating that they constitute a distinct class of P-bodies. Moreover, we demonstrate that altering the composition of ER exit sites has differential effects on core P-body proteins (Me31B, Cup, and Trailer Hitch), suggesting a potential role for ER exit sites in P-body organization. Furthermore, we show that in the absence of ER exit sites, P-body integrity is compromised and the stability and translational repression efficiency of the maternal mRNA, oskar, are reduced. Together, our data highlights the crucial role of ER exit sites in governing P-body organization.

ZW10: an emerging orchestrator of organelle dynamics during the cell division cycle

Zeste white 10 (ZW10) was first identified as a centromere/kinetochore protein encoded by the ZW10 gene in Drosophila. ZW10 guides the spindle assembly checkpoint signaling during mitotic chromosome segregation in metazoans. Recent studies have shown that ZW10 is also involved in membrane-bound organelle interactions during interphase and plays a vital role in membrane transport between the endoplasmic reticulum and Golgi apparatus. Despite these findings, the precise molecular mechanisms by which ZW10 regulates interactions between membrane-bound organelles in interphase and the assembly of membraneless organelle kinetochore in mitosis remain elusive. Here, we highlight how ZW10 forms context-dependent protein complexes during the cell cycle. These complexes are essential for mediating membrane trafficking in interphase and ensuring the accurate segregation of chromosomes in mitosis.

MCTP controls nucleocytoplasmic partitioning of AUXIN RESPONSE FACTORs during lateral root development

The plant hormone auxin orchestrates almost all aspects of plant growth and development. AUXIN RESPONSE FACTORs (ARFs) control the transcription of auxin-responsive genes, forming cytoplasmic condensates to modulate auxin sensitivity and diversify auxin response regulation. However, the dynamic control of ARF distribution across different subcellular compartments remains largely obscure. Here, we show that three MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEINs (MCTPs), MCTP3, MCTP4, and MCTP6, control ARF nucleocytoplasmic partitioning and determine lateral root development. MCTP3/4/6 are highly expressed in lateral roots and specifically interact with ARF7 and ARF19 to dissolve their cytoplasmic condensates. This promotes ARF nuclear localization in lateral root primordia and enhances auxin signaling during lateral root formation. Our findings confer MCTP as a key switch to modulate auxin responses and outline an MCTP-ARF signaling cascade that is crucial for the establishment of the plant root system.

Stress Granules in Infectious Disease: Cellular Principles and Dynamic Roles in Immunity and Organelles

Stress granules (SGs) are membrane-less aggregates that form in response to various cellular stimuli through a process called liquid-liquid phase separation (LLPS). Stimuli such as heat shock, osmotic stress, oxidative stress, and infections can induce the formation of SGs, which play crucial roles in regulating gene expression to help cells adapt to stress conditions. Various mRNAs and proteins are aggregated into SGs, particularly those associated with the protein translation machinery, which are frequently found in SGs. When induced by infections, SGs modulate immune cell activity, supporting the cellular response against infection. The roles of SGs differ in viral versus microbial infections, and depending on the type of immune cell involved, SGs function differently in response to infection. In this review, we summarize our current understanding of the implication of SGs in immunity and cellular organelles in the context of infectious diseases. Importantly, we explore insights into the regulatory functions of SGs in the context of host cells under infection.

Visualizing ER-phagy and ER architecture in vivo

ER-phagy is an evolutionarily conserved mechanism crucial for maintaining cellular homeostasis. However, significant gaps persist in our understanding of how ER-phagy and the ER network vary across cell subtypes, tissues, and organs. Furthermore, the pathophysiological relevance of ER-phagy remains poorly elucidated. Addressing these questions requires developing quantifiable methods to visualize ER-phagy and ER architecture in vivo. We generated two transgenic mouse lines expressing an ER lumen-targeting tandem RFP-GFP (ER-TRG) tag, either constitutively or conditionally. This approach enables precise spatiotemporal measurements of ER-phagy and ER structure at single-cell resolution in vivo. Systemic analysis across diverse organs, tissues, and primary cultures derived from these ER-phagy reporter mice unveiled significant variations in basal ER-phagy, both in vivo and ex vivo. Furthermore, our investigation uncovered substantial remodeling of ER-phagy and the ER network in different tissues under stressed conditions such as starvation, oncogenic transformation, and tissue injury. In summary, both reporter models represent valuable resources with broad applications in fundamental research and translational studies.

Hybrid Protocells Based on Coacervate-Templated Fatty Acid Vesicles Combine Improved Membrane Stability with Functional Interior Protocytoplasm

Prebiotically-plausible compartmentalization mechanisms include membrane vesicles formed by amphiphile self-assembly and coacervate droplets formed by liquid-liquid phase separation. Both types of structures form spontaneously and can be related to cellular compartmentalization motifs in today's living cells. As prebiotic compartments, they have complementary capabilities, with coacervates offering excellent solute accumulation and membranes providing superior boundaries. Herein, protocell models constructed by spontaneous encapsulation of coacervate droplets by mixed fatty acid/phospholipid and by purely fatty acid membranes are described. Coacervate-supported membranes form over a range of coacervate and lipid compositions, with membrane properties impacted by charge-charge interactions between coacervates and membranes. Vesicles formed by coacervate-templated membrane assembly exhibit profoundly different permeability than traditional fatty acid or blended fatty acid/phospholipid membranes without a coacervate interior, particularly in the presence of magnesium ions (Mg2+). While fatty acid and blended membrane vesicles are disrupted by the addition of Mg2+, the corresponding coacervate-supported membranes remain intact and impermeable to externally-added solutes. With the more robust membrane, fluorescein diacetate (FDA) hydrolysis, which is commonly used for cell viability assays, can be performed inside the protocell model due to the simple diffusion of FDA and then following with the coacervate-mediated abiotic hydrolysis to fluorescein.

Behind the stoNE wall: A fervent activity for nuclear lipids

The four main types of biomolecules are nucleic acids, proteins, carbohydrates and lipids. The knowledge about their respective interactions is as important as the individual understanding of each of them. However, while, for example, the interaction of proteins with the other three groups is extensively studied, that of nucleic acids and lipids is, in comparison, very poorly explored. An iconic paradigm of physical (and likely functional) proximity between DNA and lipids is the case of the genomic DNA in eukaryotes: enclosed within the nucleus by two concentric lipid bilayers, the wealth of implications of this interaction, for example in genome stability, remains underassessed. Nuclear lipid-related phenotypes have been observed for 50 years, yet in most cases kept as mere anecdotical descriptions. In this review, we will bring together the evidence connecting lipids with both the nuclear envelope and the nucleoplasm, and will make critical analyses of these descriptions. Our exploration establishes a scenario in which lipids irrefutably play a role in nuclear homeostasis.

Synthetic Nanoassemblies for Regulating Organelles: From Molecular Design to Precision Therapeutics

Each organelle referring to a complex multiorder architecture executes respective biological processes via its distinct spatial organization and internal microenvironment. As the assembly of biomolecules is the structural basis of living cells, creating synthetic nanoassemblies with specific physicochemical and morphological properties in living cells to interfere or couple with the natural organelle architectures has attracted great attention in precision therapeutics of cancers. In this review, we give an overview of the latest advances in the synthetic nanoassemblies for precise organelle regulation, including the formation mechanisms, triggering strategies, and biomedical applications in precision therapeutics. We summarize the emerging material systems, including polymers, peptides, and deoxyribonucleic acids (DNAs), and their respective intermolecular interactions for intercellular synthetic nanoassemblies, and highlight their design principles in constructing precursors that assemble into synthetic nanoassemblies targeting specific organelles in the complex cellular environment. We further showcase the developed intracellular synthetic nanoassemblies targeting specific organelles including mitochondria, the endoplasmic reticulum, lysosome, Golgi apparatus, and nucleus and describe their underlying mechanisms for organelle regulation and precision therapeutics for cancer. Last, the essential challenges in this field and prospects for future precision therapeutics of synthetic nanoassemblies are discussed. This review should facilitate the rational design of organelle-targeting synthetic nanoassemblies and the comprehensive recognition of organelles by materials and contribute to the deep understanding and application of the synthetic nanoassemblies for precision therapeutics.

RNA granules in flux: dynamics to balance physiology and pathology

The life cycle of an mRNA is a complex process that is tightly regulated by interactions between the mRNA and RNA-binding proteins, forming molecular machines known as RNA granules. Various types of these membrane-less organelles form inside cells, including neurons, and contribute critically to various physiological processes. RNA granules are constantly in flux, change dynamically and adapt to their local environment, depending on their intracellular localization. The discovery that RNA condensates can form by liquid-liquid phase separation expanded our understanding of how compartments may be generated in the cell. Since then, a plethora of new functions have been proposed for distinct condensates in cells that await their validation in vivo. The finding that dysregulation of RNA granules (for example, stress granules) is likely to affect neurodevelopmental and neurodegenerative diseases further boosted interest in this topic. RNA granules have various physiological functions in neurons and in the brain that we would like to focus on. We outline examples of state-of-the-art experiments including timelapse microscopy in neurons to unravel the precise functions of various types of RNA granule. Finally, we distinguish physiologically occurring RNA condensation from aberrant aggregation, induced by artificial RNA overexpression, and present visual examples to discriminate both forms in neurons.

ER remodeling via lipid metabolism

Unlike most other organelles found in multiple copies, the endoplasmic reticulum (ER) is a unique singular organelle within eukaryotic cells. Despite its continuous membrane structure, encompassing more than half of the cellular endomembrane system, the ER is subdivided into specialized sub-compartments, including morphological, membrane contact site (MCS), and de novo organelle biogenesis domains. In this review, we discuss recent emerging evidence indicating that, in response to nutrient stress, cells undergo a reorganization of these sub-compartmental ER domains through two main mechanisms: non-destructive remodeling of morphological ER domains via regulation of MCS and organelle hitchhiking, and destructive remodeling of specialized domains by ER-phagy. We further highlight and propose a critical role of membrane lipid metabolism in this ER remodeling during starvation.

SigmaR1 shapes rough endoplasmic reticulum membrane sheets

Rough endoplasmic reticulum (ER) sheets are a fundamental domain of the ER and the gateway into the secretory pathway. Although reticulon proteins stabilize high-curvature ER tubules, it is unclear whether other proteins scaffold the flat membranes of rough ER sheets. Through a proteomics screen using ER sheet-localized RNA-binding proteins as bait, we identify the sigma-1 receptor (SigmaR1) as an ER sheet-shaping factor. High-resolution live cell imaging and electron tomography assign SigmaR1 as an ER sheet-localized factor whose levels determine the amount of rough ER sheets in cells. Structure-guided mutagenesis and in vitro reconstitution on giant unilamellar vesicles further support a mechanism whereby SigmaR1 oligomers use their extended arrays of amphipathic helices to bind and flatten the lumenal leaflet of ER membranes to oppose membrane curvature and stabilize rough ER sheets.

The CCT chaperonin and actin modulate the ER and RNA-binding protein condensation during oogenesis and maintain translational repression of maternal mRNA and oocyte quality

The regulation of maternal mRNAs is essential for proper oogenesis, the production of viable gametes, and to avoid birth defects and infertility. Many oogenic RNA-binding proteins have been identified with roles in mRNA metabolism, some of which localize to dynamic ribonucleoprotein granules and others that appear dispersed. Here, we use a combination of in vitro condensation assays and the in vivo Caenorhabditis elegans oogenesis model to characterize the properties of the conserved KH-domain MEX-3 protein and to identify novel regulators of MEX-3 and three other translational regulators. We demonstrate that MEX-3 undergoes phase separation and appears to have intrinsic gel-like properties in vitro. We also identify novel roles for the chaperonin-containing tailless complex polypeptide 1 (CCT) chaperonin and actin in preventing ectopic RNA-binding protein condensates in maturing oocytes that appear to be independent of MEX-3 folding. The CCT chaperonin and actin also oppose the expansion of endoplasmic reticulum sheets that may promote ectopic condensation of RNA-binding proteins. These novel regulators of condensation are also required for the translational repression of maternal mRNA which is essential for oocyte quality and fertility. The identification of this regulatory network may also have implications for understanding the role of hMex3 phase transitions in cancer.

Unveiling intracellular phase separation: advances in optical imaging of biomolecular condensates

Intracellular biomolecular condensates, which form via phase separation, display a highly organized ultrastructure and complex properties. Recent advances in optical imaging techniques, including super-resolution microscopy and innovative microscopic methods that leverage the intrinsic properties of the molecules observed, have transcended the limitations of conventional microscopies. These advances facilitate the exploration of condensates at finer scales and in greater detail. The deployment of these emerging but sophisticated imaging tools allows for precise observations of the multiphasic organization and physicochemical properties of these condensates, shedding light on their functions in cellular processes. In this review, we highlight recent progress in methodological innovations and their profound implications for understanding the organization and dynamics of intracellular biomolecular condensates.

Imaging and proteomics toolkits for studying organelle contact sites

Organelle contact sites are regions where two heterologous membranes are juxtaposed by molecular tethering complexes. These contact sites are important in inter-organelle communication and cellular functional integration. However, visualizing these minute foci and identifying contact site proteomes have been challenging. In recent years, fluorescence-based methods have been developed to visualize the dynamic physical interaction of organelles while proximity labeling approaches facilitate the profiling of proteomes at contact sites. In this review, we explain the design principle for these contact site reporters: a dual-organelle interaction mechanism based on how endogenous tethers and/or tethering complexes localize to contact sites. We classify the contact site reporters into three categories: (i) single-protein systems, (ii) two-component systems with activated reporter signal upon organelle proximity, and (iii) reporters for contact site proteomes. We also highlight advanced imaging analysis with high temporal-spatial resolution and the use of machine-learning algorithms for detecting contact sites.

Alleviating protein-condensation-associated damage at the endoplasmic reticulum enhances plant disease tolerance

Disease tolerance is an essential defense strategy against pathogens, alleviating tissue damage regardless of pathogen multiplication. However, its genetic and molecular basis remains largely unknown. Here, we discovered that protein condensation at the endoplasmic reticulum (ER) regulates disease tolerance in Arabidopsis against Pseudomonas syringae. During infection, Hematopoietic protein-1 (HEM1) and Bax-inhibitor 1 (BI-1) coalesce into ER-associated condensates facilitated by their phase-separation behaviors. While BI-1 aids in clearing these condensates via autophagy, it also sequesters lipid-metabolic enzymes within condensates, likely disturbing lipid homeostasis. Consequently, mutations in hem1, which hinder condensate formation, or in bi-1, which prevent enzyme entrapment, enhance tissue-damage resilience, and preserve overall plant health during infection. These findings suggest that the ER is a crucial hub for maintaining cellular homeostasis and establishing disease tolerance. They also highlight the potential of engineering disease tolerance as a defense strategy to complement established resistance mechanisms in combating plant diseases.

A fluorogenic complementation tool kit for interrogating lipid droplet-organelle interaction

Contact sites between lipid droplets and other organelles are essential for cellular lipid and energy homeostasis upon metabolic demands. Detection of these contact sites at the nanometer scale over time in living cells is challenging. We developed a tool kit for detecting contact sites based on fluorogen-activated bimolecular complementation at CONtact sites, FABCON, using a reversible, low-affinity split fluorescent protein, splitFAST. FABCON labels contact sites with minimal perturbation to organelle interaction. Via FABCON, we quantitatively demonstrated that endoplasmic reticulum (ER)- and mitochondria (mito)-lipid droplet contact sites are dynamic foci in distinct metabolic conditions, such as during lipid droplet biogenesis and consumption. An automated analysis pipeline further classified individual contact sites into distinct subgroups based on size, likely reflecting differential regulation and function. Moreover, FABCON is generalizable to visualize a repertoire of organelle contact sites including ER-mito. Altogether, FABCON reveals insights into the dynamic regulation of lipid droplet-organelle contact sites and generates new hypotheses for further mechanistical interrogation during metabolic regulation.

Mechanisms of lysosomal tubulation and sorting driven by LRRK2

Lysosomes are dynamic cellular structures that adaptively remodel their membrane in response to stimuli, including membrane damage. Lysosomal dysfunction plays a central role in the pathobiology of Parkinson's disease (PD). Gain-of-function mutations in Leucine-rich repeat kinase 2 (LRRK2) cause familial PD and genetic variations in its locus increase the risk of developing the sporadic form of the disease. We previously uncovered a process we term LYTL (LYsosomal Tubulation/sorting driven by LRRK2), wherein membrane-damaged lysosomes generate tubules sorted into mobile vesicles. Subsequently, these vesicles interact with healthy lysosomes. LYTL is orchestrated by LRRK2 kinase activity, via the recruitment and phosphorylation of a subset of RAB GTPases. Here, we summarize the current understanding of LYTL and its regulation, as well as the unknown aspects of this process.

Axonal endoplasmic reticulum tubules control local translation via P180/RRBP1-mediated ribosome interactions

Local mRNA translation in axons is critical for the spatiotemporal regulation of the axonal proteome. A wide variety of mRNAs are localized and translated in axons; however, how protein synthesis is regulated at specific subcellular sites in axons remains unclear. Here, we establish that the axonal endoplasmic reticulum (ER) supports axonal translation in developing rat hippocampal cultured neurons. Axonal ER tubule disruption impairs local translation and ribosome distribution. Using nanoscale resolution imaging, we find that ribosomes make frequent contacts with axonal ER tubules in a translation-dependent manner and are influenced by specific extrinsic cues. We identify P180/RRBP1 as an axonally distributed ribosome receptor that regulates local translation and binds to mRNAs enriched for axonal membrane proteins. Importantly, the impairment of axonal ER-ribosome interactions causes defects in axon morphology. Our results establish a role for the axonal ER in dynamically localizing mRNA translation, which is important for proper neuron development.

Seed longevity is controlled by metacaspases

To survive extreme desiccation, seeds enter a period of quiescence that can last millennia. Seed quiescence involves the accumulation of protective storage proteins and lipids through unknown adjustments in protein homeostasis (proteostasis). Here, we show that mutation of all six type-II metacaspase (MCA-II) proteases in Arabidopsis thaliana disturbs proteostasis in seeds. MCA-II mutant seeds fail to restrict the AAA ATPase CELL DIVISION CYCLE 48 (CDC48) at the endoplasmic reticulum to discard misfolded proteins, compromising seed storability. Endoplasmic reticulum (ER) localization of CDC48 relies on the MCA-IIs-dependent cleavage of PUX10 (ubiquitination regulatory X domain-containing 10), the adaptor protein responsible for titrating CDC48 to lipid droplets. PUX10 cleavage enables the shuttling of CDC48 between lipid droplets and the ER, providing an important regulatory mechanism sustaining spatiotemporal proteolysis, lipid droplet dynamics, and protein homeostasis. In turn, the removal of the PUX10 adaptor in MCA-II mutant seeds partially restores proteostasis, CDC48 localization, and lipid droplet dynamics prolonging seed lifespan. Taken together, we uncover a proteolytic module conferring seed longevity.

Friend or foe: The role of stress granule in neurodegenerative disease

Stress granules (SGs) are dynamic membraneless organelles that form in response to cellular stress. SGs are predominantly composed of RNA and RNA-binding proteins that assemble through liquid-liquid phase separation. Although the formation of SGs is considered a transient and protective response to cellular stress, their dysregulation or persistence may contribute to various neurodegenerative diseases. This review aims to provide a comprehensive overview of SG physiology and pathology. It covers the formation, composition, regulation, and functions of SGs, along with their crosstalk with other membrane-bound and membraneless organelles. Furthermore, this review discusses the dual roles of SGs as both friends and foes in neurodegenerative diseases and explores potential therapeutic approaches targeting SGs. The challenges and future perspectives in this field are also highlighted. A more profound comprehension of the intricate relationship between SGs and neurodegenerative diseases could inspire the development of innovative therapeutic interventions against these devastating diseases.

Surgically resectable nonsmall cell lung cancer: a contemporary approach

New treatment paradigms for resectable nonsmall cell lung cancer (NSCLC), with an emphasis on personalised care and a multidisciplinary approach, have significantly improved patient outcomes. The incorporation of immune checkpoint inhibitors into neoadjuvant, perioperative and adjuvant treatment algorithms is reshaping the standard of care for resectable NSCLC. Adjuvant targeted therapy trials have also paved the way for a much-needed personalised approach for patients with actionable genomic alterations. Innovative surgical techniques and judicious use of postoperative radiotherapy may mitigate the toxicity associated with a multimodality approach. Amid the many new treatment options, questions remain about the best approach to consider for each patient. Measurement of minimal residual disease and achievement of pathological complete response are emerging biomarkers of interest to help further refine treatment selection. This review summarises the current management of resectable NSCLC, focusing on ongoing and recent advances in surgical approaches, the role of postoperative radiotherapy and the rapidly changing field of systemic therapies.

The HRD1-SEL1L ubiquitin ligase regulates stress granule homeostasis in couple with distinctive signaling branches of ER stress

Stress granules (SGs) are membrane-less cellular compartments which are dynamically assembled via biomolecular condensation mechanism when eukaryotic cells encounter environmental stresses. SGs are important for gene expression and cell fate regulation. Dysregulation of SG homeostasis has been linked to human neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we report that the HRD1-SEL1L ubiquitin ligase complex specifically regulates the homeostasis of heat shock-induced SGs through the ubiquitin-proteasome system (UPS) and the UPS-associated ATPase p97. Mechanistically, the HRD1-SEL1L complex mediates SG homeostasis through the BiP-coupled PERK-eIF2α signaling axis of endoplasmic reticulum (ER) stress, thereby coordinating the unfolded protein response (UPR) with SG dynamics. Furthermore, we show that the distinctive branches of ER stress play differential roles in SG homeostasis. Our study indicates that the UPS and the UPR together via the HRD1-SEL1L ubiquitin ligase to maintain SG homeostasis in a stressor-dependent manner.

INF2-mediated actin polymerization at ER-organelle contacts regulates organelle size and movement

Proper regulation of organelle dynamics is critical for cellular function, but the mechanisms coordinating multiple organelles remain poorly understood. Here we show that actin polymerization mediated by the endoplasmic reticulum (ER)-anchored formin INF2 acts as a master regulator of organelle morphology and movement. Using high-resolution imaging, we demonstrate that INF2-polymerized actin filaments assemble at ER contact sites on mitochondria, endosomes, and lysosomes just prior to their fission. Genetic manipulation of INF2 activity alters the size, shape and motility of all three organelles. Our findings reveal a conserved mechanism by which the ER uses actin polymerization to control diverse organelles, with implications for understanding organelle dysfunction in neurodegenerative and other diseases. This work establishes INF2-mediated actin assembly as a central coordinator of organelle dynamics and inter-organelle communication.

The role of ER exit sites in maintaining P-body organization and transmitting ER stress response during Drosophila melanogaster oogenesis

Processing bodies (P-bodies) are cytoplasmic membrane-less organelles which host multiple mRNA processing events. While the fundamental principles of P-body organization are beginning to be elucidated in vitro, a nuanced understanding of how their assembly is regulated in vivo remains elusive. Here, we investigate the potential link between ER exit sites and P-bodies in Drosophila melanogaster egg chambers. Employing a combination of live and super-resolution imaging, we found that P-bodies associated with ER exit sites are larger and less mobile than cytoplasmic P-bodies, indicating that they constitute a distinct class of P-bodies which are more mature than their cytoplasmic counterparts. Moreover, we demonstrate that altering the composition of ER exit sites has differential effects on core P-body proteins (Me31B, Cup, and Trailer Hitch) suggesting a potential role for ER exit sites in P-body organization. We further show that in the absence of ER exit sites, P-body integrity is compromised and the stability and translational repression efficiency of the maternal mRNA, oskar, are reduced. Finally, we show that ER stress is communicated to P-bodies via ER exit sites, highlighting the pivotal role of ER exit sites as a bridge between membrane-bound and membrane-less organelles in ER stress response. Together, our data unveils the significance of ER exit sites not only in governing P-body organization, but also in facilitating inter-organellar communication during stress, potentially bearing implications for a variety of disease pathologies.

The CCT chaperonin and actin modulate the ER and RNA-binding protein condensation during oogenesis to maintain translational repression of maternal mRNA and oocyte quality

The regulation of maternal mRNAs is essential for proper oogenesis, the production of viable gametes, and to avoid birth defects and infertility. Many oogenic RNA-binding proteins have been identified with roles in mRNA metabolism, some of which localize to dynamic ribonucleoprotein granules and others that appear dispersed. Here, we use a combination of in vitro condensation assays and the in vivo C. elegans oogenesis model to determine the intrinsic properties of the conserved KH-domain MEX-3 protein and to identify novel regulators of MEX-3 and the Lsm protein, CAR-1. We demonstrate that MEX-3 undergoes liquid-liquid phase separation and appears to have intrinsic gel-like properties in vitro . We also identify novel roles for the CCT chaperonin and actin in preventing ectopic RNA-binding protein condensates in maturing oocytes that appear to be independent of MEX-3 folding. CCT and actin also oppose the expansion of ER sheets that may promote ectopic condensation of RNA-binding proteins that are associated with de-repression of maternal mRNA. This regulatory network is essential to preserve oocyte quality, prevent infertility, and may have implications for understanding the role of hMex3 phase transitions in cancer.

Significance statement

The molecular mechanisms that regulate phase transitions of oogenic RNA-binding proteins are critical to elucidate but are not fully understood.We identify novel regulators of RNA-binding protein phase transitions in maturing oocytes that are required to maintain translational repression of maternal mRNAs and oocyte quality.This study is the first to elucidate a regulatory network involving the CCT chaperonin, actin, and the ER for phase transitions of RNA-binding proteins during oogenesis. Our findings for the conserved MEX-3 protein may also be applicable to better understanding the role of hMex3 phase transitions in cancer.

Biomolecular Condensates in Contact with Membranes

Biomolecular condensates are highly versatile membraneless organelles involved in a plethora of cellular processes. Recent years have witnessed growing evidence of the interaction of these droplets with membrane-bound cellular structures. Condensates' adhesion to membranes can cause their mutual molding and regulation, and their interaction is of fundamental relevance to intracellular organization and communication, organelle remodeling, embryogenesis, and phagocytosis. In this article, we review advances in the understanding of membrane-condensate interactions, with a focus on in vitro models. These minimal systems allow the precise characterization and tuning of the material properties of both membranes and condensates and provide a workbench for visualizing the resulting morphologies and quantifying the interactions. These interactions can give rise to diverse biologically relevant phenomena, such as molecular-level restructuring of the membrane, nano- to microscale ruffling of the condensate-membrane interface, and coupling of the protein and lipid phases.

Fluorescent protein tags affect the condensation properties of a phase-separating viral protein

Fluorescent protein (FP) tags are extensively used to visualize and characterize the properties of biomolecular condensates despite a lack of investigation into the effects of these tags on phase separation. Here, we characterized the dynamic properties of µNS, a viral protein hypothesized to undergo phase separation and the main component of mammalian orthoreovirus viral factories. Our interest in the sequence determinants and nucleation process of µNS phase separation led us to compare the size and density of condensates formed by FP::µNS to the untagged protein. We found an FP-dependent increase in droplet size and density, which suggests that FP tags can promote µNS condensation. To further assess the effect of FP tags on µNS droplet formation, we fused FP tags to µNS mutants to show that the tags could variably induce phase separation of otherwise noncondensing proteins. By comparing fluorescent constructs with untagged µNS, we identified mNeonGreen as the least artifactual FP tag that minimally perturbed µNS condensation. These results show that FP tags can promote phase separation and that some tags are more suitable for visualizing and characterizing biomolecular condensates with minimal experimental artifacts.

Membrane nanotubes transform into double-membrane sheets at condensate droplets

Cellular membranes exhibit a multitude of highly curved morphologies such as buds, nanotubes, cisterna-like sheets defining the outlines of organelles. Here, we mimic cell compartmentation using an aqueous two-phase system of dextran and poly(ethylene glycol) encapsulated in giant vesicles. Upon osmotic deflation, the vesicle membrane forms nanotubes, which undergo surprising morphological transformations at the liquid-liquid interfaces inside the vesicles. At these interfaces, the nanotubes transform into cisterna-like double-membrane sheets (DMS) connected to the mother vesicle via short membrane necks. Using super-resolution (stimulated emission depletion) microscopy and theoretical considerations, we construct a morphology diagram predicting the tube-to-sheet transformation, which is driven by a decrease in the free energy. Nanotube knots can prohibit the tube-to-sheet transformation by blocking water influx into the tubes. Because both nanotubes and DMSs are frequently formed by cellular membranes, understanding the formation and transformation between these membrane morphologies provides insight into the origin and evolution of cellular organelles.

Advances of ultrasound in tumor immunotherapy

Immunotherapy has become a revolutionary method for treating tumors, offering new hope to cancer patients worldwide. Immunotherapy strategies such as checkpoint inhibitors, chimeric antigen receptor T-cell (CAR-T) therapy, and cancer vaccines have shown significant potential in clinical trials. Despite the promising results, there are still limitations that impede the overall effectiveness of immunotherapy; the response to immunotherapy is uneven, the response rate of patients is still low, and systemic immune toxicity accompanied with tumor cell immune evasion is common. Ultrasound technology has evolved rapidly in recent years and has become a significant player in tumor immunotherapy. The introductions of high intensity focused ultrasound and ultrasound-stimulated microbubbles have opened doors for new therapeutic strategies in the fight against tumor. This paper explores the revolutionary advancements of ultrasound combined with immunotherapy in this particular field.

Coupling liquid phases in 3D condensates and 2D membranes: Successes, challenges, and tools

This review describes the major experimental challenges researchers meet when attempting to couple phase separation between membranes and condensates. Although it is well known that phase separation in a 2D membrane could affect molecules capable of forming a 3D condensate (and vice versa), few researchers have quantified the effects to date. The scarcity of these measurements is not due to a lack of intense interest or effort in the field. Rather, it reflects significant experimental challenges in manipulating coupled membranes and condensates to yield quantitative values. These challenges transcend many molecular details, which means they impact a wide range of systems. This review highlights recent exciting successes in the field, and it lays out a comprehensive list of tools that address potential pitfalls for researchers who are considering coupling membranes with condensates.