Journal of Cell Science

Activation of the Wnt/β-catenin signaling pathway by CHIR99021, a specific inhibitor of GSK3β, induces Tcf7l1 protein degradation, which facilitates the maintenance of an undifferentiated state in mouse embryonic stem cells (mESCs). However, the precise mechanism is still inconclusive. Here, we showed that the overexpression of transducin-β-like protein 1 (Tbl1) or its family member Tblr1 can decrease Tcf7l1 protein levels, while the knockdown of each increases Tcf7l1 levels without affecting Tcf7l1 transcription...

WW domain-containing transcription regulator 1 (TAZ) and Yes-associated protein (YAP) are transcriptional co-activators traditionally studied together as a part of the Hippo pathway and best known for their roles in stem cell proliferation and differentiation. Despite their similarities, TAZ and YAP can exert divergent cellular effects by differentially interacting with other signaling pathways that regulate stem cell maintenance or differentiation. In this study, we show that TAZ regulates astrocytic differentiation and maturation of postnatal neural stem and progenitor cells (NPCs), and that TAZ mediates some but not all of the effects of bone morphogenetic protein (BMP) signaling on astrocytic development...

Microtubules are nucleated by γ-tubulin ring complexes (γ-TuRCs) and are essential for neuronal development. Nevertheless, γ-TuRC depletion has been reported to perturb only higher-order branching in elaborated Drosophila larval class IV dendritic arborisation (da) neurons. This relatively mild phenotype was attributed to defects in microtubule nucleation from Golgi outposts, yet most Golgi outposts lack associated γ-TuRCs. By analysing dendritic arbor regrowth in pupae, we show that γ-TuRCs are also required for the growth and branching of primary and secondary dendrites, as well as for higher-order branching...

The ADP-ribosylation factors (ARFs) and ARF-like (ARLs) GTPases serve as essential molecular switches governing a wide array of cellular processes. In this study, we utilized proximity-dependent biotin identification (BioID) to comprehensively map the interactome of 28 out of 29 ARF and ARL proteins in two cellular models. Through this approach, we identified ∼3000 high-confidence proximal interactors, enabling us to assign subcellular localizations to the family members. Notably, we uncovered previously undefined localizations for ARL4D and ARL10...

Mitochondrial fission is a tightly regulated process involving multiple proteins and cell signaling. Despite extensive studies on mitochondrial fission factors, our understanding of the regulatory mechanisms remains limited. This study shows the critical role of a mitochondrial GTPase, GTPBP8, in orchestrating mitochondrial fission. Depletion of GTPBP8 resulted in drastic elongation and interconnectedness of mitochondria. Conversely, overexpression of GTPBP8 shifted mitochondrial morphology from tubular to fragmented...

Talin couples the actomyosin cytoskeleton to integrins and transmits tension to the extracellular matrix. Talin also interacts with numerous additional proteins capable of modulating the actin-integrin linkage and thus downstream mechanosignaling cascades. Here, we demonstrate that the scaffold protein Caskin2 interacts directly with the R8 domain of talin through its C-terminal LD motif. Caskin2 also associates with the WAVE Regulatory Complex to promote cell migration in an Abi1-dependent manner. Furthermore, we demonstrate that the Caskin2-Abi1 interaction is regulated by growth factor-induced phosphorylation of Caskin2 on serine 878...

During development neurons achieve a stereotyped neuron type-specific morphology, which relies on dynamic support by microtubules (MTs). An important player is augmin which binds to existing MT filaments and recruits the γ-Tubulin Ring Complex (γ-TuRC), to form branched MTs. In cultured neurons, augmin is important for neurite formation. However, little is known about the role of augmin during neurite formation in vivo. Here, we have revisited the role of mammalian augmin in culture and then turned towards the class four Drosophila dendritic arborization (c4da) neurons...

Endosomal-lysosomal trafficking is accompanied by the acidification of endosomal compartments by the H+-V-ATPase to reach low lysosomal pH. Disruption of proper pH impairs lysosomal function and the balance of protein synthesis and degradation (proteostasis). We used the small dipeptide LLOMe, which is known to permeabilize lysosomal membranes, and find that LLOMe also impacts late endosomes (LEs) by neutralizing their pH without causing membrane permeabilization. We show that LLOMe leads to hyper-activation of Rab7 and disruption of tubulation and mannose-6-phosphate receptor (CI-M6PR) recycling on pH-neutralized LEs...

Transition fibres and distal appendages surround the distal end of mature basal bodies and are essential for ciliogenesis, but only a few proteins have been identified and functionally characterised. Here, through genome-wide analysis, we have identified 30 transition fibre proteins (TFPs) and mapped their arrangement in the flagellated eukaryote Trypanosoma brucei. We discovered TFPs are recruited to the mature basal body pre- and post-basal body duplication with differential expression of TFPs at the assembling new flagellum compared to the existing fixed-length old flagellum of 4 TFPs...

Angiogenesis is a tightly controlled dynamic process demanding a delicate equilibrium between pro-angiogenic signals and factors that promote vascular stability. The spatiotemporal activation of the transcriptional co-factors YAP/TAZ is crucial to allow for efficient collective endothelial migration in angiogenesis. The focal adhesion protein Deleted-in-liver-cancer-1 (DLC1) was recently described as a transcriptional downstream target of YAP/TAZ in endothelial cells. In this study, we uncover a negative feedback loop between DLC1 expression and YAP activity during collective migration and sprouting angiogenesis...

Primary cilia are essential eukaryotic organelles required for signalling and secretion. Dynein-2 is a microtubule-motor protein complex and is required for ciliogenesis via its role in facilitating retrograde intraflagellar transport from the cilia tip to the cell body. Dynein-2 must be assembled and loaded onto IFT-trains for entry into cilia for this process to occur but how dynein-2 is assembled and how it is recycled back into a cilium remain poorly understood. Here, we identify Centrosomal Protein of 170 kDa (CEP170) as a dynein-2 interacting protein...

Connexins are channel forming proteins that function to facilitate gap junctional intercellular communication. Here we use dual cell voltage clamp and dye transfer studies to corroborate past findings that Cx31.1 is defective in gap junction channel formation; illustrating that Cx31.1 alone does not form functional gap junction channels in connexin-deficient cells. Rather Cx31.1 transiently localizes to the secretory pathway with a subpopulation reaching the cell surface which is rarely seen in puncta reminiscent of gap junctions...

In neurons, the microtubule (MT) cytoskeleton forms the basis for long-distance protein transport from the cell body into and out of dendrites and axons. To maintain neuronal polarity, the axon initial segment (AIS) serves as a physical barrier, separating the axon from the somatodendritic compartment and acting as a filter for axonal cargo. Selective trafficking is further instructed by axonal enrichment of MT post-translational modifications, which affect MT dynamics and the activity of motor proteins. Here, we compared two knockout mouse lines lacking the respective enzymes for MT tyrosination and detyrosination and found that both knockouts led to a shortening of the AIS...

Natural killer (NK) cells have the ability to lyse other cells through the release of lytic granules (LG). This is in part mediated by the small GTPase Rab27a, which was first identified to play a critical role in degranulation through the study of patients harboring mutations in the gene encoding Rab27a. However, the guanine nucleotide exchange factor (GEF) regulating the activation of Rab27a in cytotoxic lymphocytes was unknown. Here we show that knockout of MADD significantly decreased GTP-bound Rab27a in both resting and stimulated NK cells, and MADD-deficient NK cells and CD8+ T cells displayed severely reduced degranulation and cytolytic ability, similar to that seen with Rab27a deficiency...

Clathrin-mediated endocytosis (CME) is vital for the regulation of plant growth and development by controlling plasma membrane protein composition and cargo uptake. CME relies on the precise recruitment of regulators for vesicle maturation and release. Homologues of components of mammalian vesicle scission are strong candidates to be part of the scission machinery in plants, but the precise roles of these proteins in this process are not fully understood. Here, we characterised the roles of Plant Dynamin-Related Proteins 2 (DRP2s) and SH3-domain containing protein 2 (SH3P2), the plant homologue to Dynamins' recruiters, like Endophilin and Amphiphysin, in the CME by combining high-resolution imaging of endocytic events in vivo and characterisation of the purified proteins in vitro...

CSL (CBF1/RBP-Jκ/Suppressor of Hairless/LAG-1) proteins are conserved transcription factors found in animals and fungi. In fission yeast, they regulate various cellular processes, including cell cycle progression, lipid metabolism, and cell adhesion. CSL proteins bind to DNA through their N-terminal Rel-like domain and central beta-trefoil domain. Here, we investigated the importance of DNA binding for CSL functions in the fission yeast Schizosaccharomyces pombe. We created CSL mutants with disrupted DNA binding and found that the vast majority of CSL functions depend on intact DNA binding...

Biogenesis of inclusion bodies (IBs) facilitates protein quality control (PQC). Canonical aggresomes execute degradation of misfolded proteins while non-degradable amyloids quarantine into Insoluble Protein Deposits. Lewy Bodies (LBs) are filamentous amyloid inclusions of α-Synuclein but PQC-benefits and drawbacks associated with LB-like IBs remain underexplored. Here, we report that a crosstalk between filamentous LB-like IBs and aggresome-like IBs of α-Synuclein (Syn-aggresomes) buffer the load, aggregation state, and turnover of the amyloidogenic protein...

Vertebrate photoreceptors detect light through a large cilium-based outer segment, which is filled with photopigment-laden membranous discs. Surrounding the base of the outer segment are microvilli-like calyceal processes (CPs). While CP disruption has been associated with altered outer segment morphology and photoreceptor degeneration, the role of the processes remains elusive. Here, we used zebrafish as a model to characterize CPs. We quantified CP parameters and report a strong disparity in outer segment coverage between photoreceptor subtypes...

Axonal transport in neurons is essential for cargo movement between the cell body and synapses. UNC-104/KIF1A, a Kinesin-3 motor in C. elegans that anterogradely transports precursors of synaptic vesicles (pre-SVs), is degraded at synapses. Touch neurons-specific knockdown of the E1 ubiquitin-activating enzyme, uba-1, leads to UNC-104 accumulation at neuronal ends and synapses. An RNAi screen identified fbxb-65, an F-box protein, that leads to UNC-104 accumulation at neuronal distal ends, alters UNC-104 net anterograde movement and levels of UNC-104 on cargo without changing synaptic UNC-104 levels...

Male meiotic division exhibits two consecutive chromosome separation events without apparent pausing. Several studies showed spermatocyte divisions are not stringently regulated as in mitotic cells. In this study, we investigated the role of the canonical spindle assembly (SAC) pathway in C. elegans spermatogenesis. We found the intensity of chromosome-associated outer kinetochore protein BUB-1 and SAC effector MDF-1 oscillate between two divisions. However, SAC target securin is degraded during the first division and remains undetectable for the second division...