Focal adhesions are essential to drive zebrafish heart valve morphogenesis
We report the initial events of collective migration of AV endocardial cells (ECs) into the extracellular matrix (ECM), and their subsequent rearrangements to form the leaflets. We functionally characterize integrin-based focal adhesions (FAs), critical mediators of cell–ECM interactions, during valve morphogenesis. Using transgenes to block FA signaling specifically in AV ECs as well as loss-of-function approaches, we show that FA signaling mediated by Integrin α5β1 and Talin1 promotes AV EC migration and overall shaping of the valve leaflets. Altogether, our investigation reveals the critical processes d...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Gunawan, F., Gentile, A., Fukuda, R., Tsedeke, A. T., Jimenez-Amilburu, V., Ramadass, R., Iida, A., Sehara-Fujisawa, A., Stainier, D. Y. R. Tags: Cytoskeleton, Migration, Motility, Development Articles Source Type: research

Cryo-EM of retinoschisin branched networks suggests an intercellular adhesive scaffold in the retina
Mutations in the retinal protein retinoschisin (RS1) cause progressive loss of vision in young males, a form of macular degeneration called X-linked retinoschisis (XLRS). We previously solved the structure of RS1, a 16-mer composed of paired back-to-back octameric rings. Here, we show by cryo–electron microscopy that RS1 16-mers can assemble into extensive branched networks. We classified the different configurations, finding four types of interaction between the RS1 molecules. The predominant configuration is a linear strand with a wavy appearance. Three less frequent types constitute the branch points of the networ...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Heymann, J. B., Vijayasarathy, C., Huang, R. K., Dearborn, A. D., Sieving, P. A., Steven, A. C. Tags: Disease, Adhesion, Structural Biology Articles Source Type: research

Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix
Information processing by the nervous system depends on neurotransmitter release from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures via largely unknown protein interactions. The very C-terminal region of Bruchpilot (Brp), a key component of the Drosophila melanogaster CAZ, participates in SV tethering. Here, we identi...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Scholz, N., Ehmann, N., Sachidanandan, D., Imig, C., Cooper, B. H., Jahn, O., Reim, K., Brose, N., Meyer, J., Lamberty, M., Altrichter, S., Bormann, A., Hallermann, S., Pauli, M., Heckmann, M., Stigloher, C., Langenhan, T., Kittel, R. J. Tags: Cell Signaling, Neuroscience Articles Source Type: research

Cul4 ubiquitin ligase cofactor DCAF12 promotes neurotransmitter release and homeostatic plasticity
We genetically characterized the synaptic role of the Drosophila homologue of human DCAF12, a putative cofactor of Cullin4 (Cul4) ubiquitin ligase complexes. Deletion of Drosophila DCAF12 impairs larval locomotion and arrests development. At larval neuromuscular junctions (NMJs), DCAF12 is expressed presynaptically in synaptic boutons, axons, and nuclei of motor neurons. Postsynaptically, DCAF12 is expressed in muscle nuclei and facilitates Cul4-dependent ubiquitination. Genetic experiments identified several mechanistically independent functions of DCAF12 at larval NMJs. First, presynaptic DCAF12 promotes evoked neurotran...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Patron, L. A., Nagatomo, K., Eves, D. T., Imad, M., Young, K., Torvund, M., Guo, X., Rogers, G. C., Zinsmaier, K. E. Tags: Cell Signaling, Neuroscience Articles Source Type: research

Methionine triggers Ppz-mediated dephosphorylation of Art1 to promote cargo-specific endocytosis
Regulation of plasma membrane (PM) protein abundance by selective endocytosis is critical for cellular adaptation to stress or changing nutrient availability. One example involves rapid endocytic turnover of Mup1, a yeast methionine transporter, in response to increased methionine availability. Here, we report that methionine triggers rapid translocation of the ubiquitin ligase adaptor Art1 to the PM and dephosphorylation of Art1 at specific threonine residues. This methionine-induced dephosphorylation of Art1 is mediated by Ppz phosphatases, and analysis of phosphomimetic and phosphorylation-defective variants of Art1 ind...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Lee, S., Ho, H.-C., Tumolo, J. M., Hsu, P.-C., MacGurn, J. A. Tags: Cell Signaling, Trafficking, Biochemistry Articles Source Type: research

Rab5 GTPases are required for optimal TORC2 function
Target of rapamycin complex-2 (TORC2), a conserved protein kinase complex, is an indispensable regulator of plasma membrane homeostasis. In budding yeast (Saccharomyces cerevisiae), the essential downstream effector of TORC2 is protein kinase Ypk1 and its paralog Ypk2. Muk1, a Rab5-specific guanine nucleotide exchange factor (GEF), was identified in our prior global screen for candidate Ypk1 targets. We confirm here that Muk1 is a substrate of Ypk1 and demonstrate that Ypk1-mediated phosphorylation stimulates Muk1 function in vivo. Strikingly, yeast lacking its two Rab5 GEFs (Muk1 and Vps9) or its three Rab5 paralogs (Vps2...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Locke, M. N., Thorner, J. Tags: Cell Signaling, Biochemistry, Genetics Articles Source Type: research

The AAA+ ATPase/ubiquitin ligase mysterin stabilizes cytoplasmic lipid droplets
Mysterin, also known as RNF213, is an intracellular protein that forms large toroidal oligomers. Mysterin was originally identified in genetic studies of moyamoya disease (MMD), a rare cerebrovascular disorder of unknown etiology. While mysterin is known to exert ubiquitin ligase and putative mechanical ATPase activities with a RING finger domain and two adjacent AAA+ modules, its biological role is poorly understood. Here, we report that mysterin is targeted to lipid droplets (LDs), ubiquitous organelles specialized for neutral lipid storage, and markedly increases their abundance in cells. This effect was exerted primari...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Sugihara, M., Morito, D., Ainuki, S., Hirano, Y., Ogino, K., Kitamura, A., Hirata, H., Nagata, K. Tags: Organelles, Metabolism Articles Source Type: research

ER-to-Golgi trafficking of procollagen in the absence of large carriers
Secretion and assembly of collagen are fundamental to the function of the extracellular matrix. Defects in the assembly of a collagen matrix lead to pathologies including fibrosis and osteogenesis imperfecta. Owing to the size of fibril-forming procollagen molecules it is assumed that they are transported from the endoplasmic reticulum to the Golgi in specialized large COPII-dependent carriers. Here, analyzing endogenous procollagen and a new engineered GFP-tagged form, we show that transport to the Golgi occurs in the absence of large (>350 nm) carriers. Large GFP-positive structures were observed occasionally, but the...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: McCaughey, J., Stevenson, N. L., Cross, S., Stephens, D. J. Tags: Organelles, Trafficking Articles Source Type: research

ATM is activated by ATP depletion and modulates mitochondrial function through NRF1
Ataxia-telangiectasia (A-T) is an autosomal recessive disease caused by mutation of the ATM gene and is characterized by loss of cerebellar Purkinje cells, neurons with high physiological activity and dynamic ATP demands. Here, we show that depletion of ATP generates reactive oxygen species that activate ATM. We find that when ATM is activated by oxidative stress, but not by DNA damage, ATM phosphorylates NRF1. This leads to NRF1 dimerization, nuclear translocation, and the up-regulation of nuclear-encoded mitochondrial genes, thus enhancing the capacity of the electron transport chain (ETC) and restoring mitochondrial fun...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Chow, H.-M., Cheng, A., Song, X., Swerdel, M. R., Hart, R. P., Herrup, K. Tags: Disease, Cell Metabolism, Neuroscience Articles Source Type: research

Myosin IIB assembly state determines its mechanosensitive dynamics
Dynamical cell shape changes require a highly sensitive cellular system that can respond to chemical and mechanical inputs. Myosin IIs are key players in the cell’s ability to react to mechanical inputs, demonstrating an ability to accumulate in response to applied stress. Here, we show that inputs that influence the ability of myosin II to assemble into filaments impact the ability of myosin to respond to stress in a predictable manner. Using mathematical modeling for Dictyostelium myosin II, we predict that myosin II mechanoresponsiveness will be biphasic with an optimum established by the percentage of myosin II a...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Schiffhauer, E. S., Ren, Y., Iglesias, V. A., Kothari, P., Iglesias, P. A., Robinson, D. N. Tags: Cytoskeleton, Biophysics, Systems and Computational Biology Articles Source Type: research

The dynein adaptor Hook2 plays essential roles in mitotic progression and cytokinesis
Hook proteins are evolutionarily conserved dynein adaptors that promote assembly of highly processive dynein–dynactin motor complexes. Mammals express three Hook paralogs, namely Hook1, Hook2, and Hook3, that have distinct subcellular localizations and expectedly, distinct cellular functions. Here we demonstrate that Hook2 binds to and promotes dynein–dynactin assembly specifically during mitosis. During the late G2 phase, Hook2 mediates dynein–dynactin localization at the nuclear envelope (NE), which is required for centrosome anchoring to the NE. Independent of its binding to dynein, Hook2 regulates mic...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Dwivedi, D., Kumari, A., Rathi, S., Mylavarapu, S. V. S., Sharma, M. Tags: Cytoskeleton, Cell Cycle and Division, Physiology Articles Source Type: research

GLP-1 signaling suppresses menins transcriptional block by phosphorylation in {beta} cells
Both menin and glucagon-like peptide 1 (GLP-1) pathways play central yet opposing role in regulating β cell function, with menin suppressing, and GLP-1 promoting, β cell function. However, little is known as to whether or how GLP-1 pathway represses menin function. Here, we show that GLP-1 signaling–activated protein kinase A (PKA) directly phosphorylates menin at the serine 487 residue, relieving menin-mediated suppression of insulin expression and cell proliferation. Mechanistically, Ser487-phosphorylated menin gains increased binding affinity to nuclear actin/myosin IIa proteins and gets sequestrated fro...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Xing, B., Ma, J., Jiang, Z., Feng, Z., Ling, S., Szigety, K., Su, W., Zhang, L., Jia, R., Sun, Y., Zhang, L., Kong, X., Ma, X., Hua, X. Tags: Disease, Cell Signaling, Biochemistry Articles Source Type: research

The anaphase-promoting complex regulates the degradation of the inner nuclear membrane protein Mps3
The nucleus is enclosed by the inner nuclear membrane (INM) and the outer nuclear membrane (ONM). While the ONM is continuous with the endoplasmic reticulum (ER), the INM is independent and separates the nucleoplasm from the ER lumen. Turnover of ER proteins has been well characterized by the ER-associated protein degradation (ERAD) pathway, but very little is known about turnover of resident INM proteins. Here we show that the anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase, regulates the degradation of Mps3, a conserved integral protein of the INM. Turnover of Mps3 requires the ubiquitin-conjugating ...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Koch, B. A., Jin, H., Tomko, R. J., Yu, H.-G. Tags: Protein Homeostasis, Genetics Articles Source Type: research

Heterochromatic foci and transcriptional repression by an unstructured MET-2/SETDB1 co-factor LIN-65
The segregation of the genome into accessible euchromatin and histone H3K9-methylated heterochromatin helps silence repetitive elements and tissue-specific genes. In Caenorhabditis elegans, MET-2, the homologue of mammalian SETDB1, catalyzes H3K9me1 and me2, yet like SETDB1, its regulation is enigmatic. Contrary to the cytosolic enrichment of overexpressed MET-2, we show that endogenous MET-2 is nuclear throughout development, forming perinuclear foci in a cell cycle–dependent manner. Mass spectrometry identified two cofactors that bind MET-2: LIN-65, a highly unstructured protein, and ARLE-14, a conserved GTPase eff...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Delaney, C. E., Methot, S. P., Guidi, M., Katic, I., Gasser, S. M., Padeken, J. Tags: Chromatin or Epigenetics, Development, Genetics Articles Source Type: research

Distinct roles for dynein light intermediate chains in neurogenesis, migration, and terminal somal translocation
Cytoplasmic dynein participates in multiple aspects of neocortical development. These include neural progenitor proliferation, morphogenesis, and neuronal migration. The cytoplasmic dynein light intermediate chains (LICs) 1 and 2 are cargo-binding subunits, though their relative roles are not well understood. Here, we used in utero electroporation of shRNAs or LIC functional domains to determine the relative contributions of the two LICs in the developing rat brain. We find that LIC1, through BicD2, is required for apical nuclear migration in neural progenitors. In newborn neurons, we observe specific roles for LIC1 in the...
Source: Journal of Cell Biology - March 3, 2019 Category: Cytology Authors: Goncalves, J. C., Dantas, T. J., Vallee, R. B. Tags: Migration, Motility, Development, Neuroscience Reports Source Type: research