bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trafficking and signaling through the cytoskeleton: a specific mechanism
Authors: Shafrir Yinon , ben-Avraham Daniel , Forgacs Gabor 
Published: April 2021

ABSTRACT
A specific mechanism for the intracellular translocation of nonvesicle-associated proteins is proposed. This movement machinery is based on the assumption that the cytoskeleton represents an interconnected network of filamentous macromolecules, which extends over the entire cytoplasm. Diffusion along the filaments provides an efficient way for movement and with this, for signal transduction, between various intracellular compartments. We calculate the First Passage Time (FPT), the average time it takes a signaling molecule, diffusing along the cytoskeleton, to arrive from the cell surface to the nucleus for the first time. We compare our results with the FPT of free diffusion and of diffusion in the permeating cytoplasm. The latter is hindered by intracellular organelles and the cytoskeleton itself. We find that for filament concentrations even below physiological values, the FPT along cytoskeletal filaments converges to that for free diffusion. When filaments are considered as obstacles, the FPT grows steadily with filament concentration. At realistic filament concentrations the FPT is insensitive to local modifications in the cytoskeletal network, including bundle formation. We conclude that diffusion along cytoskeletal tracks is a reliable alternative to other established ways of intracellular trafficking and signaling, and therefore provides an additional level of cell function regulation.
SOCS: physiological suppressors of cytokine signaling
Authors: Krebs Danielle L. , Hilton Douglas J. 
Published: April 2021

ABSTRACT
Cytokines regulate cellular behavior by interacting with receptors on the plasma membrane of target cells and activating intracellular signal transduction cascades such as the JAK-STAT pathway. Suppressors of cytokine signaling (SOCS) proteins negatively regulate cytokine signaling. The SOCS family consists of eight proteins: SOCS1-SOCS7 and CIS, each of which contains a central Src-homology 2 (SH2) domain and a C-terminal SOCS box. The expression of CIS, SOCS1, SOCS2 and SOCS3 is induced in response to stimulation by a wide variety of cytokines, and overexpression of these proteins in cell lines results in inhibition of cytokine signaling. Thus, SOCS roteins appear to form part of a classical negative feedback loop. The analysis of mice lacking SOCS1 has revealed that it is critical in the negative regulation of IFNγ signaling and in the differentiation of T cells. Additionally, the analysis of mouse embryos lacking SOCS3 suggests that SOCS3 negatively regulates fetal liver erythropoiesis, probably through its ability to modulate erythropoietin (Epo) signaling. Thus, the use of gene targeting has confirmed that SOCS proteins regulate cytokine signaling in a physiological setting.
RLIP76, an effector of the GTPase Ral, interacts with the AP2 complex: involvement of the Ral pathway in receptor endocytosis
Authors: Jullien-Flores Viviana , Mahé Yannick , Mirey Gladys , Leprince Corinne , Meunier-Bisceuil Brigitte , Sorkin Alexander , Camonis Jacques H. 
Published: April 2021

ABSTRACT
RLIP76 is a modular protein that was identified as a putative effector of Ral, a GTPase activated during Ras signaling. To explore further the contribution of the Ral- RLIP76 pathway to Ras signaling, we have looked for partners of RLIP76. μ2, the medium chain of the AP2 complex is shown to interact with RLIP76. We show also that in vivo endogenous AP2 and RLIP76 form a complex and that this in vivo interaction is independent of cells being stimulated by a growth factor. Furthermore, RLIP76 differentiates AP2 from AP1 in vivo as RLIP76 differentiates μ2 from μ1 in vitro and in two hybrid assays. We show that activated Ral interferes with both tranferrin receptor endocytosis and epidermal growth factor (EGF) receptor endocytosis in HeLa cells. We propose a model where the Ral-RLIP76 pathway connects signal transduction and endocytosis through interaction on one hand between the Ras-Ral pathway and RLIP, on the other hand between RLIP and proteins belonging to the endocytotic machinery.
Laminin and α7β1 integrin regulate agrin-induced clustering of acetylcholine receptors
Authors: Burkin Dean J. , Kim Jae Eun , Gu Maojian , Kaufman Stephen J. 
Published: April 2021

ABSTRACT
The clustering of acetylcholine receptors (AChRs) in the post-synaptic membrane of skeletal muscle is an early developmental event in the formation of the neuromuscular junction. Several studies show that laminin, as well as neural agrin, can induce AChR clustering in C2C12 myofibers. We recently showed that specific isoforms of the α7β1 integrin (a receptor normally found at neuromuscular junctions) colocalize and physically interact with AChR clusters in a laminin-dependent fashion. In contrast, induction with agrin alone fails to promote localization of the integrin with AChR clusters. Together both agrin and laminin enhance the interaction of the integrin with AChRs and their aggregation into clusters. To further understand this mechanism we investigated cluster formation and the association of the α7β1 integrin and AChR over time following induction with laminin and/or agrin. Our results show that the α7β1 integrin associates with AChRs early during the formation of the post-synaptic membrane and that laminin modulates this recruitment. Laminin induces a rapid stable association of the integrin and AChRs and this association is independent of clustering. In addition to laminin-1, merosin (laminin-2/4) is present both before and after formation of neuromuscular junctions and also promotes AChR clustering and colocalization with the integrin as well as synergism with agrin. Using site directed mutagenesis we demonstrate that a tyrosine residue in the cytoplasmic domain of both α7A and α7B chains regulates the localization of the integrin with AChR clusters. We also provide evidence that laminin, through its association with the α7β1 integrin, reduces by 20-fold the concentration of agrin required to promote AChR clustering and accelerates the formation of clusters. Thus laminin, agrin and the α7β1 integrin act in a concerted manner early in the development of the post-synaptic membrane, with laminin priming newly formed myofibers to rapidly and vigorously respond to low concentrations of neural agrin produced by innervating motor neurons.
Somatic linker histone H1 is present throughout mouse embryogenesis and is not replaced by variant H1°
Authors: Adenot Pierre G. , Campion Evelyne , Legouy Edith , Allis C. David , Dimitrov Stefan , Renard Jean-Paul , Thompson Eric M. 
Published: April 2021

ABSTRACT
A striking feature of early embryogenesis in a number of organisms is the use of embryonic linker histones or high mobility group proteins in place of somatic histone H1. The transition in chromatin composition towards somatic H1 appears to be correlated with a major increase in transcription at the activation of the zygotic genome. Previous studies have supported the idea that the mouse embryo essentially follows this pattern, with the significant difference that the substitute linker histone might be the differentiation variant H1°, rather than an embryonic variant. We show that histone H1° is not a major linker histone during early mouse development. Instead, somatic H1 was present throughout this period. Though present in mature oocytes, somatic H1 was not found on maternal metaphase II chromatin. Upon formation of pronuclear envelopes, somatic H1 was rapidly incorporated onto maternal and paternal chromatin, and the amount of somatic H1 steadily increased on embryonic chromatin through to the 8-cell stage. Microinjection of somatic H1 into oocytes, and nuclear transfer experiments, demonstrated that factors in the oocyte cytoplasm and the nuclear envelope, played central roles in regulating the loading of H1 onto chromatin. Exchange of H1 from transferred nuclei onto maternal chromatin required breakdown of the nuclear envelope and the extent of exchange was inversely correlated with the developmental advancement of the donor nucleus.
The C-terminal tail domain of neurofilament protein-H (NF-H) forms the crossbridges and regulates neurofilament bundle formation
Authors: Chen Jianguo , Nakata Takao , Zhang Zhizeng , Hirokawa Nobutaka 
Published: April 2021

ABSTRACT
In order to study the role of NF-H in a neurofilament network formation in neurons, we coexpressed NF-H with neurofilament protein-L (NF-L) in Sf9 cells using the baculovirus expression system. Electron microscopy observations revealed that parallel arrays of 10 nm filaments with frequent crossbridges between adjacent filaments were formed in the cytoplasm of Sf9 cells infected with the recombinant virus that co-expressed NF-L and NF-H. To explore the function of the C-terminal tail domain of NF-H, various deletion mutants lacking portions of the tail domain were constructed, and each of them was coexpressed with NF-L. The results show that the tail domain of NF-H is a structural component of crossbridges and is involved in parallel bundle formation of neurofilaments, as core filaments of the axon. The last 191 amino acids of the C-terminal tail domain of NF-H play a key role in crossbridge formation.
Expression-site-associated gene 8 (ESAG8) of Trypanosoma brucei is apparently essential and accumulates in the nucleolus
Authors: Hoek Maarten , Engstler Markus , Cross George A. M. 
Published: April 2021

ABSTRACT
Trypanosoma brucei variant surface glycoprotein expression sites are interesting examples of genomic loci under complex epigenetic control. In the infectious bloodstream stage, only one of about 20 expression sites is actively transcribed. In the Tsetse midgut (procyclic) stage, chromatin remodeling silences all expression sites. We have begun to explore the function of one of the expression-site-associated genes, ESAG8. Gene knockout experiments implied that ESAG8 is essential. ESAG8 is present at a very low level and apparently accumulates in the nucleolus. A 32-amino-acid domain, which contains a putative bipartite nuclear localization signal (NLS), is both necessary and sufficient to target fusions of ESAG8, with Aequorea victoria green fluorescent protein, to the trypanosome nucleolus. This same sequence functioned only as an NLS in mammalian cells, supporting the idea that nucleolar accumulation requires specific interactions. These results have implications for models of ESAG8 function.
High dosage expression of a zinc finger protein, Grt1, suppresses a mutant of fission yeast slp1+, a homolog of CDC20/p55CDC/Fizzy
Authors: Yamada Hiroshi Y. , Matsumoto Sanae , Matsumoto Tomohiro 
Published: April 2021

ABSTRACT
Selective proteolysis at and after the onset of anaphase is a key cell cycle event required for sister chromatid separation as well as for exit from mitosis. It requires ubiquitination of substrates by Anaphase Promoting Complex(APC)/ Cyclosome. Slp1, a WD-repeat protein, is a putative activator for APC in fission yeast. With another WD-repeat protein, Ste9/Srw1, it is thought to promote the proteolysis in a substrate-specific manner. We report here characterization of a temperature-sensitive (ts) slp1 mutant and its high-dosage suppressor, grt1+. In cells arrested in metaphase, wild-type Slp1 was preferentially found in a complex with hyperphosphorylated Cut9 (subunit of APC), whereas the ts Slp1 protein, lacking the last 113 amino acids, failed to interact with Cut9. The temperature sensitivity was suppressed by high dosage expression of a zinc finger protein, Grt1. The ts slp1 mutant was unable to maintain the normal level of Grt1 protein. The reduction in the Grt1 level may be a primary defect since high dosage expression of grt1+rescues the slp1 mutant. The grt1-suppression had an additive effect to Δste9 and wee1-50, both of which partially suppress the ts slp1 mutant. Therefore, grt1+ would define an independent pathway that facilitates the function of Slp1.
Connexin-specific distribution within gap junctions revealed in living cells
Authors: Falk Matthias M. 
Published: April 2021

ABSTRACT
To study the organization of gap junctions in living cells, the connexin isotypes α1(Cx43), β1(Cx32) and β2(Cx26) were tagged with the autofluorescent tracer green fluorescent protein (GFP) and its cyan (CFP) and yellow (YFP) color variants. The cellular fate of the tagged connexins was followed by high-resolution fluorescence deconvolution microscopy and time-lapse imaging. Comprehensive analyses demonstrated that the tagged channels were functional as monitored by dye transfer, even under conditions where the channels were assembled solely from tagged connexins. High-resolution images revealed a detailed structural organization, and volume reconstructions provided a three-dimensional view of entire gap junction plaques. Specifically, deconvolved dual-color images of gap junction plaques assembled from CFP- and YFP-tagged connexins revealed that different connexin isotypes gathered within the same plaques. Connexins either codistributed homogeneously throughout the plaque, or each connexin isotype segregated into well-separated domains. The studies demonstrate that the mode of channel distribution strictly depends on the connexin isotypes. Based on previous studies on the synthesis and assembly of connexins I suggest that channel distribution is regulated by intrinsic connexin isotype specific signals.
Movies available on-line: http://www.biologists.com/JCS/movies/jcs1735.html, Movie 2, Movie 3, Movie 4, Movie 5
Book Reviews
Authors: Witkowski J. 
Published: April 2021

ABSTRACT
If you are anywhere on the spectrum from frequent Cold Spring Harbor visitor to someone who barely knows that Symposia of that name were until recently published in maroon covers, and if you want to learn more of the history of this remarkable research centre, then this book is for you. At first sight, Illuminating Life looks like a coffee table book, but it is much more than that. Jan Witkowski has assembled a history of the Cold Spring Harbor Laboratories from their inception in 1890 through to 1968, illustrated by a selection of research papers from 1903 to 1969. Each one or two papers is preceded by an interpretative essay and a biographical note on the principal author(s), and the whole is introduced by an informative historical preface. At the end are three obituaries from the literature summarizing the lives of three key players, Davenport, Harris and Demerec.
The FHA domain mediates phosphoprotein interactions
Authors: Li Jia , Lee Gui-in , Doren Steven R. Van , Walker John C. 
Published: April 2021

ABSTRACT
The forkhead-associated (FHA) domain is a phosphopeptide-binding domain first identified in a group of forkhead transcription factors but is present in a wide variety of proteins from both prokaryotes and eukaryotes. In yeast and human, many proteins containing an FHA domain are found in the nucleus and involved in DNA repair, cell cycle arrest, or pre-mRNA processing. In plants, the FHA domain is part of a protein that is localized to the plasma membrane and participates in the regulation of receptor-like protein kinase signaling pathways. Recent studies show that a functional FHA domain consists of 120-140 amino acid residues, which is significantly larger than the sequence motif first described. Although FHA domains do not exhibit extensive sequence similarity, they share similar secondary and tertiary structures, featuring a sandwich of two anti-parallel β-sheets. One intriguing finding is that FHA domains may bind phosphothreonine, phosphoserine and sometimes phosphotyrosine, distinguishing them from other well-studied phosphoprotein-binding domains. The diversity of proteins containing FHA domains and potential differences in binding specificities suggest the FHA domain is involved in coordinating diverse cellular processes.
Live analysis of lagging chromosomes during anaphase and their effect on spindle elongation rate in fission yeast
Authors: Pidoux Alison L. , Uzawa Satoru , Perry Paul E. , Cande W. Zacheus , Allshire Robin C. 
Published: April 2021

ABSTRACT
The fission yeast Schizosaccharomyces pombe is widely used as a model system for studies of the cell cycle and chromosome biology. To enhance these studies we have fused GFP to the chromodomain protein Swi6p, thus allowing nuclear and chromosome behaviour to be followed in living cells using time-lapse fluorescence microscopy. Like endogenous Swi6p, GFP-Swi6p localises to the nucleus and is concentrated at the heterochromatic centromeres and telomeres. The nucleus is highly dynamic during interphase: the clustered centromeres, in particular, are highly mobile. By expressing GFP-α2-tubulin and GFP-Swi6p in the same cells we observe that the clustered centromeres move in concert with the cytoplasmic microtubules, which is likely to reflect their association with the spindle pole body. Drug treatment indicates that this movement is dependent on intact cytoplasmic microtubules. We have also used GFP-Swi6p to investigate the properties of lagging chromosomes observed in mutants with defects in chromosome segregation. Lagging chromosomes display a variety of behaviours on anaphase spindles, most surprisingly, chromosomes appear to initiate microtubule interactions and move to the poles late in anaphase B. Interestingly, in cells displaying lagging chromosomes, the rate of spindle elongation is slowed by a factor of two. This suggests that cells are able to sense the presence of a lagging chromosome and slow anaphase B in order to allow it extra time to reach the pole. However, this mechanism is not dependent on the spindle checkpoint proteins Bub1p or Dma1p, raising the possibility that a novel checkpoint mechanism operates to retard spindle elongation if lagging chromosomes are detected. An alternative model is also discussed in which single defective kinetochores on lagging chromatids are able to interact simultaneously with microtubules emanating from both poles and affect spindle dynamics by counteracting the spindle elongation force.
Movies available on-line: http://www.biologists.com/JCS/movies/jcs1686.html, Movie FIG2A, Movie FIG2B, Movie FIG2C, Movie FIG2D, Movie FIG3A, Movie FIG3B, Movie FIG3C, Movie FIG5A, Movie FIG5B, Movie FIG5C, Movie FIG5D, Movie FIG5E, Movie FIG5F, Movie FIG5G, Movie FIG5H, Movie FIG5I, Movie FIG5J, Movie FIG8CSP10-2
Intracellular traffic of the ecto-nucleotide pyrophosphatase/phosphodiesterase NPP3 to the apical plasma membrane of MDCK and Caco-2 cells: apical targeting occurs in the absence of N-glycosylation
Authors: Meerson Nirina Rajho , Bello Valérie , Delaunay Jean-Louis , Aït Slimane Tounsia , Delautier Danièle , Lenoir Christelle , Trugnan Germain , Maurice Michèle 
Published: April 2021

ABSTRACT
Glycosylation was considered the major signal candidate for apical targeting of transmembrane proteins in polarized epithelial cells. However, direct demonstration of the role of glycosylation has proved difficult because non-glycosylated apical transmembrane proteins usually do not reach the cell surface. Here we were able to follow the targeting of the apical transmembrane glycoprotein NPP3 both when glycosylated and non-glycosylated. Transfected in polarized MDCK and Caco-2 cells, NPP3 was exclusively expressed at the apical membrane. The transport kinetics of the protein to the cell surface were studied after metabolic 35S-labeling and surface immunoprecipitation. The newly synthesized protein was mainly targeted directly to the apical surface in MDCK cells, whereas 50% transited through the basolateral surface in Caco-2 cells. In both cell types, the basolaterally targeted pool was effectively transcytosed to the apical surface. In the presence of tunicamycin, NPP3 was not N-glycosylated. The non-glycosylated protein was partially retained intracellularly but the fraction that reached the cell surface was nevertheless predominantly targeted apically. However, transcytosis of the non-glycosylated protein was partially impaired in MDCK cells. These results provide direct evidence that glycosylation cannot be considered an apical targeting signal for NPP3, although glycosylation is necessary for correct trafficking of the protein to the cell surface.
p125 focal adhesion kinase promotes malignant astrocytoma cell proliferation in vivo
Authors: Wang Dongyan , Grammer J. Robert , Cobbs Charles S. , Stewart Jerry E. , Liu Zhiyong , Rhoden Rosaline , Hecker Timothy P. , Ding Qiang , Gladson Candece L. 
Published: April 2021

ABSTRACT
p125 focal adhesion kinase (p125FAK) is a cytoplasmic tyrosine kinase that is activated upon engagement of integrin cell adhesion receptors, and initiates several signaling events that modulate cell function in vitro. To determine the biologic role of p125FAK in malignant astrocytic tumor cells, U-251MG human malignant astrocytoma cells were stably transfected with p125FAK cDNA using the TET-ON system, and stable clones isolated that exhibited an estimated 5-or 20-fold increase in p125FAK expression on administration of 0.1 or 2.0 μg/ml doxycycline, respectively. In vitro studies demonstrated that induction of p125FAK resulted in a 2-to 3-fold increase in cell migration, increased p130CAS phosphorylation, localization of exogenous p125FAK to focal adhesions, and a 2-fold increase in soft agar growth. To determine the role of p125FAK in vivo, clones were injected stereotactically into the brains of scid mice. A 4.5-fold estimated increase in p125FAK expression was induced by administration of doxycycline in the drinking water. Analysis of xenograft brains demonstrated that, upon induction of p125FAK, there was a 1.6-to 2.8-fold increase in tumor cell number, and an increase in mAb PCNA-labeling of tumor cells in the absence of a change in the apoptotic index. Compared to normal brain, the expression of p125FAK was elevated in malignant astrocytic tumor biopsies from patient samples. These data demonstrate for the first time that p125FAK promotes tumor cell proliferation in vivo, and that the underlying mechanism is not associated with a reduction in apoptosis.
Contractile apparatus of the normal and abortive cytokinetic cells during mouse male meiosis
Authors: Manandhar G. , Moreno R. D. , Simerly C. , Toshimori K. , Schatten G. 
Published: April 2021

ABSTRACT
Mouse male meiotic cytokinesis was studied using immunofluorescent probes against various elements of cytokinetic apparatus and electron microscopy. In normal mice, some spermatocytes fail to undergo cytokinesis after meiotic I or II nuclear divisions, forming syncytial secondary spermatocytes and spermatids. Abnormal cytokinetic cells develop sparse and dispersed midzone spindles during the early stage. However, during late stages, single and compact midzone spindles are formed as in normal cells, but localize asymmetrically and attach to the cortex. Myosin and f-actin were observed in the midzone spindle and midbody regions of normally cleaving cells as well as in those cells that failed to develop a cytokinetic furrow, implying that cytokinetic failure is unlikely to be due to defect in myosin or actin assembly. Depolymerization of microtubules by nocodazole resulted in the loss of the midbody-associated f-actin and myosin. These observations suggest that actin-myosin localization in the midbody could be a microtubule-dependent process that may not play a direct role in cytokinetic furrowing. Anti-centrin antibody labels the putative centrioles while anti-γ-tubulin antibody labels the minus-ends of the midzone spindles of late-stage normal and abnormal cytokinetic cells, suggesting that the centrosome and midzone spindle nucleation in abnormal cytokinetic cells is not different from those of normally cleaving cells. Possible use of mouse male meiotic cells as a model system to study cytokinesis has been discussed.