609 research outputs found
Plus-End-Tracking Proteins and Their Interactions at Microtubule Ends
Microtubules are cytoskeletal elements that are essential for a large number of intracellular processes, including mitosis, cell differentiation and migration, and vesicle transport. In many cells, the microtubule network is organized in a radial manner, with one end of a microtubule (the minus end) embedded near the nucleus and the other end (the plus end) exploring cytoplasmic space, switching between episodes of growth and shrinkage. Mammalian plus-end-tracking proteins (+TIPs) localize to the ends of growing microtubules and regulate both the dynamic behavior of microtubules as well as the interactions of microtubules with other cellular components. Because of these crucial roles, +TIPs and the mechanisms underlying their association with microtubule ends have been intensively investigated. Results indicate that +TIPs reach microtubule ends by motor-mediated transport or diffusion. Individual +TIP molecules exchange rapidly on microtubule end-binding sites that are formed during microtubule polymerization and that have a slower turnover. Most +TIPs associate with the end-binding (EB) proteins, and appear to require these âcoreâ +TIPs for localization at microtubule ends. Accumulation of +TIPs may also involve structural features of the microtubule end and interactions with other +TIPs. This complexity makes it difficult to assign discrete roles to specific +TIPs. Given that +TIPs concentrate at microtubule ends and that each +TIP binds in a conformationally distinct manner, I propose that the ends of growing microtubules are ânano-platformsâ for productive interactions between selected proteins and that these interactions might persist and be functional elsewhere in the cytoplasm than at the microtubule end at which they originated
CTCF orchestrates the germinal centre transcriptional program and prevents premature plasma cell differentiation
In germinal centres (GC) mature B cells undergo intense proliferation and immunoglobulin gene modification before they differentiate into memory B cells or long-lived plasma cells (PC). GC B-cell-to-PC transition involves a major transcriptional switch that promotes a halt in cell proliferation and the production of secreted immunoglobulins. Here we show that the CCCTC-binding factor (CTCF) is required for the GC reaction in vivo, whereas in vitro the requirement for CTCF is not universal and instead depends on the pathways used for B-cell activation. CTCF maintains the GC transcriptional programme, allows a high proliferation rate, and represses the expression of Blimp-1, the master regulator of PC differentiation. Restoration of Blimp-1 levels partially rescues the proliferation defect of CTCF-deficient B cells. Thus, our data reveal an essential function of CTCF in maintaining the GC transcriptional programme and preventing premature PC differentiation
Ontwikkeling tussen Cultuur en Structuur
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The male germ cell gene regulator CTCFL is functionally different from CTCF and binds CTCF-like consensus sites in a nucleosome composition-dependent manner
This is an Open Access article distributed under the terms of the Creative Commons Attribution License.-- et al.[Background]: CTCF is a highly conserved and essential zinc finger protein expressed in virtually all cell types. In conjunction with cohesin, it organizes chromatin into loops, thereby regulating gene expression and epigenetic events. The function of CTCFL or BORIS, the testis-specific paralog of CTCF, is less clear.
[Results]: Using immunohistochemistry on testis sections and fluorescence-based microscopy on intact live seminiferous tubules, we show that CTCFL is only transiently present during spermatogenesis, prior to the onset of meiosis, when the protein co-localizes in nuclei with ubiquitously expressed CTCF. CTCFL distribution overlaps completely with that of Stra8, a retinoic acid-inducible protein essential for the propagation of meiosis. We find that absence of CTCFL in mice causes sub-fertility because of a partially penetrant testicular atrophy. CTCFL deficiency affects the expression of a number of testis-specific genes, including Gal3st1 and Prss50. Combined, these data indicate that CTCFL has a unique role in spermatogenesis. Genome-wide RNA expression studies in ES cells expressing a V5- and GFP-tagged form of CTCFL show that genes that are downregulated in CTCFL-deficient testis are upregulated in ES cells. These data indicate that CTCFL is a male germ cell gene regulator. Furthermore, genome-wide DNA-binding analysis shows that CTCFL binds a consensus sequence that is very similar to that of CTCF. However, only ~3,700 out of the ~5,700 CTCFL- and ~31,000 CTCF-binding sites overlap. CTCFL binds promoters with loosely assembled nucleosomes, whereas CTCF favors consensus sites surrounded by phased nucleosomes. Finally, an ES cell-based rescue assay shows that CTCFL is functionally different from CTCF.
[Conclusions]: Our data suggest that nucleosome composition specifies the genome-wide binding of CTCFL and CTCF. We propose that the transient expression of CTCFL in spermatogonia and preleptotene spermatocytes serves to occupy a subset of promoters and maintain the expression of male germ cell genes.This work was supported by the Earth and Life Sciences (ALW) and Medical Sciences (ZonMw) divisions of the Netherlands Organization for Scientific Research (NWO), the Dutch Cancer Society (KWF), the Dutch Cancer Genomics Centre (CGC) and Centre for Biomedical Genetics (CBG), an EC Integrated Project (EuTRACC), and the Spanish Fondo Investigaciones Sanitarias.Peer Reviewe
The protective protein : a multifunctional lysosomal enzyme
This thesis describes the characterization of a lysosomal protein, the 'protective
protein', that has at least two functions. On the one hand it protects lysosomal ~galactosidase
and neuraminidase from degradation within the lysosome, hence its
name. On the other hand it has peptidase and deamidase activities, that could be
involved in protein turnover in lysosomes and hormone (in)activation. Degradation
is distinguished here from proteolytic processing, although both involve peptide
hydrolysis. The first is, however, an aspecific random process, carried out at multiple
sites, whereas the second is a highly specific (single) event. Given the putative
function of the protective protein it seemed appropriate to start with an overview of
intracellular sites of protein degradation, followed by a section on the biogenesis of
lysosomes. The introduction ends with a summary on what is known about lysosomal
storage disorders, a group of genetic diseases that are due to defects in lysosomal
proteins. The protective protein itself is impaired in the rare disorder galactosialidosis
and studies on this disease have been the basis for the discovery of the
protein and analysis of its functions
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