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[Report] Dengue diversity across spatial and temporal scales: Local structure and the effect of host population size

Vie, 03/24/2017 - 00:00
A fundamental mystery for dengue and other infectious pathogens is how observed patterns of cases relate to actual chains of individual transmission events. These pathways are intimately tied to the mechanisms by which strains interact and compete across spatial scales. Phylogeographic methods have been used to characterize pathogen dispersal at global and regional scales but have yielded few insights into the local spatiotemporal structure of endemic transmission. Using geolocated genotype (800 cases) and serotype (17,291 cases) data, we show that in Bangkok, Thailand, 60% of dengue cases living <200 meters apart come from the same transmission chain, as opposed to 3% of cases separated by 1 to 5 kilometers. At distances <200 meters from a case (encompassing an average of 1300 people in Bangkok), the effective number of chains is 1.7. This number rises by a factor of 7 for each 10-fold increase in the population of the “enclosed” region. This trend is observed regardless of whether population density or area increases, though increases in density over 7000 people per square kilometer do not lead to additional chains. Within Thailand these chains quickly mix, and by the next dengue season viral lineages are no longer highly spatially structured within the country. In contrast, viral flow to neighboring countries is limited. These findings are consistent with local, density-dependent transmission and implicate densely populated communities as key sources of viral diversity, with home location the focal point of transmission. These findings have important implications for targeted vector control and active surveillance. Authors: Henrik Salje, Justin Lessler, Irina Maljkovic Berry, Melanie C. Melendrez, Timothy Endy, Siripen Kalayanarooj, Atchareeya A-Nuegoonpipat, Sumalee Chanama, Somchai Sangkijporn, Chonticha Klungthong, Butsaya Thaisomboonsuk, Ananda Nisalak, Robert V. Gibbons, Sopon Iamsirithaworn, Louis R. Macareo, In-Kyu Yoon, Areerat Sangarsang, Richard G. Jarman, Derek A. T. Cummings

[Report] Lysosomal cholesterol activates mTORC1 via an SLC38A9–Niemann-Pick C1 signaling complex

Vie, 03/24/2017 - 00:00
The mechanistic target of rapamycin complex 1 (mTORC1) protein kinase is a master growth regulator that becomes activated at the lysosome in response to nutrient cues. Here, we identify cholesterol, an essential building block for cellular growth, as a nutrient input that drives mTORC1 recruitment and activation at the lysosomal surface. The lysosomal transmembrane protein, SLC38A9, is required for mTORC1 activation by cholesterol through conserved cholesterol-responsive motifs. Moreover, SLC38A9 enables mTORC1 activation by cholesterol independently from its arginine-sensing function. Conversely, the Niemann-Pick C1 (NPC1) protein, which regulates cholesterol export from the lysosome, binds to SLC38A9 and inhibits mTORC1 signaling through its sterol transport function. Thus, lysosomal cholesterol drives mTORC1 activation and growth signaling through the SLC38A9-NPC1 complex. Authors: Brian M. Castellano, Ashley M. Thelen, Ofer Moldavski, McKenna Feltes, Reini E. N. van der Welle, Laurel Mydock-McGrane, Xuntian Jiang, Robert J van Eijkeren, Oliver B. Davis, Sharon M. Louie, Rushika M. Perera, Douglas F. Covey, Daniel K. Nomura, Daniel S. Ory, Roberto Zoncu

[Report] A conserved NAD+ binding pocket that regulates protein-protein interactions during aging

Vie, 03/24/2017 - 00:00
DNA repair is essential for life, yet its efficiency declines with age for reasons that are unclear. Numerous proteins possess Nudix homology domains (NHDs) that have no known function. We show that NHDs are NAD+ (oxidized form of nicotinamide adenine dinucleotide) binding domains that regulate protein-protein interactions. The binding of NAD+ to the NHD domain of DBC1 (deleted in breast cancer 1) prevents it from inhibiting PARP1 [poly(adenosine diphosphate–ribose) polymerase], a critical DNA repair protein. As mice age and NAD+ concentrations decline, DBC1 is increasingly bound to PARP1, causing DNA damage to accumulate, a process rapidly reversed by restoring the abundance of NAD+. Thus, NAD+ directly regulates protein-protein interactions, the modulation of which may protect against cancer, radiation, and aging. Authors: Jun Li, Michael S. Bonkowski, Sébastien Moniot, Dapeng Zhang, Basil P. Hubbard, Alvin J. Y. Ling, Luis A. Rajman, Bo Qin, Zhenkun Lou, Vera Gorbunova, L. Aravind, Clemens Steegborn, David A. Sinclair

[Report] A macrophage relay for long-distance signaling during postembryonic tissue remodeling

Vie, 03/24/2017 - 00:00
Macrophages have diverse functions in immunity as well as in development and homeostasis. We identified a function for these cells in long-distance communication during postembryonic tissue remodeling. Ablation of macrophages in zebrafish prevented melanophores from coalescing into adult pigment stripes. Melanophore organization depends on signals provided by cells of the yellow xanthophore lineage via airinemes, long filamentous projections with vesicles at their tips. We show that airineme extension from originating cells, as well as vesicle deposition on target cells, depend on interactions with macrophages. These findings identify a role for macrophages in relaying long-range signals between nonimmune cells. This signaling modality may function in the remodeling and homeostasis of other tissues during normal development and disease. Authors: Dae Seok Eom, David M. Parichy

[Report] Notch-Jagged complex structure implicates a catch bond in tuning ligand sensitivity

Vie, 03/24/2017 - 00:00
Notch receptor activation initiates cell fate decisions and is distinctive in its reliance on mechanical force and protein glycosylation. The 2.5-angstrom-resolution crystal structure of the extracellular interacting region of Notch1 complexed with an engineered, high-affinity variant of Jagged1 (Jag1) reveals a binding interface that extends ~120 angstroms along five consecutive domains of each protein. O-Linked fucose modifications on Notch1 epidermal growth factor–like (EGF) domains 8 and 12 engage the EGF3 and C2 domains of Jag1, respectively, and different Notch1 domains are favored in binding to Jag1 than those that bind to the Delta-like 4 ligand. Jag1 undergoes conformational changes upon Notch binding, exhibiting catch bond behavior that prolongs interactions in the range of forces required for Notch activation. This mechanism enables cellular forces to regulate binding, discriminate among Notch ligands, and potentiate Notch signaling. Authors: Vincent C. Luca, Byoung Choul Kim, Chenghao Ge, Shinako Kakuda, Di Wu, Mehdi Roein-Peikar, Robert S. Haltiwanger, Cheng Zhu, Taekjip Ha, K. Christopher Garcia

[Report] PI3K pathway regulates ER-dependent transcription in breast cancer through the epigenetic regulator KMT2D

Vie, 03/24/2017 - 00:00
Activating mutations in PIK3CA, the gene encoding phosphoinositide-(3)-kinase α (PI3Kα), are frequently found in estrogen receptor (ER)–positive breast cancer. PI3Kα inhibitors, now in late-stage clinical development, elicit a robust compensatory increase in ER-dependent transcription that limits therapeutic efficacy. We investigated the chromatin-based mechanisms leading to the activation of ER upon PI3Kα inhibition. We found that PI3Kα inhibition mediates an open chromatin state at the ER target loci in breast cancer models and clinical samples. KMT2D, a histone H3 lysine 4 methyltransferase, is required for FOXA1, PBX1, and ER recruitment and activation. AKT binds and phosphorylates KMT2D, attenuating methyltransferase activity and ER function, whereas PI3Kα inhibition enhances KMT2D activity. These findings uncover a mechanism that controls the activation of ER by the posttranslational modification of epigenetic regulators, providing a rationale for epigenetic therapy in ER-positive breast cancer. Authors: Eneda Toska, Hatice U. Osmanbeyoglu, Pau Castel, Carmen Chan, Ronald C. Hendrickson, Moshe Elkabets, Maura N. Dickler, Maurizio Scaltriti, Christina S. Leslie, Scott A. Armstrong, José Baselga

[Report] Stem cell divisions, somatic mutations, cancer etiology, and cancer prevention

Vie, 03/24/2017 - 00:00
Cancers are caused by mutations that may be inherited, induced by environmental factors, or result from DNA replication errors (R). We studied the relationship between the number of normal stem cell divisions and the risk of 17 cancer types in 69 countries throughout the world. The data revealed a strong correlation (median = 0.80) between cancer incidence and normal stem cell divisions in all countries, regardless of their environment. The major role of R mutations in cancer etiology was supported by an independent approach, based solely on cancer genome sequencing and epidemiological data, which suggested that R mutations are responsible for two-thirds of the mutations in human cancers. All of these results are consistent with epidemiological estimates of the fraction of cancers that can be prevented by changes in the environment. Moreover, they accentuate the importance of early detection and intervention to reduce deaths from the many cancers arising from unavoidable R mutations. Authors: Cristian Tomasetti, Lu Li, Bert Vogelstein

[New Products] New Products

Vie, 03/24/2017 - 00:00
A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.

[Working Life] Learning from rejections

Vie, 03/24/2017 - 00:00
Author: Andy Tay

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