329 research outputs found
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Oncogenic senescence: a multi-functional perspective.
Cellular senescence is defined as an irreversible growth arrest with the acquisition of a distinctive secretome. The growth arrest is a potent anticancer mechanism whereas the secretome facilitates wound healing, tissue repair, and development. The senescence response has also become increasingly recognized as an important contributor to aging and age-related diseases, including cancer. Although oncogenic mutations are capable of inducing a beneficial senescence response that prevents the growth of premalignant cells and promotes cancer immune-surveillance, the secretome of senescent cells also includes factors with pro-tumorigenic properties. On June 23rd and 24th, 2016, the Division of Cancer Biology of the National Cancer Institute sponsored a workshop to discuss the complex role of cellular senescence in tumorigenesis with the goal to define the major challenges and opportunities within this important field of cancer research. Additionally, it was noted how the development of novel tools and technologies are required to accelerate research into a mechanistic understanding of senescent cells in carcinogenesis in order to overcome the current limitations in this exciting, yet ill-defined area
Invasive alien species in the food chain : advancing risk assessment models to address climate change, economics and uncertainty
Economic globalization depends on the movement of people and goods between countries. As these exchanges increase, so does the potential for translocation of harmful pests, weeds, and pathogens capable of impacting our crops, livestock and natural resources (Hulme 2009), with concomitant impacts on global food security (Cook et al. 2011)
Bub1 mediates cell death in response to chromosome missegregation and acts to suppress spontaneous tumorigenesis
The physiological role of the mitotic checkpoint protein Bub1 is unknown. To study this role, we generated a series of mutant mice with a gradient of reduced Bub1 expression using wild-type, hypomorphic, and knockout alleles. Bub1 hypomorphic mice are viable, fertile, and overtly normal despite weakened mitotic checkpoint activity and high percentages of aneuploid cells. Bub1 haploinsufficient mice, which have a milder reduction in Bub1 protein than Bub1 hypomorphic mice, also exhibit reduced checkpoint activity and increased aneuploidy, but to a lesser extent. Although cells from Bub1 hypomorphic and haploinsufficient mice have similar rates of chromosome missegregation, cell death after an aberrant separation decreases dramatically with declining Bub1 levels. Importantly, Bub1 hypomorphic mice are highly susceptible to spontaneous tumors, whereas Bub1 haploinsufficient mice are not. These findings demonstrate that loss of Bub1 below a critical threshold drives spontaneous tumorigenesis and suggest that in addition to ensuring proper chromosome segregation, Bub1 is important for mediating cell death when chromosomes missegregate
Rae1 is an essential mitotic checkpoint regulator that cooperates with Bub3 to prevent chromosome missegregation
The WD-repeat proteins Rae1 and Bub3 show extensive sequence homology, indicative of functional similarity. However, previous studies have suggested that Rae1 is involved in the mRNA export pathway and Bub3 in the mitotic checkpoint. To determine the in vivo roles of Rae1 and Bub3 in mammals, we generated knockout mice that have these genes deleted individually or in combination. Here we show that haplo-insufficiency of either Rae1 or Bub3 results in a similar phenotype involving mitotic checkpoint defects and chromosome missegregation. We also show that overexpression of Rae1 can correct for Rae1 haplo-insufficiency and, surprisingly, Bub3 haplo-insufficiency. Rae1-null and Bub3-null mice are embryonic lethal, although cells from these mice did not have a detectable defect in nuclear export of mRNA. Unlike null mice, compound haplo-insufficient Rae1/Bub3 mice are viable. However, cells from these mice exhibit much greater rates of premature sister chromatid separation and chromosome missegregation than single haplo-insufficient cells. Finally, we show that mice with mitotic checkpoint defects are more susceptible to dimethylbenzanthrene-induced tumorigenesis than wild-type mice. Thus, our data demonstrate a novel function for Rae1 and characterize Rae1 and Bub3 as related proteins with essential, overlapping, and cooperating roles in the mitotic checkpoint
Reduced Life- and Healthspan in Mice Carrying a Mono-Allelic BubR1 MVA Mutation
Mosaic Variegated Aneuploidy (MVA) syndrome is a rare autosomal recessive disorder characterized by inaccurate chromosome segregation and high rates of near-diploid aneuploidy. Children with MVA syndrome die at an early age, are cancer prone, and have progeroid features like facial dysmorphisms, short stature, and cataracts. The majority of MVA cases are linked to mutations in BUBR1, a mitotic checkpoint gene required for proper chromosome segregation. Affected patients either have bi-allelic BUBR1 mutations, with one allele harboring a missense mutation and the other a nonsense mutation, or mono-allelic BUBR1 mutations combined with allelic variants that yield low amounts of wild-type BubR1 protein. Parents of MVA patients that carry single allele mutations have mild mitotic defects, but whether they are at risk for any of the pathologies associated with MVA syndrome is unknown. To address this, we engineered a mouse model for the nonsense mutation 2211insGTTA (referred to as GTTA) found in MVA patients with bi-allelic BUBR1 mutations. Here we report that both the median and maximum lifespans of the resulting BubR1(+/GTTA) mice are significantly reduced. Furthermore, BubR1(+/GTTA) mice develop several aging-related phenotypes at an accelerated rate, including cataract formation, lordokyphosis, skeletal muscle wasting, impaired exercise ability, and fat loss. BubR1(+/GTTA) mice develop mild aneuploidies and show enhanced growth of carcinogen-induced tumors. Collectively, these data demonstrate that the BUBR1 GTTA mutation compromises longevity and healthspan, raising the interesting possibility that mono-allelic changes in BUBR1 might contribute to differences in aging rates in the general population
Early aging–associated phenotypes in Bub3/Rae1 haploinsufficient mice
Aging is a highly complex biological process that is believed to involve multiple mechanisms. Mice that have small amounts of the mitotic checkpoint protein BubR1 age much faster than normal mice, but whether other mitotic checkpoint genes function to prevent the early onset of aging is unknown. In this study, we show that several aging-associated phenotypes appear early in mice that are double haploinsufficient for the mitotic checkpoint genes Bub3 and Rae1 but not in mice that are single haploinsufficient for these genes. Mouse embryonic fibroblasts (MEFs) from Bub3/Rae1 haploinsufficient mice undergo premature senescence and accumulate high levels of p19, p53, p21, and p16, whereas MEFs from single haploinsufficient mice do not. Furthermore, although BubR1 hypomorphic mice have less aneuploidy than Bub3/Rae1 haploinsufficient mice, they age much faster. Our findings suggest that early onset of aging-associated phenotypes in mice with mitotic checkpoint gene defects is linked to cellular senescence and activation of the p53 and p16 pathways rather than to aneuploidy
Whole system radar modelling::Simulation and validation
The ever-expanding horizon of radar applications demands solutions with high-end radar functionalities and technologies and is often limited by the available radar equipment, cost and time. A practical method to tackle the situation is to rely on the modelling and simulation of radar systems based on the user requirements. The comprehensive system-level modelling of a pulsed Doppler radar in MATLAB/Simulink consisting of all the fundamental blocks in the transmit chain, the environment, the receive chain, and the data processing chain is presented in this article. The first half of the article discusses the high-fidelity simulation of each building block in the radar model. In the second half of the article, the range-Doppler plot generated from the high-fidelity radar model is compared and validated using the range-Doppler plot from a real radar trial. The radar phase noise plays a crucial role in the detection of slowly moving, low radar cross-section targets in the presence of strong clutter. The article also briefly discusses the effects of radar oscillator phase noise in the range-Doppler plot. The validated, fully flexible radar model has the advantage of supporting the addition of further building blocks and optimising the parameters based on user requirements
Senescent cells limit p53 activity via multiple mechanisms to remain viable
Super-enhancers regulate genes with important functions in processes that are cell type-specific or define cell identity. Mouse embryonic fibroblasts establish 40 senescence-associated super-enhancers regardless of how they become senescent, with 50 activated genes located in the vicinity of these enhancers. Here we show, through gene knockdown and analysis of three core biological properties of senescent cells that a relatively large number of senescence-associated super-enhancer-regulated genes promote survival of senescent mouse embryonic fibroblasts. Of these, Mdm2, Rnase4, and Ang act by suppressing p53-mediated apoptosis through various mechanisms that are also engaged in response to DNA damage. MDM2 and RNASE4 transcription is also elevated in human senescent fibroblasts to restrain p53 and promote survival. These insights identify key survival mechanisms of senescent cells and provide molecular entry points for the development of targeted therapeutics that eliminate senescent cells at sites of pathology
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