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Search Results: 1 - 10 of 497908 matches for " Michael A. Riehle "
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Manipulating insulin signaling to enhance mosquito reproduction
Anam J Arik, Jason L Rasgon, Kendra M Quicke, Michael A Riehle
BMC Physiology , 2009, DOI: 10.1186/1472-6793-9-15
Abstract: Knockdown of AaegPTEN or its specific splice variant AaegPTEN6 (the splice variant thought to regulate reproduction in the ovary and fat body) using RNAi led to a 15–63% increase in egg production with no adverse effects on egg viability during the first reproductive cycle. Knockdown of AaegPTEN3, expressed predominantly in the head, had no effect on reproduction. We also characterized the protein expression patterns of these two splice variants during development and in various tissues during a reproductive cycle.Previous studies in a range of organisms, including Drosophila melanogaster and Caenorhabditis elegans, have demonstrated that disruption of the IIS cascade leads to decreased reproduction or sterility. In this study we demonstrate that knockdown of the IIS inhibitor PTEN can actually increase reproduction in the mosquito, at least during the first reproductive cycle.Mosquito-borne diseases such as dengue, malaria and lymphatic filariasis are an increasing global health problem. Dengue, along with dengue hemorrhagic fever (DHF), is transmitted by the mosquito Aedes aegypti and is becoming an increasing threat in more than one hundred countries [1]. A better understanding of the mosquito's reproductive physiology could lead to novel control strategies that could complement or replace current methods of control. It has been theorized that increased reproductive effort results in a trade-off with lifespan. Such a trade-off is supported by studies conducted on a wide range of organisms, including birds, mammals, fruit flies and roundworms [2-4]. However, recent studies also indicate that lifespan and reproduction can be uncoupled [5]. The insulin/insulin growth factor I signaling (IIS) cascade lies at the heart of this interplay between reproduction and lifespan in eukaryotic organisms [6-8]. Studies in Caenorhabditis elegans and Drosophila melanogaster show that gene mutations in signaling molecules within the IIS cascade affect lifespan and reproduction [9-1
Aging Field Collected Aedes aegypti to Determine Their Capacity for Dengue Transmission in the Southwestern United States
Teresa K. Joy,Eileen H. Jeffrey Gutierrez,Kacey Ernst,Kathleen R. Walker,Yves Carriere,Mohammad Torabi,Michael A. Riehle
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046946
Abstract: Aedes aegypti, the primary vector of dengue virus, is well established throughout urban areas of the Southwestern US, including Tucson, AZ. Local transmission of the dengue virus, however, has not been reported in this area. Although many factors influence the distribution of the dengue virus, we hypothesize that one contributing factor is that the lifespan of female Ae. aegypti mosquitoes in the Southwestern US is too short for the virus to complete development and be transmitted to a new host. To test this we utilized two age grading techniques. First, we determined parity by analyzing ovarian tracheation and found that only 40% of Ae. aegypti females collected in Tucson, AZ were parous. The second technique determined transcript levels of an age-associated gene, Sarcoplasmic calcium-binding protein 1 (SCP-1). SCP-1 expression decreased in a predictable manner as the age of mosquitoes increased regardless of rearing conditions and reproductive status. We developed statistical models based on parity and SCP-1 expression to determine the age of individual, field collected mosquitoes within three age brackets: nonvectors (0–5 days post-emergence), unlikely vectors (6–14 days post-emergence), and potential vectors (15+ days post-emergence). The statistical models allowed us to accurately group individual wild mosquitoes into the three age brackets with high confidence. SCP-1 expression levels of individual, field collected mosquitoes were analyzed in conjunction with parity status. Based on SCP-1 transcript levels and parity data, 9% of collected mosquitoes survived more than 15 days post emergence.
Human IGF1 Regulates Midgut Oxidative Stress and Epithelial Homeostasis to Balance Lifespan and Plasmodium falciparum resistance in Anopheles stephensi
Anna L. Drexler,Jose E. Pietri,Nazzy Pakpour,Eric Hauck,Bo Wang,Elizabeth K. K. Glennon,Martha Georgis,Michael A. Riehle,Shirley Luckhart
PLOS Pathogens , 2014, DOI: doi/10.1371/journal.ppat.1004231
Abstract: Insulin and insulin-like growth factor signaling (IIS) regulates cell death, repair, autophagy, and renewal in response to stress, damage, and pathogen challenge. Therefore, IIS is fundamental to lifespan and disease resistance. Previously, we showed that insulin-like growth factor 1 (IGF1) within a physiologically relevant range (0.013–0.13 μM) in human blood reduced development of the human parasite Plasmodium falciparum in the Indian malaria mosquito Anopheles stephensi. Low IGF1 (0.013 μM) induced FOXO and p70S6K activation in the midgut and extended mosquito lifespan, whereas high IGF1 (0.13 μM) did not. In this study the physiological effects of low and high IGF1 were examined in detail to infer mechanisms for their dichotomous effects on mosquito resistance and lifespan. Following ingestion, low IGF1 induced phosphorylation of midgut c-Jun-N-terminal kinase (JNK), a critical regulator of epithelial homeostasis, but high IGF1 did not. Low and high IGF1 induced midgut mitochondrial reactive oxygen species (ROS) synthesis and nitric oxide (NO) synthase gene expression, responses which were necessary and sufficient to mediate IGF1 inhibition of P. falciparum development. However, increased ROS and apoptosis-associated caspase-3 activity returned to baseline levels following low IGF1 treatment, but were sustained with high IGF1 treatment and accompanied by aberrant expression of biomarkers for mitophagy, stem cell division and proliferation. Low IGF1-induced ROS are likely moderated by JNK-induced epithelial cytoprotection as well as p70S6K-mediated growth and inhibition of apoptosis over the lifetime of A. stephensi to facilitate midgut homeostasis and enhanced survivorship. Hence, mitochondrial integrity and homeostasis in the midgut, a key signaling center for IIS, can be targeted to coordinately optimize mosquito fitness and anti-pathogen resistance for improved control strategies for malaria and other vector-borne diseases.
Probability Densities for Fluorescent Photons Emitted by a Two-State Atom Driven by a Laser
Robertsen A. Riehle,Henk F. Arnoldus
ISRN Optics , 2012, DOI: 10.5402/2012/745871
Abstract:
Probability Densities for Fluorescent Photons Emitted by a Two-State Atom Driven by a Laser
Robertsen A. Riehle,Henk F. Arnoldus
ISRN Optics , 2012, DOI: 10.5402/2012/745871
Abstract: Fluorescent photons emitted by a two-state atom in a laser beam are correlated. We have obtained the probability density for the emission of the th photon after a random initial time . It is shown that the correlations between the photons lead to a deviation from the poissonian value for this function (the probability density for independent events), although the deviation is not as significant as one may expect. 1. Introduction When a two-state atom, with energy level separation , is immersed in a laser beam with an angular frequency , then photons are exchanged between the atom and the field in stimulated absorption and emission, provided that is near . We shall consider the case of resonance, so . In addition, photons are emitted in spontaneous transitions from the excited state to the ground state, and these photons are emitted in all direction as electric dipole radiation. The emission of these fluorescent photons can be considered as a random event process on the time axis, and we assume that the duration of each event is negligible (dots on the time axis). This interpretation can be justified with the theory of photon detection from an electromagnetic field [1, 2]. Let be the Einstein coefficient for spontaneous transitions from the excited state to the ground state [3] and let be the population of the excited state. Then, the number of emitted photons per second is equal to and this is the intensity of the random process. We shall assume that the atom is in the steady state, so that is independent of time. The temporal statistics of photon emissions can be represented by the probability densities , with , 2,…. Let be the time at which the th photon is emitted, after an initial time . Since photons are emitted randomly, is a random variable, and its probability density is : We shall evaluate for the emission of fluorescent photons. If photons were emitted independently of each other, then the emission process would be a Poisson process, and the probability for the emission of photons in would be The probability for the emission of the th photon in is . If this emission would be independent of previous emissions, then so that 2. Photon Correlations in Resonance Fluorescence Correlations between random events are expressed through the intensity correlation functions [4, 5]: For resonance fluorescence, these correlation functions take the form [6, 7] involving the function . This function equals the population of the excited state at time , under the condition that the atom is in the ground state at . Therefore, From (7), we then see that an
The Empirical Commit Frequency Distribution of Open Source Projects
Carsten Kolassa,Dirk Riehle,Michel A. Salim
Computer Science , 2014, DOI: 10.1145/2491055.2491073
Abstract: A fundamental unit of work in programming is the code contribution ("commit") that a developer makes to the code base of the project in work. An author's commit frequency describes how often that author commits. Knowing the distribution of all commit frequencies is a fundamental part of understanding software development processes. This paper presents a detailed quantitative analysis of commit frequencies in open-source software development. The analysis is based on a large sample of open source projects, and presents the overall distribution of commit frequencies. We analyze the data to show the differences between authors and projects by project size; we also includes a comparison of successful and non successful projects and we derive an activity indicator from these analyses. By measuring a fundamental dimension of programming we help improve software development tools and our understanding of software development. We also validate some fundamental assumptions about software development.
A Model of the Commit Size Distribution of Open Source
Carsten Kolassa,Dirk Riehle,Michel A. Salim
Computer Science , 2014, DOI: 10.1007/978-3-642-35843-2_6
Abstract: A fundamental unit of work in programming is the code contribution ("commit") that a developer makes to the code base of the project in work. We use statistical methods to derive a model of the probabilistic distribution of commit sizes in open source projects and we show that the model is applicable to different project sizes. We use both graphical as well as statistical methods to validate the goodness of fit of our model. By measuring and modeling a fundamental dimension of programming we help improve software development tools and our understanding of software development.
Developer Belief vs. Reality: The Case of the Commit Size Distribution
Dirk Riehle,Carsten Kolassa,Michel A. Salim
Computer Science , 2014,
Abstract: The design of software development tools follows from what the developers of such tools believe is true about software development. A key aspect of such beliefs is the size of code contributions (commits) to a software project. In this paper, we show that what tool developers think is true about the size of code contributions is different by more than an order of magnitude from reality. We present this reality, called the commit size distribution, for a large sample of open source and selected closed source projects. We suggest that these new empirical insights will help improve software development tools by aligning underlying design assumptions closer with reality.
Activation of Akt Signaling Reduces the Prevalence and Intensity of Malaria Parasite Infection and Lifespan in Anopheles stephensi Mosquitoes
Vanessa Corby-Harris equal contributor,Anna Drexler equal contributor,Laurel Watkins de Jong,Yevgeniya Antonova,Nazzy Pakpour,Rolf Ziegler,Frank Ramberg,Edwin E. Lewis,Jessica M. Brown,Shirley Luckhart,Michael A. Riehle
PLOS Pathogens , 2010, DOI: 10.1371/journal.ppat.1001003
Abstract: Malaria (Plasmodium spp.) kills nearly one million people annually and this number will likely increase as drug and insecticide resistance reduces the effectiveness of current control strategies. The most important human malaria parasite, Plasmodium falciparum, undergoes a complex developmental cycle in the mosquito that takes approximately two weeks and begins with the invasion of the mosquito midgut. Here, we demonstrate that increased Akt signaling in the mosquito midgut disrupts parasite development and concurrently reduces the duration that mosquitoes are infective to humans. Specifically, we found that increased Akt signaling in the midgut of heterozygous Anopheles stephensi reduced the number of infected mosquitoes by 60–99%. Of those mosquitoes that were infected, we observed a 75–99% reduction in parasite load. In homozygous mosquitoes with increased Akt signaling parasite infection was completely blocked. The increase in midgut-specific Akt signaling also led to an 18–20% reduction in the average mosquito lifespan. Thus, activation of Akt signaling reduced the number of infected mosquitoes, the number of malaria parasites per infected mosquito, and the duration of mosquito infectivity.
Epistolography as Autobiography: Remarks on the Letter-Collections of Nikephoros Choumnos
Alexander Riehle
Parekbolai : an Electronic Journal for Byzantine Literature , 2012,
Abstract: This article highlights challenges involved in understanding and interpreting Byzantine epistolary literature, and suggests that we pay closer attention to the transmission of letters and its hermeneutic ramifications. The letters penned by the late Byzantine court official Nikephoros Choumnos are a case in point. The author assembled, revised and arranged his letters, which were originally composed and dispatched mostly for pragmatic purposes (e.g., letters of request). By embedding these missives into the framework of a collection, he created an autobiographical narrative that was to promote and perpetuate his multi-faceted persona.
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