University of Fribourg

About: University of Fribourg is a education organization based out in Fribourg, Freiburg, Switzerland. It is known for research contribution in the topics: Population & Context (language use). The organization has 6040 authors who have published 14975 publications receiving 542500 citations. The organization is also known as: UNIFR & Universität Freiburg.

Predicting Missing Links via Local Information

Abstract: Missing link prediction of networks is of both theoretical interest and practical significance in modern science. In this paper, we empirically investigate a simple framework of link prediction on the basis of node similarity. We compare nine well-known local similarity measures on six real networks. The results indicate that the simplest measure, namely common neighbors, has the best overall performance, and the Adamic-Adar index performs the second best. A new similarity measure, motivated by the resource allocation process taking place on networks, is proposed and shown to have higher prediction accuracy than common neighbors. It is found that many links are assigned same scores if only the information of the nearest neighbors is used. We therefore design another new measure exploited information of the next nearest neighbors, which can remarkably enhance the prediction accuracy.

Apoptosis without caspases: an inefficient molecular guillotine?

Abstract: Since the discovery that the cysteine protease CED-3 was essential for developmental death in the nematode C. elegans, the search has been on to identify homologous proteases governing mammalian apoptosis. Fourteen of these proteases, now called caspases, have been found to date, and studies with natural or chemical inhibitors, and more recently knock-out mice, confirmed the involvement of at least a subset of these proteases in various forms of mammalian apoptosis. However, there has been recent evidence that some apoptotic morphologies, such as cell shrinkage, membrane blebbing and nuclear condensation, are not blocked by caspase inhibitors and that the cells continue to die in a protracted and inefficient manner. This has led to the notion that caspases are not required for all aspects of apoptosis in mammals. Here we review the current knowledge about caspase-independent apoptosis, discuss the strengths and weaknesses of the reasoning that led to its proposition and provide insights into its possible regulation and physiological significance.

C26-CoA-dependent ceramide synthesis of Saccharomyces cerevisiae is operated by Lag1p and Lac1p

Abstract: Lag1p and Lac1p are two highly homologous membrane proteins of the endoplasmic reticulum (ER). When both genes are deleted, cells cannot transport glycosylphosphatidylinositol (GPI)-anchored proteins from the ER to the Golgi at a normal rate. Here we show that microsomes or detergent extracts from lag1Δlac1Δ double mutants lack an activity transferring C26 fatty acids from C26-coenzyme A onto dihydrosphingosine or phytosphingosine. As a consequence, in intact cells, the normal ceramides and inositolphosphorylceramides are drastically reduced. lag1Δlac1Δ cells compensate for the lack of normal sphingolipids by making increased amounts of C26 fatty acids, which become incorporated into glycerophospholipids. They also contain 20- to 25-fold more free long chain bases than wild type and accumulate very large amounts of abnormally polar ceramides. They make small amounts of abnormal mild base-resistant inositolphospholipids. The lipid remodelling of GPI-anchored proteins is severely compromised in lag1Δlac1Δ double mutants since only few and mostly abnormal ceramides are incorporated into the GPI anchors. The participation of Lag1p and Lac1p in ceramide synthesis may explain their role in determining longevity.

Influence of Expectation of Different Rewards on Behavior-Related Neuronal Activity in the Striatum

Abstract: This study investigated how different expected rewards influence behavior-related neuronal activity in the anterior striatum. In a spatial delayed-response task, monkeys reached for a left or right target and obtained a small quantity of one of two juices (apple, grenadine, orange, lemon, black currant, or raspberry). In each trial, an initial instruction picture indicated the behavioral target and predicted the reward. Nonmovement trials served as controls for movement relationships. Consistent preferences in special reward choice trials and differences in anticipatory licks, performance errors, and reaction times indicated that animals differentially expected the rewards predicted by the instructions. About 600 of >2,500 neurons in anterior parts of caudate nucleus, putamen, and ventral striatum showed five forms of task-related activations, comprising responses to instructions, spatial or nonspatial activations during the preparation or execution of the movement, and activations preceding or following the rewards. About one-third of the neurons showed different levels of task-related activity depending on which liquid reward was predicted at trial end. Activations were either higher or lower for rewards that were preferred by the animals as compared with nonpreferred rewards. These data suggest that the expectation of an upcoming liquid reward may influence a fraction of task-related neurons in the anterior striatum. Apparently the information about the expected reward is incorporated into the neuronal activity related to the behavioral reaction leading to the reward. The results of this study are in general agreement with an account of goal-directed behavior according to which the outcome should be represented already at the time at which the behavior toward the outcome is performed.