Summary: Non-coding RNAs (ncRNAs) play a vital role in many cellular processes such as RNA splicing, translation, gene regulation. However the vast majority of ncRNAs still have no functional annotation. One prominent approach for putative function assignment is clustering of transcripts according to sequence and secondary structure. However sequence information is changed by post-transcriptional modifications, and secondary structure is only a proxy for the true 3D conformation of the RNA polymer. A different type of information that does not suffer from these issues and that can be used for the detection of RNA classes, is the pattern of processing and its traces in small RNA-seq reads data. Here we introduce BlockClust, an efficient approach to detect transcripts with similar processing patterns. We propose a novel way to encode expression profiles in compact discrete structures, which can then be processed using fast graph-kernel techniques. We perform both unsupervised clustering and develop family specific discriminative models; finally we show how the proposed approach is scalable, accurate and robust across different organisms, tissues and cell lines. Availability: The whole BlockClust galaxy workflow including all tool dependencies is available at http://toolshed.g2.bx.psu.edu/view/rnateam/blockclust_workflow. Contact: backofen@informatik.uni-freiburg.de; costa@informatik.uni-freiburg.de Supplementary information: Supplementary data are available at Bioinformatics online.
De novo motif discovery has been an important challenge of bioinformatics for the past two decades. Since the emergence of high-throughput techniques like ChIP-seq, ChIP-exo and protein-binding microarrays (PBMs), the focus of de novo motif discovery has shifted to runtime and accuracy on large data sets. For this purpose, specialized algorithms have been designed for discovering motifs in ChIP-seq or PBM data. However, none of the existing approaches work perfectly for all three high-throughput techniques. In this article, we propose Dimont, a general approach for fast and accurate de novo motif discovery from high-throughput data. We demonstrate that Dimont yields a higher number of correct motifs from ChIP-seq data than any of the specialized approaches and achieves a higher accuracy for predicting PBM intensities from probe sequence than any of the approaches specifically designed for that purpose. Dimont also reports the expected motifs for several ChIP-exo data sets. Investigating differences between in vitro and in vivo binding, we find that for most transcription factors, the motifs discovered by Dimont are in good accordance between techniques, but we also find notable exceptions. We also observe that modeling intra-motif dependencies may increase accuracy, which indicates that more complex motif models are a worthwhile field of research.
Insertion Sequences (ISs) are small DNA segments that have the ability of moving themselves into genomes. These types of mobile genetic elements (MGEs) seem to play an essential role in genomes rearrangements and evolution of prokaryotic genomes, but the tools that deal with discovering ISs in an efficient and accurate way are still too few and not totally precise. Two main factors have big effects on IS discovery, namely: genes annotation and functionality prediction. Indeed, some specific genes called "transposases" are enzymes that are responsible of the production and catalysis for such transposition, but there is currently no fully accurate method that could decide whether a given predicted gene is either a real transposase or not. This is why authors of this article aim at designing a novel pipeline for ISs detection and classification, which embeds the most recently available tools developed in this field of research, namely OASIS (Optimized Annotation System for Insertion Sequence) and ISFinder database (an up-to-date and accurate repository of known insertion sequences). As this latter depend on predicted coding sequences, the proposed pipeline will encompass too various kinds of bacterial genes annotation tools (that is, Prokka, BASys, and Prodigal). A complete IS detection and classification pipeline is then proposed and tested on a set of 23 complete genomes of Pseudomonas aeruginosa. This pipeline can also be used as an investigator of annotation tools performance, which has led us to conclude that Prodigal is the best software for IS prediction. A deepen study regarding IS elements in P.aeruginosa has then been conducted, leading to the conclusion that close genomes inside this species have also a close numbers of IS families and groups.
For visualizing and analyzing subcellular localizations, we presented the subcellular localization charts in 2013 [1]. After a concrete localization scenario is found, it can be visualized in the context of a virtual cell environment. To acquire the heterogeneous localization data, two information sources where combined with the CELLmicrocosmos 4.2 PathwayIntegration, DAWIS-M.D. and ANDCell [2], [3].
The creation of a virtual cell scenario is a multidisciplinary vision. Cell modeling is a specific field which can be applied to a number of quite diverse approaches, starting from simulation-based ones, such as the Virtual Cell project – which is able to convert biological descriptions into a mathematical system of ordinary and/or partial differential equations – to visualization-based approaches, such as cellPACK – which is based on the idea to create visual filled cell representations [1], [2]. Integrative Bioinformatics is a field which tries to unite different information sources to solve biological questions. The CELLmicrocosmos project consists of a number of different projects trying to approach the vision of a virtual cell environment, such as [3], [4]. Starting from 2004, a remarkable number of students were involved in the aforementioned projects. In addition to our custom tools, also external tools, such as Blender, Fiji (IsJustImageJ), or GROMACS played an important role in our daily work [5–7].
We review the level of genomic specificity regarding actinobacterial pathogenicity. As they occupy various niches in diverse habitats, one may assume the existence of lifestyle-specific genomic features. We include 240 actinobacteria classified into four pathogenicity classes: human pathogens (HPs), broad-spectrum pathogens (BPs), opportunistic pathogens (OPs) and non-pathogenic (NP). We hypothesize: (H1) Pathogens (HPs and BPs) possess specific pathogenicity signature genes. (H2) The same holds for OPs. (H3) Broad-spectrum and exclusively HPs cannot be distinguished from each other because of an observation bias, i.e. many HPs might yet be unclassified BPs. (H4) There is no intrinsic genomic characteristic of OPs compared with pathogens, as small mutations are likely to play a more dominant role to survive the immune system. To study these hypotheses, we implemented a bioinformatics pipeline that combines evolutionary sequence analysis with statistical learning methods (Random Forest with feature selection, model tuning and robustness analysis). Essentially, we present orthologous gene sets that computationally distinguish pathogens from NPs (H1). We further show a clear limit in differentiating OPs from both NPs (H2) and pathogens (H4). HPs may also not be distinguished from bacteria annotated as BPs based only on a small set of orthologous genes (H3), as many HPs might as well target a broad range of mammals but have not been annotated accordingly. In conclusion, we illustrate that even in the post-genome era and despite next-generation sequencing technology, our ability to efficiently deduce real-world conclusions, such as pathogenicity classification, remains quite limited.
The visualization and localization of biochemical networks represent major tasks of bioinformatics. In the future, they could be used as additional criteria to find potential -omics interaction partners. Moreover, this visualization and localization can help scientists to find appropriate experiments or to create detailed problem-oriented pathways. Today, we can use database integration and text mining methods for the prediction of biological networks. However, we can use the same applications for the localization prediction of biological networks and their components [1]. Using this information, we are able to model and visualize biochemical networks in 2D or 3D. For this purpose, we use our database integration infrastructure BioDWH with the DAWIS-M.D., as well as ANDCell as the base for the subcellular localization of the CELLmicrocosmos 4.2 PathwayIntegration (CmPI) project [1–4]. Here, we discuss how this approach can be extended by using the new FraMeTex text mining framework.
Web browsers and web applications have become common tools in bioinformatics over the past decades. Many existing web applications revolve around server-client interaction, where heavy computational tasks are often outsourced to the server and the presentation is handled on the the client-side. However, more recent additions to the web browser technology embrace the capability of handling more complex operations on the client-side itself, cutting out most of the server-client interaction except for data loading. This paper contributes to the exploration of the potential of approaches to implement and speed up computational expensive tasks, like image cluster analysis, within a client-side web browser environment. The experimental results, incorporating the well known k-means algorithm which serves as a platform for various parallelization approaches, indicate the possibility to achieve real time image clustering. Especially for the available MALDI-MSI data set the results look promising. Despite good results of multi-threading approaches, algorithmic approaches appear to be relevant too. Therefore advancements in accelerating the k-means algorithm itself are considered.
Increasing our knowledge about molecular processes in response to a certain treatment or infection in plants, insects, or other organisms requires the identification of the genes involved in this response. In this paper, we propose the Profile Interaction Finder (PIF) to identify such genes from gene expression data which is based on a convex linear model, and we investigate its efficacy for two applications related to stimulus response. First, we seek to identify sets of putative regulatory genes that explain the expression levels of a gene under different stimuli best. Second, we aim at identifying genes that show a specific response to a stimulus or a combination of stimuli. For both applications, we study the expression response of two Arabidopsis species to treatment with the plant hormone auxin and of Apis mellifera to pathogen infection. The proposed approach may be of general utility for analyzing expression data with a focus on genes and gene sets that explain specific stimulus response.
Intracellular processes in living organisms are described by metabolic models. A visualization of metabolic models assists interpretation of data or analyzing results. We introduce the visualization tool DaViMM creating personalized graphical representations of metabolic networks for model comparison or the display of measurements or analyzing results. The tool is coupled to a relational database containing graphical network properties like coordinates, which ensure an intuitive network layout. A combination of DaViMM, the graphical database, and available biochemical databases enables an automated creation of metabolic network maps. The flexibility of this combination is demonstrated with some application examples.
In metagenomics, the discovery of functional novelty has always been pursued in a gene-centered manner. In that way, sequence-based analysis has been restricted to particular features and to a sufficient length of the sequences. We propose a statistical approach that is independent from the identification of single sequences but rather yields an overall characterization of a metagenome. Our method is based on the analysis of significant differences between the functional profile of a metagenome and its reconstruction from a combination of genomic profiles using the Taxy-Pro mixture model. Here, protein families with a large proportion of domain hits that cannot be explained by the model are interesting candidates for the exploration of metagenomic novelty. The results of three case studies indicate that our method is able to characterize metagenomic novelty in terms of the protein families that significantly contribute to unexplained domain counts. We found a good correspondence between our predictions and the discoveries in the original studies as well as specific indicators of functional novelty that have not yet been described.
The reliable identification of genes is a challenging and crucial part of genome research. Various methods aiming at accurate predictions have evolved that predict genes ab initio on reference sequences or evidence based with help of additional information. With high-throughput RNA-Seq data reflecting currently expressed genes, a particularly meaningful source of information has become commonly available. However, a particular challenge in including RNA-Seq data is the difficult handling of ambiguously mapped reads. Therefore we developed GIIRA, a novel gene finder that is exclusively based on RNA-Seq data and inherently includes ambiguously mapped reads. Evaluation on simulated and real data and comparison with existing methods incorporating RNA-Seq information highlight the accuracy of GIIRA in identifying the expressed genes. Further, we developed a framework to integrate GIIRA and other gene finders to obtain a verified and accurate set of gene predictions.
The analysis of protein domains has gained considerable attention over the last years. Many new insights on protein modular evolution, combined with improved domain detection, have paved the way for an integrated analysis of protein families from a domain-centric perspective. We recently released DoMosaics, a JAVA application that facilitates the interactive analysis of protein domain arrangements. DoMosaics combines guided domain annotation, a highly-customisable visualization of arrangements, and a number of analysis tools. It also integrates domain-centric algorithms such as CODD, which is used for the detection of divergent domain occurences that have escaped Pfam thresholds, as well as RADS/RAMPAGE which provides means to search for proteins with a domain arrangement similar to a given query. RADS provides an alignment of domain strings as opposed to amino-acid sequences, while RAMPAGE produces an amino-acid alignment guided by RADS results. Hence, RADS/RAMPAGE produces fast and yet accurate alignments, and associated ranking, of proteins with similar domain arrangements. Together, these tools greatly simplify the domain-centric analysis of protein function, structure and evolution.
Promoter prediction in bacteria is a classical bioinformatics problem, where available methods for regulatory element detection exhibit a very high number of false positives. We here argue that accurate transcription start site (TSS) prediction is a complex problem, where available methods for sequence motif discovery are not in itself well adopted for solving the problem. We here instead propose that the problem requires integration of quantitative understanding of transcription initiation with careful description of promoter sequence specificity. We review evidence for this viewpoint based on our recent work, and discuss a current progress on accurate TSS detection on the example of sigma70 transcription start sites in E. coli.
The explosion of the biological data has dramatically reformed today’s biological research. The need to integrate and analyze high-dimensional biological data on a large scale is driving the development of novel bioinformatics approaches. Biclustering, also known as simultaneous clustering or co-clustering, has been successfully utilized to discover local patterns in gene expression data and similar biomedical data types. Here, we contribute a new approach: Bi-Force. It is based on the weighted bicluster editing model, to perform biclustering on arbitrary sets of biological entities, given any kind of similarity function. We first evaluated the power of Bi-Force to solve dedicated bicluster editing problems by comparing Bi-Force with two existing algorithms in the BiCluE software package. We then followed a biclustering evaluation protocol from a recent review paper from Eren et al. and compared Bi-Force against eight existing tools: FABIA, QUBIC, Cheng and Church, Plaid, Bimax, Spectral, xMOTIFS and ISA. To this end, a suite of synthetic data sets as well as nine large gene expression data sets from Gene Expression Omnibus were analyzed. All resulting biclusters were subsequently investigated by Gene Ontology enrichment analysis to evaluate their biological relevance. The distinct theoretical foundation of Bi-Force (bicluster editing) is more powerful than strict biclustering. We thus outperformed existing tools with Bi-Force at least when following the evaluation protocols from Eren et al.. Bi-Force is implemented in Java and integrated into the open source software package of BiCluE. The software as well as all used data sets are publicly available at http://biclue.mpi-inf.mpg.de.
