Bart Hooghe

ORegAnno: an open-access community-driven resource for regulatory annotation

ORegAnno is an open-source, open-access database and literature curation system for community-based annotation of experimentally identified DNA regulatory regions, transcription factor binding sites and regulatory variants. The current release comprises 30 145 records curated from 922 publications and describing regulatory sequences for over 3853 genes and 465 transcription factors from 19 species. A new feature called the ‘publication queue’ allows users to input relevant papers from scientific literature as targets for annotation. The queue contains 4438 gene regulation papers entered by experts and another 54 351 identified by text-mining methods. Users can enter or ‘check out’ papers from the queue for manual curation using a series of user-friendly annotation pages. A typical record entry consists of species, sequence type, sequence, target gene, binding factor, experimental outcome and one or more lines of experimental evidence. An evidence ontology was developed to describe and categorize these experiments. Records are cross-referenced to Ensembl or Entrez gene identifiers, PubMed and dbSNP and can be visualized in the Ensembl or UCSC genome browsers. All data are freely available through search pages, XML data dumps or web services at: http://www.oreganno.org.

Continuous Cell Injury Promotes Hepatic Tumorigenesis in Cdc42-Deficient Mouse Liver

BACKGROUND & AIMS The Rho small guanosine triphosphatase Cdc42 is critical for diverse cellular functions, including regulation of actin organization, cell polarity, intracellular membrane trafficking, transcription, cell-cycle progression, and cell transformation. This implies that Cdc42 might be required for liver function. METHODS Mice in which Cdc42 was ablated in hepatocytes and bile duct cells were generated by Cre-loxP technology. Livers were examined by histologic, immunohistochemical, ultrastructural, and serum analysis to define the effect of loss of Cdc42 on liver structure. RESULTS Mice lacking Cdc42 in their hepatocytes were born at Mendelian ratios. They did not show increased mortality but showed chronic jaundice. They developed hepatomegaly soon after birth, and signs of liver transformation, such as formation of nodules and tumors, became visible macroscopically at age 6 months. Hepatocellular carcinoma was observed 8 months after birth. Tumors grew slowly and lacked expression of nuclear beta-catenin. Lung metastases were observed at the late stage of carcinogenesis. Immunofluorescent examination and electron microscopy revealed severe defects in the liver. At the age of 2 months, the canaliculi between hepatocytes were greatly enlarged, although the tight junctions flanking the canaliculi appeared normal. Regular liver plates were absent. E-cadherin expression pattern and gap junction localization were distorted. Analysis of serum samples indicated cholestasis. CONCLUSIONS We describe a mouse model in which chronic liver disease leads to hepatocarcinogenesis.

ConTra v2: a tool to identify transcription factor binding sites across species, update 2011

Transcription factors are important gene regulators with distinctive roles in development, cell signaling and cell cycling, and they have been associated with many diseases. The ConTra v2 web server allows easy visualization and exploration of predicted transcription factor binding sites in any genomic region surrounding coding or non-coding genes. In this new version, users can choose from nine reference organisms ranging from human to yeast. ConTra v2 can analyze promoter regions, 5′-UTRs, 3′-UTRs and introns or any other genomic region of interest. Hundreds of position weight matrices are available to choose from, but the user can also upload any other matrices for detecting specific binding sites. A typical analysis is run in four simple steps of choosing the gene, the transcript, the region of interest and then selecting one or more transcription factor binding sites. The ConTra v2 web server is freely available at http://bioit.dmbr.ugent.be/contrav2/index.php.

ConTra: a promoter alignment analysis tool for identification of transcription factor binding sites across species

Transcription factors (TFs) are key components in signaling pathways, and the presence of their binding sites in the promoter regions of DNA is essential for their regulation of the expression of the corresponding genes. Orthologous promoter sequences are commonly used to increase the specificity with which potentially functional transcription factor binding sites (TFBSs) are recognized and to detect possibly important similarities or differences between the different species. The ConTra (conserved TFBSs) web server provides the biologist at the bench with a user-friendly tool to interactively visualize TFBSs predicted using either TransFac (1) or JASPAR (2) position weight matrix libraries, on a promoter alignment of choice. The visualization can be preceded by a simple scoring analysis to explore which TFs are the most likely to bind to the promoter of interest. The ConTra web server is available at http://bioit.dmbr.ugent.be/ConTra/index.php.

A flexible integrative approach based on random forest improves prediction of transcription factor binding sites

Transcription factor binding sites (TFBSs) are DNA sequences of 6–15 base pairs. Interaction of these TFBSs with transcription factors (TFs) is largely responsible for most spatiotemporal gene expression patterns. Here, we evaluate to what extent sequence-based prediction of TFBSs can be improved by taking into account the positional dependencies of nucleotides (NPDs) and the nucleotide sequence-dependent structure of DNA. We make use of the random forest algorithm to flexibly exploit both types of information. Results in this study show that both the structural method and the NPD method can be valuable for the prediction of TFBSs. Moreover, their predictive values seem to be complementary, even to the widely used position weight matrix (PWM) method. This led us to combine all three methods. Results obtained for five eukaryotic TFs with different DNA-binding domains show that our method improves classification accuracy for all five eukaryotic TFs compared with other approaches. Additionally, we contrast the results of seven smaller prokaryotic sets with high-quality data and show that with the use of high-quality data we can significantly improve prediction performance. Models developed in this study can be of great use for gaining insight into the mechanisms of TF binding.

PhysBinder: improving the prediction of transcription factor binding sites by flexible inclusion of biophysical properties

The most important mechanism in the regulation of transcription is the binding of a transcription factor (TF) to a DNA sequence called the TF binding site (TFBS). Most binding sites are short and degenerate, which makes predictions based on their primary sequence alone somewhat unreliable. We present a new web tool that implements a flexible and extensible algorithm for predicting TFBS. The algorithm makes use of both direct (the sequence) and several indirect readout features of protein–DNA complexes (biophysical properties such as bendability or the solvent-excluded surface of the DNA). This algorithm significantly outperforms state-of-the-art approaches for in silico identification of TFBS. Users can submit FASTA sequences for analysis in the PhysBinder integrative algorithm and choose from >60 different TF-binding models. The results of this analysis can be used to plan and steer wet-lab experiments. The PhysBinder web tool is freely available at http://bioit.dmbr.ugent.be/physbinder/index.php.

A distance difference matrix approach to identifying transcription factors that regulate differential gene expression

We introduce a method that considers target genes of a transcription factor, and searches for transcription factor binding sites (TFBSs) of secondary factors responsible for differential responses among these targets. Based on the distance difference matrix concept, the method simultaneously integrates statistical overrepresentation and co-occurrence of TFBSs. Our approach is validated on datasets of differentially regulated human genes and is shown to be highly effective in detecting TFBSs responsible for the observed differential gene expression.We introduce a method that considers target genes of a transcription factor, and searches for transcription factor binding sites (TFBSs) of secondary factors responsible for differential responses among these targets. Based on the distance difference matrix concept, the method simultaneously integrates statistical overrepresentation and co-occurrence of TFBSs. Our approach is validated on datasets of differentially regulated human genes and is shown to be highly effective in detecting TFBSs responsible for the observed differential gene expression.

ACE inhibitor captopril reduces ecdysteroids and oviposition in moths.

Abstract: By using the selective ACE inhibitor captopril, we studied the effect of the angiotensin converting enzyme (ACE) on larval growth, metamorphosis, and reproduction in a lepidopteran species, the cotton leafworm, Spodoptera littoralis. Captopril was detrimental to adult formation and oviposition, and in female moths it elicited decreasing ecdysteroid levels, but increasing trypsin activities. Our results suggest that captopril downregulates oviposition by two independent pathways. Apparently, oviposition is influenced by a complex interaction of ACE, trypsin activity, and ecdysteroid levels.