A network module-based method for identifying cancer prognostic signatures

Discovering robust prognostic gene signatures as biomarkers using genomics data can be challenging. We have developed a simple but efficient method for discovering prognostic biomarkers in cancer gene expression data sets using modules derived from a highly reliable gene functional interaction network. When applied to breast cancer, we discover a novel 31-gene signature associated with patient survival. The signature replicates across 5 independent gene expression studies, and outperforms 48 published gene signatures. When applied to ovarian cancer, the algorithm identifies a 75-gene signature associated with patient survival. A Cytoscape plugin implementation of the signature discovery method is available at http://wiki.reactome.org/index.php/Reactome_FI_Cytoscape_Plugin     

Discovering the hidden sub-network component in a ranked list of genes or proteins derived from genomic experiments

Genomic experiments (e.g. differential gene expression, single-nucleotide polymorphism association) typically produce ranked list of genes. We present a simple but powerful approach which uses protein–protein interaction data to detect sub-networks within such ranked lists of genes or proteins. We performed an exhaustive study of network parameters that allowed us concluding that the average number of components and the average number of nodes per component are the parameters that best discriminate between real and random networks. A novel aspect that increases the efficiency of this strategy in finding sub-networks is that, in addition to direct connections, also connections mediated by intermediate nodes are considered to build up the sub-networks. The possibility of using of such intermediate nodes makes this approach more robust to noise. It also overcomes some limitations intrinsic to experimental designs based on differential expression, in which some nodes are invariant across conditions. The proposed approach can also be used for candidate disease-gene prioritization. Here, we demonstrate the usefulness of the approach by means of several case examples that include a differential expression analysis in Fanconi Anemia, a genome-wide association study of bipolar disorder and a genome-scale study of essentiality in cancer genes. An efficient and easy-to-use web interface (available at http://www.babelomics.org) based on HTML5 technologies is also provided to run the algorithm and represent the network.     

Comparative Analysis of Pdf-Mediated Circadian Behaviors Between Drosophila melanogaster and D. virilis

PAR proteins (partitioning defective) are major regulators of cell polarity and asymmetric cell division. One of the par genes, par-1, encodes a Ser/Thr kinase that is conserved from yeast to mammals. In Caenorhabditis elegans, par-1 governs asymmetric cell division by ensuring the polar distribution of cell fate determinants. However the precise mechanisms by which PAR-1 regulates asymmetric cell division in C. elegans remain to be elucidated. We performed a genomewide RNAi screen and identified six genes that specifically suppress the embryonic lethal phenotype associated with mutations in par-1. One of these suppressors is mpk-1, the C. elegans homolog of the conserved mitogen activated protein (MAP) kinase ERK. Loss of function of mpk-1 restored embryonic viability, asynchronous cell divisions, the asymmetric distribution of cell fate specification markers, and the distribution of PAR-1 protein in par-1 mutant embryos, indicating that this genetic interaction is functionally relevant for embryonic development. Furthermore, disrupting the function of other components of the MAPK signaling pathway resulted in suppression of par-1 embryonic lethality. Our data therefore indicates that MAP kinase signaling antagonizes PAR-1 signaling during early C. elegans embryonic polarization.ASYMMETRIC cell division, a process in which a mother cell divides in two different daughter cells, is a fundamental mechanism to achieve cell diversity during development. We use the early embryo of Caenorhabditis elegans as a model system to study asymmetric cell division. The C. elegans one-cell embryo divides asymmetrically along its anteroposterior axis, generating two cells of different sizes and fates: the larger anterior daughter cell will generate somatic tissues while the smaller posterior daughter cell will generate the germline (Sulston et al. 1983).A group of proteins called PAR proteins (partitioning defective) is required for asymmetric cell division in C. elegans (Kemphues et al. 1988). Depletion of any of the seven par genes (par-1 to -6 and pkc-3) leads to defects in asymmetric cell division and embryonic lethality (Kemphues et al. 1988; Kirby et al. 1990; Tabuse et al. 1998; Hung and Kemphues 1999; Hao et al. 2006). PAR-3 and PAR-6 are conserved proteins that contain PDZ-domains and form a complex with PKC-3 (Etemad-Moghadam et al. 1995; Izumi et al. 1998; Tabuse et al. 1998; Hung and Kemphues 1999). This complex becomes restricted to the anterior cortex of the embryo in response to spatially defined actomyosin contractions occurring in the embryo upon fertilization (Goldstein and Hird 1996; Munro et al. 2004). The posterior cortex of the embryo that becomes devoid of the anterior PAR proteins is occupied by the RING protein PAR-2 and the Ser/Thr kinase PAR-1 (Guo and Kemphues 1995; Boyd et al. 1996; Cuenca et al. 2003). Once polarized, the anterior and posterior PAR proteins mutually exclude each other from their respective cortices (Etemad-Moghadam et al. 1995; Boyd et al. 1996; Cuenca et al. 2003; Hao et al. 2006). Loss of function of the gene par-1, as opposed to loss of most other par genes, results in embryos that exhibit only subtle effects on the polarized cortical domains occupied by the other PAR proteins (Cuenca et al. 2003). However defects in this gene are associated with a more symmetric division in size, an aberrant distribution of cell fate specification markers, altered cell fates of the daughter cells of the embryo, and ultimately embryonic lethality (Kemphues et al. 1988; Guo and Kemphues 1995).PAR-1 controls asymmetric cell division and cell fate specification by regulating the localization of the two highly similar CCCH-type zinc-finger proteins MEX-5 and MEX-6 (referred to as MEX-5/6). MEX-5 and MEX-6 are 70% identical in their amino acid sequence and fulfill partially redundant functions in the embryo (Schubert et al. 2000). In wild-type animals, endogenous MEX-5 and GFP fusions of MEX-6 localize primarily to the anterior of the embryo while both proteins are evenly distributed in par-1 mutant embryos (Schubert et al. 2000; Cuenca et al. 2003). This suggests that in wild-type animals, PAR-1 acts in part by restricting MEX-5 and MEX-6 to the anterior of the embryo. The precise mechanism of this regulation is not known, but an elegant study performed for MEX-5 indicates that differential protein mobility in the anterior and posterior cytoplasm of the one-cell embryo contributes to this asymmetry (Tenlen et al. 2008). While increased mobility in the posterior of the one-cell embryo correlates with a par-1- and par-4-dependent phosphorylation on MEX-5, the kinase directly phosphorylating MEX-5 remains to be identified (Tenlen et al. 2008).Some of the phenotypes associated with loss of par-1 function are dependent on the function of mex-5 and mex-6. First, loss of function of par-1 leads to a decreased stability and aberrant localization of the posterior cell fate specification marker PIE-1, a protein that is usually inherited by the posterior daughter cell in wild-type animals and ensures the correct specification of the germline (Mello et al. 1996; Seydoux et al. 1996). This decreased stability is dependent on mex-5/6 function as PIE-1 levels are restored, albeit with symmetrical distribution, in mex-6(RNAi); mex-5(RNAi); par-1(b274) embryos (Schubert et al. 2000; Cuenca et al. 2003; Derenzo et al. 2003). Second, embryos lacking par-1 function exhibit decreased amounts of P granules in the one-cell embryo, while these markers are present in mex-6(pk440); mex-5(zu199); par-1(RNAi) embryos of comparable age (Cheeks et al. 2004). Third, in par-1(RNAi) one-cell embryos the posterior cortical domain occupied by the polarity protein PAR-2 is extended anteriorly, when compared to wild-type embryos (Cuenca et al. 2003). This anterior extension is rescued in embryos deficient for both par-1 and mex-5/6 (Cuenca et al. 2003). Taken together, these results indicate that par-1 acts in the embryo—at least in part—by regulating the localization and/or activity of the proteins MEX-5 and MEX-6. However, it remains unclear whether other proteins can modulate PAR-1 function to affect MEX-5/6 activity.To gain insight into the mechanisms of par-1 function in the embryo, we sought to identify genes that act together with par-1 during embryonic development. We performed an RNAi-based screen for genetic interactors of the temperature-sensitive allele par-1(zu310), using the embryonic lethal phenotype of this mutant as a readout. This method has proven successful in previous screens to identify genes involved in early embryonic processes (Labbé et al. 2006; O''Rourke et al. 2007). We were able to identify six genes that, upon disruption of their function, suppress the embryonic lethal phenotype of par-1 mutant embryos. One of these genes is mpk-1, the C. elegans homolog of the highly conserved MAP kinase ERK. Closer analysis subsequently showed that reduction of function of mpk-1 not only increases viability of par-1 mutant embryos, but also reverts several polarity phenotypes associated with loss of function of par-1. Our data indicate that mpk-1 antagonizes par-1 activity to regulate polarization and asymmetric cell divisions in the early embryo.     

SECISearch3 and Seblastian: new tools for prediction of SECIS elements and selenoproteins

Selenoproteins are proteins containing an uncommon amino acid selenocysteine (Sec). Sec is inserted by a specific translational machinery that recognizes a stem-loop structure, the SECIS element, at the 3′ UTR of selenoprotein genes and recodes a UGA codon within the coding sequence. As UGA is normally a translational stop signal, selenoproteins are generally misannotated and designated tools have to be developed for this class of proteins. Here, we present two new computational methods for selenoprotein identification and analysis, which we provide publicly through the web servers at http://gladyshevlab.org/SelenoproteinPredictionServer or http://seblastian.crg.es. SECISearch3 replaces its predecessor SECISearch as a tool for prediction of eukaryotic SECIS elements. Seblastian is a new method for selenoprotein gene detection that uses SECISearch3 and then predicts selenoprotein sequences encoded upstream of SECIS elements. Seblastian is able to both identify known selenoproteins and predict new selenoproteins. By applying these tools to diverse eukaryotic genomes, we provide a ranked list of newly predicted selenoproteins together with their annotated cysteine-containing homologues. An analysis of a representative candidate belonging to the AhpC family shows how the use of Sec in this protein evolved in bacterial and eukaryotic lineages.     

Gene characterization index: assessing the depth of gene annotation

Background

We introduce the Gene Characterization Index, a bioinformatics method for scoring the extent to which a protein-encoding gene is functionally described. Inherently a reflection of human perception, the Gene Characterization Index is applied for assessing the characterization status of individual genes, thus serving the advancement of both genome annotation and applied genomics research by rapid and unbiased identification of groups of uncharacterized genes for diverse applications such as directed functional studies and delineation of novel drug targets.

Methodology/Principal Findings

The scoring procedure is based on a global survey of researchers, who assigned characterization scores from 1 (poor) to 10 (extensive) for a sample of genes based on major online resources. By evaluating the survey as training data, we developed a bioinformatics procedure to assign gene characterization scores to all genes in the human genome. We analyzed snapshots of functional genome annotation over a period of 6 years to assess temporal changes reflected by the increase of the average Gene Characterization Index. Applying the Gene Characterization Index to genes within pharmaceutically relevant classes, we confirmed known drug targets as high-scoring genes and revealed potentially interesting novel targets with low characterization indexes. Removing known drug targets and genes linked to sequence-related patent filings from the entirety of indexed genes, we identified sets of low-scoring genes particularly suited for further experimental investigation.

Conclusions/Significance

The Gene Characterization Index is intended to serve as a tool to the scientific community and granting agencies for focusing resources and efforts on unexplored areas of the genome. The Gene Characterization Index is available from http://cisreg.ca/gci/.     

Effect of Genetic Variation in a Drosophila Model of Diabetes-Associated Misfolded Human Proinsulin

The identification and validation of gene–gene interactions is a major challenge in human studies. Here, we explore an approach for studying epistasis in humans using a Drosophila melanogaster model of neonatal diabetes mellitus. Expression of the mutant preproinsulin (hINS^C96Y) in the eye imaginal disc mimics the human disease: it activates conserved stress-response pathways and leads to cell death (reduction in eye area). Dominant-acting variants in wild-derived inbred lines from the Drosophila Genetics Reference Panel produce a continuous, highly heritable distribution of eye-degeneration phenotypes in a hINS^C96Y background. A genome-wide association study (GWAS) in 154 sequenced lines identified a sharp peak on chromosome 3L, which mapped to a 400-bp linkage block within an intron of the gene sulfateless (sfl). RNAi knockdown of sfl enhanced the eye-degeneration phenotype in a mutant-hINS-dependent manner. RNAi against two additional genes in the heparan sulfate (HS) biosynthetic pathway (ttv and botv), in which sfl acts, also modified the eye phenotype in a hINS^C96Y-dependent manner, strongly suggesting a novel link between HS-modified proteins and cellular responses to misfolded proteins. Finally, we evaluated allele-specific expression difference between the two major sfl-intronic haplotypes in heterozygtes. The results showed significant heterogeneity in marker-associated gene expression, thereby leaving the causal mutation(s) and its mechanism unidentified. In conclusion, the ability to create a model of human genetic disease, map a QTL by GWAS to a specific gene, and validate its contribution to disease with available genetic resources and the potential to experimentally link the variant to a molecular mechanism demonstrate the many advantages Drosophila holds in determining the genetic underpinnings of human disease.     

In vivo response to methotrexate forecasts outcome of acute lymphoblastic leukemia and has a distinct gene expression profile

Background

Childhood acute lymphoblastic leukemia (ALL) is the most common cancer in children, and can now be cured in approximately 80% of patients. Nevertheless, drug resistance is the major cause of treatment failure in children with ALL. The drug methotrexate (MTX), which is widely used to treat many human cancers, is used in essentially all treatment protocols worldwide for newly diagnosed ALL. Although MTX has been extensively studied for many years, relatively little is known about mechanisms of de novo resistance in primary cancer cells, including leukemia cells. This lack of knowledge is due in part to the fact that existing in vitro methods are not sufficiently reliable to permit assessment of MTX resistance in primary ALL cells. Therefore, we measured the in vivo antileukemic effects of MTX and identified genes whose expression differed significantly in patients with a good versus poor response to MTX.

Methods and Findings

We utilized measures of decreased circulating leukemia cells of 293 newly diagnosed children after initial “up-front” in vivo MTX treatment (1 g/m²) to elucidate interpatient differences in the antileukemic effects of MTX. To identify genomic determinants of these effects, we performed a genome-wide assessment of gene expression in primary ALL cells from 161 of these newly diagnosed children (1–18 y). We identified 48 genes and two cDNA clones whose expression was significantly related to the reduction of circulating leukemia cells after initial in vivo treatment with MTX. This finding was validated in an independent cohort of children with ALL. Furthermore, this measure of initial MTX in vivo response and the associated gene expression pattern were predictive of long-term disease-free survival (p < 0.001, p = 0.02).

Conclusions

Together, these data provide new insights into the genomic basis of MTX resistance and interpatient differences in MTX response, pointing to new strategies to overcome MTX resistance in childhood ALL.Trial registrations: Total XV, Therapy for Newly Diagnosed Patients With Acute Lymphoblastic Leukemia, http://www.ClinicalTrials.gov ({"type":"clinical-trial","attrs":{"text":"NCT00137111","term_id":"NCT00137111"}}NCT00137111); Total XIIIBH, Phase III Randomized Study of Antimetabolite-Based Induction plus High-Dose MTX Consolidation for Newly Diagnosed Pediatric Acute Lymphocytic Leukemia at Intermediate or High Risk of Treatment Failure (NCI-T93-0101D); Total XIIIBL, Phase III Randomized Study of Antimetabolite-Based Induction plus High-Dose MTX Consolidation for Newly Diagnosed Pediatric Acute Lymphocytic Leukemia at Lower Risk of Treatment Failure (NCI-T93-0103D).     

Skip the alignment: degenerate, multiplex primer and probe design using K-mer matching instead of alignments

PriMux is a new software package for selecting multiplex compatible, degenerate primers and probes to detect diverse targets such as viruses. It requires no multiple sequence alignment, instead applying k-mer algorithms, hence it scales well for large target sets and saves user effort from curating sequences into alignable groups. PriMux has the capability to predict degenerate primers as well as probes suitable for TaqMan or other primer/probe triplet assay formats, or simply probes for microarray or other single-oligo assay formats. PriMux employs suffix array methods for efficient calculations on oligos 10-∼100 nt in length. TaqMan® primers and probes for each segment of Rift Valley fever virus were designed using PriMux, and lab testing comparing signatures designed using PriMux versus those designed using traditional methods demonstrated equivalent or better sensitivity for the PriMux-designed signatures compared to traditional signatures. In addition, we used PriMux to design TaqMan® primers and probes for unalignable or poorly alignable groups of targets: that is, all segments of Rift Valley fever virus analyzed as a single target set of 198 sequences, or all 2863 Dengue virus genomes for all four serotypes available at the time of our analysis. The PriMux software is available as open source from http://sourceforge.net/projects/PriMux.     

Prediction of drought-resistant genes in Arabidopsis thaliana using SVM-RFE

Background

Identifying genes with essential roles in resisting environmental stress rates high in agronomic importance. Although massive DNA microarray gene expression data have been generated for plants, current computational approaches underutilize these data for studying genotype-trait relationships. Some advanced gene identification methods have been explored for human diseases, but typically these methods have not been converted into publicly available software tools and cannot be applied to plants for identifying genes with agronomic traits.

Methodology

In this study, we used 22 sets of Arabidopsis thaliana gene expression data from GEO to predict the key genes involved in water tolerance. We applied an SVM-RFE (Support Vector Machine-Recursive Feature Elimination) feature selection method for the prediction. To address small sample sizes, we developed a modified approach for SVM-RFE by using bootstrapping and leave-one-out cross-validation. We also expanded our study to predict genes involved in water susceptibility.

Conclusions

We analyzed the top 10 genes predicted to be involved in water tolerance. Seven of them are connected to known biological processes in drought resistance. We also analyzed the top 100 genes in terms of their biological functions. Our study shows that the SVM-RFE method is a highly promising method in analyzing plant microarray data for studying genotype-phenotype relationships. The software is freely available with source code at http://ccst.jlu.edu.cn/JCSB/RFET/.     

OrthoRBH: A streamlined pipeline for mining large gene family sequences in related species

Plant and animal genomes are replete with large gene families, making the task of ortholog identification difficult and labor intensive. OrthoRBH is an automated reciprocal blast pipeline tool enabling the rapid identification of specific gene families of interest in related species, streamlining the collection of homologs prior to downstream molecular evolutionary analysis. The efficacy of OrthoRBH is demonstrated with the identification of the 13-member PYR/PYL/RCAR gene family in Hordeum vulgare using Oryza sativa query sequences. OrthoRBH runs on the Linux command line and is freely available at SourceForge.

Availability

http://sourceforge.net/projects/ orthorbh/     

A Novel Cholinergic Action of Alcohol and the Development of Tolerance to That Effect in Caenorhabditis elegans

The Prp43 DExD/H-box protein is required for progression of the biochemically distinct pre-messenger RNA and ribosomal RNA (rRNA) maturation pathways. In Saccharomyces cerevisiae, the Spp382/Ntr1, Sqs1/Pfa1, and Pxr1/Gno1 proteins are implicated as cofactors necessary for Prp43 helicase activation during spliceosome dissociation (Spp382) and rRNA processing (Sqs1 and Pxr1). While otherwise dissimilar in primary sequence, these Prp43-binding proteins each contain a short glycine-rich G-patch motif required for function and thought to act in protein or nucleic acid recognition. Here yeast two-hybrid, domain-swap, and site-directed mutagenesis approaches are used to investigate G-patch domain activity and portability. Our results reveal that the Spp382, Sqs1, and Pxr1 G-patches differ in Prp43 two-hybrid response and in the ability to reconstitute the Spp382 and Pxr1 RNA processing factors. G-patch protein reconstitution did not correlate with the apparent strength of the Prp43 two-hybrid response, suggesting that this domain has function beyond that of a Prp43 tether. Indeed, while critical for Pxr1 activity, the Pxr1 G-patch appears to contribute little to the yeast two-hybrid interaction. Conversely, deletion of the primary Prp43 binding site within Pxr1 (amino acids 102–149) does not impede rRNA processing but affects small nucleolar RNA (snoRNA) biogenesis, resulting in the accumulation of slightly extended forms of select snoRNAs, a phenotype unexpectedly shared by the prp43 loss-of-function mutant. These and related observations reveal differences in how the Spp382, Sqs1, and Pxr1 proteins interact with Prp43 and provide evidence linking G-patch identity with pathway-specific DExD/H-box helicase activity.