Effect of electron avalanche breakdown on a high-purity semi-insulating 4H-SiC photoconductive semiconductor switch under intrinsic absorption.

High-power photoconductive semiconductor switching devices were fabricated from a high-purity, semi-insulating 4H-SiC wafer. A highly n-doped GaN subcontact layer was inserted between the contact metal and the high-resistivity SiC wafer. The minimum ON-state resistance of the device was less than 1 ohm when the energy of a 355 nm laser was 10.5 mJ with a bias voltage of 6 kV. The maximum device lifetime is 3151 pulses, after which the device completely fails. The failure mechanisms are determined using several analysis methods. Under a strong electric field, the failure mechanism differs for the two electrodes. Near the edge of the anode electrode, the switch is damaged due to the thermal stress caused by impact ionization. At the edge of the cathode electrode, the electrode erosion is the main reason for the failure to operate for long periods of time. These two different damage mechanisms are both important factors influencing the device performance. The electron avalanche breakdown at the edge of the anode electrode causes the formation of cracks between the electrodes, which is the root cause of the switch failure.

Comparing computational methods for identification of allele-specific expression based on next generation sequencing data.

Allele-specific expression (ASE) studies have wide-ranging implications for genome biology and medicine. Whole transcriptome RNA sequencing (RNA-Seq) has emerged as a genome-wide tool for identifying ASE, but suffers from mapping bias favoring reference alleles. Two categories of methods are adopted nowadays, to reduce the effect of mapping bias on ASE identification-normalizing RNA allelic ratio with the parallel genomic allelic ratio (pDNAar) and modifying reference genome to make reads carrying both alleles with the same chance to be mapped (mREF). We compared the sensitivity and specificity of both methods with simulated data, and demonstrated that the pDNAar, though ideally practical, was lower in sensitivity, because of its lower mapping rate of reads carrying nonreference (alternative) alleles, although mREF achieved higher sensitivity and specificity for its efficiency in mapping reads carrying both alleles. Application of these two methods in real sequencing data showed that mREF were able to identify more ASE loci because of its higher mapping efficiency, and able to correcting some seemly incorrect ASE loci identified by pDNAar due to the inefficiency in mapping reads carrying alternative alleles of pDNAar. Our study provides useful information for RNA sequencing data processing in the identification of ASE.

SchistoDB: an updated genome resource for the three key schistosomes of humans.

The new release of SchistoDB (http://SchistoDB.net) provides a rich resource of genomic data for key blood flukes (genus Schistosoma) which cause disease in hundreds of millions of people worldwide. SchistoDB integrates whole-genome sequence and annotation of three species of the genus and provides enhanced bioinformatics analyses and data-mining tools. A simple, yet comprehensive web interface provided through the Strategies Web Development Kit is available for the mining and visualization of the data. Genomic scale data can be queried based on BLAST searches, annotation keywords and gene ID searches, gene ontology terms, sequence motifs, protein characteristics and phylogenetic relationships. Search strategies can be saved within a user's profile for future retrieval and may also be shared with other researchers using a unique web address.

cGRNB: a web server for building combinatorial gene regulatory networks through integrated engineering of seed-matching sequence information and gene expression datasets.

BACKGROUND: We are witnessing rapid progress in the development of methodologies for building the combinatorial gene regulatory networks involving both TFs (Transcription Factors) and miRNAs (microRNAs). There are a few tools available to do these jobs but most of them are not easy to use and not accessible online. A web server is especially needed in order to allow users to upload experimental expression datasets and build combinatorial regulatory networks corresponding to their particular contexts. METHODS: In this work, we compiled putative TF-gene, miRNA-gene and TF-miRNA regulatory relationships from forward-engineering pipelines and curated them as built-in data libraries. We streamlined the R codes of our two separate forward-and-reverse engineering algorithms for combinatorial gene regulatory network construction and formalized them as two major functional modules. As a result, we released the cGRNB (combinatorial Gene Regulatory Networks Builder): a web server for constructing combinatorial gene regulatory networks through integrated engineering of seed-matching sequence information and gene expression datasets. The cGRNB enables two major network-building modules, one for MPGE (miRNA-perturbed gene expression) datasets and the other for parallel miRNA/mRNA expression datasets. A miRNA-centered two-layer combinatorial regulatory cascade is the output of the first module and a comprehensive genome-wide network involving all three types of combinatorial regulations (TF-gene, TF-miRNA, and miRNA-gene) are the output of the second module. CONCLUSIONS: In this article we propose cGRNB, a web server for building combinatorial gene regulatory networks through integrated engineering of seed-matching sequence information and gene expression datasets. Since parallel miRNA/mRNA expression datasets are rapidly accumulated by the advance of next-generation sequencing techniques, cGRNB will be very useful tool for researchers to build combinatorial gene regulatory networks based on expression datasets. The cGRNB web-server is free and available online at http://www.scbit.org/cgrnb.

PMRD: a curated database for genes and mutants involved in plant male reproduction.

BACKGROUND: Male reproduction is an essential biological event in the plant life cycle separating the diploid sporophyte and haploid gametophyte generations, which involves expression of approximately 20,000 genes. The control of male reproduction is also of economic importance for plant breeding and hybrid seed production. With the advent of forward and reverse genetics and genomic technologies, a large number of male reproduction-related genes have been identified. Thus it is extremely challenging for individual researchers to systematically collect, and continually update, all the available information on genes and mutants related to plant male reproduction. The aim of this study is to manually curate such gene and mutant information and provide a web-accessible resource to facilitate the effective study of plant male reproduction. DESCRIPTION: Plant Male Reproduction Database (PMRD) is a comprehensive resource for browsing and retrieving knowledge on genes and mutants related to plant male reproduction. It is based upon literature and biological databases and includes 506 male sterile genes and 484 mutants with defects of male reproduction from a variety of plant species. Based on Gene Ontology (GO) annotations and literature, information relating to a further 3697 male reproduction related genes were systematically collected and included, and using in text curation, gene expression and phenotypic information were captured from the literature. PMRD provides a web interface which allows users to easily access the curated annotations and genomic information, including full names, symbols, locations, sequences, expression patterns, functions of genes, mutant phenotypes, male sterile categories, and corresponding publications. PMRD also provides mini tools to search and browse expression patterns of genes in microarray datasets, run BLAST searches, convert gene ID and generate gene networks. In addition, a Mediawiki engine and a forum have been integrated within the database, allowing users to share their knowledge, make comments and discuss topics. CONCLUSION: PMRD provides an integrated link between genetic studies and the rapidly growing genomic information. As such this database provides a global view of plant male reproduction and thus aids advances in this important area.

Database and analyses of known alternatively spliced genes in plants.

Alternative splicing is an important cellular mechanism that increases the diversity of gene products. The number of alternatively spliced genes reported so far in plants is much smaller than that in mammals, but is increasing as a result of the explosive growth of available EST and genomic sequences. We have searched for all alternatively spliced genes reported in GenBank and PubMed in all plant species under Viridiplantae. After careful merging and manual review of the search results, we obtained a comprehensive, high-quality collection of 168 genes reported to be alternatively spliced in plants, spanning 44 plant species (March 22, 2003 update). We developed a relational database with Web-based user interface to store and present the data, named the Plant Alternative Splicing Database (PASDB), freely available at http://pasdb.genomics.org.cn. We analyzed the functional categories that these genes belong to using the Gene Ontology. We also analyzed in detail the biological roles and gene structures of the four genes that are known to be alternatively spliced in more than one plant species. Finally, we studied the structural features of the splice sites in the alternatively spliced genes.

Gene identification and expression analysis of 86,136 Expressed Sequence Tags (EST) from the rice genome.

Expressed Sequence Tag (EST) analysis has pioneered genome-wide gene discovery and expression profiling. In order to establish a gene expression index in the rice cultivar indica, we sequenced and analyzed 86,136 ESTs from nine rice cDNA libraries from the super hybrid cultivar LYP9 and its parental cultivars. We assembled these ESTs into 13,232 contigs and leave 8,976 singletons. Overall, 7,497 sequences were found similar to existing sequences in GenBank and 14,711 are novel. These sequences are classified by molecular function, biological process and pathways according to the Gene Ontology. We compared our sequenced ESTs with the publicly available 95,000 ESTs from japonica, and found little sequence variation, despite the large difference between genome sequences. We then assembled the combined 173,000 rice ESTs for further analysis. Using the pooled ESTs, we compared gene expression in metabolism pathway between rice and Arabidopsis according to KEGG. We further profiled gene expression patterns in different tissues, developmental stages, and in a conditional sterile mutant, after checking the libraries are comparable by means of sequence coverage. We also identified some possible library specific genes and a number of enzymes and transcription factors that contribute to rice development.

EST pipeline system: detailed and automated EST data processing and mining.

Expressed sequence tags (ESTs) are widely used in gene survey research these years. The EST Pipeline System, software developed by Hangzhou Genomics Institute (HGI), can automatically analyze different scalar EST sequences by suitable methods. All the analysis reports, including those of vector masking, sequence assembly, gene annotation, Gene Ontology classification, and some other analyses, can be browsed and searched as well as downloaded in the Excel format from the web interface, saving research efforts from routine data processing for biological rules embedded in the data.