Generation of the Brucella melitensis ORFeome Version 1.1

The bacteria of the Brucella genus are responsible for a worldwide zoonosis called brucellosis. They belong to the α-proteobacteria group, as many other bacteria that live in close association with a eukaryotic host. Importantly, the Brucellae are mainly intracellular pathogens, and the molecular mechanisms of their virulence are still poorly understood. Using the complete genome sequence of Brucella melitensis, we generated a database of protein-coding open reading frames (ORFs) and constructed an ORFeome library of 3091 Gateway Entry clones, each containing a defined ORF. This first version of the Brucella ORFeome (v1.1) provides the coding sequences in a user-friendly format amenable to high-throughput functional genomic and proteomic experiments, as the ORFs are conveniently transferable from the Entry clones to various Expression vectors by recombinational cloning. The cloning of the Brucella ORFeome v1.1 should help to provide a better understanding of the molecular mechanisms of virulence, including the identification of bacterial protein-protein interactions, but also interactions between bacterial effectors and their host's targets.     

C. elegans ORFeome Version 3.1: Increasing the Coverage of ORFeome Resources With Improved Gene Predictions

The first version of the Caenorhabditis elegans ORFeome cloning project, based on release WS9 of Wormbase (August 1999), provided experimental verifications for ~55% of predicted protein-encoding open reading frames (ORFs). The remaining 45% of predicted ORFs could not be cloned, possibly as a result of mispredicted gene boundaries. Since the release of WS9, gene predictions have improved continuously. To test the accuracy of evolving predictions, we attempted to PCR-amplify from a highly representative worm cDNA library and Gateway-clone ~4200 ORFs missed earlier and for which new predictions are available in WS100 (May 2003). In this set we successfully cloned 63% of ORFs with supporting experimental data (“touched” ORFs), and 42% of ORFs with no supporting experimental evidence (“untouched” ORFs). Approximately 2000 full-length ORFs were cloned in-frame, 13% of which were corrected in their exon/intron structure relative to WS100 predictions. In total, ~12,500 C. elegans ORFs are now available as Gateway Entry clones for various reverse proteomics (ORFeome v3.1). This work illustrates why the cloning of a complete C. elegans ORFeome, and likely the ORFeomes of other multicellular organisms, needs to be an iterative process that requires multiple rounds of experimental validation together with gradually improving gene predictions.     

High-Throughput Expression of C. elegans Proteins

Proteome-scale studies of protein three-dimensional structures should provide valuable information for both investigating basic biology and developing therapeutics. Critical for these endeavors is the expression of recombinant proteins. We selected Caenorhabditis elegans as our model organism in a structural proteomics initiative because of the high quality of its genome sequence and the availability of its ORFeome, protein-encoding open reading frames (ORFs), in a flexible recombinational cloning format. We developed a robotic pipeline for recombinant protein expression, applying the Gateway cloning/expression technology and utilizing a stepwise automation strategy on an integrated robotic platform. Using the pipeline, we have carried out heterologous protein expression experiments on 10,167 ORFs of C. elegans. With one expression vector and one Escherichia coli strain, protein expression was observed for 4854 ORFs, and 1536 were soluble. Bioinformatics analysis of the data indicates that protein hydrophobicity is a key determining factor for an ORF to yield a soluble expression product. This protein expression effort has investigated the largest number of genes in any organism to date. The pipeline described here is applicable to high-throughput expression of recombinant proteins for other species, both prokaryotic and eukaryotic, provided that ORFeome resources become available.     

High-Throughput Generation of P. falciparum Functional Molecules by Recombinational Cloning

Large-scale functional genomics studies for malaria vaccine and drug development will depend on the generation of molecular tools to study protein expression. We examined the feasibility of a high-throughput cloning approach using the Gateway system to create a large set of expression clones encoding Plasmodium falciparum single-exon genes. Master clones and their ORFs were transferred en masse to multiple expression vectors. Target genes (n = 303) were selected using specific sets of criteria, including stage expression and secondary structure. Upon screening four colonies per capture reaction, we achieved 84% cloning efficiency. The genes were subcloned in parallel into three expression vectors: a DNA vaccine vector and two protein expression vectors. These transfers yielded a 100% success rate without any observed recombination based on single colony screening. The functional expression of 95 genes was evaluated in mice with DNA vaccine constructs to generate antibody against various stages of the parasite. From these, 19 induced antibody titers against the erythrocytic stages and three against sporozoite stages. We have overcome the potential limitation of producing large P. falciparum clone sets in multiple expression vectors. This approach represents a powerful technique for the production of molecular reagents for genome-wide functional analysis of the P. falciparum genome and will provide for a resource for the malaria resource community distributed through public repositories.     

A First Version of the Caenorhabditis elegans Promoterome

An important aspect of the development of systems biology approaches in metazoans is the characterization of expression patterns of nearly all genes predicted from genome sequences. Such “localizome” maps should provide information on where (in what cells or tissues) and when (at what stage of development or under what conditions) genes are expressed. They should also indicate in what cellular compartments the corresponding proteins are localized. Caenorhabditis elegans is particularly suited for the development of a localizome map since all its 959 adult somatic cells can be visualized by microscopy, and its cell lineage has been completely described. Here we address one of the challenges of C. elegans localizome mapping projects: that of obtaining a genome-wide resource of C. elegans promoters needed to generate transgenic animals expressing localization markers such as the green fluorescent protein (GFP). To ensure high flexibility for future uses, we utilized the newly developed MultiSite Gateway system. We generated and validated “version 1.1” of the Promoterome: a resource of ~6000 C. elegans promoters. These promoters can be transferred easily into various Gateway Destination vectors to drive expression of markers such as GFP, alone (promoter::GFP constructs), or in fusion with protein-encoding open reading frames available in ORFeome resources (promoter::ORF::GFP).     

Selecting open reading frames from DNA

We describe a method to select DNA encoding functional open reading frames (ORFs) from noncoding DNA within the context of a specific vector. Phage display has been used as an example, but any system requiring DNA encoding protein fragments, for example, the yeast two-hybrid system, could be used. By cloning DNA fragments upstream of a fusion gene, consisting of the beta-lactamase gene flanked by lox recombination sites, which is, in turn, upstream of gene 3 from fd phage, only those clones containing DNA fragments encoding ORFs confer ampicillin resistance and survive. After selection, the beta-lactamase gene can be removed by Cre recombinase, leaving a standard phage display vector with ORFs fused to gene 3. This vector has been tested on a plasmid containing tissue transglutaminase. All surviving clones analyzed by sequencing were found to contain ORFs, of which 83% were localized to known genes, and at least 80% produced immunologically detectable polypeptides. Use of a specific anti-tTG monoclonal antibody allowed the identification of clones containing the correct epitope. This approach could be applicable to the efficient selection of random ORFs representing the coding potential of whole organisms, and their subsequent downstream use in a number of different systems.     

Toward Improving Caenorhabditis elegans Phenome Mapping With an ORFeome-Based RNAi Library

The recently completed Caenorhabditis elegans genome sequence allows application of high-throughput (HT) approaches for phenotypic analyses using RNA interference (RNAi). As large phenotypic data sets become available, “phenoclustering” strategies can be used to begin understanding the complex molecular networks involved in development and other biological processes. The current HT-RNAi resources represent a great asset for phenotypic profiling but are limited by lack of flexibility. For instance, existing resources do not take advantage of the latest improvements in RNAi technology, such as inducible hairpin RNAi. Here we show that a C. elegans ORFeome resource, generated with the Gateway cloning system, can be used as a starting point to generate alternative HT-RNAi resources with enhanced flexibility. The versatility inherent to the Gateway system suggests that additional HT-RNAi libraries can now be readily generated to perform gene knockdowns under various conditions, increasing the possibilities for phenome mapping in C. elegans.     

The Pseudomonas aeruginosa PA01 Gene Collection

Pseudomonas aeruginosa, a common inhabitant of soil and water, is an opportunistic pathogen of growing clinical relevance. Its genome, one of the largest among bacteria [5570 open reading frames (ORFs)] approaches that of simple eukaryotes. We have constructed a comprehensive gene collection for this organism utilizing the annotated genome of P. aeruginosa PA01 and a highly automated and laboratory information management system (LIMS)-supported production line. All the individual ORFs have been successfully PCR-amplified and cloned into a recombination-based cloning system. We have isolated and archived four independent isolates of each individual ORF. Full sequence analysis of the first isolate for one-third of the ORFs in the collection has been completed. We used two sets of genes from this repository for high-throughput expression and purification of recombinant proteins in different systems. The purified proteins have been used to set up biochemical and immunological assays directed towards characterization of histidine kinases and identification of bacterial proteins involved in the immune response of cystic fibrosis patients. This gene repository provides a powerful tool for proteome- and genome-scale research of this organism, and the strategies adopted to generate this repository serve as a model for building clone sets for other bacteria.     

Construction of cloning‐friendly minigenes for mammalian expression of full‐length human NF1 isoforms

The neurofibromatosis type 1 (NF1) tumor suppressor gene is one of the most frequently mutated genes in human tumors. Research on the NF1 proteins has been partially hindered by the difficulties in cloning and propagating the full‐length coding cDNAs. We have now established a condition for propagating the natural open reading frames (ORFs) and have assembled the ORFs for human NF1 type 1 and 2 isoforms. Furthermore, we were able to eliminate the cDNA cloning toxicity by introducing a mini‐intron. These NF1 minigenes were expressed similarly to the intronless version and could be used to purify full‐length NF1 proteins. The NF1 isoforms expressed from the minigenes showed Ras‐GAP activity in vivo and in vitro, while the type 1 was more potent. Our constructs expand currently available full‐length NF1 constructs and should be valuable tools in expediting the understanding of NF1, particularly the isoform‐specific functions and regulation.     

FLEXGene repository: from sequenced genomes to gene repositories for high-throughput functional biology and proteomics.

The vast amount of information generated by the human genome sequencing project and related projects has given rise to a new paradigm in experimental biology. This new paradigm invokes the experimentation and data analysis at genome-wide scales, as well as the generation of new technologies and resources that take full advantage of the available sequence information. The Institute of Proteomics at Harvard Medical School is building a comprehensive, characterized, arrayed and flexible gene repository that will allow full exploitation of the genomic information by enabling functional genomics as well as protein expression, purification and analysis at genome wide scale. The FLEXGene repository (Full Length EXpression-ready) will contain clones representing the complete set of open reading frames (ORFs) of different organisms including H. sapiens and several pathogens and model organisms. The clones are constructed using recombination-based cloning technology so that hundreds or thousands of coding regions can be transferred into any expression vector in a parallel and timely mode, allowing the broadest variety of experiments to be carried out.     

dbNSFP v3.0: A One‐Stop Database of Functional Predictions and Annotations for Human Nonsynonymous and Splice‐Site SNVs

The purpose of the dbNSFP is to provide a one‐stop resource for functional predictions and annotations for human nonsynonymous single‐nucleotide variants (nsSNVs) and splice‐site variants (ssSNVs), and to facilitate the steps of filtering and prioritizing SNVs from a large list of SNVs discovered in an exome‐sequencing study. A list of all potential nsSNVs and ssSNVs based on the human reference sequence were created and functional predictions and annotations were curated and compiled for each SNV. Here, we report a recent major update of the database to version 3.0. The SNV list has been rebuilt based on GENCODE 22 and currently the database includes 82,832,027 nsSNVs and ssSNVs. An attached database dbscSNV, which compiled all potential human SNVs within splicing consensus regions and their deleteriousness predictions, add another 15,030,459 potentially functional SNVs. Eleven prediction scores (MetaSVM, MetaLR, CADD, VEST3, PROVEAN, 4× fitCons, fathmm‐MKL, and DANN) and allele frequencies from the UK10K cohorts and the Exome Aggregation Consortium (ExAC), among others, have been added. The original seven prediction scores in v2.0 (SIFT, 2× Polyphen2, LRT, MutationTaster, MutationAssessor, and FATHMM) as well as many SNV and gene functional annotations have been updated. dbNSFP v3.0 is freely available at http://sites.google.com/site/jpopgen/dbNSFP .     

High-throughput functional profiling of the human fungal pathogen Candida albicans genome

Candida albicans is a major fungal pathogen of humans. Although its genome has been sequenced more than two decades ago, there are still over 4300 uncharacterized C. albicans genes. We previously generated an ORFeome as well as a collection of destination vectors to facilitate overexpression of C. albicans ORFs. Here, we report the construction of ～2500 overexpression mutants and their evaluation by in vitro spotting on rich medium and in a liquid pool experiment in rich medium, allowing the identification of genes whose overexpression has a fitness cost. The candidates were further validated at the individual strain level. This new resource allows large-scale screens in different growth conditions to be performed routinely. Altogether, based on the concept of identifying functionally related genes by cluster analysis, the availability of this overexpression mutant collection will facilitate the characterization of gene functions in C. albicans.     

A novel expression system for genomic DNA loci using a human artificial chromosome vector with transformation-associated recombination cloning

Following the recent completion of the human genome sequence, genomics research has shifted its focus to understanding gene complexity, expression, and regulation. However, in order to investigate such issues, there is a need to develop a practical system for genomic DNA expression. Transformation-associated recombination (TAR) cloning has proven to be a convenient tool for selective isolation of a genetic locus from a complex genome as a circular YAC using recombination in yeast. The human artificial chromosome (HAC) vector containing an acceptor loxP site has served as a platform for the reproducible expression of transgenes. In this study, we describe a system that efficiently expresses a genetic locus in mammalian cells by retrofitting a TAR-YAC with the donor loxP site and loading it onto the HAC vector by the Cre/loxP system. In order to demonstrate functional expression of genomic loci, the entire human hypoxanthine phosphoribosyl transferase (HPRT) locus contained in a 100 kb YAC was loaded onto the HAC vector and was shown to complement the genetic defect in Hprt-deficient CHO cells. Thus, the combination of TAR cloning and the HAC vector may serve as a powerful tool for functional genomic studies.     

The carboxy-terminal tail region of human Cav2.1 (P/Q-type) channel is not an essential determinant for its subcellular localization in cultured neurones

A recent report on the mechanism of synaptic targeting of Ca(v)2.2 channel suggested that this process depends upon the presence of long C-terminal tail and that protein interactions mediated by SH3-binding and PDZ-binding motifs in the tail region are important. To examine the possibility that C-terminal tail of the Ca(v)2.1 channel and the polyglutamine stretch therein are also involved in the mechanism for channel localization, we constructed several expression plasmids for human Ca(v)2.1 channel tagged with enhanced green fluorescent protein (EGFP) and introduced them into mouse hippocampal neuronal culture. HC construct encodes short version of Ca(v)2.1, and HS and HL encode Ca(v)2.1 channel with a long C-terminal tail, which contains polyglutamine tract of 13 (normal range) and 28 (SCA6 disease range) repeat units, respectively. Surprisingly, transfection with HC, HS, and HL gave essentially the same results: EGFP signal was observed in cell soma, dendrites, and the axon as well. Furthermore, mutation of the PDZ-binding motif located at the C-terminus of the long version of Ca(v)2.1, by adding FLAG tag, did not affect the localization patterns of HS and HL as well. Therefore, the C-terminal region is not indispensable for the subcellular localization of Ca(v)2.1 channel, nor expansion of polyglutamine length affected the localization of the channel. Thus, it is possible that the localization mechanism of Ca(v)2.1 channel is different from that of Ca(v)2.2, though these channels share various structural and functional characteristics.     

Closing in on the C. elegans ORFeome by cloning TWINSCAN predictions

The genome of Caenorhabditis elegans was the first animal genome to be sequenced. Although considerable effort has been devoted to annotating it, the standard WormBase annotation contains thousands of predicted genes for which there is no cDNA or EST evidence. We hypothesized that a more complete experimental annotation could be obtained by creating a more accurate gene-prediction program and then amplifying and sequencing predicted genes. Our approach was to adapt the TWINSCAN gene prediction system to C. elegans and C. briggsae and to improve its splice site and intron-length models. The resulting system has 60% sensitivity and 58% specificity in exact prediction of open reading frames (ORFs), and hence, proteins-the best results we are aware of any multicellular organism. We then attempted to amplify, clone, and sequence 265 TWINSCAN-predicted ORFs that did not overlap WormBase gene annotations. The success rate was 55%, adding 146 genes that were completely absent from WormBase to the ORF clone collection (ORFeome). The same procedure had a 7% success rate on 90 Worm Base "predicted" genes that do not overlap TWINSCAN predictions. These results indicate that the accuracy of WormBase could be significantly increased by replacing its partially curated predicted genes with TWINSCAN predictions. The technology described in this study will continue to drive the C. elegans ORFeome toward completion and contribute to the annotation of the three Caenorhabditis species currently being sequenced. The results also suggest that this technology can significantly improve our knowledge of the "parts list" for even the best-studied model organisms.