Biomedical subjects

Trees-Juen Chuang

Publications and source records attributed to Trees-Juen Chuang.

8 recordsLinked to original sources

PubMed2007

Plant Gene and Alternatively Spliced Variant Annotator. A plant genome annotation pipeline for rice gene and alternatively spliced variant identification with cross-species expressed sequence tag conservation from seven plant species.

The completion of the rice (Oryza sativa) genome draft has brought unprecedented opportunities for genomic studies of the world's most important food crop. Previous rice gene annotations have relied mainly on ab initio methods, which usually yield a high rate of false-positive predictions and give only limited information regarding alternative splicing in rice genes. Comparative approaches based on expressed sequence tags (ESTs) can compensate for the drawbacks of ab initio methods because they can simultaneously identify experimental data-supported genes and alternatively spliced transcripts. Furthermore, cross-species EST information can be used to not only offset the insufficiency of same-species ESTs but also derive evolutionary implications. In this study, we used ESTs from seven plant species, rice, wheat (Triticum aestivum), maize (Zea mays), barley (Hordeum vulgare), sorghum (Sorghum bicolor), soybean (Glycine max), and Arabidopsis (Arabidopsis thaliana), to annotate the rice genome. We developed a plant genome annotation pipeline, Plant Gene and Alternatively Spliced Variant Annotator (PGAA). Using this approach, we identified 852 genes (931 isoforms) not annotated in other widely used databases (i.e. the Institute for Genomic Research, National Center for Biotechnology Information, and Rice Annotation Project) and found 87% of them supported by both rice and nonrice EST evidence. PGAA also identified more than 44,000 alternatively spliced events, of which approximately 20% are not observed in the other three annotations. These novel annotations represent rich opportunities for rice genome research, because the functions of most of our annotated genes are currently unknown. Also, in the PGAA annotation, the isoforms with non-rice-EST-supported exons are significantly enriched in transporter activity but significantly underrepresented in transcription regulator activity. We have also identified potential lineage-specific and conserved isoforms, which are important markers in evolutionary studies. The data and the Web-based interface, RiceViewer, are available for public access at http://RiceViewer.genomics.sinica.edu.tw/.

Base Sequence↗

PubMed2006

Human-specific insertions and deletions inferred from mammalian genome sequences.

It has been suggested that insertions and deletions (indels) have contributed to the sequence divergence between the human and chimpanzee genomes more than do nucleotide changes (3% vs. 1.2%). However, although there have been studies of large indels between the two genomes, no systematic analysis of small indels (i.e., indels </= 100 bp) has been published. In this study, we first estimated that the false-positive rate of small indels inferred from human-chimpanzee pairwise sequence alignments is quite high, suggesting that the chimpanzee genome draft is not sufficiently accurate for our purpose. We have therefore inferred only human-specific indels using multiple sequence alignments of mammalian genomes. We identified >840,000 "small" indels, which affect >7000 UCSC-annotated human genes (>11,000 transcripts). These indels, however, amount to only approximately 0.21% sequence change in the human lineage for the regions compared, whereas in pseudogenes indels contribute to a sequence divergence of 1.40%, suggesting that most of the indels that occurred in genic regions have been eliminated. Functional analysis reveals that the genes whose coding exons have been affected by human-specific indels are enriched in transcription and translation regulatory activities but are underrepresented in catalytic and transporter activities, cellular and physiological processes, and extracellular region/matrix. This functional bias suggests that human-specific indels might have contributed to human unique traits by causing changes at the RNA and protein level.

Animals↗

PubMed2006

The effects of multiple features of alternatively spliced exons on the K(A)/K(S) ratio test.

BACKGROUND: The evolution of alternatively spliced exons (ASEs) is of primary interest because these exons are suggested to be a major source of functional diversity of proteins. Many exon features have been suggested to affect the evolution of ASEs. However, previous studies have relied on the KA/KS ratio test without taking into consideration information sufficiency (i.e., exon length > 75 bp, cross-species divergence > 5%) of the studied exons, leading to potentially biased interpretations. Furthermore, which exon feature dominates the results of the KA/KS ratio test and whether multiple exon features have additive effects have remained unexplored. RESULTS: In this study, we collect two different datasets for analysis - the ASE dataset (which includes lineage-specific ASEs and conserved ASEs) and the ACE dataset (which includes only conserved ASEs). We first show that information sufficiency can significantly affect the interpretation of relationship between exons features and the KA/KS ratio test results. After discarding exons with insufficient information, we use a Boolean method to analyze the relationship between test results and four exon features (namely length, protein domain overlapping, inclusion level, and exonic splicing enhancer (ESE) frequency) for the ASE dataset. We demonstrate that length and protein domain overlapping are dominant factors, and they have similar impacts on test results of ASEs. In addition, despite the weak impacts of inclusion level and ESE motif frequency when considered individually, combination of these two factors still have minor additive effects on test results. However, the ACE dataset shows a slightly different result in that inclusion level has a marginally significant effect on test results. Lineage-specific ASEs may have contributed to the difference. Overall, in both ASEs and ACEs, protein domain overlapping is the most dominant exon feature while ESE frequency is the weakest one in affecting test results. CONCLUSION: The proposed method can easily find additive effects of individual or multiple factors on the KA/KS ratio test results of exons. Therefore, the system can analyze complex conditions in evolution where multiple features are involved. More factors can also be added into the system to extend the scope of evolutionary analysis of exons. In addition, our method may be useful when orthologous exons can not be found for the KA/KS ratio test.

Alternative Splicing↗

PubMed2006

Identification and evolutionary analysis of novel exons and alternative splicing events using cross-species EST-to-genome comparisons in human, mouse and rat.

BACKGROUND: Alternative splicing (AS) is important for evolution and major biological functions in complex organisms. However, the extent of AS in mammals other than human and mouse is largely unknown, making it difficult to study AS evolution in mammals and its biomedical implications. RESULTS: Here we describe a cross-species EST-to-genome comparison algorithm (ENACE) that can identify novel exons for EST-scanty species and distinguish conserved and lineage-specific exons. The identified exons represent not only novel exons but also evolutionarily meaningful AS events that are not previously annotated. A genome-wide AS analysis in human, mouse and rat using ENACE reveals a total of 758 novel cassette-on exons and 167 novel retained introns that have no EST evidence from the same species. RT-PCR-sequencing experiments validated approximately 50 approximately 80% of the tested exons, indicating high presence of exons predicted by ENACE. ENACE is particularly powerful when applied to closely related species. In addition, our analysis shows that the ENACE-identified AS exons tend not to pass the nonsynonymous-to-synonymous substitution ratio test and not to contain protein domain, implying that such exons may be under positive selection or relaxed negative selection. These AS exons may contribute to considerable inter-species functional divergence. Our analysis further indicates that a large number of exons may have been gained or lost during mammalian evolution. Moreover, a functional analysis shows that inter-species divergence of AS events may be substantial in protein carriers and receptor proteins in mammals. These exons may be of interest to studies of AS evolution. The ENACE programs and sequences of the ENACE-identified AS events are available for download. CONCLUSION: ENACE can identify potential novel cassette exons and retained introns between closely related species using a comparative approach. It can also provide information regarding lineage- or species-specificity in transcript isoforms, which are important for evolutionary and functional studies.

Algorithms↗

PubMed2005

Alternatively and constitutively spliced exons are subject to different evolutionary forces.

There has been a controversy on whether alternatively spliced exons (ASEs) evolve faster than constitutively spliced exons (CSEs). Although it has been noted that ASEs are subject to weaker selective constraints than CSEs, so they evolve faster, there have also been studies that indicated slower evolution in ASEs than in CSEs. In this study, we retrieve more than 5,000 human-mouse orthologous exons and calculate the synonymous (KS) and nonsynonymous (KA) substitution rates in these exons. Our results show that ASEs have higher KA values and higher KA/KS ratios than CSEs, indicating faster amino acid-level evolution in ASEs. The faster evolution may be in part due to weaker selective constraints. It is also possible that the faster rate is in part due to faster functional evolution in ASEs. On the other hand, the majority of ASEs have lower KS values than CSEs. With reference to the substitution rate in introns, we show that the KS values in ASEs are close to the neutral substitution rate, whereas the synonymous substitution rate in CSEs has likely been accelerated. The elevated synonymous rate in CSEs is not related to CpG dinucleotides or low-complexity regions of protein but may be weakly related to codon usage bias. The overall trends of higher KA and lower KS in ASEs than in CSEs are also observed in human-rat and mouse-rat comparisons. Therefore, our observations hold for mammals of different molecular clocks.

Animals↗

PubMed2005

ESTviewer: a web interface for visualizing mouse, rat, cattle, pig and chicken conserved ESTs in human genes and human alternatively spliced variants.

ESTviewer is a web application for interactively visualizing human gene structures, with emphasis on mammalian and avian expressed sequence tags (ESTs) that are conserved in the human genome and alternatively spliced (AS) variants. AS variants from the UCSC, Vega and PSEP annotations are presented in this application for comparison. EST data from six species, human, mouse, rat, cattle, pig and chicken, are mapped to the human genome to show cross-species EST conservation in annotated exonic and intronic regions. Cross-species EST conservation is evolutionarily and functionally important because it represents the effects of selection pressure on genic regions and transcriptome over evolutionary time. Emphatically, ESTviewer provides a convenient tool to compare highly conserved non-human ESTs and human AS variants. The application takes human gene accession Ids or coordinates of genomic sequences as inputs and presents annotated gene structures and their AS variants. In addition, the lengths and percentages of human genic regions covered by ESTs are displayed to show the level of EST coverage of different species. The percentages of the UCSC, Vega and PSEP annotated exons covered by ESTs of the six studied species are also displayed in the interface.

Animals↗

PubMed2004

A comparative method for identification of gene structures and alternatively spliced variants.

MOTIVATION: Alternative splicing (AS) serves as a mechanism to create diversity among functional proteins. Increasing evidence indicates that a large portion of genes have AS forms. Hence AS variants should be considered while analyzing gene structures. RESULTS: A new cross-species gene identification and AS analysis system, PSEP, has been developed. The system is based on expressed sequence tag (EST)-to-genome and genome-to-genome comparisons and is implemented in two steps: sequence alignment and a series of post-alignment processes, including progressive signal extraction and patching. For gene identification, these post-alignment processes serve as noise filters and enable PSEP to eliminate approximately 88% of potential overprediction. The overall accuracy of PSEP is better than or comparable to that of other well-known cross-species gene prediction programs, including the ROSETTA program, TWINSCAN, SGP-1/-2 and SLAM, when tested on three benchmark datasets (the ELN gene region, the HoxA cluster and the ROSETTA set). In addition, 76.2 and 76.0% of multiple-exon genes in the ROSETTA dataset and human chromosome 20, respectively, are found to have AS forms. Approximately 23% of the 210 elementary alternatives identified in the ROSETTA dataset are not conserved between the human and mouse genomes, and none of the 210 transcripts is found in the RefSeq annotation. With its dual functions in cross-species conserved sequence analysis and AS analysis, PSEP is highly suitable for studying the evolution of AS patterns and for finding unidentified gene expression features.

Algorithms↗

PubMed2003

A complexity reduction algorithm for analysis and annotation of large genomic sequences.

DNA is a universal language encrypted with biological instruction for life. In higher organisms, the genetic information is preserved predominantly in an organized exon/intron structure. When a gene is expressed, the exons are spliced together to form the transcript for protein synthesis. We have developed a complexity reduction algorithm for sequence analysis (CRASA) that enables direct alignment of cDNA sequences to the genome. This method features a progressive data structure in hierarchical orders to facilitate a fast and efficient search mechanism. CRASA implementation was tested with already annotated genomic sequences in two benchmark data sets and compared with 15 annotation programs (10 ab initio and 5 homology-based approaches) against the EST database. By the use of layered noise filters, the complexity of CRASA-matched data was reduced exponentially. The results from the benchmark tests showed that CRASA annotation excelled in both the sensitivity and specificity categories. When CRASA was applied to the analysis of human Chromosomes 21 and 22, an additional 83 potential genes were identified. With its large-scale processing capability, CRASA can be used as a robust tool for genome annotation with high accuracy by matching the EST sequences precisely to the genomic sequences.

Algorithms↗