Annotation adds features and information to a DNA sequence – such as genes and their locations, structures, and functions. A good introduction to annotation can be found in the paper A beginner’s guide to eukaryotic genome annotation. We'll also suggest the DNA Subway's primer on annotation evidence. This guide contains an explanation of basic functions for this line, as well as exercises that might be used in the classroom.
Some things to remember about the platform
- On Red Line, you can annotate up to 150KB of your own DNA sequence
- We provide sample sequence for you to try, or you can upload your own
Note
DNA Subway is transitioning away from the original Java-based Apollo software as most popular web browsers will no longer support Java. The new Apollo is Java-free.
Log-in to DNA Subway - unregistered users may 'Enter as Guest'
Click ‘Annotate a genomic sequence.’ (Red Square); select the 'Web Apollo' version
For 'Select Organism type' choose 'Animal' or 'Plant' and then select the appropriate subtype.
Tip
The 'Select Organism' step will load appropriate sample sequences and will also adjust the models used in the de novo gene finding process.
For 'Select Sequence Source' select a sample sequence.
Note
Currently, the Java-free Apollo version of Subway does not support upload of a custom DNA Sequence. This feature is coming soon, but we will help you upload custom genomes/regions for your use in the classroom
- (Optional) If you have a GFF file of annotated features, you may load these import these annotations from the Green Line, or from a custom GFF file.
- Name your project and organism (required) and give a description if desired. Click 'Continue' to proceed.
In this and subsequent steps, we will annotate a 75KB section of Arabidopsis chromosome I.
- Log-in to DNA Subway - unregistered users may 'Enter as Guest'.
- Click ‘Annotate a genomic sequence.’ (Red Square); select the 'Web Apollo' version.
- For 'Select Organism type' choose 'Plant' and then 'Dicotyledon'.
- from 'Select a sample sequence' chose 'Arabidopsis thaliana (mouse-ear cress) chr1, 75.00 kb'.
- Provide your project with a title, then Click ‘Continue.’
Tip
You can view your DNA sequence by clicking the 'Sequence' link in the 'Project Information' tab at the bottom of the page.
One you have created a Red Line Project, you may begin the process of generating and assembling predictions and evidence that can be used to annotate genes.
Click ‘RepeatMasker’
When 'RepeatMasker' turns 'green' and the icon displays a 'V' (view); click 'RepeatMasker' again to view results.
- Example Sequence: Arabidopsis thaliana (mouse-ear cress) ChrI, 75 kb
- Tool(s): RepeatMasker
- Concept(s): Non-coding DNA, sequence repeats, mobile genetic elements (transposons)
Following the RepeatMasking steps for the Arabidopsis ChrI sample above, answer the following discussion questions:
- How many hits were detected in your sample?
- RepeatMasker reports the length of the repetitive sequences (Length) as well as the class (Attributes).
- What is the average length of sequences identified as “simple repeats”?
- What is the average length of sequences identified as “low complexity”?
- What is the total percentage of repetitive DNA in your sequence? (Sum of the length of all repetitive sequence / sequence length (75 kb)
Tip
Some Useful Definitions for Repetitive Sequence
- Simple repeats: 1-5bp repeats (e.g. repetitive dinucleotides ‘AT’ etc.)
- Low Complexity DNA: Poly-purine/ poly-pyrimidine stretches, or regions of extremely high AT or GC content.
- Processed Pseudogenes, SINES, Retrotranscripts: Non-functional RNAs present within genomic sequence.
- Transposons (DNA, Retroviral, LINES): Genetic elements which have the ability to be amplified and redistributed within a genome.
Additional Investigation: In the results table under ‘Attributes’ each repeat sequence is labeled “RepeatMasker#-XXX” The ‘#’ is the ordinal number of the hit, the XXX is the class of DNA element (e.g. “Simple_repeat” or “Low_complexity”). There are other types of repetitive elements such as transposons and pseudogenes (e.g. Helitron and COPIA) Use online resources to learn more: (http://gydb.org/index.php/Main_Page).
De novo gene predictors can be run on a sample sequence to generate predictions of gene structure and location based solely on the sequence nucleotides.
- Click on one or more gene prediction tools under the 'Gene Prediction' stop. to view the results table, click the gene predictor again once the indicator displays 'V' (view).
- Example Sequence: Arabidopsis thaliana (mouse-ear cress) ChrI, 75 kb
- Tool(s): Augustus, FGenesH, Snap, tRNA Scan
- Concept(s): Genomic DNA, Gene Structure, Canonical sequences
Following the gene prediction steps for the Arabidopsis ChrI sample above, answer the following discussion questions:
Look at the ‘Type’ column in the gene prediction report. Considering the Augustus results, find the 6th gene prediction (hint: AUGUSTUS006;ID=g6) and then locate the first mention of the term ‘gene’ and copy down the gene’s ‘start’ (i.e. the starting basepair). Note the number of times you see the term ‘exon’ (i.e. number of exons predicted).
Gene Predictor
Exon Start (bp)
Exon Stop (bp)
Augustus
23456
23684
Augustus
Augustus
Augustus
Augustus
Based on the chart, did all the gene predictors yield genes starting at the same location? Did all the gene predictions have the same number of exons?
Looking at the number of results returned by tRNA Scan, why are they so different from results made by other predictors? Are their places in the genome where tRNAs are more or less densely concentrated?
Additional Investigation: Look for the background link at the bottom of the DNA Subway home page and review the section entitled ‘Gene Finding,’
A genome browser is an essential tool for visualization genomic data in context. The integrated JBrowse genome browser will allow you to see the visualized gene predictions generated so far.
Click ‘JBrowse’ and allow browser to load.
Zoom into a region (for example, paste the region 1:3740638..3749063 into the location window.
Tip
- JBrowse will load multiple tracks of data. Since the entire genome is loaded, we recommend using the 'highlight a region' feature to help keep your place. You may also wish to record the coordinates you are viewing as shown in the coordinates window.
- You may also adjust the settings for a particular track by clicking on the track name.
- Right-click on any gene to view additional details about that gene.
Examine gene details by double-clicking on a gene to select; then right-click to open the 'View Details' menu.
To view more tracks, click on 'Full-Screen View' in the upper-left of the JBrowse window to see any additional tracks available.
Tip
Some Useful Definitions
Genome Browser: A GUI (Graphical User Interface) for viewing biological information. GBrowse (DNA Subway’s Browser) is “designed to view genomes. It displays a graphical representation of a section of a genome, and shows the positions of genes and other functional elements. It can be configured to show both qualitative data such as the splicing structure of a gene, and quantitative data such as microarray expression levels.” [citation]
Track: The individual regions of the display where information imported into the browser. For each type (or source) of information, there is usually an associated track.
- Example Sequence: Arabidopsis thaliana (mouse-ear cress) ChrI, 75 kb
- Tool(s): Local Browser (JBrowse)
- Concept(s): Gene orientation/structure, transposons, chromosome organization
Following the gene browser steps for the Arabidopsis ChrI sample above, answer the following discussion questions (the locations of the genes are given in parentheses and can be pasted into the browser):
Considering the following genes:
- BFN1-201 (1:3748591..3753070)
- SCAMP5-201 (1:3744556..3749035)
- STP1-201 (1:3776366..3780845)
- At1G11270.2 (1:3780041..3789000)
- Do all the gene predictors agree with each other?
- Which gene predictions seem to match the Ensemble genes most closely?
DNA Subway searches customized versions of UniGene and UniProt that contain only validated plant proteins, and are free of predicted or hypothetical proteins.
- Click ‘BLASTN’; wait until the flashing icon displays ‘V’ (view)
- Click ‘BLASTN’ again to view the results.
- Click ‘BLASTX’; wait until the flashing icon displays ‘V’ (view).
- Click ‘BLASTX’ again to view the results.
- Click on 'JBrowse' and then click 'Full-screen View' in the upper-left.
- In the 'Available Tracks' menu, add the Blastn and Blastx tracks.
Tip
Some Useful Definitions
- BLAST: Basic Local Alignment Search Tool (BLAST) is an algorithm that search databases of biological sequence information (e.g. DNA, RNA, or Protein sequence) and return matches. The BLASTN program is specific to nucleotide data, and the BLASTX algorithm works with sequence data translated into amino acid sequences.
- UniGene: A database of transcript data, “each UniGene entry is a set of transcript sequences that appear to come from the same transcription locus (gene or expressed pseudogene), together with information on protein similarities, gene expression, cDNA clone reagents, and genomic location.” [citation]
- cDNA: DNA produced by reverse transcribing mRNA using reverse transcriptase. cDNAs are used to investigate mRNA within a biological sample.
- ESTs: “Small pieces of DNA sequence (usually 200 to 500 nucleotides long) that are generated by sequencing either one or both ends of an expressed gene. The idea is to sequence bits of DNA that represent genes expressed in certain cells, tissues, or organs from different organisms.” [citation]
- Example Sequence: Arabidopsis thaliana (mouse-ear cress) ChrI, 75 kb
- Tool(s): BLASTN, BLASTX, Upload Data
- Concept(s): RNA, cDNAs, ESTs, Biological Databases
Following the BLAST steps for the Arabidopsis ChrI sample above, answer the following discussion questions (the locations of the genes are given in parentheses and can be pasted into the browser):
- Both BLASTN and BLASTX returns the ‘Length’ of your resulting matches. Do you notice differences in the average lengths of BLASTN and BLASTX matches? Explain.
- Under ‘Type’ both BLASTN and BLASTX returns ‘match’ and ‘match_part.’ ‘Match’ is describing the overall length of a single match, but individual significant matches may be fragmented, i.e. ‘match_part.’ Do BLASTN and BLASTX return ‘match’ and ‘match_part’ results in different frequencies? Explain.
Apollo is an extension of JBrowse which allows the user to build and edit gene models. Apollo has a number of features but in this tutorial, we will give brief intro covering the conceptual steps.
A. Import Blastn model to match for transcript length Blast searches are matched against UniGene(blastn) and UniProt(blasts). UniGen models are derived from cDNA and ESTs (transcriptome evidence) produced by experiment.
Open Apollo and zoom into a region of interest (e.g. 1:3793981..3802033)
- Ensure at least the following tracks are selected (on):
- Augustus (and other gene predictors: FGenesH, SNAP, etc.)
- Blastn
Double-click on the Blastn result, and drag this transcript into the yellow 'User-created Annotations' section.
B. Select a scaffold model Use transcriptome evidence (UniGene - BLASTN) to select the best possible gene model for a scaffold. If no gene model exists or significantly reflects the UniGene model, use the UniGene model itself as a scaffold.
- Drag a plausible model into the yellow 'User-created Annotations' - in this case we will choose the Augustus model; double-click the Augustus model to select the entire model and drag into 'User-created Annotations'.
- Adjust the Augustus model to match the 5' and 3' configuration of the blastn model
- Delete the extraneous 5' exon (single-click to select; right-click to delete)
- Adjust the new 5' end to match the length of the blastn-derived transcript
- Adjust the 3' end of the Augustus-derived model (single-click to select; use your cursor/mouse to adjust the model length)
C. Edit model for splice sites and variants Protein and EST data can be used to examine possible alternative transcripts. Proteins give clues to the actual length of the translated protein at that locus and its reading frame. Like full length cDNAs, ESTs give valuable information on transcript diversity. ESTs are generated by high throughput methods, and although the data may be fragmentary, it may capture biologically relevant information about splice variants.
Turn on the blastx track
Examine the additional evidence to consider making adjustments to your Augustus-derived model. If you wish to make additional isoforms of your gene:
- Double-click to select the entire Augustus-derived model
- Right-click on the model to duplicate
- Make adjustments to the model as desired
You also have the option of adding additional EST evidence. For the Arabodopsis 75KB section, we have prepared a selection of EST data. You will need to close Apollo to load this data.
Download the Arabidopsis ESTs for this region to your computer from this link
Click on 'Upload Data'; under "Add DNA data in FASTA format" upload the EST file from the link in step 1.
Click on 'User BLASTN' to align the ESTs to this section of the Arabidopsis genome
Open 'Web Apollo'. The "Blastn User" track should be loaded. You may move this track to a convenient position on the browser
While EST evidence is always incomplete, these sequences can help you determine features of the gene model.
Tip
Learn More about Gene Evidence:
- J.Craig Venter on ESTs
- "Dynamic Gene" Evidence animation (requires Flash)
D. Determine translation start/stop sites After making your adjustments, you can confirm that your gene model(s) represents the longest possible transcripts:
- Double-click the model; right-click and select 'Set longest ORF'
E. Compare gene model(s) with existing annotations After making your gene models you can compare them with existing annotations by turning on the 'Ensemble genes' track. In this case, our work confirms the first gene model made, but a potential isoform supported by blastx data is likely incorrect.
- Example Sequence: Arabidopsis thaliana (mouse-ear cress) ChrI, 75 kb
- Tool(s): Apollo
- Concept(s): Synthesizing multiple lines of evidence
Following the Apollo steps for the Arabidopsis ChrI sample above, answer the following discussion questions (the locations of the genes are given in parentheses and can be pasted into the browser):
Try annotation of the following genes and take notes on your annotation ( right-click on the gene model, open the 'Information Editor' and scroll down to the comments section to enter comments). How do your annotations compare with the Ensembl annotations?
Genes to try:
- AT1G11270.2 (1:3781511..3790520)
- STP1-201 (1:3776261..3785270)
- T28P6.11-201 (1:3762877..3764678)
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