Sequence Comparison and Genome Alignment in the Human Genome
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Transcript of Sequence Comparison and Genome Alignment in the Human Genome
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Sequence Comparison and
Genome Alignment in the Human Genome
Jian Ma
Powerpoint: Casey Hanson
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IntroductionThis goals of the lab are as follows:
1. Gain experience using BLAST and Genome Browsers by looking at repeat families in the VHL gene.
2. Become familiar with BLAT and the UCSC website by discovering the identity of a mystery sequence.
3. Visualize pairwise multi-genome alignment and chromosomal rearrangements.
4. View phylogeny based multi-genome alignment.
5. Use UCSC tools and Galaxy to intersect annotated functional regions between human and other placental animals.
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Step 0: Shared Desktop Directory
For viewing and manipulating files on the classroom computers, we provide a shared directory in the following folder on the desktop:
classes/mayo
In today’s lab, we will be using the following folder in the shared directory:
classes/mayo/ma
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BLAST & Genome BrowserIn this exercise, we will use BLAST (Basic Local Alignment Search Tool) to search for significant occurrences of a class of transposable elements (TEs) called Short INterspersed Elements (SINEs), specifically of the ALU family, in the well-known VHL tumor suppressor gene.
The goal of this exercise is to gain experience using BLAST, particularly blastN, and the UCSC genome browser to answer biologically relevant questions.
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Step 1A: BLAST VLH in ALU DatabaseGo to the following web page: http://blast.ncbi.nlm.nih.gov/Blast.cgi
Click nucleotide_blast
In the Enter Query Sequence box, paste the accession # for VHL:
AF010238
In the Database drop-down list, select the following:
Human ALU repeat elements (alu_repeats)
Click the BLAST button.
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Step 1B: BLAST VLH in ALU Database
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Step 2A: Interpreting BLAST Results
Coordinates of VHL gene
Very Good Matches
Color Indicates Quality of Match
Good Matches
Okay Matches
A match is a significant similarity between a region of the query and a region of a database sequence.
Lines between boxes indicate ‘gaps’ between matches in the query sequence. (The next slide has a legend for interpretation)
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Step 2B: Interpreting BLAST Results
Jian Ma | Sequence Comparison and Genome Alignment
Exonic regions less likely to have ALU repeats.
Matches like this are likely to be located in intronic regions.
Note the following legend for interpreting a match.
Excellent Match
Good Match Okay MatchExo
n
Intron
IntronExon
Intron
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Step 3A: Examine VHL in UCSC BrowserLet’s look at the structure of the VHL gene in a Genome Browser to verify that ALU elements are confined to the introns.
Go to the following web page: http://genome.ucsc.edu/
Click Genome Browser
In the search term, type VHL
Click submit
Click the 2nd link: VHL (uc003bvd.3) at chr3:10183319-10195354
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Step 3B: Examine VHL in UCSC BrowserEnter chr3:10,177,301-10,201,372 into input box and click go.
Right click on tracks NOT shown below and hide them.
Right click on the RepeatMasker track and click full. It is dense by default.
Adjust the zoom until you get a view you are comfortable with.
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Step 3C: Examine VHL in UCSC Browser
Repeat tracks are 3’ to the gene, 5’ to the gene, or in the intronic region. This validates our hypothesis.
ALUs are not the only family of SINEs located in the intronic regions. What other SINE families does VHL have? What about other TE classes other than SINE?(Answers provided in separate pdf)
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BLATIn this exercise, we will use BLAT (Basic Local Alignment Tool) to search for the identity of a mystery gene annotated in the human genome.
The goal of this exercise is to gain experience using BLAST, particularly blastN, and the UCSC genome browser to answer biologically relevant questions.
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BLAST v. BLAT
BLAST Can find matches to a query in any set of GenBank sequences.
Not limited to a given k-mer size.
× Consumes a lot of memory.
× Slow compared to BLAT.
BLAT× Limited to matches to a query in a particular reference genome.
× Limited to non-overlapping 11-mers for DNA.
Can fit an entire genome in memory ( < 1GB) of RAM.
Fast compared to BLAST.
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Step 1A: BLAT the Mystery Sequence Go to the following web page: http://genome.ucsc.edu/
Click BLAT
Open our mystery sequence, located below, in Notepad.
classes/mayo/ma/mystery_sequence.txt
Paste the sequence into the textarea
Click submit
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Step 1B: BLAT the Mystery SequenceScreenshot of the web form for BLAT.
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Step 2A: Identify Mystery SequenceBLAT will return a list of significant matches in the genome.
Investigate the matches in the list by clicking browser for each match
For example, click the first browser link here.
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Step 2B: Identify Mystery SequenceThe screenshot below shows UCSC and RefSeq genes aligned to the Mysterious Sequence. In particular, CYP2A13.
Examine the other matches on the previous slide in the genome browser.
Keep in mind 2 questions: (Answers provided at the end of the document)
A. How many potential genes does the mystery sequence come from?
B. What is the relationship among these genes?
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Pairwise Whole Genome AlignmentsIn this exercise, we will utilize the UCSC Genome Browser to view whole genome alignments computed by lastZ of the following genomes individually to human: organutan, mouse, dog, and opossum. We will investigate these alignments to see if we can discover chromosomal rearrangements.
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Step 1: Create a Custom UCSC TrackGo to the UCSC Genome Browser: http://genome.ucsc.edu/index.html
Under the My Data Tab, click Create Custom Tracks:
In the Paste URLs textbox paste the following and click submit: (no commas)
chr13 58481798 58486558
On the next page, click Go to Genome Browser
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Step 2A: Track Addition
The track should look similar to what is below:
’
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Step 2B: Track Addition and RemovalTo get ‘Pairwise Alignments’ we need to turn a few tracks on and one track off.
Specifically, we need to select:
Primate Chain/Net Placental Chain/Net Vertebrate Chain/Net.
Underneath the Comparative Genomics Tab, turn these tracks to dense.
Additionally, set Conservation to hide and click refresh.
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Step 2C: Track AdditionThe resulting view should look like the figure below.
There is one problem: our species of interest are not being displayed.
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Step 2D: Species SelectionTo select the correct species, go back to the Comparative Genomics Tab.
Click on the Primate Chain/Net link.
In the resulting window, set Chains to hide and make sure only Orangutan is selected. Click submit
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Step 2E: Species Selection ContinuedConduct Step 2D for the other two tracks:
Placental Chain/Net Vertebrate Chain/Net
Make sure your configuration resembles the screenshots below:
Placental Chain/Net Vertebrate Chain/Net
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Step 2F: Expand TracksOn the tracks for each species, Right Click and select Full.
The resulting Genome Browser (after moving the tracks to the top) should look like the following:
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Step 3: Whole Genome Alignment Analysis.Investigate the tracks for each species and answer the following questions.
A. Are the sequence counterparts co-linear with respect to human? If not, is their evidence of genomics rearrangements in this region? Which kind?
B. Can you infer when these rearrangements happened evolutionarily on the diagram to the right?
Answers provided in separate pdf.
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Phylogeny Based Whole Genome AlignmentIn this exercise, we will utilize the UCSC Genome Browser to view a refined whole genome alignment of orangutan, mouse, dog, and opossum genomes to human. This alignment is produced by Multiz, a program that utilizes pairwise whole genome alignments of many species and, using a phylogenetic tree, improves the alignment.
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Step 1: Setup Multiz Visualization
Go to the UCSC Genome Browser: http://genome.ucsc.edu/index.html
Upload the following as a Custom Track and go to the genome browser, as in the previous exercise: (no commas)
chr20 61733467 61733528
Under the Comparative Genomics tab in the genome browser, click on Conservation.
Ensure the following settings are in place on the next 2 pages:
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Step 1B: Setup Multiz Visualization
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Step 1C: Setup Multiz Visualization
Once your configuration resembles the last 2 figures, click submit
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Step 2: Multiz Visualization Analysis
Investigate the tracks for each species and answer the following questions:
A. Is this region highly conserved in mammals?
B. Look closely at the Multiz track. Do you see anything strange in the human sequence compared to the other species? What could be the reason for this discrepancy?
(Answers provided in separate pdf)
After rearranging tracks, the genome browser should resemble the figure below:
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Intersection of Annotated Regulatory Regions in Human and Placental MammalsIn this exercise, we will use Galaxy to intersect annotated regulatory regions in human with annotated regions in other placental mammals.
We will then view the intersection in the UCSC genome browser
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Step 1A: Place Regulatory Data in GalaxyLogin to Galaxy : https://galaxy.illinois.edu/
Upload the sequence of predicted regulatory regions in h19 to Galaxy:
classes/mayo/ma/PRe_Mod_hg19.bed
Make sure to identify hg19 as your reference genome.
Acquire all conserved regions in placental mammals from the UCSC Main Table Browser in Galaxy:
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Step 1B: Place Regulatory Data in GalaxySelect Comparative Genomics for Group
Select Mammal E1: phastConsElements45wayPlacental for table.
Select Genome for region.
Select Galaxy for send output to.
Click Get Output
On the next screen, click Send Query to Galaxy.
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Step 2: Intersect Datasets
Go to Operate on Genomic Intervals in Galaxy and select Interesect.
Select the parameters below and click Execute.
When finished, click display at UCSC in history pane.
UCSC Resultschr19 regulatory regions.
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Step 3: Predicted Modules Overlap with PAX5 Regulators
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Exploratory Exercise
Pick a gene of interest. (VHL, CMYC, ETS1, TBP, USF2, GATA-1, …)
Visualize the intersected intervals in the UCSC Genome Browser.
See how this region correlates with results from ENCODE to assess their functional roles.
We will come around to help.