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ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Richard TalbotRoslin Institute and R(D)SVS
University of Edinburgh
Microarrays overview, one and two colour systems
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray uses
• Definition• A microarray is a high density of DNA probes of
known sequence arrayed across a solid surface
• Uses• Gene Expression• Comparative Genome Hybridisation (CGH)• Single Nucleotide polymorphisms (SNP)• DNA methylation• Copy Number variation (CNV)
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Experimental modelGene expression in the developing limb
model: During development different genes are expressed in a choreographed order for the spatial patterning of tissues. Chick limb buds at stage 20 (~3 days) show patterning of Sonic Hedgehog a major transcription factor controlling the anterior-posterior axis in the limb bud.
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Experimental questions
1. What are the genes associated with patterning in the limb bud?
2. What are the genes influenced by the presence of Sonic Hedgehog protein?
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Experimental plans
Posterior expression
Anterior expression
Question 1
V’s
Anterior bead expression
Posterior expression
V’s
Anterior expression
Anterior Bead expression
V’s
Question 2
Anterior Gli3 expression
Posterior expression
V’s
Anterior expression
Anterior GLi3 expression
V’s
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Reference design
Reference
Anterior bead expression
Anterior expression
Posterior expression
Anterior Gli3 expression
One Colour Experiment
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Types of Microarrays
• Probe type
• cDNA
• Oligonucleotide short (<35 bases)
• Oligonucleotide long (>35 bases)
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Oligonucleotide synthesis
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
RNA quality
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
RNA LabellingTotal RNA
cDNA
Reverse transcription
AAAAAAAAAAAA
AAAAAAAAAAAA
Aminoallyl-UTP
a a a a
a a a a
a a a a
a a a a
cDNA
* * * *
* * * *
* * * *
* * * *
Cy3*-CTP or Cy5*-CTP
* * * *
* * * *
* * * ** * * *
Dye CouplingCy3* or Cy5*
Indirect Direct
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
RNA amplification
Total RNA cDNAReverse
transcription
In Vitrotranscription
Remove RNA and ds-cDNA
AAAAAAAAAAAA
AAAAAAAAAAAA
AAAAAA-T7TTTTTT-T7
AAAAAA-T7TTTTTT-T7
AAAAAA-T7TTTTTT-T7
AAAAAA-T7TTTTTT-T7
T7T7
T7T7
T7T7
T7T7
cRNA
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Affymetrix Single Channel Microarray Experiment
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray Experiment
Reverse Transcription
Dye Coupling
Cy3 Cy5
Mix on Slide
Excitation Emission
Hybridise
Scanning
Control RNA Treatment RNA
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Hybridisation
•Temperature control•Mixing•Multi-chamber•Loading sample•Washing
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Scanning
•Set laser power•Set PMT gain or auto adjust•Set scan area•Apply griding file•Align griding file•Flag problem features•Extract Values
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Sources of variation 1Microarray production
• Print-pin anomalies• Variations in printed probe
quantities even with the same pin
• Chip batch variation (due to many sources of unknown variations)
• Differences in sequence length of the immobilized DNA
• Variations in chemical probe attachment levels to the slide
mRNA• Differences in conditions.• Differences between
experimental subjects within the same covariate level.
• Differences between samples from the same subject.
• Variation in mRNA extraction methods from original sample.
• Variations in reverse transcription.
• Differences in PCR amplification.
• Different labelling efficiencies.
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Sources of variation 2
Scanning/imaging• Different scanners.• Different photo-multiplier
gain.• Different spot-finding
software.• Different grid alignments.• Different laser power
Hybridization process• Different dye sensitivities.• Inequalities in the application
of mRNA to the slide.• Variations in the washing
efficiencies of non-hybridized mRNA on the slide.
• Other differences in hybridization parameters, such as:• temperature• experimenter• time of the day
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Normalisation (two dye)
• Used to remove systematic bias form the image data
• Methods• Global
• All genes
• Housekeeping/spike genes
• Loess• Global
• Pin tip
• Spatial
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Normalisation (one dye)
Method depends on slide system• Affymetrix
• MAS5.0• RMA• Plier
• Agilent• Spatial normalisation
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Differential expression
• T-Test • Multiple testing - False Discovery Rate (FDR)• ANOVA
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Microarray experiment
• Define the questions• Choose microarray• RNA preparation• Target labelling• Array Hybridisation• Image scanning and analysis• Statistical analysis• Reporting results
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Minimal Information About a Microarray Experiment
• Database of microarray experiment
Samples
Data Analysis
Protocols Experiment
ARRAYHybridisation
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Gene Expression Data Repositories
• Major public repositories • ArrayExpress (EBI) - http://www.ebi.ac.uk/microarray-as/ae/• GEO (NCBI) - http://www.ncbi.nlm.nih.gov/geo/• CIBEX (DDBJ) – http://cibex.nig.ac.jp/index.jsp
• Submission tools• Tab2Mage - http://www.ebi.ac.uk/cgi-bin/microarray/tab2mage.cgi• GEOarchive -
http://www.ncbi.nlm.nih.gov/projects/geo/info/spreadsheet.html#GEOarchive
• Cibex - http://cibex.nig.ac.jp/submission/index.jsp
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
After the Gene list
Electronic• Annotation• Clustering• Pathways• Text mining• Networks
Practical• qPCR• In Situ hybridisation• Northern blot• Western Blot• Immunohistochemistry• siRNA• Pharmacology
ARK-Genomics: Centre for Comparative and Functional Genomics in Farm Animals
Conclusions
• Several successful microarray platforms are available• Choice of platform is based on experimental design
and cost• It is key to know the questions being asked • Many steps in a microarray experiment contribute to
the overall variance • Normalisation can be used to remove technical
variance • Microarrays are a tool to answer a specific question
have a plan on how to confirm the answer.
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