Transcript Document

Genomics of Gene Regulation
Genomic and Proteomic Approaches to Heart, Lung, Blood and Sleep Disorders
Jackson Laboratories
Ross Hardison
September 9, 2008
Heritable variation in gene regulation
“Simple” Mendelian traits, e.g. thalassemias
Variation in expression is common in normal
individuals
Variation in expression may be a major contributor
to complex traits (including heart, lung, blood and
sleep disorders)
Deletions of noncoding DNA can affect gene expression
Forget and Hardison, Chapter in Disorders of Hemoglobin, 2nd edition
Substitutions in promoters can affect expression
Forget and Hardison, Chapter in Disorders of Hemoglobin, 2nd edition
Variation of gene expression among individuals
• Levels of expression of many genes varies in humans (and other
species)
• Variation in expression is heritable
• Determinants of variability map to discrete genomic intervals
• Often multiple determinants
• Points to an abundance of cis-regulatory variation in the human
genome
• "We predict that variants in regulatory regions make a greater
contribution to complex disease than do variants that affect protein
sequence" Manolis Dermitzakis, ScienceDaily
– Microarray expression analyses of 3554 genes in 14 families
• Morley M … Cheung VG (2004) Nature 430:743-747
– Expression analysis of EBV-transformed lymphoblastoid cells from all 270
individuals genotypes in HapMap
• Stranger BE … Dermitzakis E (2007) Nature Genetics 39:1217-1224
Risk loci in noncoding regions
(2007) Science 316: 1336-1341
DNA sequences involved in regulation of
gene transcription
Protein-DNA interactions
Chromatin effects
Specific DNA sequences bind proteins
that recruit transcriptional machinery
Maston G, Evans S and Green MR (2006)
Annu Rev Genomics Hum Genetics 7:29-59
Distinct classes of regulatory regions
Act in cis, affecting
expression of a gene
on the same
chromosome.
Cis-regulatory modules
(CRMs)
Maston G, Evans S and Green M (2006) Annu Rev Genomics Hum Genetics 7:29-59
CRMs are clusters of specific binding sites for
transcription factors
Hardison (2002) on-line textbook Working with Molecular Genetics http://www.bx.psu.edu/~ross/
Silent and repressed chromatin
Hardison (2002) on-line textbook Working with Molecular Genetics http://www.bx.psu.edu/~ross/
Transcription initiation and pausing
Repressors bind
to negative control
elements
General transcription
initiation factors, GTIFs
Assemble on promoter
Basal and activated transcription
Activators bind to
enhancers
Histone modifications modulate chromatin structure
H3K4me2, 3
http://www.imt.uni-marburg.de/bauer/images/fig2.jpg
H3K27me3
Uta-Maria Bauer
Biochemical features of DNA in CRMs
Accessible to cleavage:
DNase hypersensitive site
Clusters of binding site motifs
Bound by specific transcription factors
Coactivators
Pol
Pol IIa
II
Associated with RNA polymerase
and general transcription factors
Nucleosomes with histone modifications:
Acetylation of H3 and H4
Methylation of H3K4
Examples of genome-wide data on CRM features
• RNA polymerase II, preinitiation complex
– IMR90 cells: Kim TH …Ren B (2005) Nature 436: 876-880
• Start sites for transcription
– Carninci et al. (2006) Nature Genetics 38:626-635
• Histone modifications
– T cells: Roh ... Zhao K (2006) PNAS 103:15782-15878
• Insulator protein CTCF
– Primary fibroblasts: Kim TH … Ren B (2007) Cell 128:1231-1245
• DNase hypersensitive sites
– CD4+ T cells: Boyle… Crawford G (2008) Cell 132:311-322
• Many datastreams: ENCODE project
– Birney et al. (2007) Nature 477:799-816
Chromatin immunoprecipitation: Greatly enrich
for DNA occupied by a protein
Elaine Mardis (2007) Nature
Methods 4: 613-614
ChIP-chip: High throughput mapping of
DNA sequences occupied by protein
http://www.chiponchip.org
Bing Ren’s lab
Enrichment of sequence tags reveals function
Barbara Wold & Richard M Myers (2008) “Sequence Census Methods” Nature Methods 5:19-21
Genomic features at T2D risk variants
Overlap of SNP rh564398 with DHS suggests a role in transcriptional regulation,
but overlap with an exon of a noncoding RNA suggests a role in post-transcriptional
regulation. Different hypotheses to test in future work.
GATA-1 occupancy in erythroid cells
GATA-1 is required for erythroid maturation
Common
myeloid
progenitor
MEP
Hematopoietic
stem cell
G1E cells
GATA-1
Myeloblast
Common
lymphoid
progenitor
G1E-ER4 cells
Basophil
Eosinophil
Neutrophil
Aria Rad, 2007 http://commons.wikimedia.org/wiki/Image:Hematopoiesis_(human)_diagram.png
Monocyte,
macrophage
GATA-1 occupancy over a large chromosomal region
enhancer
----(
)---Ahsp
ChIP: antibody to GATA-1
chip: NimbleGen high density tiling array
Yong Cheng, Lou Dore,…Xinmin Zhang, Roland Green, Mitch Weiss, R.H.
ChIP-chip for GATA-1 at Hbb locus
GATA-1 ChIP-chip hits localize to targets of
this transcription factor
GATA-1
Almost all sites occupied by GATA-1 have
the consensus binding site motif WGATAR
•
Of the 63 validated ChIP-chip hits, 60 (95%) have at least one WGATAR motif
– Other 3 have AGATAT, GGATAT, CGATAG, …
– Of 6000 randomly chosen DNA intervals of 500bp from the 66Mb, 3886 (65%)
have a WGATAR motif
– Occupied sites are about 1.4-fold enriched for the motif
•
GATA-1 discriminates exquisitely among available sites
– Only 94 out of 78,013 potential sites (500bp interval with at least one WGATAR)
are occupied
– About 1 in 1000 intervals are occupied
– Indicates exquisite specificity of the ChIP-chip data (<99%)
DNA segments occupied by GATA-1 were tested for
enhancer activity on transfected plasmids
Occupied
segments
Some of the DNA segments occupied by
GATA-1 are active as enhancers
Comparative genomics for predicting CRMs
• Sometimes high quality data on biochemical signatures of CRMs is
not available
• Use sequence properties of CRMs for prediction
• Clusters of binding site motifs for transcription factors
– Low specificity - MANY false positives
• Deep conservation of noncoding DNA sequences, from humans to
fish or chicken
– Low sensitivity - less than 5% of CRMs show signs of constraint across
vertebrates
• Conservation of clusters of transcription factor binding sites in
mammals
• Conservation patterns that distinguish CRMs from neutral DNA
Finding clusters of binding sites for transcription factors
• Resources and servers for finding transcription factor binding sites
(TFBSs)
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TRANSFAC http://www.gene-regulation.com/
JASPAR http://jaspar.cgb.ki.se/cgi-bin/jaspar_db.pl
TESS
http://www.cbil.upenn.edu/cgi-bin/tess/tess
MOTIF (GenomeNet) http://motif.genome.jp/
MatInspector http://www.genomatix.de/
Finding known motifs in a query sequence
MatInspector at http://www.genomatix.de/
K. Cartharius et al. (2006) MatInspector and beyond: promoter analysis based on transcription factor
binding sites. Bioinformatics 21:2933-2942. Genomatix Software GmbH, Munchen, Germany
Query: an
enhancer
in SOX6
1356 bp
About 1 in 4
bp is the start
of a TFBS
match!
Three modes of evolution
Negative and positive selection observed at
different phylogenetic distances
:
phastCons score identifies conserved DNA segments
Siepel et al. 2005,
Genome Research
Ultraconserved elements = UCEs
• At least 200 bp with no interspecies differences
–
–
–
–
Bejerano et al. (2004) Science 304:1321-1325
481 UCEs with no changes among human, mouse and rat
Also conserved between out to dog and chicken
More highly conserved than vast majority of coding regions
• Most do not code for protein
– Only 111 out of 481overlap with protein-coding exons
– Some are developmental enhancers.
– Nonexonic UCEs tend to cluster in introns or in vicinity of genes encoding
transcription factors regulating development
– 88 are more than 100 kb away from an annotated gene; may be distal
enhancers
Intronic UCE in SOX6 enhances expression
in melanocytes in transgenic mice
UCEs
Tested UCEs
Pennacchio et al.,
http://enhancer.lbl.gov/
Distinctive divergence rates for different types of
functional DNA sequences
pTRRs: putative
transcriptional regulatory
region; likely CRMs
Sites identified as occupied
by sequence-specific
transcription factors based on
high-throughput chromatin
immunoprecipitation assayed
by hybridization to high
density tiling arrays of
genomic DNA= ChIP-chip
Genes likely regulated by clade-specific pTRRs
are enriched for distinctive functions
Percentage of
pTRRs that align
no further than:
Enriched GO
categories
q-value
for FDR
Immune
response
0.0006
David King
Primates: 3%
Millions of
years
91
Eutherians: 71%
173
310
Marsupials: 21%
Protease
inhibition
Ion transport
Mitosis and
cell cycle
0.0005
0.012
0.0005
450
Tetrapods: 4%
Transcriptional
0.004
regulation
Vertebrates: 1%
King, Taylor, et al. (2007) Genome Research
Conservation of TFBSs between species
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•
Servers to find conserved matches to factor binding sites
– Comparative genomics at Lawrence Livermore http://www.dcode.org/
• zPicture and rVista
• Mulan and multiTF
• ECR browser
– Consite http://mordor.cgb.ki.se/cgi-bin/CONSITE/consite
Conserved TFBSs are available for some assemblies of human genome at UCSC Genome Browser
Binding site for GATA-1
Clusters of conserved TFBSs: PReMods
http://genomequebec.
mcgill.ca/PReMod/
Blanchette et al.
(2006) Genome
Research
ESPERR
Evolutionary and Sequence Pattern
Extraction through Reduced
Representation
Taylor et al. (2006) Genome Research 16:1596-1604
ESPERR: a different approach
• Don’t assume a database of known binding
motifs
• Don’t assume strict conservation of the important
sequence signals
• Instead, use alignments of validated examples to
learn sequence and evolutionary patterns that
characterize a class of elements
• Machine learning approach to discriminate
functional classes of DNA based on patterns in
alignments
Regulatory potential (RP) to distinguish
functional classes
Good performance of ESPERR for gene
regulatory regions (RP)
-1
Predicted cis-Regulatory Modules (preCRMs)
Around Erythroid Genes
- Gene is known to respond to the restoration of GATA-1 in an erythroid cell line
- DNA segment with positive regulatory potential (RP) score
- DNA segment contains at least one match to the GATA-1 binding site (WGATAR)
that is preserved in multiple mammalian lineages
Wang et al. (2006) Genome Research 16: 1480-1492
Examples of validated preCRMs
Validation status for 99 tested fragments
cc = consensus binding site motif is conserved and matches the consensus in
multiple mammalian lineages
cnc = binding site motif has a mismatch from the consensus but is conserved
Wang et al. (2006) Genome Research 16: 1480-1492
preCRMs with High RP and Conserved
Consensus GATA-1 Tend To Be Validated
Accurate prediction of a GATA-1
responsive enhancer for miR-144, 451
A
Dore L, Amigo JD et al. (2008) PNAS 105:3333-3338.
Constraint on a binding site motif in an occupied DNA
segment strongly correlates with enhancement
Cheng et al. (2008) revised manuscript submitted
Comparative genomics signals suggestive of
CRMs around T2D risk variants
Summary: Genomics of Gene Regulation
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Genetic determinants of variation in expression levels may contribute to
complex traits - phenotype is not just determined by coding regions
Biochemical features associated with cis-regulatory modules are being
determined genome-wide for a range of cell types.
These can be used to predict CRMs, but occupancy does not necessarily
mean that the DNA is actively involved in regulation.
Comparative genomics is a complementary approach to predicting CRMs.
Evolutionary preservation of binding site motifs within regions containing
other indicators of CRMs (e.g. regulatory potential or protein occupancy) is a
good predictor of function.
Many thanks …
RP scores and other bioinformatic input:
Francesca Chiaromonte, James Taylor
Yong Cheng, Demesew Abebe, Christine Dorman,
…, Ying Zhang, David King, Swathi Ashok Kumar
Erythroid cell biology and biochemistry:
Mitch Weiss, Gerd Blobel, Barry Paw
Alignments, chains, nets, browsers, ideas, …
Webb Miller, Jim Kent, David Haussler
Funding from NIDDK, NHGRI, Huck Institutes of Life Sciences at PSU