Early Nutrition and the Establishment of Epigenotype at Metastable Epialleles
Rob WaterlandHouston, Texas
The Waterland Lab
Funding: NIH-NIDDK, March of Dimes, USDA
Metabolic Imprinting
Adaptive responses to early nutrition
Persistent effect
Susceptibility limited to critical period of development
Waterland & Garza Am J Clin Nutr 1999;69
Early Nutrition and DNA Methylation
• Most cytosines within CpG dinucleotides are methylated
• Tissue-specific patterns of CpG methylation are established during development
• Methylation requires dietary methyl donors and cofactors
• Mitotically heritable
NH2
O
H
H
N
N
NH2
O
CH3
H
N
N
DNMT
SAM SAHR R
Cytosine 5-Methylcytosine
Mammalian One Carbon Metabolism
THF
5CH3THF
B12
1 2
6B6
3
4
5
Methionine
SAM
SAH
Homocysteine
B6
Cystathionine
Cysteine
Glutathione
CH3-X
Adenosine
X*DMG
Betaine
Choline
1 Methionine Synthase
2 Betaine-homocysteineMethyltransferase
3 Methionine Adenosyltransferase
4 Various Methyltransferases
5 SAH Hydrolase
6 Cystathionine β-Synthase
* X: Various Targets of Methylation
THF
5CH3THF
B12
1 2
6B6
3
4
5
Methionine
SAM
SAH
Homocysteine
B6
Cystathionine
Cysteine
Glutathione
CH3-X
Adenosine
X*DMG
Betaine
Choline
1 Methionine Synthase
2 Betaine-homocysteineMethyltransferase
3 Methionine Adenosyltransferase
4 Various Methyltransferases
5 SAH Hydrolase
6 Cystathionine β-Synthase
* X: Various Targets of Methylation
1 Methionine Synthase
2 Betaine-homocysteineMethyltransferase
3 Methionine Adenosyltransferase
4 Various Methyltransferases
5 SAH Hydrolase
6 Cystathionine β-Synthase
* X: Various Targets of Methylation
Early Nutrition and DNA Methylation
• Most cytosines within CpG dinucleotides are methylated
• Tissue-specific patterns of CpG methylation are established during development
• Methylation requires dietary methyl donors and cofactors
• Mitotically heritable
NH2
O
H
H
N
N
NH2
O
CH3
H
N
N
DNMT
SAM SAHR R
Cytosine 5-Methylcytosine
Overall Hypothesis
• Specific subsets of genes are especially sensitive to early nutritional influences on epigenetic regulation
– Genomically imprinted genes
– Metastable epialleles
Waterland and Jirtle, Nutrition 2004
The Viable Yellow Agouti (Avy) Mouse
Maternal Methyl Donor Supplementation Affects Coat Color of Avy/a Offspring
Waterland & Jirtle, Mol Cell Biol 2003
Supplementation Changes Coat Color by Increasing Avy Methylation
Waterland & Jirtle, Mol Cell Biol 2003
Interpretation of Avy Experiment
• Specific transposable elements induce epigenetic instability, allowing early diet to influence epigenotype
• Transposable elements (SINEs, LINEs, etc.) comprise >40% of the human genome
Metastable Epiallele
“An allele at which the epigenetic state can switch and establishment is a probabilistic event. Once established, the state is mitotically inherited.”
Rakyan et al Trends in Genetics 2002
Viable yellow agouti Axin fused
The Axin Fused (AxinFu) Mouse
• Axin regulates embryonic axis formation– Inhibitor of Wnt signaling pathway
• AxinFu caused by IAP insertion into Axin intron 6– Tail kink phenotype associated with expression of
truncated transcript originating downstream of IAP– AxinFu methylation silences the mutant transcript
IAP
6 7
Vasicek et al Genetics 1997
Methods
• C57 (+/+) dams assigned to diets 2 weeks before mating with AxinFu/+ males– Control: NIH-31– Supplemented: NIH-31 with extra
• folic acid, B12, betaine and choline
• Offspring rated for tail phenotype at age 21 d
• AxinFu CpG methylation measured by bisulfite sequencing
Classification of Tail Phenotype
None
Slightly Kinky
Kinky
Classification of Tail Phenotype
Very Kinky
Methods
• C57 (+/+) dams assigned to diets 2 weeks before mating with AxinFu/+ males– Control: NIH-31– Supplemented: NIH-31 with extra
• folic acid, B12, betaine and choline
• Offspring rated for tail phenotype at age 21 d
• AxinFu CpG methylation measured by bisulfite sequencing with phosphor-imager quantitation
Characteristics of Offspring at Weaning
Control Supplemented
Number of litters 24 22
Wean weight (g)† 8.2 ± 0.1 7.8 ± 0.1 *
Litter size† 6.0 ± 0.3 5.7 ± 0.4
Proportion AxinFu/+ pups per litter† 0.40 ± 0.04 0.56 ± 0.04 **
Total number of pups 144 125
Number of AxinFu/+ pups 56 68
† mean ± sem
* P < 0.05
** P < 0.01
AxinFu Methylation and Tail Phenotype
65’ 7 3’
5’3’IAP 1
6
200 bp
None Slightly kinky Kinky Very kinky
A
B
C
None Slightly kinky Kinky Very kinky
Tail Phenotype
% M
eth
ylat
ion
0
20
40
60
80
100
5721
29
17
65’ 7 3’
5’3’IAP 1
6
200 bp
65’ 7 3’
5’3’IAP 1
6
200 bp
None Slightly kinky Kinky Very kinky
A
B
C
None Slightly kinky Kinky Very kinky
Tail Phenotype
% M
eth
ylat
ion
0
20
40
60
80
100
5721
29
17
None Slightly kinky Kinky Very kinky
Tail Phenotype
% M
eth
ylat
ion
0
20
40
60
80
100
5721
29
17
None Slightly kinky Kinky Very kinky
Tail Phenotype
% M
eth
ylat
ion
0
20
40
60
80
100
5721
29
17
Waterland et al, submitted
Supplementation Reduces Incidence of Tail Kinks in AxinFu/+ Offspring
P=0.002
Waterland et al, submitted
None Slightly kinky Kinky Very kinky
Tail Phenotype
0
10
20
30
40
50
60 Control
Supplemented
% o
f all
Axi
nF
u /+
Off
sprin
g
None Slightly kinky Kinky Very kinky
Tail Phenotype
0
10
20
30
40
50
60 Control
Supplemented
% o
f all
Axi
nF
u /+
Off
sprin
g
P=0.002
Supplementation Does NOT Increase AxinFu Methylation in Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
ethy
latio
n
Control Supplemented
CpG Site
Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
ethy
latio
n
Control Supplemented
CpG Site
Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 61 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
ethy
latio
n
Control Supplemented
CpG Site
Liver
P=0.05
AxinFu is Hypomethylated in Tail
0
20
40
60
80
100Brain
Kidney
Liver
Tail
% M
eth
yla
tion
AxinFu/+ Mouse1 2 3 4 5 6 7 8
0
20
40
60
80
100Brain
Kidney
Liver
Tail
% M
eth
yla
tion
AxinFu/+ Mouse1 2 3 4 5 6 7 8
Supplementation Prevents Tail Kinks by Reducing Tail-Specific Loss of Methylation
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
eth
yla
tion
Control Supplemented
CpG Site
Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
eth
yla
tion
Control Supplemented
CpG Site
Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 61 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site
% M
eth
yla
tion
Control Supplemented
CpG Site
Liver
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site%
Me
thyl
atio
n
Control Supplemented
CpG Site
Tail
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site%
Me
thyl
atio
n
Control Supplemented
CpG Site
Tail
1 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 61 2 3 4 5 60
20
40
60
80
100
1 2 3 4 5 6
CpG Site%
Me
thyl
atio
n
Control Supplemented
CpG Site
Tail
P=0.009
Waterland et al, submitted
P=0.05
Significance
• Similar to Avy, epigenetic metastability at AxinFu confers lability to early nutrition
• Nutritional effects on DNA methylation during development may – Be tissue-specific – Occur at diverse ontogenic periods
Transgenerational Perpetuation of Obesity…By Epigenetic Mechanisms?
• Avy mouse is an ideal model– Spontaneously hyperphagic– Compare offspring of lean
a/a dams and obese Avy/a dams
Avy Transgenerational Obesity Study• Approach:
– Maintain two separate populations of Avy/a mice on control (NIH-31) or methyl-supplemented diet (folic acid, vitamin B12, betaine, choline)
– Pass the Avy allele through the female germline for several generations
– Assess cumulative effects on body weight of Avy/a and a/a offspring
Maternal Obesity Increases Body Weight at Weaning in F1 Offspring
0
1
2
3
4
5
6
7
8
9
10
11
a/a dam Avy/a dam
d 21
bod
y w
eigh
t (g) 56
121
Avy/aa/a
P<0.001
Dams
Offspring Body Weight
Transgenerational Effect of Maternal Obesity:Wean Weight by Generation
8
8.5
9
9.5
10
10.5
11
11.5
12
F1 F2 F3
d 21
bod
y w
eigh
t (g)
F3 vs. F1 P=0.004
131121
62
Average for
offspring of
a/a dams
Control Diet
a/a Offspring
Transgenerational Effects of Maternal Obesity Depend on Offspring Genotype and Maternal Diet
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
Control Diet
a/a Offspring Avy/a Offspring
Transgenerational Effects of Maternal Obesity Depend on Offspring Genotype and Maternal Diet
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
Control Diet
Supplemented Diet
a/a Offspring Avy/a Offspring
Transgenerational Effects of Maternal Obesity Depend on Offspring Genotype and Maternal Diet
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
Control Diet
Supplemented Diet
a/a Offspring Avy/a Offspring
Effect P valueGeneration <0.0001 Genotype <0.0001Supplementation 0.002
N=498 total
Transgenerational Effects of Maternal Obesity Depend on Offspring Genotype and Maternal Diet
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
F1 F2 F3
d 21
bod
y w
eigh
t (g
)
Genotype-Epigenotype-Diet Interaction:Can too many vitamins make us fat?
Maternal Obesity
Methyl DonorSupplementation
Avy Genotype
Epigenetic AlterationsAffecting Weight Gain?
Same Genotype, Different Epigenotype
Bisulfite Sequencing at AxinFu
T C T C
1
23
4
Site
Unaffected
AxinFu Hypermethylated
Affected
AxinFu less methylated
Validation of Quantitative Bisulfite Sequencing: Exploit H19 DMR in C57BL/6 x Cast/Ei F1 Mice
SacI digestion eliminates paternal allele
MfeI digestion eliminates maternal allele
Measure % methylation in known mixtures of SacI and MfeI digested DNA
Waterland et al Hum Mol Genet 2006