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Disruption of Imprinted Regions in a Mouse Model of Fetal Alcohol Spectrum Disorders (FASD)

Laufer, B., Diehl, E., Kleiber, M., Janus, K., Wright, E., and Singh, S.

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Nature Vs. Nurture

http://www.askdro.com/wp-content/uploads/2011/02/Nature_versus_Nurture.jpg

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http://www.cosmosmagazine.com/files/imagecache/feature/files/20071004_naturenurture.jpg

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Environmental Insults

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What is Epigenetics?

“A mitotically (or meiotically) inheritable change in gene expression, independent of an alteration in DNA sequence”

– Berger et al. (2009) Genes Dev.

Epigenetic Mechanisms

• Histone Modifications

• DNA Cytosine Methylation

• MicroRNA6

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DNA Cytosine Methylation

5’------CpG------3’3’ -----GpC------5’

CH3

CH3

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DNA Cytosine Methylation

. Metivier, R. et al. Cyclical DNA methylation of a transcriptionally active promoter. Nature 452, 45–50 (2008).

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Non Coding RNA• 95% of the human genome is transcribed and

produces a vast number of noncoding RNAs (ncRNAs).

• Two types of Interest:– MicroRNAs• Degrade target mRNA or prevent translation

– SnoRNAs• Typically involved in mRNA editing

– However, there are exceptions

Carnicini et al. 2008, Curr Opin Cell Biol

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Environmental Epigenetics

Alcohol as Environmental Insult

• Fetal Alcohol Exposure (FAE) affects gene expression, behaviour and learning.

• Changes maintained for a lifetime– Even after exposure has ceased for months

• Mechanism unknown

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Fetal Alcohol Exposure • Leading cause of preventable birth defects and

mental deficits

• FASD– Fetal Alcohol Spectrum Disorder – 1 out of 100 pregnancies– Physical abnormalities, behavioural and intellectual

problems

Continuous Preference Model

• Free choice

• Quantity monitored daily

• 70% preference for 10% EtOH– 120 - 180 mg/dl per day– DBA/2J mice has only 10%

• No Stress13

Young C, Olney JW. Neuroapoptosis in the infant mouse brain triggered by a transient small increase in blood alcohol concentration. Neurobiol Dis 2006;22:548-54.

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Hypothesis

Fetal alcohol exposure induces alterations in brain gene expression that last into adulthood and are correlated with epigenetic modifications.

Methods: Array Analysis

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Gene Expression MicroRNA DNA Methylation

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Results

3 Large Clusters of Brain Specific Imprinted noncoding RNA (ncRNA)

Genomic Imprinting

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• Genes are expressed in a parent of origin specific manner.

• Achieved by DNA Methylation.

Maternal Paternal

Normal Bialleic Gene Expression

Maternally Expressed, Paternally Imprinted

Paternally Expressed, Maternally Imprinted

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Imprinted ncRNA

• 30% of parentally imprinted transcripts are ncRNA.

• Key role in neurodevelopment and memory.– Some appear to be fully imprinted in the adult brain

only.

• Imprinted ncRNAs are not only important for early life processes, but are also functionally important for ‘online’ adult brain functions.

Morison et al. 2005, Trends Genet

Wang et al 2004, Mol Cell Biol

Davies et al. 2008, Adv Exp Med Biol

14q32.21 (Murine 12qF1)

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Pten

AKT-mTOR pathway

Tempo of newborn neuron integration during adult neurogenesis

Implicated in the developmental basis of major psychiatric disorders

Maternally Expressed, Paternally Imprinted

15q11-q13 (Murine 7qC)

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III5htr2cPre-mRNA

I II III IV Va Vb VI

Receptor with a stronger serotonin response

Inclusion of exon Vb without mRNA editing during alternative splicing

snoRNA binds to mRNA

H/MBII-52(SNORD115)

Paternally Expressed, Maternally Imprinted

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Murine 2qA1

Intron 10

Sfmbt2

Sfmbt2-AS

• Over 130 miRNAs• Mouse Specific• No Imprinting Center

Paternally Expressed, Maternally Imprinted

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Future Directions1. Confirmation of Results

2. Brain Region Specificity– Hippocampus

3. Trans-generational Effects

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What are Trans-generational effects?

http://learn.genetics.utah.edu/content/epigenetics/inheritance/images/DirectExposure.jpg

F0

F1

F2

Direct Exposure Indirect Exposure

Great Grandchildren F3

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Conclusions• The genome is environmentally

responsive.

• The epigenome serves as the bridge between environment and genome.

• Thus, the environment shapes an individual significantly for a lifetime and beyond.

• The nature vs. nurture debate has been solved by epigeneticists.

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Acknowledgements

SupervisorShiva Singh Funding:

Advisory Committee NSERCKathleen Hill CIHRAnthony Percival-Smith OMHF

Singh Lab:Raihan UddinMorgan KleiberHaroon SheikhChristina Castellani

Katarzyna JanusEric DiehlPat McDonaldKiran KumarSujit Maiti

Rachel Danielson Randa Stringer Elizabeth Yan

Aniruddho C. Hoque