1. Epigenetics and the brain; the nature of nurture? Anthony Isles Behavioural Genetics Group Cardiff University

2. “The transmission and perpetuation of information through cell division that is not based on the sequence of the DNA” (after Conrad H. Waddington c. 1942) What is epigenetics?

3. “The transmission and perpetuation of information through cell division that is not based on the sequence of the DNA” (after Conrad H. Waddington c. 1942) What is epigenetics? Development and differentiation Maintenance of cellular identity

4. Regulation, timing and level of gene expression What is epigenetics? Undifferentiated parent cell

5. Regulation, timing and level of gene expression What is epigenetics? XXXXXXXXXXX Liver cell Undifferentiated parent cell

6. Regulation, timing and level of gene expression What is epigenetics? XXXXXXXXXXX Liver cell Undifferentiated parent cell XXXXX Neural cell

7. Regulation, timing and level of gene expression What is epigenetics? XXXXXXXXXXX Liver cell Undifferentiated parent cell XXXXX Neural cell Differentiation

8. Regulation, timing and level of gene expression What is epigenetics? XXXXXXXXXXX Liver cell XXXXX Neural cell XXXXXXXXXXX Liver cell XXXXX Neural cell Maintenance of cellular identity

9. Molecular Mechanisms DNA code remains unchanged Epigenetics are another layer of information laid on top of the DNA code Two main mechanisms: →DNA methylation →Histone (chromatin) modification How is molecular control of gene expression exerted?

10. Molecular Mechanisms – DNA methylation DNA sequence made up of 4 chemical bases; adenosine, guanine, tyrosine and cytosine (A,G,T,C) One base, cytosine is epigenetically modified by DNA methylation Encoded DNA information (i.e. ‘C’) remains the same Epigenetic code has changed… DNA methylation generally = suppression of gene activity

11. Molecular Mechanisms – histone modifications Histones; proteins around which DNA is bound Histones are the main component of chromatin Chromatin compacts and provides stability and structure to the DNA

12. Molecular Mechanisms – histone modifications Modifications of residues in the histone ‘tails’ >40 possible modifications Modification alter 3-D structure and make DNA more, or less, accessible Acetylation found in regions of increased gene expression

13. Molecular Mechanisms – histone modifications Modifications of residues in the histone ‘tails’ >40 possible modifications Modification alter 3-D structure and make DNA more, or less, accessible Acetylation found in regions of increased gene expression DNA-methylation and chromatin interact – differential recruitment of histones

14. The relevance of epigenetics to brain function

15. Epigenetic mechanisms and neurodevelopment disorders Epigenetics important in cell differentiation and maintenance Rett syndrome Rubinstein-Taybi syndrome Angelman/Prader-Willi Aberrant DNA-methylation (MECP2) Lack of Chromatin Binding Protein Loss of Histone acetly-transferase Mutations in tightly regulated genes Paternally/maternally imprinted genes on 15q11-q13 Also caused by loss of epigenetic control mechanism (i.e. no DNA loss)

16. The transmission and perpetuation of information through meiosis and/or mitosis that is not based on the sequence of the DNA (after Conrad H. Waddington c. 1942) Environment and epigenetics

17. The transmission and perpetuation of information through meiosis and/or mitosis that is not based on the sequence of the DNA (after Conrad H. Waddington c. 1942) “…complex 'epigenetic' mechanisms, which regulate gene activity without altering the DNA code, have long-lasting effects within mature neurons.” Tsankova, Renthal, Kumar & Nestler 2007 Nature Neuroscience Reviews 8: 355-367 Environment and epigenetics

18. Identical twins have identical DNA Global differences in epigenetic status between twins increases with age Fraga et al. (2005) PNAS 102, 10604-10609 Environment and epigenetics - encoding life events Increased differences in methlyation Green: areas of hypermethlyation Red: areas hypomethylation Yellow: equal levels of methylation

19. Identical twins have identical DNA Global differences in epigenetic status between twins increases with age Fraga et al. (2005) PNAS 102, 10604-10609 Environment and epigenetics - encoding life events Increased differences in methlyation Green: areas of hypermethlyation Red: areas hypomethylation Yellow: equal levels of methylation Different life events give rise to different patterns of epigenetic marks

20. Female rats show varying levels of maternal care →Characterised by levels of licking and grooming of the pups Maternal care previously has long term non- genomic, effects on the offspring →Altered reactivity to stress →Altered expression of hippocampal GR →High licking and grooming in mother leads to high licking and grooming in offspring (and vice versa) Nature neuroscience 2004 7:847-54 Environment and epigenetics - programming of by early life events

21. Nature neuroscience 2004 7:847-54 Environment and epigenetics - programming of by early life events Altered DNA methylation Altered recruitment of histones

22. Environment and epigenetics - programming of by early life events McGowan et al. Nature Neuroscience 12, 342 - 348 (2009) Childhood abuse leads to long term altered expression of Glucorticoid receptor (GR) expression

23. Environment and epigenetics - programming of by early life events McGowan et al. Nature Neuroscience 12, 342 - 348 (2009) Childhood abuse leads to long term altered expression of Glucorticoid receptor (GR) expression Corresponding changes in methylation of the neuron specific GR promoter, NR3C1

24. Environment and epigenetics - where genes and environment meet Genome variation can effect gene function in several ways →Changes in encoded product (amino acid sequence) →Changes in regulatory regions that effect expression

25. Environment and epigenetics - where genes and environment meet Genome variation can effect gene function in several ways →Changes in encoded product (amino acid sequence) →Changes in regulatory regions that effect expression Epigenetics influence gene expression Epigenetic change may interact with genetic variation Provides the molecular link between genes and environment…

26. PNAS (2004) 101: 17316-17321 Science (2002) 297: 851-854 Science (2003) 301: 386-389 Biol. Psych. 18 (2006) 59: 673-680 Arch Gen Psychiatry (2004) 61:738-44 Low expressing MAO-A gene variant interacts with childhood maltreatment Effects of 5-HTT gene variant on depression moderated by care Environment and epigenetics - where genes and environment meet

28. DNA methylation usually correlates with decreased gene expression Generally occurs in regulatory regions of genes - promoters and enhancers - not in the coding regions Grayson D. R. et.al. PNAS 2005;102:9341-9346 Methylation of the reelin promoter in Schizophrenia Molecular Mechanisms – DNA methylation