1. Epigenetic Mechanisms in Memory Formation By Rabia Anjum

2. Overview Histone modifications and accessibility of transcriptional machinery Modification sites investigated: –H3K4 (trimethylation) –H3K9 (dimethylation) Mll mice – deficient in H3K4-specific methyltransferase + eed mice – deficient in general methyltransferase complex Inhibition of histone acetylases (HDACs) with NaB Zif628 and bdnf gene sequences – sites of H3K4 trimethylation

3. Histone Modifications Methylation mediated by: HMTs and HDMs H3K9me1/2 – transcriptional silencing H3K4me3 – transcriptional activation H3K9me1/2 H3K4me3

4. Methods Used Fear Conditioning Histone Extraction and Chromatin Immunoprecipitation Assay (ChIP) Real-Time PCR –Methylation specific –Methylation non-specific

5. Fear Conditioning Control – content-exposure only Latent inhibition plus fear-conditioned – pre-exposure and Pavlovian conditioning Fear-conditioned – Pavlovian conditioning

6. ChIP Assay Used to analyse DNA associated with histone proteins

7. Methylation-Specific RT-PCR Used to determine upregulation/downregulation of methylated DNA

8. Results Freezing behaviour increased due to fear conditioning Histone modification –H3K4me3 ↑ transcriptional upregulation (reversible) –H3K9me2 ↑ transcriptional downregulation (long-lasting) –H3K4me3 specific for associative memory; H3K9me2 novel context learning and associative learning Mll;eed mice – more profound effect in Mll heterozygotes HDAC inhibition –H3K4me3 ↑ H3K9me2 ↓, more freezing behaviour observed Zif268 and bdnf – more DNA methylation

9. Current Research The “Histone” Code → Neuro-epigenetics Transient and persistent changes Bidirectional relationship – learning produces novel epigenetic marks, pre-existing epigenetic marks set threshold for learning (metaplasticity) Pending further investigation –Ubiquitination and Sumoylation of Histones –Process of DNA demethylation – 5mC to 5hmC –Histone subunit exchange –Role of miRNAs Possibilities –Treatment of memory impairment disorders –Age-related memory loss –treated with HDAC inhibitors to restore memory –Extinction of traumatic memories of patients suffering from phobias or anxiety

10. Histone modifications and effects on memory consolidation Phosphorylation and acetylation of histones usually leads to enhancement of memory, while methylation of histones and DNA can lead to both enhancement and impairment, representing a complex function.

11. Epigenetic Determination of Learning and Memory Transcriptional and translational changes → structural and functional changes → changes in synaptic efficiency

12. References Gupta, S., Kim, S. Y., Artis, S., Molfese, D. L., Schumacher, A., Sweatt, J. D., … Lubin, F. D. (2010). Histone methylation regulates memory formation. The Journal of Neuroscience: The Official Journal of the Society for Neuroscience, 30, 3589–3599. doi:10.1523/JNEUROSCI.3732-09.2010 Jarome, T. J., & Lubin, F. D. (2014). Epigenetic mechanisms of memory formation and reconsolidation. Neurobiology of Learning and Memory. Josselyn, S., & Frankland, P. W. (2014). Another twist in the histone memory code. Cell Research. Levenson, J. M., O’Riordan, K. J., Brown, K. D., Trinh, M. A., Molfese, D. L., & Sweatt, J. D. (2004). Regulation of histone acetylation during memory formation in the hippocampus. Journal of Biological Chemistry, 279(39), 40545–40559. Zovkic, I. B., Guzman-Karlsson, M. C., & Sweatt, J. D. (2013). Epigenetic regulation of memory formation and maintenance. Learning & Memory (Cold Spring Harbor, N.Y.), 20, 61–74. doi:10.1101/lm.026575.112