lecture 4 - TA Hongfei Fangs office hours: Change to...

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1 TA Hongfei Fang’s office hours: Change to 6pm-7pm on Wednesday at the CLICS TA Lab
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2 Molecular Basis of Human Diseases BIMM 110 Spring 2010 Lecture 4 Epigenetics, Genomic Imprinting and X-chromosome inactivation
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3 The study of chemical modification of specific genes or gene-associated proteins of an organism. Epigenetic modifications can define how the information in genes is expressed and used by cells. We are mainly going to discuss genomic imprinting , including two related diseases, and X-chromosome inactivation in this session. Epigenetics
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4 Mendelian Genetics
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5 An allele from one parent always determines the phenotype, and the other allele, although present and not mutated, is not expressed. Paternal autosomal inheritance Maternal autosomal inheritance Genomic Imprinting!
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6 Genomic imprinting is an epigenetic phenomenon – the expression of only one allele from a parent and inactivation of the counterpart allele from the other parent. The silenced allele is generally called imprinted gene . maternally imprinted – paternally expressed paternally imprinted – maternally expressed Genomic imprinting
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7 Heritable and Reversible Heritability refers to the transmission of the gene imprint over rounds of cell division and generations. However, in NON-Mendelian fashion ! Reversibility refers to that the imprinted locus can be erased and reset depending on the sex of the parent. Genomic imprinting
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8 10_25.jpg A* - maternally imprinted; B* - paternally imprinted
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9 Any questions?
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10 DNA methylation of cytosine at CpG island is the principal means of imprinting Genomic imprinting 1 2 3 4 5 6
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11 DNA methylation methylation at sites such as 5’. .C C GG. .3’ 3’. .GG C C..5’ methyl donor: S-adenosylmethionine (SAM) enzyme: methyltransferase(s) de novo methylation maintenance methylation IE Scheffler
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12 IE Scheffler S -Adenosyl methionine
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13 de novo DNA methylation 1 maintenance DNA methylation
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14 Me Me Me Me Me Me Me Me Me Me Me Me Me Me Me Me Me Me unmethylated new DNA strands to be methylated by maintenance methyltrasferase DNA Replication Fork 5’ 3’ IE Scheffler
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15 10_18.jpg DNA methyltransferase I (DNMT1) recognizes hemimethylated site and add methyl group to cytosine
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16 How can the methylation status be experimentally determined? 1. Distinction by the use of two restriction enzymes, e.g. 5’…C C GG…3’ HpaII is sensitive to methylation 3’…GG C C…5’ MspI is insensitive to methylation 2. Sequencing DNA after special treatment
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17 Polymerase chain reaction (PCR) DNA sequencing Bisulfite sequencing
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18 10_21.jpg Gene expression in this locus is silenced DNA methylation induces histone H3 deacetylation and methylation at lysine 9. Histone H3 lysine methylation promotes the binding of HP1 (heterochromotin protein 1) and induces chromatin condensation.
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lecture 4 - TA Hongfei Fangs office hours: Change to...

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