Chromatin Remodeling *Cytosine Methylation* Glossary Epigenetic: Heritable changes in gene function, not caused by changes in the DNA sequence itself. CpG (island): Stands for Cytosine (P-bond) Guanine. Refering to a small region of DNA with a high frequency of CG sequences with respect to other regions. Heterochromatin: Highly condensed, and transcription- suppressed sections of DNA Housekeeping Genes: Undergo active transcription for basic cell functions. Glossary – Enzymes DNMT: DNA Methyltransferase -1, 3a, 3b, L H3K9: Lysine 9 of Histone 3 Suv39h: histone methyltransferase (H3K9) MeCP/MBD: Methyl CpG Binding domain protein. Glossary – Enzymes HP1: Adaptor molecule. HDAC: Histone DeAcetylating protein PcG: Polycomb Group (and repressor complexes) EZH2, Eed, Su212: series of proteins that interact with PcG. Cytosine Methylation - Overview • A method of gene regulation and suppression. • Occurs when a methyl group is added to Carbon- 5, of the pyrimidine ring via enzyme action. • An Epigenetic process • Methylation patterns are passed on to daughter strands during replication. • Closely linked to histone modification • Improper methylation can lead to the development of genetics disorders. Pattern of Inheritance • Function of DNMT 1 as a Maintenance Enzyme • CpG methylation only opposite another CpG which is already methylated. • Non-methylated CpG pairs are not recognized by DNMT 1 Pattern of Inheritance (Molecular Biology Web Book: 2005) Identifying Methylation Sites • Bisulfate sequencing • Conversion of non-methyl. Cytosine to Uracil • No change to methyl. Cytosine • Sequenced through computer software identifying locations of methylation • Two concentrations of methylation (low or high) DNA & Histone Modification • Linkage between both DNA Methylation and Histone Modifications • Histone Deacetylation, Methylation • Which process is the initiator? • Self-reinforced Model DNA & Histone Modification Methylation: • The addition of methyl groups onto sites such as H3K9 Deacetylation: • The removal of acetyl groups from histone • Loses neutral charge on molecule DNA & Histone Modification • Two opposite theories on which processes depends on which. • Theory: Histone Mod. depends on DNA methylation – DNMTs, MBDs recruiting HDAC • Theory: DNA methylation depends on Histone Mod. – Suv39h knockouts, requirements of a “reader” molecule. (Hp1) Self-Reinforced Model • Based on the idea DNA methylation and Histone Modification have a ‘flow’ of information. • Not a perfect model, does not fully explain gene silencing. However, a good explanation for permanent shut-off genes. Self-Reinforced Model • DNMT binds to HP1, DNA is methylated close to H3K9 site. • Causes MBD to bind with DNA, recruiting HDAC; H3K9 deacetylated. • MBD also attracts H3K9 methyltransferase and an additional HP1; H3K9 is methylated. Self-Reinforced Model Other DNA and Histone connections • H3K27 transcription repression (PcG, EED, EZH2 complex – “PRC” Polycomb Repressive Complex. • PRC involvement in X-inactivation, Hox gene silencing, cancer metastasis • H4K20 methylation. Lack of in some cancer cells Improper Methylation • Retts syndrome – loss of function MeCP2 (mental retardation in young girls) • ICF syndrome – DNMT3b mutation (abnormal immune system) • Total DNMT knockout in mice: fetus dies before birth • MBD2 assistance in hypermethylated cancer genes References: “A Simplified Description of DNA Methylation.” DNA Methylation Society. Oct 11, 2005. http://www.dnamethsoc.com/ Fuks, Francois. “DNA Methylation and histone modifications: teaming up to silence genes.” Current Opinion in Genetics. 15 (2005): 490-495 “ DNA Methylation and CpG Island.” Molecular Biology Web Book. 2005. http://www.web-books.com/MoBio/ “DNA Methylation.” Wikipedia, the Online Encyclopedia. 2005. http://en.wikipedia.org/wiki/DNA_methylation “Epigenetics.” Wikipedia, the Online Encyclopedia. 2005. http://en.wikipedia.org/wiki/Epigenetic “All HEPped Up about Methylation.” PLoS Biol 2(12): e433. November 23, 2004. http://biology.plosjournals.org/perlserv/?request=get- document&doi=10.1371/journal.pbio.0020433 Questions? Comments? Slipper Limpets? ?
Pages to are hidden for
"Chromatin Remodeling"Please download to view full document