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Epigenetics: ”From Phenomenon to Field” and Impact on Plastic Surgery Research. Basic Science Seminar Series University of Michigan Department of Surgery Section of Plastic Surgery Brent M. Egeland, MD October 13, 2007. Outline. Importance History Definitions Chemistry
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Epigenetics: ”From Phenomenon to Field” and Impact on Plastic Surgery Research Basic Science Seminar Series University of Michigan Department of Surgery Section of Plastic Surgery Brent M. Egeland, MD October 13, 2007
Outline • Importance • History • Definitions • Chemistry • Laboratory Techniques • Implications in Plastic Surgery
Definition: Epigenetics • Waddington 1942 • Originally a combination of the words "genetics" and "epigenesis" • Epigenesis: differentiation of cells from a totipotent state in embryonic development (used in contrast to "preformationism").
Definition: Epigenetics • 69th CSH Symposia (2004): • Conference Dedicated to Epigenetics • No definition could be agreed upon • ”An epigenetic phenomenon is a switch-like change in phenotype that is heritable, but does not involve DNA mutation.” C. David Allis
Why Epigenetics? • Post-Genomic Era • ENCODE • Genomics and proteomics is not enough • Contol of above beyond promoters and regulators is of utmost importance in: • Oncogenesis • Stem Cell Biology • Genetic therapy • Aging
History • Coalesced into field of study that affects all areas of biology • Collection of apparently disparate phenomena • Over 1000 manuscripts on topic • First observations dates to 1941 • HJ Mueller ”eversporting displacement” • McClintock noted that these positional effects were the basis of ”mutible loci”
History • X-Chromosome Inactivation • Pre-32 cell stage • mosaic cell population
History • 1980's: Molecular Biology and Genetics • 1990's: Genomics • 2003: Human Genome Complete • 2004: ENCODE • 2005: NCI announce: • Human Epigenome Project
Definition: Epigenome ”Sum of genome-wide epigenetic patterns, distinguishes and defines one tissue from another, stem cells from somatic cells, and aged from young cells.” National Cancer Institute (NCI), Division of Cancer Biology (DCB) Workshop on Defining the Epigenome: Addressing the Value and Scope of a Human Epigenome Project November 28–29, 2005 Andrew P. Feinberg and Peter A. Jones
Chromatin • Euchromatin: • Uncompacted • Active • Heterochromatin: • Compacted • Untranscribed • Changes with cell cycle
Beads on a String • H1: Linker histone: contacts the exit/entry of the DNA strand on the nucleosome. • Linker DNA between Histones
DNA Packaging • Varys greatly with Cell Cycle • DNA never completely ”naked”
Scaffold or Dynamic? • Is chromatin simply a scaffold for packaging DNA?
Dynamic • Histones are Modified • DNA is Modified • Heritable transcription states
Histone Modifications K K Acetylation = Transcriptional Competence Methylation= Transcriptionally Silenced
DNA Cellular Differentiation • All cells inherit the same DNA sequences • Cellular differentiation processes rely strongly on epigenetic rather than genetic inheritance.
DNA Modification • Chemical modification of DNA • Can be inherited without sequence change • Part of the epigenetic code • Methylation is most characterized epigenetic mechanism • Commonly occurs at ”junk” DNA
Laboratory Techniques • Chromatin Immunoprecipitation • Inhibition of Deacetylases (HDAC-I) • Site-specific analysis of histone methylation • Multigenerational assesment of above • Methylation-specific PCR in-situ Hybridization • Q-PCR in Combination with ChIP
Consequences • Genome is static • Genotype • Germ Cell Inheritance • Epigenome is dynamic • Phenotype • Somatic epigenetic inheritance • Cellular "memory" • Most terminally (irreversibly) differentiate • Morphogens activate/silence genes – DNA is not altered
Consequences • Mammals cannot respond to loss of some tissues • Inability to regenerate limbs • Plant cells do not terminally differentiate
Evolution • Short-term adaptation • allowing for reversible phenotype • Allows multigenerational revisible phenotypic switch to express and repress that particular gene • DNA message is unchanged • Differential mutation rates associated with epigenetic features to control the mutation rates of particular genes
Teratogens • Exert effects on fetus by epigenetic means • Epigenetic effects may preserve effect of teratogen throughout life of child • Can a teratogen exert influence offspring? • Diethylstilbestrol: Second and possibly Third generation effects
Plastic Surgery • Fundamentally involved in clinical epigenetics • Aging • Oncology • Wound Healing • Basic Science in Plastic Surgery • Regenerative medicine • Stem Cell biology • Organogenesis • Neural plasticity
Oncology Clin Cancer Res 2007;13(13) July 1, 2007
Aging • Chronological or Epigenetically Defined? • Free-Radicals • Oxidants • Telomeres • methylation
Aging Change in phenotype with methylation of DNA.
Neuroal Plasticity • Why does the CNS lack plasticity? • What are the possibilitys of increasing this plasticity towards regenerative capacity?
The list goes on.... • Are there differing methylation signatures of fibroblasts in normal, hypertrophic, keloid scarring. • Can fibrotic tissue (fibroblasts) be reversed to form skin, bone, muscle? • Is cleft lip epigenetically inhereited?
Can we Modify Epigenetics? • Can methylation be reversed? • Rate decreased? • Environment? • Diet? • Pharmacologically?
Diet Agouti Gene: Yellow fur, obesity, diabetes, tumorogenesis Methyl Donor Diet: (onions, garlic, beets, folic acid, B12, genestein) No Supplements .
HCC: Histone deacetylase inhibitors (HDAC-I) & Demethylating agents Journal of Clinical Oncology, 2006 ASCO Annual Meeting Proceedings Part I. Vol 24, No. 18S (June 20 Supplement), 2006: 10066
Decitabine & Azacitidine 5-aza-2'-deoxycytidine • Mechanism of action: • Phosphorylation and direct insertion into DNA • Blocks effects of DNA methyltransferase • Causing hypomethylation fo DNA. • May reverse inactivation of supressor genes • Can lead to cytotoxicity, bone marrow suppression • aza- Azacitidine
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