基因組甲基化1

基因組甲基化LiuQingyou20080318主要內(nèi)容基本概念基因組甲基化的原理基因組甲基化的研究方法基因組甲基化在胚胎發(fā)育中的模式與作用表觀遺傳學(xué)在基因組中除了DNA和RNA序列以外，還有許多調(diào)控基因的信息，它們雖然本身不改變基因的序列，但是可以通過基因修飾，蛋白質(zhì)與蛋白質(zhì)、DNA和其它分子的相互作用，而影響和調(diào)節(jié)遺傳的基因的功能和特性，并且通過細(xì)胞分裂和增殖周期影響遺傳。這就是表觀遺傳學(xué)（epigenetics），表觀遺傳學(xué)又稱為實(shí)驗(yàn)遺傳學(xué)、化學(xué)遺傳學(xué)、特異性遺傳學(xué)、后遺傳學(xué)、表遺傳學(xué)和基因外調(diào)節(jié)系統(tǒng)，它是生命科學(xué)中一個普遍而又十分重要的epigenetics是一種關(guān)于區(qū)別于DNA序列改變的基因表達(dá)可遺傳變化基因組含有兩類遺傳信息,一類是傳統(tǒng)意義上的遺傳信息,即DNA序列所提供的遺傳信息,另一類是表觀遺傳學(xué)信息,它提供了何時、何地、以何種方式去應(yīng)用遺傳信息的指令。組織細(xì)胞時空特異性的表達(dá)Nature441,143-145(11May2006)

CpGisolandCpG島位于基因的啟動子和第一個外顯子區(qū),富含CpG二核苷酸,故稱為CpG島,一般作為啟動子和基因復(fù)制的起始區(qū).在哺乳動物中,幾乎所有的甲基化位點(diǎn)均在CpG二核苷酸,并通過對CpG的甲基化來調(diào)節(jié)基因的表達(dá),因?yàn)镈NA的甲基化可改變?nèi)旧|(zhì)的結(jié)構(gòu),從而引起不同DNA結(jié)合蛋白的結(jié)合。所有管家基因和4%組織特異性基因的5′端調(diào)控區(qū)存在CpG高頻區(qū)CpG島（CpGislands）是指DNA上一個區(qū)域，此區(qū)域含有大量相聯(lián)的胞嘧啶（C）、鳥嘌呤（G），以及使兩者相連的磷酸酯鍵（p）。哺乳類基因中的啟動子上，含有約40%的CpG島（人類約70%）。一般CpG島的長度約300到3000個鹼基對（bp）。定義是指一個至少含有200bp的區(qū)域，其中GC所佔(zhàn)比例超過50%，且CpG的觀察值/預(yù)測值比例必須高於0.6。此部份的CpG島與基因相連，可用來作為限制酶的辨識位置。ZnFinger-DNAComplex

Helix-Turn-Helix

Motif

inDNABinding

DNAbindingThemodeofbindingismadesolelythroughinteractionswiththeDNAbackbone.Theplatinum-basedmolecules,“track”thebackboneofDNAthrougharepetitivemotif.ImageprovidedbyJ.Moniodis/VCU-UniversityofWesternAustralia.Farrell’sgroupmadethefindingwhileworkingtoimprovetheactionofcisplatin,oneofthemosteffectiveanti-cancerdrugsintheclinic.DiscoveryofthenewmodeofDNAbindingisthefirstsincetwoscientistsexaminingdruginteractionswithDNAmadeseparatediscoveriesinthe1960sand1970sthatsetthestandardfordrugdesignefforts.

鉑複合物需要電荷和順式位置的平衡才能表現(xiàn)其抗腫瘤效果前已知鉑複合物可以廣泛地抑制動物和人類的腫瘤DNA甲基化DNA甲基化是指真核生物以S-腺苷甲硫氨酸(SAM)作為甲基供體,在DNA甲基轉(zhuǎn)移酶(DNAmethyltransferases,DNMTs)的作用下,將甲基轉(zhuǎn)移到特定堿基C上,形成5甲基胞嘧啶(5mC)。FunctionsofDNAmethylationinmammals

TranscriptionalgenesilencingChromatincompactionGenomestabilitySuppressionofhomologousrecombinationbetweenrepeatsGenomedefense（抵御）Xchromosomeinactivation(females)Methylgroups

(red)inDNA

(mapby

Dr.CraigCooney)

DNAMethylationReactionCatalyzedbyDNAMethyltransferase(DNMT)

S-腺苷甲硫氨酸(SAM)MoleculargraphicsofmethylatedDNA

BacterialDNAmethyltransferaseintheactofcatalysis.

DNMT與DNA相互作用investigatingCalculationsofbindingaffinitiesforMGMT/inhibitorcomplexeswithcomputersimulationtechniquesDNA甲基化轉(zhuǎn)移酶今后可能象限制性內(nèi)切酶一樣成為實(shí)驗(yàn)室常用的工具酶。來自立陶宛的HHMI研究人員Saulius

Klimasauskas領(lǐng)導(dǎo)的小組利用DNA甲基化轉(zhuǎn)移酶把一些化學(xué)分子轉(zhuǎn)移到DNA上，為基因診斷和納米生物技術(shù)的應(yīng)用奠定了基礎(chǔ)，有關(guān)結(jié)果發(fā)表在《Nature

Chemical

Biology》。DNMT1themostabundantandcatalyticallyactiveenzymeinmostcelltypes,whichassociateswithS-phasereplicationfociviainteractionwithPCNA(Yokochietal.2002).

Itsprimaryroleisbelievedtobethatofamaintenancemethyltransferase(Bestor2000),copyingDNAmethylationpatternsfollowingDNAreplication.

MurineknockoutsofDnmt1areembryoniclethalatdayE8.5.

DNMT2functionremainsunclearsinceitpossessesverylowenzymaticactivity

invitroandknockoutofthegeneinmiceproducesnodiscernablephenotype(Okanoetal.1998;Yoderetal.1998;Hermannetal.2003).

DNMT3AandDNMT3Bdenovomethyltransferasessincetheyarehighlyexpressedatthestageofmurineembryonicdevelopmentwhenwavesofdenovomethylationareoccurringinthegenome(Okanoetal.1999).

MurineDnmt3aknockoutmicearebornlivebutdiebeforereachingfourweeksofage.

Dnmt3bknockoutmiceareembryoniclethalby~dayE14.5.

Dnmt3aknockoutmiceexhibitsubtleDNAmethylationdefectsinmaternallyimprintedregions(Hataetal.2002),whileDnmt3bknockoutmiceshowmarkeddemethylationofpericentromericsatelliterepeats(Okanoetal.1999).

knockoutofDnmt3L,whichisnotafunctionalenzymeduetolackofcriticalcatalyticsitemotifs,resultsinmaternalDNAmethylationimprintfailureandmalesterilityinmice(Hataetal.2002).TherearecurrentlyfivemembersoftheDNAmethyltransferasefamilyinmammaliancells.

AlloftheseproteinshavetheircatalyticdomainintheC-terminalregion,and(withtheexceptionofDNMT2)aregulatorydomainintheN-terminalregion.

Mostoftheprotein-proteininteractionsaremediatedbytheN-terminalregion.DNAmethyltransferasesinteractwithmanyotherproteins.

ProteinsinvolvedinmodulatingchromatinstructureincludepRb,HDACs,HP1,SIN3A,hSNF2H,SUV39H1,andhCAP-C/E.

Transcriptionallyactivechromatinregionstendtobehyperacetylatedandhypomethylated.

IfaregionofDNAorageneisdestinedforsilencing,chromatinremodelingenzymessuchashistonedeacetylasesandATP-dependentchromatinremodelerslikelybeginthegenesilencingprocess.

OneormoreoftheseactivitiesmayrecruitDNAmethyltransferaseresultinginDNAmethylation,followedfinallybyrecruitmentofthemethyl-CpGbindingproteins.

TheregionofDNAwillthenbeheritablymaintainedinaninactivestate.

DNM與染色質(zhì)remodelDNAMethylationasaBiomarkerforCancerLossofnormalDNAmethylationpatternsinsomaticcellsresultsinlossofcellgrowthcontrol.

Innormalcells,DNAmethylationisfoundpredominantlyintherepetitivefractionofthegenome,includingsatelliteDNAandparasiticelements(LINES,SINES,endogenousretroviruses)(Yoderetal.1997).

Tumorcellsexhibitglobalhypomethylationofthegenomeaccompaniedbyregion-specifichypermethylationevents(Baylinetal.2001).

MostofthehypomethylationoccursinrepetitiveDNAthatisnormallyheavilymethylated(Yoderetal.1997).

Innormalcells(top)DNAmethylationisconcentratedinrepetitiveregionsofthegenomeandmostCpGislandpromotersareunmethylated.

Intumorcells,thecompartmentalizationbreaksdownandrepetitiveDNAlosesmethylationwhileCpGislandpromotersacquireit,resultinginsilencingoftheassociatedgene.

TheDNMTsarelikelytargetedtoparticularregionsviaprotein-proteininteractionswithinchromatin.DNAMethylationandChromatinRemodelingModificationstothechromatinandthecorehistone‘tails’impactgeneexpressionandtheabilityofproteinsthatactonDNAtoaccesstheirtargetsequences.

Recentstudiesindicatethattheseepigeneticprocesses,aswellaschromatinremodeling,cooperatetocontrolchromatinstructureandultimatelygeneexpressionandDNAmethylationitself.

ChromatinremodelingproteinsoftheSNF2family,whichutilizeATPtoalterthestructureofchromatinthroughdisruptionofhistone/DNAcontacts(Havasetal.2001),alsoinfluenceDNAmethylationpatterns.

mammalianLsh,SNF2helicasefamilymemberexertsprofoundeffectsonDNAmethylationpatterns.

Lsh

knockoutmiceexhibitdrasticlossesofDNAmethylation,bothinrepetitiveelementsand