analysis of a piwirelated gene implicates small rnas in ：一个piwi蛋白相关基因分析表明小rna.ppt

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1、RNAiinGenomeRearrangementandChromosomeSegragationinTetrahymenaKazufumiMochizuki,YifanLiu,KathleenKarrerandMartinA.GorovskyDepartmentofBiology,UniversityofRochester,Rochester,NY,USAThetwofeaturesofTetrahymenabiologythatwillbeemphasizedareitsnucleardimorphismandthegenomerearrangementsth

2、ataccompanydevelopmentofthesomaticmacronucleus.ItisalsoworthmentioningthatstudiesinTetrahymenaaregreatlyfacilitatedbythefactthatDNA-mediatedtransformationoccursentirelybyhomologousintegrationandbytherecentavailabiltyofthecompletegenomesequenceinsearchable(butnotyetannotated)form.Featu

3、resoftheTetrahymenaSystemNucleardimorphismMassivegenomerearrangementDNA-mediatedtransformationbyhomologousintegrationGenomesequence(searchable,butnotyetannotated)TetrahymenathermophilaMetazoanFungiCiliatePlant1.The2nucleiinTetrahymenaarethemacronucleus(Mac)andthemicronucleus(mic).Thei

4、rpropertiesareillustratedonthenextslide.2.Duringthesexualphaseofthelifecycle(conjugation)2cellsmateandtheMicundergoesmeiosistogiverisetopronucleithatarereciprocallyexchangedbetweenthe2cells,followedbyfertilization.Twopost-zygoticdivisionsfollowandtheproductsdevelopintonewMacsandnewMic

5、s.WhenthenewMacsbegintodevelop,theoldMacbecomespycnotic,undergoesanapoptosis-likedegradationandthendisappears.3.Duringmacronucleardevelopment,10-15%ofthemicronucleargenomeiseliminated.NuclearDimorphisminTetrahymenathermophilaMacronucleus(Mac)TranscriptionallyInert(VegetativeCells)Dipl

6、oid(2C);N=5MitoticDivisionGermlineSomaticlineTranscriptionallyActivePolyploid(~45C);N=250AmitoticDivisionLacks10~15%ofMicGenomeMicronucleus(Mic)Thenextslideillustratesthe2processesthataccountforDNAsequenceeliminationduringMacdevelopment:IES(Internaleliminatedsequence)removalandchromos

7、omefragmentation.InIESremoval,DNAsegmentsrangingfrom0.5-20kbareremovedandthesequencesflankingthemarerejoined.IESremovaloccursatabout6000sitesinthemacronucleargenomeandishighly,butnotperfectly,reproducible.IESremovalaccountsformostofthesequenceelimination.Inchromosomefragmentation,brea

8、kagea