Diferenciación celular: Diferenzas entre revisións

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Miguelferig (conversa | contribucións)
Miguelferig (conversa | contribucións)
Liña 65:
Alternately, upon receiving differentiation signals, PcG proteins are recruited to promoters of pluripotency transcription factors. PcG-deficient ES cells can begin differentiation but cannot maintain the differentiated phenotype.<ref name= "Christophersen"/> Simultaneously, differentiation and development-promoting genes are activated by Trithorax group (TrxG) chromatin regulators and lose their repression.<ref name= "Christophersen"/><ref name = "Guenther"/> TrxG proteins are recruited at regions of high transcriptional activity, where they catalyze the trimethylation of histone H3 lysine 4 (H3K4me3) and promote gene activation through histone acetylation.<ref name = "Guenther"/> PcG and TrxG complexes engage in direct competition and are thought to be functionally antagonistic, creating at differentiation and development-promoting loci what is termed a “bivalent domain” and rendering these genes sensitive to rapid induction or repression.<ref name = "Meissner">{{cite journal |pmid=20944600 |doi=10.1038/nbt.1684 |author=Meissner A |title=Epigenetic modifications in pluripotent and differentiated cells |journal=Nat Biotechnol |year= 2010 |volume=28 |issue=10 |pages=1079–88}}</ref>
 
=====DNAMetilación methylationdo ADN=====
RegulationA ofregulación geneda expression[[expresión isxénica]] furtherconséguese achievedademais throughpor DNAmedio methylationde metilación do ADN, inna cal a metilación whichmediada thepor [[DNAADN methyltransferasemetiltransferase]]-mediated methylationde ofresiduos cytosinede residues[[citosina]] inen dinucleótidos CpG dinucleotidesmantén maintainsa heritablerepresión repressionheredable byao controlar a controllingaccesibilidade DNAde accessibilityADN.<ref name = "Meissner"/> TheA majoritymaioría ofde sitios CpG sitesen incélulas embryonicnais stemembrionais cellsnon areestán unmethylatedmetiladas ande appearparecen toestar beasociados associatedcon withnucleosomas H3K4me3-carryingque nucleosomeslevan H3K4me3.<ref name= "Christophersen"/> UponDespois differentiationda diferenciación, aun smallpequeno numbernúmero ofde genesxenes, includingcomo o OCT4 ande o NANOG,<ref name = "Meissner"/> areestán methylatedmetilados ande theiros promotersseus repressed[[promotor to(xenética)|promotores]] preventreprimidos theirpara furtherimpedir expressiona súa futura expresión. Consistently,As DNAcélulas methylation-deficientnais embryonicembrionais stemcon cellsmetilación rapidlydeficiente enterentran rapidamente en [[apoptosisapoptose]] upondespois da súa diferenciación in vitro differentiation.<ref name= "Christophersen"/>
 
=====Posicionamento de nucleosomas=====