Download - P oly c omb G roup PcG Regulators
![Page 1: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/1.jpg)
Polycomb Group PcG Regulators
Identified in Drosophila genetically
Mutations in PcG proteins cause ectopic expression of homeotic genes
ANT-C and BX-C(Antennapedia and Bithorax Complex)
![Page 2: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/2.jpg)
Homeotic mutations transcriptional regulation defects
Mutant: T3 haltere into T2 wing
![Page 3: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/3.jpg)
PcG
Three complexes
PRC2
PRC1
PhoRC
![Page 4: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/4.jpg)
![Page 5: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/5.jpg)
PRC2E(z): HMT H3K27me
enhancer of zeste
Su(z)12: Zn finger proteinsuppressor of zeste; E(z) cofactor
ESC/EED: WD40 protein interaction domainsspecificity of HMT; E(z) cofactor
extra sex combs
P55: RbApAB46/48/NURF55 (CAF subunit; sometimes complexed with HDACs)--------------------------------------------------------PCL: polycomb like; PhD and Tudor domainsStimulates enzyme activity, role in recruitment?
![Page 6: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/6.jpg)
Simon and Kingston, Nature Reviews Mol Cell Biol, 2009
![Page 7: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/7.jpg)
PRC2 unique roles
Required for X-inactivation, imprinting
Stem cell maintenance
EZH2 (human E(z)) important marker for tumor metastasis)
![Page 8: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/8.jpg)
![Page 9: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/9.jpg)
PRC2 is required for Xi in the extra-embryonic lineageand in the embryo
puts on H3K27me mark
occurs right after Xist coating
Xist is necessary and sufficient for PRC2 recruitment
![Page 10: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/10.jpg)
PRC2 recruitment by long nc RNAs
XIST (X-inactivation)
Kcnq1ot1 (Imprinting)
Hotair (Hox gene expression)
![Page 11: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/11.jpg)
![Page 12: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/12.jpg)
Pc: polycombhas N-terminal chromodomainbinds me H3K27
PH: polyhomeoticZn- finger, Q-repeats
Psc: posterior sex combs (human: Bmi1)Ring finger protein interaction domainacts also as suppressor of telomeric position effect
dRING: Ubiquitin ligase H2A K119ub
PRC1
![Page 13: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/13.jpg)
Simon and Kingston, Nature Reviews Mol Cell Biol, 2009
![Page 14: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/14.jpg)
Lund and Lohuizen COCB16 239-246 (2004)
Two step process?
PRC1 is also recruited independently of H3K27me3PRC1 occupies large domains, stable repression
![Page 15: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/15.jpg)
PRC1 functions
Inhibits transcription
Blocks SWI/SNF chromatin remdoleing
Compacts chromatin arrays
![Page 16: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/16.jpg)
Second complex: Ubiquitylation of H2A?
PRC1-like
Simon and Kingston, 2009
![Page 17: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/17.jpg)
![Page 18: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/18.jpg)
PhoRC
Pho: DNA binding protein
SFMBT: can bind to certain methylated lysines on H3
![Page 19: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/19.jpg)
YY1
![Page 20: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/20.jpg)
Mammals (and plants)Many PRC2 and PRC1 complexes
Organism complexity, response to the environment
Simon and Kingston, 2009
![Page 21: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/21.jpg)
PRE
PcG Response Element
cis-acting DNA elements that PcG proteins bind toin Drosophila
Many PREs in homeotic gene regulatory regions
PREs are comprised of many factor biding sites
![Page 22: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/22.jpg)
PREs have many binding sites for certain TFs
![Page 23: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/23.jpg)
PREs
Genomewide studies:PRC1 binding largely overlaps with Pho bindingLess (but still considerable) overlap with GAF and DSP1
Binding site mutations: Pho and GAF contribute.
![Page 24: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/24.jpg)
Drosophila
PRC1
PRC1
PRC2
![Page 25: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/25.jpg)
PcG recruitment
Noncoding RNAs can recruit PRC2PhoRC binds PRE & can recruit PRC2
result: H3K27me
H3K27me can recruit PRC1PhoRC binds PRE & can recruit PRC1
PREs are devoid of nucleosomesPhoRC can wrap DNA around itself
in presence of PRC1
![Page 26: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/26.jpg)
Simon and Kingston, 2009
![Page 27: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/27.jpg)
![Page 28: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/28.jpg)
![Page 29: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/29.jpg)
HOX gene regulation
Normal expression
![Page 30: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/30.jpg)
PREs have many binding sites for certain TFs
![Page 31: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/31.jpg)
Fab-7
Enhancer blocker between iab-6 and iab-7 regulatoryregions
Blocks enhancers and binding site PcG!
Deletion causes homeotic phenotypes
Is regulated, allows is tissue/stage specific enhancer blocker
![Page 32: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/32.jpg)
Molecular Cell, Vol. 8, 1145–1151, November, 2001,
Developmentally regulatedenhancer blockers
![Page 33: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/33.jpg)
HOX genes turned on in certain regions
PcG maintain this pattern (memory)
Also required for proper spatial regulationlater in development
![Page 34: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/34.jpg)
How does the silencing memory work?
PcG required continuously (adult)maintained through cell cyclemost PcG leaves chromatin during mitosissome remains = mark?
H3K27 = mark? PRE = mark?
Also associated with histone deacetylation
other (H3K9) histone methylationDNA methylation
memory
![Page 35: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/35.jpg)
PhoRcNoncoding RNA
![Page 36: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/36.jpg)
Mechanism for PcG repression
Generates large H3K27me domains Compacts chromatin Prevents PolII elongationForm PcG bodies (subnuclear silencing compartments)Recruits HDACs, DNMTsInhibits SWI/SNF activity
![Page 37: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/37.jpg)
Science 308 (2005)
![Page 38: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/38.jpg)
mammals
![Page 39: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/39.jpg)
Drosophila
![Page 40: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/40.jpg)
Block of transcription elongation?
Simon and Kingston, 2009
![Page 42: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/42.jpg)
Supressor screen in polycomb mutants
Look for wild-type looking fliessuppress ectopic HOX gene expression
Identified trithorax group (TrxG) proteins
![Page 43: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/43.jpg)
Simon and Kingston, 2009
![Page 44: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/44.jpg)
TrxG
Brahma: SWI/SNF ATPaseMoiraOsa
Ash1, 2
Trithorax (TRX)/MLL
Identified as suppressors of PcG mutations
![Page 45: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/45.jpg)
TrxG
TRX: H3K4 KMT
ASH1: H3K4 KMT, also H3K36
H3K4-(me)3: TrxG binding inhibits PcG binding inhibits HP1 binding
![Page 46: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/46.jpg)
PREs have many binding sites for certain TFs
![Page 47: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/47.jpg)
Often PcG and TrxG bind the same element
PRE
Continuous inactivation required for PcG silencing
Transcription through PRE causes loss of silencing
![Page 48: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/48.jpg)
Homeotic Gene Expression
Transcription initiationInduced by maternal gene products and segment identity gene products in 3.5 hr embryo
Transcription maintenance5-7 hr embryo: activators are goneTrxG maintenance of activated state of homeotic genesPcG maintenance of repressed state of homeotic genes
![Page 49: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/49.jpg)
Mammals
Some PREs recently identified
TrxG and PcG opposing roles conserved
Also in plants
![Page 50: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/50.jpg)
PcG (and TrxG)
Not just transcriptional memory
more dynamic
gets reset
Cell fate not as fixed as was previously assumed
![Page 51: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/51.jpg)
Noncoding RNA
![Page 52: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/52.jpg)
![Page 53: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/53.jpg)
Not this simple
![Page 54: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/54.jpg)
Opposing roles of TrxG and PcG
Reversibility of marks UTX JMJD3 part of TrxG complex LSD1 and JARID associate with PcG complex
![Page 55: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/55.jpg)
Bivalent domains
![Page 56: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/56.jpg)
![Page 57: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/57.jpg)
Embryonic stem cells
PcG proteins occupies promoters of
differentiation genes
prevents differentiation
![Page 58: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/58.jpg)
![Page 59: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/59.jpg)
Associated with poised polymerase
![Page 60: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/60.jpg)
Some concerns
Contradictory data
Marks not shown to be present at the same locus: population effect?
In some cases no evidence for poised PolII.
![Page 61: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/61.jpg)
Going further
Both TrXG and PcG stable epigenetic memoryBoth can be reversed; needs multiple steps/cuesGenerally TrxG and PcG have a dynamic role
Lund and Lohuizen COCB16 239-246 (2004)
![Page 62: P oly c omb G roup PcG Regulators](https://reader036.vdocuments.mx/reader036/viewer/2022081513/568158d4550346895dc61aa8/html5/thumbnails/62.jpg)
PcG silencing reversal (needs several steps)
•Resetting by transcription
•Signaling repression of PcG(WNT/TGFB/HH)
•Posttranslational modifications PcG(BMI1-P dissociates)
•Recruitment of TrxG proteinsMLL plus H3K27 demethylasechromatin remodeling