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Drosophila Kismet regulates histone H3 lysine 27 methylation and early elongation by RNA polymerase II.

Srinivasan S, Dorighi KM, Tamkun JW - PLoS Genet. (2008)

Bottom Line: Although we observed significant overlap between the distributions of KIS-L, ASH1, and TRX on polytene chromosomes, KIS-L did not bind methylated histone tails in vitro, and loss of TRX or ASH1 function did not alter the association of KIS-L with chromatin.By contrast, loss of kis function led to a dramatic reduction in the levels of TRX and ASH1 associated with chromatin and was accompanied by increased histone H3 lysine 27 methylation-a modification required for Polycomb group repression.Our findings suggest that KIS-L promotes early elongation and counteracts Polycomb group repression by recruiting the ASH1 and TRX histone methyltransferases to chromatin.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA, USA.

ABSTRACT
Polycomb and trithorax group proteins regulate cellular pluripotency and differentiation by maintaining hereditable states of transcription. Many Polycomb and trithorax group proteins have been implicated in the covalent modification or remodeling of chromatin, but how they interact with each other and the general transcription machinery to regulate transcription is not well understood. The trithorax group protein Kismet-L (KIS-L) is a member of the CHD subfamily of chromatin-remodeling factors that plays a global role in transcription by RNA polymerase II (Pol II). Mutations in CHD7, the human counterpart of kis, are associated with CHARGE syndrome, a developmental disorder affecting multiple tissues and organs. To clarify how KIS-L activates gene expression and counteracts Polycomb group silencing, we characterized defects resulting from the loss of KIS-L function in Drosophila. These studies revealed that KIS-L acts downstream of P-TEFb recruitment to stimulate elongation by Pol II. The presence of two chromodomains in KIS-L suggested that its recruitment or function might be regulated by the methylation of histone H3 lysine 4 by the trithorax group proteins ASH1 and TRX. Although we observed significant overlap between the distributions of KIS-L, ASH1, and TRX on polytene chromosomes, KIS-L did not bind methylated histone tails in vitro, and loss of TRX or ASH1 function did not alter the association of KIS-L with chromatin. By contrast, loss of kis function led to a dramatic reduction in the levels of TRX and ASH1 associated with chromatin and was accompanied by increased histone H3 lysine 27 methylation-a modification required for Polycomb group repression. A similar increase in H3 lysine 27 methylation was observed in ash1 and trx mutant larvae. Our findings suggest that KIS-L promotes early elongation and counteracts Polycomb group repression by recruiting the ASH1 and TRX histone methyltransferases to chromatin.

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Related in: MedlinePlus

Loss of TRX and ASH1 function also leads to increased H3K27 methylation.The levels of H3K27me3 (A–D, red) on polytene chromosomes isolated from wild-type (A, C), ash122/ash117 (B) and trx1 (D) larvae were detected by double-label indirect immunofluorescence microscopy. H3K27me3 levels are higher on polytene chromosomes isolated from ash122/ash117 and trx1 mutants as compared to wild-type chromosomes. As an internal control, the chromosomes were simultaneously stained with antibodies against the RPB1 subunit of RNA Pol II (inset in lower right corner of A–D, green).
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pgen-1000217-g010: Loss of TRX and ASH1 function also leads to increased H3K27 methylation.The levels of H3K27me3 (A–D, red) on polytene chromosomes isolated from wild-type (A, C), ash122/ash117 (B) and trx1 (D) larvae were detected by double-label indirect immunofluorescence microscopy. H3K27me3 levels are higher on polytene chromosomes isolated from ash122/ash117 and trx1 mutants as compared to wild-type chromosomes. As an internal control, the chromosomes were simultaneously stained with antibodies against the RPB1 subunit of RNA Pol II (inset in lower right corner of A–D, green).

Mentions: A recent study showed that loss of ash1 function in the haltere discs of third instar larvae results in the spread of H3K27me3 into the coding region of the actively transcribed Ubx gene [25]. Thus, KIS-L may indirectly counteract H3K27 methylation by promoting the association of ASH1 with chromatin. To investigate this possibility, we compared the level and distribution of H3K27me3 on the salivary gland polytene chromosomes of wild-type and ash1 mutant larvae. As observed in kis mutants, the level of H3K27me3 is dramatically elevated on the salivary gland polytene chromosomes of ash122/ash117 larvae relative to wild-type (Figure 10A and B). A similar effect was observed in trx1 homozygotes reared at 29° (Figure 10C and D). These findings suggest that KIS-L counteracts Polycomb group repression by promoting the association of ASH1 and TRX with chromatin.


Drosophila Kismet regulates histone H3 lysine 27 methylation and early elongation by RNA polymerase II.

Srinivasan S, Dorighi KM, Tamkun JW - PLoS Genet. (2008)

Loss of TRX and ASH1 function also leads to increased H3K27 methylation.The levels of H3K27me3 (A–D, red) on polytene chromosomes isolated from wild-type (A, C), ash122/ash117 (B) and trx1 (D) larvae were detected by double-label indirect immunofluorescence microscopy. H3K27me3 levels are higher on polytene chromosomes isolated from ash122/ash117 and trx1 mutants as compared to wild-type chromosomes. As an internal control, the chromosomes were simultaneously stained with antibodies against the RPB1 subunit of RNA Pol II (inset in lower right corner of A–D, green).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2563034&req=5

pgen-1000217-g010: Loss of TRX and ASH1 function also leads to increased H3K27 methylation.The levels of H3K27me3 (A–D, red) on polytene chromosomes isolated from wild-type (A, C), ash122/ash117 (B) and trx1 (D) larvae were detected by double-label indirect immunofluorescence microscopy. H3K27me3 levels are higher on polytene chromosomes isolated from ash122/ash117 and trx1 mutants as compared to wild-type chromosomes. As an internal control, the chromosomes were simultaneously stained with antibodies against the RPB1 subunit of RNA Pol II (inset in lower right corner of A–D, green).
Mentions: A recent study showed that loss of ash1 function in the haltere discs of third instar larvae results in the spread of H3K27me3 into the coding region of the actively transcribed Ubx gene [25]. Thus, KIS-L may indirectly counteract H3K27 methylation by promoting the association of ASH1 with chromatin. To investigate this possibility, we compared the level and distribution of H3K27me3 on the salivary gland polytene chromosomes of wild-type and ash1 mutant larvae. As observed in kis mutants, the level of H3K27me3 is dramatically elevated on the salivary gland polytene chromosomes of ash122/ash117 larvae relative to wild-type (Figure 10A and B). A similar effect was observed in trx1 homozygotes reared at 29° (Figure 10C and D). These findings suggest that KIS-L counteracts Polycomb group repression by promoting the association of ASH1 and TRX with chromatin.

Bottom Line: Although we observed significant overlap between the distributions of KIS-L, ASH1, and TRX on polytene chromosomes, KIS-L did not bind methylated histone tails in vitro, and loss of TRX or ASH1 function did not alter the association of KIS-L with chromatin.By contrast, loss of kis function led to a dramatic reduction in the levels of TRX and ASH1 associated with chromatin and was accompanied by increased histone H3 lysine 27 methylation-a modification required for Polycomb group repression.Our findings suggest that KIS-L promotes early elongation and counteracts Polycomb group repression by recruiting the ASH1 and TRX histone methyltransferases to chromatin.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA, USA.

ABSTRACT
Polycomb and trithorax group proteins regulate cellular pluripotency and differentiation by maintaining hereditable states of transcription. Many Polycomb and trithorax group proteins have been implicated in the covalent modification or remodeling of chromatin, but how they interact with each other and the general transcription machinery to regulate transcription is not well understood. The trithorax group protein Kismet-L (KIS-L) is a member of the CHD subfamily of chromatin-remodeling factors that plays a global role in transcription by RNA polymerase II (Pol II). Mutations in CHD7, the human counterpart of kis, are associated with CHARGE syndrome, a developmental disorder affecting multiple tissues and organs. To clarify how KIS-L activates gene expression and counteracts Polycomb group silencing, we characterized defects resulting from the loss of KIS-L function in Drosophila. These studies revealed that KIS-L acts downstream of P-TEFb recruitment to stimulate elongation by Pol II. The presence of two chromodomains in KIS-L suggested that its recruitment or function might be regulated by the methylation of histone H3 lysine 4 by the trithorax group proteins ASH1 and TRX. Although we observed significant overlap between the distributions of KIS-L, ASH1, and TRX on polytene chromosomes, KIS-L did not bind methylated histone tails in vitro, and loss of TRX or ASH1 function did not alter the association of KIS-L with chromatin. By contrast, loss of kis function led to a dramatic reduction in the levels of TRX and ASH1 associated with chromatin and was accompanied by increased histone H3 lysine 27 methylation-a modification required for Polycomb group repression. A similar increase in H3 lysine 27 methylation was observed in ash1 and trx mutant larvae. Our findings suggest that KIS-L promotes early elongation and counteracts Polycomb group repression by recruiting the ASH1 and TRX histone methyltransferases to chromatin.

Show MeSH
Related in: MedlinePlus