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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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KIS-L co-localizes with the trithorax group proteins ASH1 and TRX on polytene chromosomes.A–C) The distributions of ASH1 (A, red) and KIS-L (B, green) on wild-type polytene chromosomes are shown together with the merged image (C). D–G: Magnification of the chromosome arm bounded by the white rectangle in C is shown. Arrows in G mark examples of KIS-L bands that do not overlap with ASH1. H–J) The distributions of TRX (H, red), KIS-L (I, green) and the merged image (J) are shown. K–N: represent the magnification of the chromosome arm bound by the white rectangle in J. The arrows in N represent bands of KIS-L that do not overlap with TRX.
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pgen-1000217-g002: KIS-L co-localizes with the trithorax group proteins ASH1 and TRX on polytene chromosomes.A–C) The distributions of ASH1 (A, red) and KIS-L (B, green) on wild-type polytene chromosomes are shown together with the merged image (C). D–G: Magnification of the chromosome arm bounded by the white rectangle in C is shown. Arrows in G mark examples of KIS-L bands that do not overlap with ASH1. H–J) The distributions of TRX (H, red), KIS-L (I, green) and the merged image (J) are shown. K–N: represent the magnification of the chromosome arm bound by the white rectangle in J. The arrows in N represent bands of KIS-L that do not overlap with TRX.

Mentions: As a first step toward testing this hypothesis, we compared the distributions of KIS-L, ASH1 and TRX on polytene chromosomes. As reported previously [41], ASH1 binds to approximately one hundred sites on salivary gland polytene chromosomes (Figure 2A). Strong TRX staining is observed at about 20 sites on polytene chromosomes [42],[43], but weaker signals are evident at many other sites (Figure 2H) [44]. The chromosomal distributions of KIS-L and ASH1 are strikingly similar, with overlapping signals observed at more than 95% of the binding sites of both proteins (Figure 2A–G). The chromosomal distributions of KIS-L and TRX are also similar, but not identical, with overlapping signals present at approximately 85% of the bindings sites of both proteins (Figure 2H–N). The co-localization of KIS-L, ASH1 and TRX at the majority of active genes is consistent with a close functional relationship between the three proteins.


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

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

KIS-L co-localizes with the trithorax group proteins ASH1 and TRX on polytene chromosomes.A–C) The distributions of ASH1 (A, red) and KIS-L (B, green) on wild-type polytene chromosomes are shown together with the merged image (C). D–G: Magnification of the chromosome arm bounded by the white rectangle in C is shown. Arrows in G mark examples of KIS-L bands that do not overlap with ASH1. H–J) The distributions of TRX (H, red), KIS-L (I, green) and the merged image (J) are shown. K–N: represent the magnification of the chromosome arm bound by the white rectangle in J. The arrows in N represent bands of KIS-L that do not overlap with TRX.
© Copyright Policy
Related In: Results  -  Collection

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

pgen-1000217-g002: KIS-L co-localizes with the trithorax group proteins ASH1 and TRX on polytene chromosomes.A–C) The distributions of ASH1 (A, red) and KIS-L (B, green) on wild-type polytene chromosomes are shown together with the merged image (C). D–G: Magnification of the chromosome arm bounded by the white rectangle in C is shown. Arrows in G mark examples of KIS-L bands that do not overlap with ASH1. H–J) The distributions of TRX (H, red), KIS-L (I, green) and the merged image (J) are shown. K–N: represent the magnification of the chromosome arm bound by the white rectangle in J. The arrows in N represent bands of KIS-L that do not overlap with TRX.
Mentions: As a first step toward testing this hypothesis, we compared the distributions of KIS-L, ASH1 and TRX on polytene chromosomes. As reported previously [41], ASH1 binds to approximately one hundred sites on salivary gland polytene chromosomes (Figure 2A). Strong TRX staining is observed at about 20 sites on polytene chromosomes [42],[43], but weaker signals are evident at many other sites (Figure 2H) [44]. The chromosomal distributions of KIS-L and ASH1 are strikingly similar, with overlapping signals observed at more than 95% of the binding sites of both proteins (Figure 2A–G). The chromosomal distributions of KIS-L and TRX are also similar, but not identical, with overlapping signals present at approximately 85% of the bindings sites of both proteins (Figure 2H–N). The co-localization of KIS-L, ASH1 and TRX at the majority of active genes is consistent with a close functional relationship between the three proteins.

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