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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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Loss of kis function does not alter the distribution or level of Polycomb group proteins.A–F) The distribution of PC (A, B, green) and E(Z) (C, D, red) and the merged images of PC and E(Z) (E, F) on polytene chromosomes isolated from wild-type (A, C, E) and kisk13416 (B, D, F) larvae are shown. G–H) Comparison of the distribution of PC on the distal tip of the X chromosome of wild-type and kisk13416 larvae (G), together with the corresponding DAPI staining (H). Note that the loss of kis function does not lead to obvious changes in the level or distribution of PC or E(Z).
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pgen-1000217-g008: Loss of kis function does not alter the distribution or level of Polycomb group proteins.A–F) The distribution of PC (A, B, green) and E(Z) (C, D, red) and the merged images of PC and E(Z) (E, F) on polytene chromosomes isolated from wild-type (A, C, E) and kisk13416 (B, D, F) larvae are shown. G–H) Comparison of the distribution of PC on the distal tip of the X chromosome of wild-type and kisk13416 larvae (G), together with the corresponding DAPI staining (H). Note that the loss of kis function does not lead to obvious changes in the level or distribution of PC or E(Z).

Mentions: Genetic studies have suggested that KIS-L and other trithorax group proteins counteract Polycomb group repression [26],[27]. Two complexes of Polycomb group proteins have been identified: PRC1 and PRC2 [14]. The E(Z) subunit of PRC2 methylates lysine 27 of histone H3; this modification is thought to promote the association of PRC1 with chromatin, thereby leading to hereditable gene silencing [16],[17]. Does KIS-L prevent the binding of either PRC1 or PRC2 to chromatin? As reported previously, the level of the PC subunit of PRC1 associated with salivary gland polytene chromosomes is similar in wild-type and kisk13416 mutant larvae (Figure 8A and B) [30]. Similar results were obtained when we compared the level of E(Z) on salivary gland chromosomes of wild-type and kisk13416 mutant larvae (Figure 8C and D). The loss of KIS-L function did not alter the number or distribution of PC binding sites (Figure 8G and H), and extensive co-localization of PC and E(Z) was observed in both wild-type and kis mutant larvae (Figure 8E and F). Thus KIS-L does not appear to influence the association of either PRC1 or PRC2 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 kis function does not alter the distribution or level of Polycomb group proteins.A–F) The distribution of PC (A, B, green) and E(Z) (C, D, red) and the merged images of PC and E(Z) (E, F) on polytene chromosomes isolated from wild-type (A, C, E) and kisk13416 (B, D, F) larvae are shown. G–H) Comparison of the distribution of PC on the distal tip of the X chromosome of wild-type and kisk13416 larvae (G), together with the corresponding DAPI staining (H). Note that the loss of kis function does not lead to obvious changes in the level or distribution of PC or E(Z).
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Related In: Results  -  Collection

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

pgen-1000217-g008: Loss of kis function does not alter the distribution or level of Polycomb group proteins.A–F) The distribution of PC (A, B, green) and E(Z) (C, D, red) and the merged images of PC and E(Z) (E, F) on polytene chromosomes isolated from wild-type (A, C, E) and kisk13416 (B, D, F) larvae are shown. G–H) Comparison of the distribution of PC on the distal tip of the X chromosome of wild-type and kisk13416 larvae (G), together with the corresponding DAPI staining (H). Note that the loss of kis function does not lead to obvious changes in the level or distribution of PC or E(Z).
Mentions: Genetic studies have suggested that KIS-L and other trithorax group proteins counteract Polycomb group repression [26],[27]. Two complexes of Polycomb group proteins have been identified: PRC1 and PRC2 [14]. The E(Z) subunit of PRC2 methylates lysine 27 of histone H3; this modification is thought to promote the association of PRC1 with chromatin, thereby leading to hereditable gene silencing [16],[17]. Does KIS-L prevent the binding of either PRC1 or PRC2 to chromatin? As reported previously, the level of the PC subunit of PRC1 associated with salivary gland polytene chromosomes is similar in wild-type and kisk13416 mutant larvae (Figure 8A and B) [30]. Similar results were obtained when we compared the level of E(Z) on salivary gland chromosomes of wild-type and kisk13416 mutant larvae (Figure 8C and D). The loss of KIS-L function did not alter the number or distribution of PC binding sites (Figure 8G and H), and extensive co-localization of PC and E(Z) was observed in both wild-type and kis mutant larvae (Figure 8E and F). Thus KIS-L does not appear to influence the association of either PRC1 or PRC2 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