Limits...
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.

Show MeSH

Related in: MedlinePlus

KIS-L facilitates an early stage in transcriptional elongation.Polytene chromosomes isolated from wild-type (A, C, E, and G) and kisk13416 (B, D, F, and H) larvae were stained with antibodies against Pol IIoser2 (A, B) and the CycT subunit of P-TEFb (C, D) or the CTD of RPB1 (that recognizes hypo- and hyper-phosphorylated forms of Pol II) (E, F) and BRM (G, H). The levels of total Pol II and Pol IIoser2 are reduced in kis mutants while the levels of BRM and CycT are not altered.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2563034&req=5

pgen-1000217-g001: KIS-L facilitates an early stage in transcriptional elongation.Polytene chromosomes isolated from wild-type (A, C, E, and G) and kisk13416 (B, D, F, and H) larvae were stained with antibodies against Pol IIoser2 (A, B) and the CycT subunit of P-TEFb (C, D) or the CTD of RPB1 (that recognizes hypo- and hyper-phosphorylated forms of Pol II) (E, F) and BRM (G, H). The levels of total Pol II and Pol IIoser2 are reduced in kis mutants while the levels of BRM and CycT are not altered.

Mentions: To determine whether KIS-L is required for P-TEFb recruitment, we stained polytene chromosomes of wild-type and kisk13416 larvae with an antibody against the CycT subunit of P-TEFb [39]. As expected, the chromosomal distribution of P-TEFb and Pol IIoser2 overlap extensively in wild-type larvae (Figure 1A and C). Although the level of Pol IIoser2 associated with polytene chromosomes is dramatically reduced in kisk13416 larvae (Figure 1A and B), the loss of kis function has no obvious effect on either the level or distribution of CycT (Figure 1C and D). Thus, KIS-L affects a step in transcription downstream of the recruitment of P-TEFb to promoters.


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 facilitates an early stage in transcriptional elongation.Polytene chromosomes isolated from wild-type (A, C, E, and G) and kisk13416 (B, D, F, and H) larvae were stained with antibodies against Pol IIoser2 (A, B) and the CycT subunit of P-TEFb (C, D) or the CTD of RPB1 (that recognizes hypo- and hyper-phosphorylated forms of Pol II) (E, F) and BRM (G, H). The levels of total Pol II and Pol IIoser2 are reduced in kis mutants while the levels of BRM and CycT are not altered.
© Copyright Policy
Related In: Results  -  Collection

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

pgen-1000217-g001: KIS-L facilitates an early stage in transcriptional elongation.Polytene chromosomes isolated from wild-type (A, C, E, and G) and kisk13416 (B, D, F, and H) larvae were stained with antibodies against Pol IIoser2 (A, B) and the CycT subunit of P-TEFb (C, D) or the CTD of RPB1 (that recognizes hypo- and hyper-phosphorylated forms of Pol II) (E, F) and BRM (G, H). The levels of total Pol II and Pol IIoser2 are reduced in kis mutants while the levels of BRM and CycT are not altered.
Mentions: To determine whether KIS-L is required for P-TEFb recruitment, we stained polytene chromosomes of wild-type and kisk13416 larvae with an antibody against the CycT subunit of P-TEFb [39]. As expected, the chromosomal distribution of P-TEFb and Pol IIoser2 overlap extensively in wild-type larvae (Figure 1A and C). Although the level of Pol IIoser2 associated with polytene chromosomes is dramatically reduced in kisk13416 larvae (Figure 1A and B), the loss of kis function has no obvious effect on either the level or distribution of CycT (Figure 1C and D). Thus, KIS-L affects a step in transcription downstream of the recruitment of P-TEFb to promoters.

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