PR-Set7-dependent methylation of histone H4 Lys 20 functions in repression of gene expression and is essential for mitosis - PubMed (original) (raw)

. 2005 Feb 15;19(4):431-5.

doi: 10.1101/gad.1263005. Epub 2005 Jan 28.

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PR-Set7-dependent methylation of histone H4 Lys 20 functions in repression of gene expression and is essential for mitosis

Dmitry Karachentsev et al. Genes Dev. 2005.

Abstract

The histone methyl transferase PR-Set7 mediates histone H4 Lys 20 methylation, a mark of constitutive and facultative heterochromatin. We isolated a null mutation in Drosophila PR-Set7 that suppresses position effect variegation, indicating that PR-Set7 indeed functions in silencing general gene expression. In PR-Set7 larval leg and eye discs, the number of cells is lower than normal, and the DNA content in these cells is significantly increased. These data show that PR-Set7-dependent methylation is essential for the process of mitosis. The methylation mark is highly stable and is maintained even in the absence of PR-Set7 protein.

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Figures

Figure 1.

Figure 1.

PR-Set720 mutants lack the PR-Set7 methylase. (A) Western blot of protein extracts derived from wild-type and homozygous PR-Set720 tissue, probed with anti-Drosophila PR-Set7 antibodies. (B,C) Immunofluorescent staining of wild-type (B) and PR-Set720 (C) salivary gland chromosomes with anti-Drosophila PR-Set7 antibodies (red) and Hoechst DNA dye (blue).

Figure 2.

Figure 2.

Reduction of PR-Set7 suppresses position effect variegation (PEV). (A, right) TM3Sb/+ fly showing variegated expression of a w+ transgene. (Left) PR-Set720/+ fly has red eyes because the variegated expression of the w+ transgene has been suppressed. (B) Measurement of eye-color (OD 480 nm) of extracts from different transgenic w+ lines expression, in heterozygous PR-Set7 flies (PR-Set720/+, or Df(3R)red31/+), or wild-type flies (Bal/+). Deletion of one copy of the PR-Set7 gene increases the eye color significantly, confirming the suppression of variegation. The balancers used were TM3 and TM6. The transgenic lines used were 36C-72 and 118E-15 containing w+ in the telomeric heterochromatin of the fourth chromosome. 118E-10 contains a w+ transgene in the centromeric heterochromatin. All second and third w+ transgenic lines contain the transgene in the telomeric heterochromatin.

Figure 3.

Figure 3.

The mono-, di-, and trimethylation mark of H4-K20 is reduced in PR-Set7 mutants. Immunofluorescent staining of wild-type (A,C,E) and PR-Set720 (B,D,F) salivary gland chromosomes with anti-monomethylated (A,B), anti-dimethylated (C,D), and anti-trimethylated (E,F) H4-K20 antibodies (red) and antibody recognizing the catalytic subunit of RNA polymerase II (green). DNA dye Hoechst (blue).

Figure 4.

Figure 4.

In PR-Set720 animals, the mitotic process is interrupted. (A) Leg imaginal discs (left) and eye imaginal discs (right) of wild-type and PR-Set7 larvae stained with the DNA dye Hoechst (white). (B) Eyes of wild-type and PR-Set7 partial loss-of-function flies. Note the smaller eye size in irregular organization of the mutant eye.

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